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

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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

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[2.7] bpo-30765: Avoid blocking when PyThread_acquire_lock() is asked…
pitrou Jun 26, 2017
689446a
Remove test undef
pitrou Jun 26, 2017
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2017-06-26-14-29-50.bpo-30765.Q5iBmf.rst
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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.
46 changes: 28 additions & 18 deletions Python/thread_pthread.h
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Original file line number Diff line number Diff line change
Expand Up @@ -410,31 +410,41 @@ 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));
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