I like to consult with you regarding the flowing issue The rwlock rewrite commit: commit cc25c8b4c1196a8c29e9a45b1e096b99a87b7f8c Author: Torvald Riegel <triegel@redhat.com> Date: Thu May 22 16:00:12 2014 +0200 changed the behavior of the rwlock as well! On the previous version of Glibc (before the commit) We could release write lock with different thread as the one that owned the lock (If we like) . This is help very much for async program that has a many threads that communicate with some target. And we like to define a call back function instead of blocking on aio thread that send the data in order to release the rwlock.this improves the performance dramatically . For backward compatibility and better performance I suggest a small change as describe below: Remove the THREAD_SELF checking(See below) ,unless this change is danger! Does such fix is danger ? Do you aware why this check was added in the first place? Other option is to define anther function /Type that enable less restricted operation to not violate the API agreement and it will be on the user responsibly whether to use the new type or not for better performance. What do you think? Thx David The previous code before cc25c8b4c1196a8c29e9a45b1e096b99a87b7f8c was look like that: __pthread_rwlock_unlock (pthread_rwlock_t *rwlock) { lll_lock (rwlock->__data.__lock, rwlock->__data.__shared); if (rwlock->__data.__writer) rwlock->__data.__writer = 0; else --rwlock->__data.__nr_readers; if (rwlock->__data.__nr_readers == 0) { if (rwlock->__data.__nr_writers_queued) { Our application has many inflight IO threads After the cc25c8b4c1196a8c29e9a45b1e096b99a87b7f8c commit: int ___pthread_rwlock_unlock (pthread_rwlock_t *rwlock) { LIBC_PROBE (rwlock_unlock, 1, rwlock); /* We distinguish between having acquired a read vs. a write lock by looking at the writer TID. If it's equal to our TID, we must be the writer because nobody else can have stored this value. Also, if we are a reader, we will read from the wrunlock store with value 0 by the most recent writer because that writer happens-before us. */ if (atomic_load_relaxed (&rwlock->__data.__cur_writer) == THREAD_GETMEM (THREAD_SELF, tid)) __pthread_rwlock_wrunlock (rwlock); else __pthread_rwlock_rdunlock (rwlock); return 0; } The change I propose is : What do you think regarding such a small fix like this: if (atomic_load_relaxed (&rwlock->__data.__cur_writer)) __pthread_rwlock_wrunlock (rwlock); else __pthread_rwlock_rdunlock (rwlock); return 0; }
* David Mozes: > On the previous version of Glibc (before the commit) We could release > write lock with different thread as the one that owned the lock (If we > like) . Sorry, this misuse of the API has always been undefined according to POSIX (“Results are undefined if the read-write lock rwlock is not held by the calling thread.”). > This is help very much for async program that has a many threads that > communicate with some target. And we like to define a call back > function instead of blocking on aio thread that send the data in order > to release the rwlock.this improves the performance dramatically . Could you use a different synchronization object (perhaps a condition variable)? Thanks, Florian
Thx Florin, -----Original Message----- From: Florian Weimer <fweimer@redhat.com> Sent: Friday, March 11, 2022 3:59 PM To: David Mozes <david.mozes@silk.us> Cc: libc-help@sourceware.org Subject: Re: rwlock different behavior on glibc 2.28 then on previous versions * David Mozes: > On the previous version of Glibc (before the commit) We could release > write lock with different thread as the one that owned the lock (If we > like) . Sorry, this misuse of the API has always been undefined according to POSIX (“Results are undefined if the read-write lock rwlock is not held by the calling thread.”). >> Correct, but practically we can do it on the user's responsibility. >>Do you know if this "if" solved some synchronization issue or just enforced the undefined API? > This is help very much for async program that has a many threads that > communicate with some target. And we like to define a call back > function instead of blocking on aio thread that send the data in order > to release the rwlock.this improves the performance dramatically . Could you use a different synchronization object (perhaps a condition variable)? >> If we use a different synchronization object like semaphores, condition variable (by the way they use mutex under the same API agreement), we will need to write self rwlock , which has less performance than other undefined states. >>If we like to keep the API agreement, why not define the different async programming unlock functions? Thanks Florian Thx David
Hi, Where are we with this? Also, the current implementation of the __pthread_rwlock_unlock is problematic. On the one hand, it checks the API agreement. However, on the case of violation, the user don't have any induction And function return OK See example code below: struct threadInfo{ pthread_t* tid; pthread_rwlock_t *rwlock; }; void *lockerThreadFunction(void *vargp) { km_status stat = KM_OK; struct threadInfo* Tinfo = (struct threadInfo*)vargp; do { stat = pthread_rwlock_trywrlock(Tinfo->rwlock); if (KM_OK == stat) { printf("[INFO] - FIRST thread 0x%x locked %p \n", *(Tinfo->tid), Tinfo->rwlock); sleep(10); stat = pthread_rwlock_unlock(Tinfo->rwlock); if (KM_OK == stat) { printf("[INFO] FIRST thread 0x%x released %p \n", *(Tinfo->tid), Tinfo->rwlock); sleep(1); } } }while(KM_OK != stat); return NULL; } void *secondThreadFunction(void *vargp) { km_status stat = KM_OK; struct threadInfo* Tinfo = (struct threadInfo*)vargp; sleep(5); do { stat = pthread_rwlock_unlock(Tinfo->rwlock); if (KM_OK == stat) { printf("[INFO] SECOND thread 0x%x released %p \n", *(Tinfo->tid), Tinfo->rwlock); sleep(1); } else printf("[INFO] SECOND thread 0x%x try_to_released %p erro status is: %d \n", *(Tinfo->tid), Tinfo->rwlock,stat); }while(KM_OK != stat); return NULL; } void *thirdThreadFunction(void *vargp) { km_status stat = KM_OK; struct threadInfo* Tinfo = (struct threadInfo*)vargp; sleep(2); do { stat = pthread_rwlock_trywrlock(Tinfo->rwlock); if (KM_OK == stat) { printf("[INFO] THIRD thread 0X%x locked %x\n", *(Tinfo->tid), Tinfo->rwlock); sleep(5); } else { printf("[ERROR]: THIRD thread 0x%x failed Locking %p status is %d\n", *(Tinfo->tid), Tinfo->rwlock,stat); sleep(1); } }while(KM_OK != stat); return NULL; } void main() { km_status stat = KM_OK; /* km_rwlock lock; */ pthread_rwlock_t rwlock; pthread_t lockerTid = 0, releaseTid = 0, thirdTid=0; struct threadInfo firstTinfo, secondTinfo, thirdTinfo; /* stat = km_rwlock_init(&rwlock, KM_TRUE); */ stat = pthread_rwlock_init (&rwlock, NULL); if (KM_OK == stat) { printf("read\\writer lock initialized\n"); printf("Before Thread\n"); firstTinfo.tid = &lockerTid; firstTinfo.rwlock = &rwlock; secondTinfo.tid = &releaseTid; secondTinfo.rwlock = &rwlock; thirdTinfo.tid = &thirdTid; thirdTinfo.rwlock = &rwlock; pthread_create(&lockerTid, NULL, lockerThreadFunction, &firstTinfo); pthread_create(&releaseTid, NULL, secondThreadFunction, &secondTinfo); pthread_create(&thirdTid, NULL, thirdThreadFunction, &thirdTinfo); printf("After