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* [Bug nptl/7057] New: pthread rwlock does not implement 'writer preferred' option
@ 2008-11-26 15:57 udig at il dot ibm dot com
2008-11-26 16:11 ` [Bug nptl/7057] " drepper at redhat dot com
2008-11-30 17:35 ` sjmunroe at us dot ibm dot com
0 siblings, 2 replies; 4+ messages in thread
From: udig at il dot ibm dot com @ 2008-11-26 15:57 UTC (permalink / raw)
To: glibc-bugs
When creating a rwlock, ask for PTHREAD_RWLOCK_PREFER_WRITER_NP.
The resulting behavior is identical to PTHREAD_RWLOCK_PREFER_READER_NP, as can
be seen in the source.
The following test case shows that as long as there are readers holding the
lock, a writer thread will be starved forever.
However, if the PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP option is used, the
writer thread gets to run. It is not allowed to be recursive, however.
-------------------------------------------------------------
#define _XOPEN_SOURCE 600
#include <pthread.h>
#include <stdio.h>
#include <unistd.h>
#include <assert.h>
#include <time.h>
#include <error.h>
#include <string.h>
#define NUM_THREADS (250)
pthread_rwlock_t lock;
void *readfunc(void *arg)
{
long long id = (long long)arg;
while (1) {
struct timespec ts = {.tv_sec = 0,.tv_nsec = (id%25 +1)*1000*1000 };
assert(0==pthread_rwlock_rdlock(&lock));
nanosleep(&ts,NULL);
assert(0==pthread_rwlock_unlock(&lock));
}
}
void *writefunc(void *arg)
{
sleep(1);
assert(0==pthread_rwlock_wrlock(&lock));
// assert(0==pthread_rwlock_wrlock(&lock)); //would fail if non-recursive
printf("Writer got a chance!\n");
// assert(0==pthread_rwlock_unlock(&lock));
assert(0==pthread_rwlock_unlock(&lock));
return 0;
}
int main(int argc,char *argv[])
{
pthread_t writer,readers[NUM_THREADS];
pthread_rwlockattr_t lockattr;
assert(0==pthread_rwlockattr_init(&lockattr));
assert(0==pthread_rwlockattr_setkind_np(&lockattr,PTHREAD_RWLOCK_PREFER_WRITER_NP));
assert(0==pthread_rwlock_init(&lock,&lockattr));
assert(0==pthread_rwlockattr_destroy(&lockattr));
for (long long i=0;i<NUM_THREADS;i++)
assert(0==pthread_create(readers+i,NULL,readfunc,(void *)i));
assert(0==pthread_create(&writer,NULL,writefunc,0));
printf("main waits\n");
pthread_join(writer,NULL);
return 0;
}
--
Summary: pthread rwlock does not implement 'writer preferred'
option
Product: glibc
Version: unspecified
Status: NEW
Severity: normal
Priority: P2
Component: nptl
AssignedTo: drepper at redhat dot com
ReportedBy: udig at il dot ibm dot com
CC: glibc-bugs at sources dot redhat dot com
http://sourceware.org/bugzilla/show_bug.cgi?id=7057
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* [Bug nptl/7057] pthread rwlock does not implement 'writer preferred' option
2008-11-26 15:57 [Bug nptl/7057] New: pthread rwlock does not implement 'writer preferred' option udig at il dot ibm dot com
@ 2008-11-26 16:11 ` drepper at redhat dot com
2008-11-30 17:35 ` sjmunroe at us dot ibm dot com
1 sibling, 0 replies; 4+ messages in thread
From: drepper at redhat dot com @ 2008-11-26 16:11 UTC (permalink / raw)
To: glibc-bugs
------- Additional Comments From drepper at redhat dot com 2008-11-26 16:10 -------
And there won't be any implementation.
--
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution| |WONTFIX
http://sourceware.org/bugzilla/show_bug.cgi?id=7057
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* [Bug nptl/7057] pthread rwlock does not implement 'writer preferred' option
2008-11-26 15:57 [Bug nptl/7057] New: pthread rwlock does not implement 'writer preferred' option udig at il dot ibm dot com
2008-11-26 16:11 ` [Bug nptl/7057] " drepper at redhat dot com
@ 2008-11-30 17:35 ` sjmunroe at us dot ibm dot com
1 sibling, 0 replies; 4+ messages in thread
From: sjmunroe at us dot ibm dot com @ 2008-11-30 17:35 UTC (permalink / raw)
To: glibc-bugs
------- Additional Comments From sjmunroe at us dot ibm dot com 2008-11-30 17:33 -------
Uli I think this question deserves a more complete explanation.
This seems like a reasonable request. If you disagree then it would not hurt
to explain why.
There seems to be a valid concern related to reliable implementation of
recursive read locks with writer priority. As in this discusion:
http://sources.redhat.com/ml/libc-alpha/2000-01/msg00055.html
If this your concern then saying so would help resolve/close this issue.
--
What |Removed |Added
----------------------------------------------------------------------------
CC| |bmark at us dot ibm dot com
http://sourceware.org/bugzilla/show_bug.cgi?id=7057
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* [Bug nptl/7057] pthread rwlock does not implement 'writer preferred' option
[not found] <bug-7057-131@http.sourceware.org/bugzilla/>
@ 2014-07-01 21:11 ` fweimer at redhat dot com
0 siblings, 0 replies; 4+ messages in thread
From: fweimer at redhat dot com @ 2014-07-01 21:11 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=7057
Florian Weimer <fweimer at redhat dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Flags| |security-
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end of thread, other threads:[~2014-07-01 21:11 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2008-11-26 15:57 [Bug nptl/7057] New: pthread rwlock does not implement 'writer preferred' option udig at il dot ibm dot com
2008-11-26 16:11 ` [Bug nptl/7057] " drepper at redhat dot com
2008-11-30 17:35 ` sjmunroe at us dot ibm dot com
[not found] <bug-7057-131@http.sourceware.org/bugzilla/>
2014-07-01 21:11 ` fweimer at redhat dot com
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