* [PATCH 1/2] [gdb] Rename variable main_thread to main_thread_id @ 2023-07-28 10:59 Tom de Vries 2023-07-28 10:59 ` [PATCH 2/2] [gdb] Initialize main_thread_id earlier Tom de Vries 2023-07-28 13:06 ` [PATCH 1/2] [gdb] Rename variable main_thread to main_thread_id Tom Tromey 0 siblings, 2 replies; 11+ messages in thread From: Tom de Vries @ 2023-07-28 10:59 UTC (permalink / raw) To: gdb-patches I noticed that the variable main_thread: ... /* The main thread. */ static std::thread::id main_thread; ... has a confusing name and corresponding comment, because it doesn't contain the main thread, but rather the main thread's std::thread::id. Fix this by renaming to main_thread_id. Tested on x86_64-linux. --- gdb/run-on-main-thread.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/gdb/run-on-main-thread.c b/gdb/run-on-main-thread.c index c7d9de0afc8..91d25dae28f 100644 --- a/gdb/run-on-main-thread.c +++ b/gdb/run-on-main-thread.c @@ -39,9 +39,9 @@ static std::vector<std::function<void ()>> runnables; static std::mutex runnable_mutex; -/* The main thread. */ +/* The main thread's thread id. */ -static std::thread::id main_thread; +static std::thread::id main_thread_id; #endif @@ -100,7 +100,7 @@ bool is_main_thread () { #if CXX_STD_THREAD - return std::this_thread::get_id () == main_thread; + return std::this_thread::get_id () == main_thread_id; #else return true; #endif @@ -111,7 +111,7 @@ void _initialize_run_on_main_thread () { #if CXX_STD_THREAD - main_thread = std::this_thread::get_id (); + main_thread_id = std::this_thread::get_id (); #endif runnable_event = make_serial_event (); add_file_handler (serial_event_fd (runnable_event), run_events, nullptr, base-commit: 29c108c9610640439daa5244a573348b7c47d994 -- 2.35.3 ^ permalink raw reply [flat|nested] 11+ messages in thread
* [PATCH 2/2] [gdb] Initialize main_thread_id earlier 2023-07-28 10:59 [PATCH 1/2] [gdb] Rename variable main_thread to main_thread_id Tom de Vries @ 2023-07-28 10:59 ` Tom de Vries 2023-07-28 13:10 ` Tom Tromey 2023-07-28 15:36 ` Pedro Alves 2023-07-28 13:06 ` [PATCH 1/2] [gdb] Rename variable main_thread to main_thread_id Tom Tromey 1 sibling, 2 replies; 11+ messages in thread From: Tom de Vries @ 2023-07-28 10:59 UTC (permalink / raw) To: gdb-patches I wrote a patch using is_main_thread (), and found it returning false in the main thread due to main_thread_id not being initialized yet. Initialization currently takes place in _initialize_run_on_main_thread, but that's too late for earlier uses. Fix this by also initializing on first use. Tested on x86_64-linux. --- gdb/run-on-main-thread.c | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-) diff --git a/gdb/run-on-main-thread.c b/gdb/run-on-main-thread.c index 91d25dae28f..bee5885d9a6 100644 --- a/gdb/run-on-main-thread.c +++ b/gdb/run-on-main-thread.c @@ -94,12 +94,27 @@ run_on_main_thread (std::function<void ()> &&func) serial_event_set (runnable_event); } +#if CXX_STD_THREAD +static void +initialize_main_thread_id (void) +{ + static bool initialized = false; + + if (initialized) + return; + initialized = true; + + main_thread_id = std::this_thread::get_id (); +} +#endif + /* See run-on-main-thread.h. */ bool is_main_thread () { #if CXX_STD_THREAD + initialize_main_thread_id (); return std::this_thread::get_id () == main_thread_id; #else return true; @@ -111,7 +126,7 @@ void _initialize_run_on_main_thread () { #if CXX_STD_THREAD - main_thread_id = std::this_thread::get_id (); + initialize_main_thread_id (); #endif runnable_event = make_serial_event (); add_file_handler (serial_event_fd (runnable_event), run_events, nullptr, -- 2.35.3 ^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH 2/2] [gdb] Initialize main_thread_id earlier 2023-07-28 10:59 ` [PATCH 2/2] [gdb] Initialize main_thread_id earlier Tom de Vries @ 2023-07-28 13:10 ` Tom Tromey 2023-08-02 14:26 ` Tom de Vries 2023-07-28 15:36 ` Pedro Alves 1 sibling, 1 reply; 11+ messages in thread From: Tom Tromey @ 2023-07-28 13:10 UTC (permalink / raw) To: Tom de Vries via Gdb-patches; +Cc: Tom de Vries >>>>> "Tom" == Tom de Vries via Gdb-patches <gdb-patches@sourceware.org> writes: Tom> I wrote a patch using is_main_thread (), and found it returning false in the Tom> main thread due to main_thread_id not being initialized yet. Tom> Initialization currently takes place in _initialize_run_on_main_thread, but Tom> that's too late for earlier uses. Tom> Fix this by also initializing on first use. I wonder if it's enough to have: static std::thread::id main_thread_id = std::this_thread::get_id (); Tom> +#if CXX_STD_THREAD Tom> +static void Tom> +initialize_main_thread_id (void) "(void)" is only needed for C, you can just write "()" here. Tom ^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH 2/2] [gdb] Initialize main_thread_id earlier 2023-07-28 13:10 ` Tom Tromey @ 2023-08-02 14:26 ` Tom de Vries 2023-08-02 16:55 ` Tom Tromey 0 siblings, 1 reply; 11+ messages in thread From: Tom de Vries @ 2023-08-02 14:26 UTC (permalink / raw) To: Tom Tromey, Tom de Vries via Gdb-patches On 7/28/23 15:10, Tom Tromey wrote: >>>>>> "Tom" == Tom de Vries via Gdb-patches <gdb-patches@sourceware.org> writes: > > Tom> I wrote a patch using is_main_thread (), and found it returning false in the > Tom> main thread due to main_thread_id not being initialized yet. > > Tom> Initialization currently takes place in _initialize_run_on_main_thread, but > Tom> that's too late for earlier uses. > > Tom> Fix this by also initializing on first use. > > I wonder if it's enough to have: > > static std::thread::id main_thread_id = std::this_thread::get_id (); > In principle it's enough but it does expose us to the "Static Initialization Order Fiasco" [1], so I prefer this solution. > Tom> +#if CXX_STD_THREAD > Tom> +static void > Tom> +initialize_main_thread_id (void) > > "(void)" is only needed for C, you can just write "()" here. > Ack, I'll update it in my reply to Pedro. Thanks, - Tom [1] https://en.cppreference.com/w/cpp/language/siof ^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH 2/2] [gdb] Initialize main_thread_id earlier 2023-08-02 14:26 ` Tom de Vries @ 2023-08-02 16:55 ` Tom Tromey 2023-08-02 18:46 ` Tom de Vries 0 siblings, 1 reply; 11+ messages in thread From: Tom Tromey @ 2023-08-02 16:55 UTC (permalink / raw) To: Tom de Vries via Gdb-patches; +Cc: Tom Tromey, Tom de Vries >>>>> "Tom" == Tom de Vries via Gdb-patches <gdb-patches@sourceware.org> writes: >> I wonder if it's enough to have: >> static std::thread::id main_thread_id = std::this_thread::get_id (); Tom> In principle it's enough but it does expose us to the "Static Tom> Initialization Order Fiasco" [1], so I prefer this solution. If we think it's safe enough to initialize it on first use, just moving the definition into is_main_thread is enough to avoid this problem. Now, in theory it is possible for gdb to start a thread very early and then have that thread call is_main_thread, setting the global incorrectly. If we care about that then we need an explicit call to set it early during startup. Tom ^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH 2/2] [gdb] Initialize main_thread_id earlier 2023-08-02 16:55 ` Tom Tromey @ 2023-08-02 18:46 ` Tom de Vries 2023-08-02 20:48 ` Tom Tromey 0 siblings, 1 reply; 11+ messages in thread From: Tom de Vries @ 2023-08-02 18:46 UTC (permalink / raw) To: Tom Tromey, Tom de Vries via Gdb-patches [-- Attachment #1: Type: text/plain, Size: 888 bytes --] On 8/2/23 18:55, Tom Tromey wrote: >>>>>> "Tom" == Tom de Vries via Gdb-patches <gdb-patches@sourceware.org> writes: > >>> I wonder if it's enough to have: >>> static std::thread::id main_thread_id = std::this_thread::get_id (); > > Tom> In principle it's enough but it does expose us to the "Static > Tom> Initialization Order Fiasco" [1], so I prefer this solution. > > If we think it's safe enough to initialize it on first use, just moving > the definition into is_main_thread is enough to avoid this problem. > Done. > Now, in theory it is possible for gdb to start a thread very early and > then have that thread call is_main_thread, setting the global > incorrectly. If we care about that then we need an explicit call to set > it early during startup. Yes, Pedro had the same remark, that was already fixed in the previous version. Any further comments? Thanks, - Tom [-- Attachment #2: 0001-gdb-Initialize-main_thread_id-earlier.patch --] [-- Type: text/x-patch, Size: 2694 bytes --] From dc19a86c9fd189bb2e7394199e5fda0179d8e6cb Mon Sep 17 00:00:00 2001 From: Tom de Vries <tdevries@suse.de> Date: Fri, 28 Jul 2023 11:41:07 +0200 Subject: [PATCH] [gdb] Initialize main_thread_id earlier I wrote a patch using is_main_thread (), and found it returning false in the main thread due to main_thread_id not being initialized yet. Initialization currently takes place in _initialize_run_on_main_thread, but that's too late for earlier uses. Fix this by initializing, either: - when entering main, or - on an earlier first use. Tested on x86_64-linux. --- gdb/gdb.c | 7 +++++++ gdb/run-on-main-thread.c | 19 ++++++++++++++++++- 2 files changed, 25 insertions(+), 1 deletion(-) diff --git a/gdb/gdb.c b/gdb/gdb.c index 71a3fd12ba1..6e3ff0755ab 100644 --- a/gdb/gdb.c +++ b/gdb/gdb.c @@ -19,10 +19,17 @@ #include "defs.h" #include "main.h" #include "interps.h" +#include "run-on-main-thread.h" int main (int argc, char **argv) { + /* The first call to is_main_thread () should be from the main thread. + If this is the first call, then that requirement is fulfilled here. + If this is not the first call, then this verifies that the first call + fulfilled that requirement. */ + gdb_assert (is_main_thread ()); + struct captured_main_args args; memset (&args, 0, sizeof args); diff --git a/gdb/run-on-main-thread.c b/gdb/run-on-main-thread.c index 91d25dae28f..e5c9a775b13 100644 --- a/gdb/run-on-main-thread.c +++ b/gdb/run-on-main-thread.c @@ -94,12 +94,24 @@ run_on_main_thread (std::function<void ()> &&func) serial_event_set (runnable_event); } +#if CXX_STD_THREAD +static bool main_thread_id_initialized = false; +#endif + /* See run-on-main-thread.h. */ bool is_main_thread () { #if CXX_STD_THREAD + /* Initialize main_thread_id on first use of is_main_thread. */ + if (!main_thread_id_initialized) + { + main_thread_id_initialized = true; + + main_thread_id = std::this_thread::get_id (); + } + return std::this_thread::get_id () == main_thread_id; #else return true; @@ -111,7 +123,12 @@ void _initialize_run_on_main_thread () { #if CXX_STD_THREAD - main_thread_id = std::this_thread::get_id (); + /* The variable main_thread_id should be initialized when entering main, or + at an earlier use, so it should already