Thread %x\n", lockerTid); pthread_join(lockerTid, NULL); pthread_join(releaseTid, NULL); pthread_join(thirdTid, NULL); the output we saw is this: the ouput we saw is this: [root@Rocky85Mozes thread_lock]# ./rw_test read\writer lock initialized Before Thread [INFO] - FIRST thread 0x461f700 locked 0x7ffcda053cc0 After Thread 461f700 [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 -> first thread take the rwlock [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 [INFO] SECOND thread 0x3e1e700 released 0x7ffcda053cc0 -> Second thread unlock the rwlock -- > and get OK!! [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 [INFO] FIRST thread 0x461f700 released 0x7ffcda053cc0 [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 -----Original Message----- From: David Mozes Sent: Sunday, March 13, 2022 12:23 PM To: Florian Weimer <fweimer@redhat.com> Cc: libc-help@sourceware.org Subject: RE: rwlock different behavior on glibc 2.28 then on previous versions Thx Florin, -----Original Message----- From: Florian Weimer <fweimer@redhat.com> Sent: Friday, March 11, 2022 3:59 PM To: David Mozes <david.mozes@silk.us> Cc: libc-help@sourceware.org Subject: Re: rwlock different behavior on glibc 2.28 then on previous versions * David Mozes: > On the previous version of Glibc (before the commit) We could release > write lock with different thread as the one that owned the lock (If we > like) . Sorry, this misuse of the API has always been undefined according to POSIX (“Results are undefined if the read-write lock rwlock is not held by the calling thread.”). >> Correct, but practically we can do it on the user's responsibility. >>Do you know if this "if" solved some synchronization issue or just enforced the undefined API? > This is help very much for async program that has a many threads that > communicate with some target. And we like to define a call back > function instead of blocking on aio thread that send the data in order > to release the rwlock.this improves the performance dramatically . Could you use a different synchronization object (perhaps a condition variable)? >> If we use a different synchronization object like semaphores, condition variable (by the way they use mutex under the same API agreement), we will need to write self rwlock , which has less performance than other undefined states. >>If we like to keep the API agreement, why not define the different async programming unlock functions? Thanks Florian Thx David
Hallo David,
did you try to run your program with Helgrind already? Helgrind was
designed to catch problems like this. Maybe Thread Sanitizer would also
detect the issue.
Best regards,
Christian
On 3/20/22 5:44 PM, David Mozes wrote:
> Hi,
> Where are we with this?
> Also, the current implementation of the __pthread_rwlock_unlock is problematic.
> On the one hand, it checks the API agreement. However, on the case of violation, the user don't have any induction
> And function return OK
> See example code below:
>
>
> struct threadInfo{
> pthread_t* tid;
> pthread_rwlock_t *rwlock;
> };
>
> void *lockerThreadFunction(void *vargp)
> {
> km_status stat = KM_OK;
> struct threadInfo* Tinfo = (struct threadInfo*)vargp;
>
> do {
> stat = pthread_rwlock_trywrlock(Tinfo->rwlock);
> if (KM_OK == stat) {
> printf("[INFO] - FIRST thread 0x%x locked %p \n", *(Tinfo->tid), Tinfo->rwlock);
> sleep(10);
> stat = pthread_rwlock_unlock(Tinfo->rwlock);
> if (KM_OK == stat) {
> printf("[INFO] FIRST thread 0x%x released %p \n", *(Tinfo->tid), Tinfo->rwlock);
> sleep(1);
> }
> }
> }while(KM_OK != stat);
> return NULL;
> }
>
>
> void *secondThreadFunction(void *vargp)
> {
> km_status stat = KM_OK;
> struct threadInfo* Tinfo = (struct threadInfo*)vargp;
>
> sleep(5);
> do {
> stat = pthread_rwlock_unlock(Tinfo->rwlock);
> if (KM_OK == stat) {
> printf("[INFO] SECOND thread 0x%x released %p \n", *(Tinfo->tid), Tinfo->rwlock);
> sleep(1);
> } else
> printf("[INFO] SECOND thread 0x%x try_to_released %p erro status is: %d \n", *(Tinfo->tid), Tinfo->rwlock,stat);
>
> }while(KM_OK != stat);
> return NULL;
> }
>
> void *thirdThreadFunction(void *vargp)
> {
> km_status stat = KM_OK;
> struct threadInfo* Tinfo = (struct threadInfo*)vargp;
>
> sleep(2);
> do {
> stat = pthread_rwlock_trywrlock(Tinfo->rwlock);
> if (KM_OK == stat) {
> printf("[INFO] THIRD thread 0X%x locked %x\n", *(Tinfo->tid), Tinfo->rwlock);
> sleep(5);
> }
> else {
> printf("[ERROR]: THIRD thread 0x%x failed Locking %p status is %d\n", *(Tinfo->tid), Tinfo->rwlock,stat);
> sleep(1);
> }
> }while(KM_OK != stat);
> return NULL;
> }
>
> void main()
> {
> km_status stat = KM_OK;
> /* km_rwlock lock; */
> pthread_rwlock_t rwlock;
> pthread_t lockerTid = 0, releaseTid = 0, thirdTid=0;
> struct threadInfo firstTinfo, secondTinfo, thirdTinfo;
>
> /* stat = km_rwlock_init(&rwlock, KM_TRUE); */
> stat = pthread_rwlock_init (&rwlock, NULL);
>
> if (KM_OK == stat) {
> printf("read\\writer lock initialized\n");
> printf("Before Thread\n");
>
> firstTinfo.tid = &lockerTid;
> firstTinfo.rwlock = &rwlock;
> secondTinfo.tid = &releaseTid;
> secondTinfo.rwlock = &rwlock;
> thirdTinfo.tid = &thirdTid;
> thirdTinfo.rwlock = &rwlock;
>
>
> pthread_create(&lockerTid, NULL, lockerThreadFunction, &firstTinfo);
> pthread_create(&releaseTid, NULL, secondThreadFunction, &secondTinfo);
> pthread_create(&thirdTid, NULL, thirdThreadFunction, &thirdTinfo);
> printf("After Thread %x\n", lockerTid);
>
> pthread_join(lockerTid, NULL);
> pthread_join(releaseTid, NULL);
> pthread_join(thirdTid, NULL);
>
>
>
> the output we saw is this:
>
>
> the ouput we saw is this:
>
> [root@Rocky85Mozes thread_lock]# ./rw_test
> read\writer lock initialized
> Before Thread
> [INFO] - FIRST thread 0x461f700 locked 0x7ffcda053cc0
> After Thread 461f700
> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 -> first thread take the rwlock
> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16
> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16
> [INFO] SECOND thread 0x3e1e700 released 0x7ffcda053cc0 -> Second thread unlock the rwlock -- > and get OK!!
> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16
> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16
> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16
> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16
> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16
> [INFO] FIRST thread 0x461f700 released 0x7ffcda053cc0
> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16
>
>
> -----Original Message-----
> From: David Mozes
> Sent: Sunday, March 13, 2022 12:23 PM
> To: Florian Weimer <fweimer@redhat.com>
> Cc: libc-help@sourceware.org
> Subject: RE: rwlock different behavior on glibc 2.28 then on previous versions
>
> Thx Florin,
>
>
> -----Original Message-----
> From: Florian Weimer <fweimer@redhat.com>
> Sent: Friday, March 11, 2022 3:59 PM
> To: David Mozes <david.mozes@silk.us>
> Cc: libc-help@sourceware.org
> Subject: Re: rwlock different behavior on glibc 2.28 then on previous versions
>
> * David Mozes:
>
>> On the previous version of Glibc (before the commit) We could release
>> write lock with different thread as the one that owned the lock (If we
>> like) .
