Skip to content

[2.7] bpo-30765: Avoid blocking when PyThread_acquire_lock() is asked not to (GH-2403) #2420

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
pitrou merged 2 commits into from
Jun 26, 2017
Merged

[2.7] bpo-30765: Avoid blocking when PyThread_acquire_lock() is asked not to (GH-2403) #2420

Show file tree
Hide file tree
Changes from 1 commit
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
afaaf4b
[2.7] bpo-30765: Avoid blocking when PyThread_acquire_lock() is asked…
pitrou Jun 26, 2017
689446a
Remove test undef
pitrou Jun 26, 2017
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
Next Next commit
[2.7] bpo-30765: Avoid blocking when PyThread_acquire_lock() is asked… 
… not to (GH-2403)

* bpo-30765: Avoid blocking when PyThread_acquire_lock() is asked not to lock

This is especially important if PyThread_acquire_lock() is called reentrantly
(for example from a signal handler).

* Update 2017-06-26-14-29-50.bpo-30765.Q5iBmf.rst

* Avoid core logic when taking the mutex failed.
(cherry picked from commit f84ac42)
  • Loading branch information
@pitrou
pitrou committed Jun 26, 2017
commit afaaf4b2c57c997430c71ad815bf979d2639969f
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2017-06-26-14-29-50.bpo-30765.Q5iBmf.rst
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Avoid blocking in pthread_mutex_lock() when PyThread_acquire_lock() is asked
not to block.
47 changes: 29 additions & 18 deletions Python/thread_pthread.h
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -81,6 +81,7 @@
#else
# undef USE_SEMAPHORES
#endif
# undef USE_SEMAPHORES


/* On platforms that don't use standard POSIX threads pthread_sigmask()
Expand Down Expand Up @@ -410,31 +411,41 @@ PyThread_free_lock(PyThread_type_lock lock)
int
PyThread_acquire_lock(PyThread_type_lock lock, int waitflag)
{
int success;
int success = 0;
pthread_lock *thelock = (pthread_lock *)lock;
int status, error = 0;

dprintf(("PyThread_acquire_lock(%p, %d) called\n", lock, waitflag));

status = pthread_mutex_lock( &thelock->mut );
CHECK_STATUS("pthread_mutex_lock[1]");
success = thelock->locked == 0;

if ( !success && waitflag ) {
/* continue trying until we get the lock */

/* mut must be locked by me -- part of the condition
* protocol */
while ( thelock->locked ) {
status = pthread_cond_wait(&thelock->lock_released,
&thelock->mut);
CHECK_STATUS("pthread_cond_wait");
if (waitflag) {
status = pthread_mutex_lock( &thelock->mut );
CHECK_STATUS("pthread_mutex_lock[1]");
}
else {
status = pthread_mutex_trylock( &thelock->mut );
if (status != EBUSY)
CHECK_STATUS("pthread_mutex_trylock[1]");
}
if (status == 0) {
success = thelock->locked == 0;

if ( !success && waitflag ) {
/* continue trying until we get the lock */

/* mut must be locked by me -- part of the condition
* protocol */
while ( thelock->locked ) {
status = pthread_cond_wait(&thelock->lock_released,
&thelock->mut);
CHECK_STATUS("pthread_cond_wait");
}
success = 1;
}
success = 1;

if (success) thelock->locked = 1;
status = pthread_mutex_unlock( &thelock->mut );
CHECK_STATUS("pthread_mutex_unlock[1]");
}
if (success) thelock->locked = 1;
status = pthread_mutex_unlock( &thelock->mut );
CHECK_STATUS("pthread_mutex_unlock[1]");

if (error) success = 0;
dprintf(("PyThread_acquire_lock(%p, %d) -> %d\n", lock, waitflag, success));
Expand Down