be initialized here. */ + gdb_assert (main_thread_id_initialized); + + /* Assume that we execute this in the main thread. */ + gdb_assert (is_main_thread ()); #endif runnable_event = make_serial_event (); add_file_handler (serial_event_fd (runnable_event), run_events, nullptr, base-commit: 86bb2d76c901a558e5b2dd29df95874ce6e78dae -- 2.35.3 ^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH 2/2] [gdb] Initialize main_thread_id earlier 2023-08-02 18:46 ` Tom de Vries @ 2023-08-02 20:48 ` Tom Tromey 2023-08-02 21:21 ` Tom de Vries 0 siblings, 1 reply; 11+ messages in thread From: Tom Tromey @ 2023-08-02 20:48 UTC (permalink / raw) To: Tom de Vries via Gdb-patches; +Cc: Tom Tromey, Tom de Vries >>>>> "Tom" == Tom de Vries via Gdb-patches <gdb-patches@sourceware.org> writes: >> If we think it's safe enough to initialize it on first use, just >> moving >> the definition into is_main_thread is enough to avoid this problem. >> Tom> Done. This wasn't really what I meant but it's not important. Approved-By: Tom Tromey <tom@tromey.com> Tom ^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH 2/2] [gdb] Initialize main_thread_id earlier 2023-08-02 20:48 ` Tom Tromey @ 2023-08-02 21:21 ` Tom de Vries 0 siblings, 0 replies; 11+ messages in thread From: Tom de Vries @ 2023-08-02 21:21 UTC (permalink / raw) To: Tom Tromey, Tom de Vries via Gdb-patches On 8/2/23 22:48, Tom Tromey wrote: >>>>>> "Tom" == Tom de Vries via Gdb-patches <gdb-patches@sourceware.org> writes: > >>> If we think it's safe enough to initialize it on first use, just >>> moving >>> the definition into is_main_thread is enough to avoid this problem. >>> > > Tom> Done. > > This wasn't really what I meant but it's not important. > Thanks for the review. Sorry for misunderstanding this, if you'd like me to follow up in any way, let me know. Committed. Thanks, - Tom > Approved-By: Tom Tromey <tom@tromey.com> > > Tom ^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH 2/2] [gdb] Initialize main_thread_id earlier 2023-07-28 10:59 ` [PATCH 2/2] [gdb] Initialize main_thread_id earlier Tom de Vries 2023-07-28 13:10 ` Tom Tromey @ 2023-07-28 15:36 ` Pedro Alves 2023-08-02 14:45 ` Tom de Vries 1 sibling, 1 reply; 11+ messages in thread From: Pedro Alves @ 2023-07-28 15:36 UTC (permalink / raw) To: Tom de Vries, gdb-patches On 2023-07-28 11:59, Tom de Vries via Gdb-patches wrote: > I wrote a patch using is_main_thread (), and found it returning false in the > main thread due to main_thread_id not being initialized yet. > > Initialization currently takes place in _initialize_run_on_main_thread, but > that's too late for earlier uses. > > Fix this by also initializing on first use. > > Tested on x86_64-linux. > --- > gdb/run-on-main-thread.c | 17 ++++++++++++++++- > 1 file changed, 16 insertions(+), 1 deletion(-) > > diff --git a/gdb/run-on-main-thread.c b/gdb/run-on-main-thread.c > index 91d25dae28f..bee5885d9a6 100644 > --- a/gdb/run-on-main-thread.c > +++ b/gdb/run-on-main-thread.c > @@ -94,12 +94,27 @@ run_on_main_thread (std::function<void ()> &&func) > serial_event_set (runnable_event); > } > > +#if CXX_STD_THREAD > +static void > +initialize_main_thread_id (void) > +{ > + static bool initialized = false; > + > + if (initialized) > + return; > + initialized = true; > + > + main_thread_id = std::this_thread::get_id (); > +} > +#endif > + > /* See run-on-main-thread.h. */ > > bool > is_main_thread () > { > #if CXX_STD_THREAD > + initialize_main_thread_id (); This is assuming that is_main_thread() will always be called once by the main thread, before