> Sorry, this misuse of the API has always been undefined according to
> POSIX (“Results are undefined if the read-write lock rwlock is not held
> by the calling thread.”).
>
> >> Correct, but practically we can do it on the user's responsibility.
>>> Do you know if this "if" solved some synchronization issue or just enforced the undefined API?
>> This is help very much for async program that has a many threads that
>> communicate with some target. And we like to define a call back
>> function instead of blocking on aio thread that send the data in order
>> to release the rwlock.this improves the performance dramatically .
> Could you use a different synchronization object (perhaps a condition
> variable)?
>
>>> If we use a different synchronization object like semaphores, condition variable (by the way they use mutex under the same API agreement), we will need to write self rwlock , which has less performance than other undefined states.
>>> If we like to keep the API agreement, why not define the different async programming unlock functions?
> Thanks
> Florian
>
> Thx
> David
Hello Christain,
Yes, Thread Sanitizer caught it.
However, we can't run it all the time on the production code.
We need to make a small change of the unlock code to have async programing and backward compatibility for older code.
Thx
David
-----Original Message-----
From: Christian Hoff <christian_hoff@gmx.net>
Sent: Monday, March 21, 2022 8:20 AM
To: David Mozes <david.mozes@silk.us>; Florian Weimer <fweimer@redhat.com>
Cc: libc-help@sourceware.org
Subject: Re: rwlock different behavior on glibc 2.28 then on previous versions
Hallo David,
did you try to run your program with Helgrind already? Helgrind was
designed to catch problems like this. Maybe Thread Sanitizer would also
detect the issue.
Best regards,
Christian
On 3/20/22 5:44 PM, David Mozes wrote:
> Hi,
> Where are we with this?
> Also, the current implementation of the __pthread_rwlock_unlock is problematic.
> On the one hand, it checks the API agreement. However, on the case of violation, the user don't have any induction
> And function return OK
> See example code below:
>
>
> struct threadInfo{
> pthread_t* tid;
> pthread_rwlock_t *rwlock;
> };
>
> void *lockerThreadFunction(void *vargp)
> {
> km_status stat = KM_OK;
> struct threadInfo* Tinfo = (struct threadInfo*)vargp;
>
> do {
> stat = pthread_rwlock_trywrlock(Tinfo->rwlock);
> if (KM_OK == stat) {
> printf("[INFO] - FIRST thread 0x%x locked %p \n", *(Tinfo->tid), Tinfo->rwlock);
> sleep(10);
> stat = pthread_rwlock_unlock(Tinfo->rwlock);
> if (KM_OK == stat) {
> printf("[INFO] FIRST thread 0x%x released %p \n", *(Tinfo->tid), Tinfo->rwlock);
> sleep(1);
> }
> }
> }while(KM_OK != stat);
> return NULL;
> }
>
>
> void *secondThreadFunction(void *vargp)
> {
> km_status stat = KM_OK;
> struct threadInfo* Tinfo = (struct threadInfo*)vargp;
>
> sleep(5);
> do {
> stat = pthread_rwlock_unlock(Tinfo->rwlock);
> if (KM_OK == stat) {
> printf("[INFO] SECOND thread 0x%x released %p \n", *(Tinfo->tid), Tinfo->rwlock);
> sleep(1);
> } else
> printf("[INFO] SECOND thread 0x%x try_to_released %p erro status is: %d \n", *(Tinfo->tid), Tinfo->rwlock,stat);
>
> }while(KM_OK != stat);
> return NULL;
> }
>
> void *thirdThreadFunction(void *vargp)
> {
> km_status stat = KM_OK;
> struct threadInfo* Tinfo = (struct threadInfo*)vargp;
>
> sleep(2);
> do {
> stat = pthread_rwlock_trywrlock(Tinfo->rwlock);
> if (KM_OK == stat) {
> printf("[INFO] THIRD thread 0X%x locked %x\n", *(Tinfo->tid), Tinfo->rwlock);
> sleep(5);
> }
> else {
> printf("[ERROR]: THIRD thread 0x%x failed Locking %p status is %d\n", *(Tinfo->tid), Tinfo->rwlock,stat);
> sleep(1);
> }
> }while(KM_OK != stat);
> return NULL;
> }
>
> void main()
> {
> km_status stat = KM_OK;
> /* km_rwlock lock; */
> pthread_rwlock_t rwlock;
> pthread_t lockerTid = 0, releaseTid = 0, thirdTid=0;
> struct threadInfo firstTinfo, secondTinfo, thirdTinfo;
>
> /* stat = km_rwlock_init(&rwlock, KM_TRUE); */
> stat = pthread_rwlock_init (&rwlock, NULL);
>
> if (KM_OK == stat) {
> printf("read\\writer lock initialized\n");
> printf("Before Thread\n");
>
> firstTinfo.tid = &lockerTid;
> firstTinfo.rwlock = &rwlock;
> secondTinfo.tid = &releaseTid;
> secondTinfo.rwlock = &rwlock;
> thirdTinfo.tid = &thirdTid;
> thirdTinfo.rwlock = &rwlock;
>
>
> pthread_create(&lockerTid, NULL, lockerThreadFunction, &firstTinfo);
> pthread_create(&releaseTid, NULL, secondThreadFunction, &secondTinfo);
> pthread_create(&thirdTid, NULL, thirdThreadFunction, &thirdTinfo);
> printf("After Thread %x\n", lockerTid);
>
> pthread_join(lockerTid, NULL);
> pthread_join(releaseTid, NULL);
> pthread_join(thirdTid, NULL);
>
>
>
> the output we saw is this:
>
>
> the ouput we saw is this:
>
> [root@Rocky85Mozes thread_lock]# ./rw_test
> read\writer lock initialized
> Before Thread
> [INFO] - FIRST thread 0x461f700 locked 0x7ffcda053cc0
> After Thread 461f700
> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 -> first thread take the rwlock
> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16
> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16
> [INFO] SECOND thread 0x3e1e700 released 0x7ffcda053cc0 -> Second thread unlock the rwlock -- > and get OK!!
> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16
> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16
> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16
> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16
> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16
> [INFO] FIRST thread 0x461f700 released 0x7ffcda053cc0
> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16
>
>
> -----Original Message-----
> From: David Mozes
> Sent: Sunday, March 13, 2022 12:23 PM
> To: Florian Weimer <fweimer@redhat.com>
> Cc: libc-help@sourceware.org
> Subject: RE: rwlock different behavior on glibc 2.28 then on previous versions
>
> Thx Florin,
>
>
> -----Original Message-----
> From: Florian Weimer <fweimer@redhat.com>
> Sent: Friday, March 11, 2022 3:59 PM
> To: David Mozes <david.mozes@silk.us>
> Cc: libc-help@sourceware.org
> Subject: Re: rwlock different behavior on glibc 2.28 then on previous versions
>
> * David Mozes:
>
>> On the previous version of Glibc (before the commit) We could release
>> write lock with different thread as the one that owned the lock (If we
>> like) .