any other thread could call it. Otherwise if is_main_thread is called by some other thread first, is_main_thread -> initialize_main_thread_id will record the wrong thread id in the main_thread_id. At least a comment somewhere would be warranted. I think putting: gdb_assert (is_main_thread ()); somewhere in the early main code would be good. It would prevent such situation from ever happening undetected. ^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH 2/2] [gdb] Initialize main_thread_id earlier 2023-07-28 15:36 ` Pedro Alves @ 2023-08-02 14:45 ` Tom de Vries 0 siblings, 0 replies; 11+ messages in thread From: Tom de Vries @ 2023-08-02 14:45 UTC (permalink / raw) To: Pedro Alves, gdb-patches, Tom Tromey [-- Attachment #1: Type: text/plain, Size: 1908 bytes --] On 7/28/23 17:36, Pedro Alves wrote: > On 2023-07-28 11:59, Tom de Vries via Gdb-patches wrote: >> I wrote a patch using is_main_thread (), and found it returning false in the >> main thread due to main_thread_id not being initialized yet. >> >> Initialization currently takes place in _initialize_run_on_main_thread, but >> that's too late for earlier uses. >> >> Fix this by also initializing on first use. >> >> Tested on x86_64-linux. >> --- >> gdb/run-on-main-thread.c | 17 ++++++++++++++++- >> 1 file changed, 16 insertions(+), 1 deletion(-) >> >> diff --git a/gdb/run-on-main-thread.c b/gdb/run-on-main-thread.c >> index 91d25dae28f..bee5885d9a6 100644 >> --- a/gdb/run-on-main-thread.c >> +++ b/gdb/run-on-main-thread.c >> @@ -94,12 +94,27 @@ run_on_main_thread (std::function<void ()> &&func) >> serial_event_set (runnable_event); >> } >> >> +#if CXX_STD_THREAD >> +static void >> +initialize_main_thread_id (void) >> +{ >> + static bool initialized = false; >> + >> + if (initialized) >> + return; >> + initialized = true; >> + >> + main_thread_id = std::this_thread::get_id (); >> +} >> +#endif >> + >> /* See run-on-main-thread.h. */ >> >> bool >> is_main_thread () >> { >> #if CXX_STD_THREAD >> + initialize_main_thread_id (); > Hi Pedro, thanks for the review. > This is assuming that is_main_thread() will always be called once by > the main thread, before any other thread could call it. Otherwise if > is_main_thread is called by some other thread first, > is_main_thread -> initialize_main_thread_id will record the wrong thread > id in the main_thread_id. At least a comment somewhere would > be warranted. I think putting: > > gdb_assert (is_main_thread ()); > > somewhere in the early main code would be good. It would prevent such > situation from ever happening undetected. > Updated accordingly. Any further comments? Thanks, - Tom [-- Attachment #2: 0001-gdb-Initialize-main_thread_id-earlier.patch --] [-- Type: text/x-patch, Size: 2775 bytes --] From 3886892551c9e35b6ea36a6df23167fa3690a319 Mon Sep 17 00:00:00 2001 From: Tom de Vries <tdevries@suse.de> Date: Fri, 28 Jul 2023 11:41:07 +0200 Subject: [PATCH] [gdb] Initialize main_thread_id earlier I wrote a patch using is_main_thread (), and found it returning false in the main thread due to main_thread_id not being initialized yet. Initialization currently takes place in _initialize_run_on_main_thread, but that's too late for earlier uses. Fix this by initializing, either: - when entering main, or - on an earlier first use. Tested on x86_64-linux. --- gdb/gdb.c | 7 +++++++ gdb/run-on-main-thread.c | 24 +++++++++++++++++++++++- 2 files changed, 30 insertions(+), 1 deletion(-) diff --git a/gdb/gdb.c b/gdb/gdb.c index 71a3fd12ba1..6e3ff0755ab 100644 --- a/gdb/gdb.c +++ b/gdb/gdb.c @@ -19,10 +19,17 @@ #include "defs.h" #include "main.h" #include "interps.h" +#include "run-on-main-thread.h" int main (int argc, char **argv) { + /* The first call to is_main_thread () should be from the main thread. + If this is the first call, then that requirement is fulfilled here. + If this is not the first call, then this verifies that the first call + fulfilled that requirement. */ + gdb_assert (is_main_thread ()); + struct captured_main_args args; memset (&args, 0, sizeof args); diff --git a/gdb/run-on-main-thread.c b/gdb/run-on-main-thread.c index 91d25dae28f..5d453ffe612 100644 --- a/gdb/run-on-main-thread.c +++ b/gdb/run-on-main-thread.c @@ -94,12 +94,29 @@ run_on_main_thread (std::function<void ()> &&func) serial_event_set (runnable_event); } +#if CXX_STD_THREAD +static bool main_thread_id_initialized = false; + +static void +initialize_main_thread_id () +{ + if ( main_thread_id_initialized) + return; + main_thread_id_initialized = true; + + main_thread_id = std::this_thread::get_id (); +} +#endif + /* See run-on-main-thread.h. */ bool is_main_thread () { #if CXX_STD_THREAD + /* Initialize main_thread_id on first use of is_main_thread. */ + initialize_main_thread_id (); + return std::this_thread::get_id () == main_thread_id; #else return true; @@ -111,7 +128,12 @@ void _initialize_run_on_main_thread () { #if CXX_STD_THREAD - main_thread_id = std::this_thread::get_id (); + /* The variable main_thread_id should be initialized when entering main, or + at an earlier use, so it should already be initialized here. */ + gdb_assert (main_thread_id_initialized); + + /* Assume that we execute this in the main thread. */ + gdb_assert (is_main_thread ()); #endif runnable_event = make_serial_event (); add_file_handler (serial_event_fd (runnable_event), run_events, nullptr, base-commit: b5c37946cce4b41af0436529b139fa3d23e61f73 -- 2.35.3 ^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH 1/2] [gdb] Rename variable main_thread to main_thread_id 2023-07-28 10:59 [PATCH 1/2] [gdb] Rename variable main_thread to main_thread_id Tom de Vries 2023-07-28 10:59 ` [PATCH 2/2] [gdb] Initialize main_thread_id earlier Tom de Vries @ 2023-07-28 13:06 ` Tom Tromey 1 sibling, 0 replies; 11+ messages in thread From: Tom Tromey @ 2023-07-28 13:06 UTC (permalink / raw) To: Tom de Vries via Gdb-patches; +Cc: Tom de Vries >>>>> "Tom" == Tom de Vries via Gdb-patches <gdb-patches@sourceware.org> writes: Tom> I noticed that the variable main_thread: Tom> ... Tom> /* The main thread. */ Tom> static std::thread::id main_thread; Tom> ... Tom> has a confusing name and corresponding comment, because it doesn't contain the Tom> main thread, but rather the main thread's std::thread::id. Tom> Fix this by renaming to main_thread_id. Thanks. Approved-By: Tom Tromey <tom@tromey.com> Tom ^ permalink raw reply [flat|nested] 11+ messages in thread
end of thread, other threads:[~2023-08-02 21:21 UTC | newest] Thread overview: 11+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2023-07-28 10:59 [PATCH 1/2] [gdb] Rename variable main_thread to main_thread_id Tom de Vries 2023-07-28 10:59 ` [PATCH 2/2] [gdb] Initialize main_thread_id earlier Tom de Vries 2023-07-28 13:10 ` Tom Tromey 2023-08-02 14:26 ` Tom de Vries 2023-08-02 16:55 ` Tom Tromey 2023-08-02 18:46 ` Tom de Vries 2023-08-02 20:48 ` Tom Tromey 2023-08-02 21:21 ` Tom de Vries 2023-07-28 15:36 ` Pedro Alves 2023-08-02 14:45 ` Tom de Vries 2023-07-28 13:06 ` [PATCH 1/2] [gdb] Rename variable main_thread to main_thread_id Tom Tromey
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