> Sorry, this misuse of the API has always been undefined according to
> POSIX (“Results are undefined if the read-write lock rwlock is not held
> by the calling thread.”).
>
> >> Correct, but practically we can do it on the user's responsibility.
>>> Do you know if this "if" solved some synchronization issue or just enforced the undefined API?
>> This is help very much for async program that has a many threads that
>> communicate with some target. And we like to define a call back
>> function instead of blocking on aio thread that send the data in order
>> to release the rwlock.this improves the performance dramatically .
> Could you use a different synchronization object (perhaps a condition
> variable)?
>
>>> If we use a different synchronization object like semaphores, condition variable (by the way they use mutex under the same API agreement), we will need to write self rwlock , which has less performance than other undefined states.
>>> If we like to keep the API agreement, why not define the different async programming unlock functions?
> Thanks
> Florian
>
> Thx
> David
As Florian has put, this is essentially a misuse of the API has always been
undefined. The rwlock implementation uses __cur_write to both make a fast
deadlock check and to know whether to handle the lock as a writer or reader
one. The former is a implementation detail that we might change (although
it is useful in some case), but to handle the former will most likely to
refactor and change the rdlock algorithm (just removing the check as you are
proposing is not suffice).
Since it is not a bug in our implementation, I think you will need to discuss
it further on the libc-alpha to see if other are willing to actually make
this change. I foresee that the algorithm change won't be simple to keep
interface requirements and allow the specific case you are asking. In fact
I think it might not be actually possible without change the rwlock semantic
(not sure though).
Carlos has fixed some issue on the rwlock, he might have some comments.
On 21/03/2022 11:01, David Mozes wrote:
> Hello Christain,
> Yes, Thread Sanitizer caught it.
> However, we can't run it all the time on the production code.
> We need to make a small change of the unlock code to have async programing and backward compatibility for older code.
>
> Thx
> David
>
> -----Original Message-----
> From: Christian Hoff <christian_hoff@gmx.net>
> Sent: Monday, March 21, 2022 8:20 AM
> To: David Mozes <david.mozes@silk.us>; Florian Weimer <fweimer@redhat.com>
> Cc: libc-help@sourceware.org
> Subject: Re: rwlock different behavior on glibc 2.28 then on previous versions
>
> Hallo David,
>
> did you try to run your program with Helgrind already? Helgrind was
> designed to catch problems like this. Maybe Thread Sanitizer would also
> detect the issue.
>
>
> Best regards,
>
> Christian
>
> On 3/20/22 5:44 PM, David Mozes wrote:
>> Hi,
>> Where are we with this?
>> Also, the current implementation of the __pthread_rwlock_unlock is problematic.
>> On the one hand, it checks the API agreement. However, on the case of violation, the user don't have any induction
>> And function return OK
>> See example code below:
>>
>>
>> struct threadInfo{
>> pthread_t* tid;
>> pthread_rwlock_t *rwlock;
>> };
>>
>> void *lockerThreadFunction(void *vargp)
>> {
>> km_status stat = KM_OK;
>> struct threadInfo* Tinfo = (struct threadInfo*)vargp;
>>
>> do {
>> stat = pthread_rwlock_trywrlock(Tinfo->rwlock);
>> if (KM_OK == stat) {
>> printf("[INFO] - FIRST thread 0x%x locked %p \n", *(Tinfo->tid), Tinfo->rwlock);
>> sleep(10);
>> stat = pthread_rwlock_unlock(Tinfo->rwlock);
>> if (KM_OK == stat) {
>> printf("[INFO] FIRST thread 0x%x released %p \n", *(Tinfo->tid), Tinfo->rwlock);
>> sleep(1);
>> }
>> }
>> }while(KM_OK != stat);
>> return NULL;
>> }
>>
>>
>> void *secondThreadFunction(void *vargp)
>> {
>> km_status stat = KM_OK;
>> struct threadInfo* Tinfo = (struct threadInfo*)vargp;
>>
>> sleep(5);
>> do {
>> stat = pthread_rwlock_unlock(Tinfo->rwlock);
>> if (KM_OK == stat) {
>> printf("[INFO] SECOND thread 0x%x released %p \n", *(Tinfo->tid), Tinfo->rwlock);
>> sleep(1);
>> } else
>> printf("[INFO] SECOND thread 0x%x try_to_released %p erro status is: %d \n", *(Tinfo->tid), Tinfo->rwlock,stat);
>>
>> }while(KM_OK != stat);
>> return NULL;
>> }
>>
>> void *thirdThreadFunction(void *vargp)
>> {
>> km_status stat = KM_OK;
>> struct threadInfo* Tinfo = (struct threadInfo*)vargp;
>>
>> sleep(2);
>> do {
>> stat = pthread_rwlock_trywrlock(Tinfo->rwlock);
>> if (KM_OK == stat) {
>> printf("[INFO] THIRD thread 0X%x locked %x\n", *(Tinfo->tid), Tinfo->rwlock);
>> sleep(5);
>> }
>> else {
>> printf("[ERROR]: THIRD thread 0x%x failed Locking %p status is %d\n", *(Tinfo->tid), Tinfo->rwlock,stat);
>> sleep(1);
>> }
>> }while(KM_OK != stat);
>> return NULL;
>> }
>>
>> void main()
>> {
>> km_status stat = KM_OK;
>> /* km_rwlock lock; */
>> pthread_rwlock_t rwlock;
>> pthread_t lockerTid = 0, releaseTid = 0, thirdTid=0;
>> struct threadInfo firstTinfo, secondTinfo, thirdTinfo;
>>
>> /* stat = km_rwlock_init(&rwlock, KM_TRUE); */
>> stat = pthread_rwlock_init (&rwlock, NULL);
>>
>> if (KM_OK == stat) {
>> printf("read\\writer lock initialized\n");
>> printf("Before Thread\n");
>>
>> firstTinfo.tid = &lockerTid;
>> firstTinfo.rwlock = &rwlock;
>> secondTinfo.tid = &releaseTid;
>> secondTinfo.rwlock = &rwlock;
>> thirdTinfo.tid = &thirdTid;
>> thirdTinfo.rwlock = &rwlock;
>>
>>
>> pthread_create(&lockerTid, NULL, lockerThreadFunction, &firstTinfo);
>> pthread_create(&releaseTid, NULL, secondThreadFunction, &secondTinfo);
>> pthread_create(&thirdTid, NULL, thirdThreadFunction, &thirdTinfo);
>> printf("After Thread %x\n", lockerTid);
>>
>> pthread_join(lockerTid, NULL);
>> pthread_join(releaseTid, NULL);
>> pthread_join(thirdTid, NULL);
>>
>>
>>
>> the output we saw is this:
>>
>>
>> the ouput we saw is this:
>>
>> [root@Rocky85Mozes thread_lock]# ./rw_test
>> read\writer lock initialized
>> Before Thread
>> [INFO] - FIRST thread 0x461f700 locked 0x7ffcda053cc0
>> After Thread 461f700
>> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 -> first thread take the rwlock
>> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16
>> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16
>> [INFO] SECOND thread 0x3e1e700 released 0x7ffcda053cc0 -> Second thread unlock the rwlock -- > and get OK!!
>> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16
>> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16
>> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16
>> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16
>> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16
>> [INFO] FIRST thread 0x461f700 released 0x7ffcda053cc0
>> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16
>>
>>
>> -----Original Message-----
>> From: David Mozes
>> Sent: Sunday, March 13, 2022 12:23 PM
>> To: Florian Weimer <fweimer@redhat.com>
>> Cc: libc-help@sourceware.org
>> Subject: RE: rwlock different behavior on glibc 2.28 then on previous versions
>>
>> Thx Florin,
>>
>>
>> -----Original Message-----
>> From: Florian Weimer <fweimer@redhat.com>
>> Sent: Friday, March 11, 2022 3:59 PM
>> To: David Mozes <david.mozes@silk.us>
>> Cc: libc-help@sourceware.org
>> Subject: Re: rwlock different behavior on glibc 2.28 then on previous versions
>>
>> * David Mozes:
>>
>>> On the previous version of Glibc (before the commit) We could release
>>> write lock with different thread as the one that owned the lock (If we
>>> like) .
>> Sorry, this misuse of the API has always been undefined according to
>> POSIX (“Results are undefined if the read-write lock rwlock is not held
>> by the calling thread.”).
>>
>> >> Correct, but practically we can do it on the user's responsibility.
>>>> Do you know if this "if" solved some synchronization issue or just enforced the undefined API?
>>> This is help very much for async program that has a many threads that
>>> communicate with some target. And we like to define a call back
>>> function instead of blocking on aio thread that send the data in order
>>> to release the rwlock.this improves the performance dramatically .
>> Could you use a different synchronization object (perhaps a condition
>> variable)?
>>
>>>> If we use a different synchronization object like semaphores, condition variable (by the way they use mutex under the same API agreement), we will need to write self rwlock , which has less performance than other undefined states.
>>>> If we like to keep the API agreement, why not define the different async programming unlock functions?
>> Thanks
>> Florian
>>
>> Thx
>> David
Thanks Adhemerval, For the suggestion! I suggest to remove the check just on the unlock function.I tested it with very high load and with application with 3k active threads. Can you on a case or bug(dedlock or something) that removing thIs check will expose? Thx David On Mar 21, 2022, at 7:02 PM, Adhemerval Zanella <adhemerval.zanella@linaro.org> wrote: As Florian has put, this is essentially a misuse of the API has always been undefined. The rwlock implementation uses __cur_write to both make a fast deadlock check and to know whether to handle the lock as a writer or reader one. The former is a implementation detail that we might change (although it is useful in some case), but to handle the former will most likely to refactor and change the rdlock algorithm (just removing the check as you are proposing is not suffice). Since it is not a bug in our implementation, I think you will need to discuss it further on the libc-alpha to see if other are willing to actually make this change. I foresee that the algorithm change won't be simple to keep interface requirements and allow the specific case you are asking. In fact I think it might not be actually possible without change the rwlock semantic (not sure though). Carlos has fixed some issue on the rwlock, he might have some comments. On 21/03/2022 11:01, David Mozes wrote: Hello Christain, Yes, Thread Sanitizer caught it. However, we can't run it all the time on the production code. We need to make a small change of the unlock code to have async programing and backward compatibility for older code. Thx David -----Original Message----- From: Christian Hoff <christian_hoff@gmx.net> Sent: Monday, March 21, 2022 8:20 AM To: David Mozes <david.mozes@silk.us>; Florian Weimer <fweimer@redhat.com> Cc: libc-help@sourceware.org Subject: Re: rwlock different behavior on glibc 2.28 then on previous versions Hallo David, did you try to run your program with Helgrind already? Helgrind was designed to catch problems like this. Maybe Thread Sanitizer would also detect the issue. Best regards, Christian On 3/20/22 5:44 PM, David Mozes wrote: Hi, Where are we with this? Also, the current implementation of the __pthread_rwlock_unlock is problematic. On the one hand, it checks the API agreement. However, on the case of violation, the user don't have any induction And function return OK See example code below: struct threadInfo{ pthread_t* tid; pthread_rwlock_t *rwlock; }; void *lockerThreadFunction(void *vargp) { km_status stat = KM_OK; struct threadInfo* Tinfo = (struct threadInfo*)vargp; do { stat = pthread_rwlock_trywrlock(Tinfo->rwlock); if (KM_OK == stat) { printf("[INFO] - FIRST thread 0x%x locked %p \n", *(Tinfo->tid), Tinfo->rwlock); sleep(10); stat = pthread_rwlock_unlock(Tinfo->rwlock); if (KM_OK == stat) { printf("[INFO] FIRST thread 0x%x released %p \n", *(Tinfo->tid), Tinfo->rwlock); sleep(1); } } }while(KM_OK != stat); return NULL; } void *secondThreadFunction(void *vargp) { km_status stat = KM_OK; struct threadInfo* Tinfo = (struct threadInfo*)vargp; sleep(5); do { stat = pthread_rwlock_unlock(Tinfo->rwlock); if (KM_OK == stat) { printf("[INFO] SECOND thread 0x%x released %p \n", *(Tinfo->tid), Tinfo->rwlock); sleep(1); } else printf("[INFO] SECOND thread 0x%x try_to_released %p erro status is: %d \n", *(Tinfo->tid), Tinfo->rwlock,stat); }while(KM_OK != stat); return NULL; } void *thirdThreadFunction(void *vargp) { km_status stat = KM_OK; struct threadInfo* Tinfo = (struct threadInfo*)vargp; sleep(2); do { stat = pthread_rwlock_trywrlock(Tinfo->rwlock); if (KM_OK == stat) { printf("[INFO] THIRD thread 0X%x locked %x\n", *(Tinfo->tid), Tinfo->rwlock); sleep(5); } else { printf("[ERROR]: THIRD thread 0x%x failed Locking %p status is %d\n", *(Tinfo->tid), Tinfo->rwlock,stat); sleep(1); } }while(KM_OK != stat); return NULL; } void main() { km_status stat = KM_OK; /* km_rwlock lock; */ pthread_rwlock_t rwlock; pthread_t lockerTid = 0, releaseTid = 0, thirdTid=0; struct threadInfo firstTinfo, secondTinfo, thirdTinfo; /* stat = km_rwlock_init(&rwlock, KM_TRUE); */ stat = pthread_rwlock_init (&rwlock, NULL); if (KM_OK == stat) { printf("read\\writer lock initialized\n"); printf("Before Thread\n"); firstTinfo.tid = &lockerTid; firstTinfo.rwlock = &rwlock; secondTinfo.tid = &releaseTid; secondTinfo.rwlock = &rwlock; thirdTinfo.tid = &thirdTid; thirdTinfo.rwlock = &rwlock; pthread_create(&lockerTid, NULL, lockerThreadFunction, &firstTinfo); pthread_create(&releaseTid, NULL, secondThreadFunction, &secondTinfo); pthread_create(&thirdTid, NULL, thirdThreadFunction, &thirdTinfo); printf("After Thread %x\n", lockerTid); pthread_join(lockerTid, NULL); pthread_join(releaseTid, NULL); pthread_join(thirdTid, NULL); the output we saw is this: the ouput we saw is this: [root@Rocky85Mozes thread_lock]# ./rw_test read\writer lock initialized Before Thread [INFO] - FIRST thread 0x461f700 locked 0x7ffcda053cc0 After Thread 461f700 [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 -> first thread take the rwlock [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 [INFO] SECOND thread 0x3e1e700 released 0x7ffcda053cc0 -> Second thread unlock the rwlock -- > and get OK!! [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 [INFO] FIRST thread 0x461f700 released 0x7ffcda053cc0 [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 -----Original Message----- From: David Mozes Sent: Sunday, March 13, 2022 12:23 PM To: Florian Weimer <fweimer@redhat.com> Cc: libc-help@sourceware.org Subject: RE: rwlock different behavior on glibc 2.28 then on previous versions Thx Florin, -----Original Message----- From: Florian Weimer <fweimer@redhat.com> Sent: Friday, March 11, 2022 3:59 PM To: David Mozes <david.mozes@silk.us> Cc: libc-help@sourceware.org Subject: Re: rwlock different behavior on glibc 2.28 then on previous versions * David Mozes: On the previous version of Glibc (before the commit) We could release write lock with different thread as the one that owned the lock (If we like) . Sorry, this misuse of the API has always been undefined according to POSIX (“Results are undefined if the read-write lock rwlock is not held by the calling thread.”). Correct, but practically we can do it on the user's responsibility. Do you know if this "if" solved some synchronization issue or just enforced the undefined API? This is help very much for async program that has a many threads that communicate with some target. And we like to define a call back function instead of blocking on aio thread that send the data in order to release the rwlock.this improves the performance dramatically . Could you use a different synchronization object (perhaps a condition variable)? If we use a different synchronization object like semaphores, condition variable (by the way they use mutex under the same API agreement), we will need to write self rwlock , which has less performance than other undefined states. If we like to keep the API agreement, why not define the different async programming unlock functions? Thanks Florian Thx David
On 21/03/2022 16:46, David Mozes wrote: > > Thanks Adhemerval, > For the suggestion! > > I suggest to remove the check just on the unlock function.I tested it with very high load and with application with 3k active threads. > Can you on a case or bug(dedlock or something) that removing thIs check will expose? I am no sure, so I would suggest you to maybe start a discussion on libc-alpha. However __pthread_rwlock_wrunlock and __pthread_rwlock_rdunlock have different semantic allowing unlocking write locks on different threads will require a lot of analysis on why it would trigger any more regression (and sorry, but stating it works on our environment is not suffice). > Thx > David >> On Mar 21, 2022, at 7:02 PM, Adhemerval Zanella <adhemerval.zanella@linaro.org> wrote: >> >> As Florian has put, this is essentially a misuse of the API has always been >> undefined. The rwlock implementation uses __cur_write to both make a fast >> deadlock check and to know whether to handle the lock as a writer or reader >> one. The former is a implementation detail that we might change (although >> it is useful in some case), but to handle the former will most likely to >> refactor and change the rdlock algorithm (just removing the check as you are >> proposing is not suffice). >> >> Since it is not a bug in our implementation, I think you will need to discuss >> it further on the libc-alpha to see if other are willing to actually make >> this change. I foresee that the algorithm change won't be simple to keep >> interface requirements and allow the specific case you are asking. In fact >> I think it might not be actually possible without change the rwlock semantic >> (not sure though). >> >> Carlos has fixed some issue on the rwlock, he might have some comments. >> >> On 21/03/2022 11:01, David Mozes wrote: >>> Hello Christain, >>> Yes, Thread Sanitizer caught it. >>> However, we can't run it all the time on the production code. >>> We need to make a small change of the unlock code to have async programing and backward compatibility for older code. >>> >>> Thx >>> David >>> >>> -----Original Message----- >>> From: Christian Hoff <christian_hoff@gmx.net> >>> Sent: Monday, March 21, 2022 8:20 AM >>> To: David Mozes <david.mozes@silk.us>; Florian Weimer <fweimer@redhat.com> >>> Cc: libc-help@sourceware.org >>> Subject: Re: rwlock different behavior on glibc 2.28 then on previous versions >>> >>> Hallo David, >>> >>> did you try to run your program with Helgrind already? Helgrind was >>> designed to catch problems like this. Maybe Thread Sanitizer would also >>> detect the issue. >>> >>> >>> Best regards, >>> >>> Christian >>> >>> On 3/20/22 5:44 PM, David Mozes wrote: >>>> Hi, >>>> Where are we with this? >>>> Also, the current implementation of the __pthread_rwlock_unlock is problematic. >>>> On the one hand, it checks the API agreement. However, on the case of violation, the user don't have any induction >>>> And function return OK >>>> See example code below: >>>> >>>> >>>> struct threadInfo{ >>>> pthread_t* tid; >>>> pthread_rwlock_t *rwlock; >>>> }; >>>> >>>> void *lockerThreadFunction(void *vargp) >>>> { >>>> km_status stat = KM_OK; >>>> struct threadInfo* Tinfo = (struct threadInfo*)vargp; >>>> >>>> do { >>>> stat = pthread_rwlock_trywrlock(Tinfo->rwlock); >>>> if (KM_OK == stat) { >>>> printf("[INFO] - FIRST thread 0x%x locked %p \n", *(Tinfo->tid), Tinfo->rwlock); >>>> sleep(10); >>>> stat = pthread_rwlock_unlock(Tinfo->rwlock); >>>> if (KM_OK == stat) { >>>> printf("[INFO] FIRST thread 0x%x released %p \n", *(Tinfo->tid), Tinfo->rwlock); >>>> sleep(1); >>>> } >>>> } >>>> }while(KM_OK != stat); >>>> return NULL; >>>> } >>>> >>>> >>>> void *secondThreadFunction(void *vargp) >>>> { >>>> km_status stat = KM_OK; >>>> struct threadInfo* Tinfo = (struct threadInfo*)vargp; >>>> >>>> sleep(5); >>>> do { >>>> stat = pthread_rwlock_unlock(Tinfo->rwlock); >>>> if (KM_OK == stat) { >>>> printf("[INFO] SECOND thread 0x%x released %p \n", *(Tinfo->tid), Tinfo->rwlock); >>>> sleep(1); >>>> } else >>>> printf("[INFO] SECOND thread 0x%x try_to_released %p erro status is: %d \n", *(Tinfo->tid), Tinfo->rwlock,stat); >>>> >>>> }while(KM_OK != stat); >>>> return NULL; >>>> } >>>> >>>> void *thirdThreadFunction(void *vargp) >>>> { >>>> km_status stat = KM_OK; >>>> struct threadInfo* Tinfo = (struct threadInfo*)vargp; >>>> >>>> sleep(2); >>>> do { >>>> stat = pthread_rwlock_trywrlock(Tinfo->rwlock); >>>> if (KM_OK == stat) { >>>> printf("[INFO] THIRD thread 0X%x locked %x\n", *(Tinfo->tid), Tinfo->rwlock); >>>> sleep(5); >>>> } >>>> else { >>>> printf("[ERROR]: THIRD thread 0x%x failed Locking %p status is %d\n", *(Tinfo->tid), Tinfo->rwlock,stat); >>>> sleep(1); >>>> } >>>> }while(KM_OK != stat); >>>> return NULL; >>>> } >>>> >>>> void main() >>>> { >>>> km_status stat = KM_OK; >>>> /* km_rwlock lock; */ >>>> pthread_rwlock_t rwlock; >>>> pthread_t lockerTid = 0, releaseTid = 0, thirdTid=0; >>>> struct threadInfo firstTinfo, secondTinfo, thirdTinfo; >>>> >>>> /* stat = km_rwlock_init(&rwlock, KM_TRUE); */ >>>> stat = pthread_rwlock_init (&rwlock, NULL); >>>> >>>> if (KM_OK == stat) { >>>> printf("read\\writer lock initialized\n"); >>>> printf("Before Thread\n"); >>>> >>>> firstTinfo.tid = &lockerTid; >>>> firstTinfo.rwlock = &rwlock; >>>> secondTinfo.tid = &releaseTid; >>>> secondTinfo.rwlock = &rwlock; >>>> thirdTinfo.tid = &thirdTid; >>>> thirdTinfo.rwlock = &rwlock; >>>> >>>> >>>> pthread_create(&lockerTid, NULL, lockerThreadFunction, &firstTinfo); >>>> pthread_create(&releaseTid, NULL, secondThreadFunction, &secondTinfo); >>>> pthread_create(&thirdTid, NULL, thirdThreadFunction, &thirdTinfo); >>>> printf("After Thread %x\n", lockerTid); >>>> >>>> pthread_join(lockerTid, NULL); >>>> pthread_join(releaseTid, NULL); >>>> pthread_join(thirdTid, NULL); >>>> >>>> >>>> >>>> the output we saw is this: >>>> >>>> >>>> the ouput we saw is this: >>>> >>>> [root@Rocky85Mozes thread_lock]# ./rw_test >>>> read\writer lock initialized >>>> Before Thread >>>> [INFO] - FIRST thread 0x461f700 locked 0x7ffcda053cc0 >>>> After Thread 461f700 >>>> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 -> first thread take the rwlock >>>> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 >>>> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 >>>> [INFO] SECOND thread 0x3e1e700 released 0x7ffcda053cc0 -> Second thread unlock the rwlock -- > and get OK!! >>>> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 >>>> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 >>>> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 >>>> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 >>>> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 >>>> [INFO] FIRST thread 0x461f700 released 0x7ffcda053cc0 >>>> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 >>>> >>>> >>>> -----Original Message----- >>>> From: David Mozes >>>> Sent: Sunday, March 13, 2022 12:23 PM >>>> To: Florian Weimer <fweimer@redhat.com> >>>> Cc: libc-help@sourceware.org >>>> Subject: RE: rwlock different behavior on glibc 2.28 then on previous versions >>>> >>>> Thx Florin, >>>> >>>> >>>> -----Original Message----- >>>> From: Florian Weimer <fweimer@redhat.com> >>>> Sent: Friday, March 11, 2022 3:59 PM >>>> To: David Mozes <david.mozes@silk.us> >>>> Cc: libc-help@sourceware.org >>>> Subject: Re: rwlock different behavior on glibc 2.28 then on previous versions >>>> >>>> * David Mozes: >>>> >>>>> On the previous version of Glibc (before the commit) We could release >>>>> write lock with different thread as the one that owned the lock (If we >>>>> like) . >>>> Sorry, this misuse of the API has always been undefined according to >>>> POSIX (“Results are undefined if the read-write lock rwlock is not held >>>> by the calling thread.”). >>>> >>>>>> Correct, but practically we can do it on the user's responsibility. >>>>>> Do you know if this "if" solved some synchronization issue or just enforced the undefined API? >>>>> This is help very much for async program that has a many threads that >>>>> communicate with some target. And we like to define a call back >>>>> function instead of blocking on aio thread that send the data in order >>>>> to release the rwlock.this improves the performance dramatically . >>>> Could you use a different synchronization object (perhaps a condition >>>> variable)? >>>> >>>>>> If we use a different synchronization object like semaphores, condition variable (by the way they use mutex under the same API agreement), we will need to write self rwlock , which has less performance than other undefined states. >>>>>> If we like to keep the API agreement, why not define the different async programming unlock functions? >>>> Thanks >>>> Florian >>>> >>>> Thx >>>> David
Thx sure! I will start a discussion on the Alpha soon. So you mean that if (atomic_load_relaxed (&rwlock->__data.__cur_writer) - == THREAD_GETMEM (THREAD_SELF, tid)) Used the THREAD_GETMEM (THREAD_SELF, tid)) for protection regarding the load_releax ? You may have a suggestion on how to make async programming with rw_lock? Thx David -----Original Message----- From: Adhemerval Zanella <adhemerval.zanella@linaro.org> Sent: Monday, March 21, 2022 10:20 PM To: David Mozes <david.mozes@silk.us> Cc: Christian Hoff <christian_hoff@gmx.net>; Florian Weimer <fweimer@redhat.com>; libc-help@sourceware.org; Carlos O'Donell <carlos@redhat.com> Subject: Re: rwlock different behavior on glibc 2.28 then on previous versions On 21/03/2022 16:46, David Mozes wrote: > > Thanks Adhemerval, > For the suggestion! > > I suggest to remove the check just on the unlock function.I tested it with very high load and with application with 3k active threads. > Can you on a case or bug(dedlock or something) that removing thIs check will expose? I am no sure, so I would suggest you to maybe start a discussion on libc-alpha. However __pthread_rwlock_wrunlock and __pthread_rwlock_rdunlock have different semantic allowing unlocking write locks on different threads will require a lot of analysis on why it would trigger any more regression (and sorry, but stating it works on our environment is not suffice). > Thx > David >> On Mar 21, 2022, at 7:02 PM, Adhemerval Zanella <adhemerval.zanella@linaro.org> wrote: >> >> As Florian has put, this is essentially a misuse of the API has always been >> undefined. The rwlock implementation uses __cur_write to both make a fast >> deadlock check and to know whether to handle the lock as a writer or reader >> one. The former is a implementation detail that we might change (although >> it is useful in some case), but to handle the former will most likely to >> refactor and change the rdlock algorithm (just removing the check as you are >> proposing is not suffice). >> >> Since it is not a bug in our implementation, I think you will need to discuss >> it further on the libc-alpha to see if other are willing to actually make >> this change. I foresee that the algorithm change won't be simple to keep >> interface requirements and allow the specific case you are asking. In fact >> I think it might not be actually possible without change the rwlock semantic >> (not sure though). >> >> Carlos has fixed some issue on the rwlock, he might have some comments. >> >> On 21/03/2022 11:01, David Mozes wrote: >>> Hello Christain, >>> Yes, Thread Sanitizer caught it. >>> However, we can't run it all the time on the production code. >>> We need to make a small change of the unlock code to have async programing and backward compatibility for older code. >>> >>> Thx >>> David >>> >>> -----Original Message----- >>> From: Christian Hoff <christian_hoff@gmx.net> >>> Sent: Monday, March 21, 2022 8:20 AM >>> To: David Mozes <david.mozes@silk.us>; Florian Weimer <fweimer@redhat.com> >>> Cc: libc-help@sourceware.org >>> Subject: Re: rwlock different behavior on glibc 2.28 then on previous versions >>> >>> Hallo David, >>> >>> did you try to run your program with Helgrind already? Helgrind was >>> designed to catch problems like this. Maybe Thread Sanitizer would also >>> detect the issue. >>> >>> >>> Best regards, >>> >>> Christian >>> >>> On 3/20/22 5:44 PM, David Mozes wrote: >>>> Hi, >>>> Where are we with this? >>>> Also, the current implementation of the __pthread_rwlock_unlock is problematic. >>>> On the one hand, it checks the API agreement. However, on the case of violation, the user don't have any induction >>>> And function return OK >>>> See example code below: >>>> >>>> >>>> struct threadInfo{ >>>> pthread_t* tid; >>>> pthread_rwlock_t *rwlock; >>>> }; >>>> >>>> void *lockerThreadFunction(void *vargp) >>>> { >>>> km_status stat = KM_OK; >>>> struct threadInfo* Tinfo = (struct threadInfo*)vargp; >>>> >>>> do { >>>> stat = pthread_rwlock_trywrlock(Tinfo->rwlock); >>>> if (KM_OK == stat) { >>>> printf("[INFO] - FIRST thread 0x%x locked %p \n", *(Tinfo->tid), Tinfo->rwlock); >>>> sleep(10); >>>> stat = pthread_rwlock_unlock(Tinfo->rwlock); >>>> if (KM_OK == stat) { >>>> printf("[INFO] FIRST thread 0x%x released %p \n", *(Tinfo->tid), Tinfo->rwlock); >>>> sleep(1); >>>> } >>>> } >>>> }while(KM_OK != stat); >>>> return NULL; >>>> } >>>> >>>> >>>> void *secondThreadFunction(void *vargp) >>>> { >>>> km_status stat = KM_OK; >>>> struct threadInfo* Tinfo = (struct threadInfo*)vargp; >>>> >>>> sleep(5); >>>> do { >>>> stat = pthread_rwlock_unlock(Tinfo->rwlock); >>>> if (KM_OK == stat) { >>>> printf("[INFO] SECOND thread 0x%x released %p \n", *(Tinfo->tid), Tinfo->rwlock); >>>> sleep(1); >>>> } else >>>> printf("[INFO] SECOND thread 0x%x try_to_released %p erro status is: %d \n", *(Tinfo->tid), Tinfo->rwlock,stat); >>>> >>>> }while(KM_OK != stat); >>>> return NULL; >>>> } >>>> >>>> void *thirdThreadFunction(void *vargp) >>>> { >>>> km_status stat = KM_OK; >>>> struct threadInfo* Tinfo = (struct threadInfo*)vargp; >>>> >>>> sleep(2); >>>> do { >>>> stat = pthread_rwlock_trywrlock(Tinfo->rwlock); >>>> if (KM_OK == stat) { >>>> printf("[INFO] THIRD thread 0X%x locked %x\n", *(Tinfo->tid), Tinfo->rwlock); >>>> sleep(5); >>>> } >>>> else { >>>> printf("[ERROR]: THIRD thread 0x%x failed Locking %p status is %d\n", *(Tinfo->tid), Tinfo->rwlock,stat); >>>> sleep(1); >>>> } >>>> }while(KM_OK != stat); >>>> return NULL; >>>> } >>>> >>>> void main() >>>> { >>>> km_status stat = KM_OK; >>>> /* km_rwlock lock; */ >>>> pthread_rwlock_t rwlock; >>>> pthread_t lockerTid = 0, releaseTid = 0, thirdTid=0; >>>> struct threadInfo firstTinfo, secondTinfo, thirdTinfo; >>>> >>>> /* stat = km_rwlock_init(&rwlock, KM_TRUE); */ >>>> stat = pthread_rwlock_init (&rwlock, NULL); >>>> >>>> if (KM_OK == stat) { >>>> printf("read\\writer lock initialized\n"); >>>> printf("Before Thread\n"); >>>> >>>> firstTinfo.tid = &lockerTid; >>>> firstTinfo.rwlock = &rwlock; >>>> secondTinfo.tid = &releaseTid; >>>> secondTinfo.rwlock = &rwlock; >>>> thirdTinfo.tid = &thirdTid; >>>> thirdTinfo.rwlock = &rwlock; >>>> >>>> >>>> pthread_create(&lockerTid, NULL, lockerThreadFunction, &firstTinfo); >>>> pthread_create(&releaseTid, NULL, secondThreadFunction, &secondTinfo); >>>> pthread_create(&thirdTid, NULL, thirdThreadFunction, &thirdTinfo); >>>> printf("After Thread %x\n", lockerTid); >>>> >>>> pthread_join(lockerTid, NULL); >>>> pthread_join(releaseTid, NULL); >>>> pthread_join(thirdTid, NULL); >>>> >>>> >>>> >>>> the output we saw is this: >>>> >>>> >>>> the ouput we saw is this: >>>> >>>> [root@Rocky85Mozes thread_lock]# ./rw_test >>>> read\writer lock initialized >>>> Before Thread >>>> [INFO] - FIRST thread 0x461f700 locked 0x7ffcda053cc0 >>>> After Thread 461f700 >>>> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 -> first thread take the rwlock >>>> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 >>>> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 >>>> [INFO] SECOND thread 0x3e1e700 released 0x7ffcda053cc0 -> Second thread unlock the rwlock -- > and get OK!! >>>> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 >>>> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 >>>> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 >>>> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 >>>> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 >>>> [INFO] FIRST thread 0x461f700 released 0x7ffcda053cc0 >>>> [ERROR]: THIRD thread 0x361d700 failed Locking 0x7ffcda053cc0 status is 16 >>>> >>>> >>>> -----Original Message----- >>>> From: David Mozes >>>> Sent: Sunday, March 13, 2022 12:23 PM >>>> To: Florian Weimer <fweimer@redhat.com> >>>> Cc: libc-help@sourceware.org >>>> Subject: RE: rwlock different behavior on glibc 2.28 then on previous versions >>>> >>>> Thx Florin, >>>> >>>> >>>> -----Original Message----- >>>> From: Florian Weimer <fweimer@redhat.com> >>>> Sent: Friday, March 11, 2022 3:59 PM >>>> To: David Mozes <david.mozes@silk.us> >>>> Cc: libc-help@sourceware.org >>>> Subject: Re: rwlock different behavior on glibc 2.28 then on previous versions >>>> >>>> * David Mozes: >>>> >>>>> On the previous version of Glibc (before the commit) We could release >>>>> write lock with different thread as the one that owned the lock (If we >>>>> like) . >>>> Sorry, this misuse of the API has always been undefined according to >>>> POSIX (“Results are undefined if the read-write lock rwlock is not held >>>> by the calling thread.”). >>>> >>>>>> Correct, but practically we can do it on the user's responsibility. >>>>>> Do you know if this "if" solved some synchronization issue or just enforced the undefined API? >>>>> This is help very much for async program that has a many threads that >>>>> communicate with some target. And we like to define a call back >>>>> function instead of blocking on aio thread that send the data in order >>>>> to release the rwlock.this improves the performance dramatically . >>>> Could you use a different synchronization object (perhaps a condition >>>> variable)? >>>> >>>>>> If we use a different synchronization object like semaphores, condition variable (by the way they use mutex under the same API agreement), we will need to write self rwlock , which has less performance than other undefined states. >>>>>> If we like to keep the API agreement, why not define the different async programming unlock functions? >>>> Thanks >>>> Florian >>>> >>>> Thx >>>> David