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bpo-30765: Avoid blocking when PyThread_acquire_lock() is asked not to #2403

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Merged
pitrou merged 4 commits into from
Jun 26, 2017
Merged

bpo-30765: Avoid blocking when PyThread_acquire_lock() is asked not to #2403

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bpo-30765: Avoid blocking when PyThread_acquire_lock() is asked not t…
pitrou Jun 26, 2017
03ba2b4
Update 2017-06-26-14-29-50.bpo-30765.Q5iBmf.rst
pitrou Jun 26, 2017
5d4b232
Avoid core logic when taking the mutex failed
pitrou Jun 26, 2017
59973f1
Merge branch 'mutex_trylock' of github.com:pitrou/cpython into mutex_…
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.
95 changes: 50 additions & 45 deletions Python/thread_pthread.h
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Original file line number Diff line number Diff line change
Expand Up @@ -466,61 +466,66 @@ PyLockStatus
PyThread_acquire_lock_timed(PyThread_type_lock lock, PY_TIMEOUT_T microseconds,
int intr_flag)
{
PyLockStatus success;
PyLockStatus success = PY_LOCK_FAILURE;
pthread_lock *thelock = (pthread_lock *)lock;
int status, error = 0;

dprintf(("PyThread_acquire_lock_timed(%p, %lld, %d) called\n",
lock, microseconds, intr_flag));

status = pthread_mutex_lock( &thelock->mut );
CHECK_STATUS_PTHREAD("pthread_mutex_lock[1]");

if (thelock->locked == 0) {
success = PY_LOCK_ACQUIRED;
} else if (microseconds == 0) {
success = PY_LOCK_FAILURE;
} else {
struct timespec ts;
if (microseconds > 0)
MICROSECONDS_TO_TIMESPEC(microseconds, ts);
/* continue trying until we get the lock */

/* mut must be locked by me -- part of the condition
* protocol */
success = PY_LOCK_FAILURE;
while (success == PY_LOCK_FAILURE) {
if (microseconds > 0) {
status = pthread_cond_timedwait(
&thelock->lock_released,
&thelock->mut, &ts);
if (status == ETIMEDOUT)
if (microseconds == 0) {
status = pthread_mutex_trylock( &thelock->mut );
if (status != EBUSY)
CHECK_STATUS_PTHREAD("pthread_mutex_trylock[1]");
}
else {
status = pthread_mutex_lock( &thelock->mut );
CHECK_STATUS_PTHREAD("pthread_mutex_lock[1]");
}
if (status == 0) {
if (thelock->locked == 0) {
success = PY_LOCK_ACQUIRED;
}
else if (microseconds != 0) {
struct timespec ts;
if (microseconds > 0)
MICROSECONDS_TO_TIMESPEC(microseconds, ts);
/* continue trying until we get the lock */

/* mut must be locked by me -- part of the condition
* protocol */
while (success == PY_LOCK_FAILURE) {
if (microseconds > 0) {
status = pthread_cond_timedwait(
&thelock->lock_released,
&thelock->mut, &ts);
if (status == ETIMEDOUT)
break;
CHECK_STATUS_PTHREAD("pthread_cond_timed_wait");
}
else {
status = pthread_cond_wait(
&thelock->lock_released,
&thelock->mut);
CHECK_STATUS_PTHREAD("pthread_cond_wait");
}

if (intr_flag && status == 0 && thelock->locked) {
/* We were woken up, but didn't get the lock. We probably received
* a signal. Return PY_LOCK_INTR to allow the caller to handle
* it and retry. */
success = PY_LOCK_INTR;
break;
CHECK_STATUS_PTHREAD("pthread_cond_timed_wait");
}
else {
status = pthread_cond_wait(
&thelock->lock_released,
&thelock->mut);
CHECK_STATUS_PTHREAD("pthread_cond_wait");
}

if (intr_flag && status == 0 && thelock->locked) {
/* We were woken up, but didn't get the lock. We probably received
* a signal. Return PY_LOCK_INTR to allow the caller to handle
* it and retry. */
success = PY_LOCK_INTR;
break;
} else if (status == 0 && !thelock->locked) {
success = PY_LOCK_ACQUIRED;
} else {
success = PY_LOCK_FAILURE;
}
else if (status == 0 && !thelock->locked) {
success = PY_LOCK_ACQUIRED;
}
}
}
if (success == PY_LOCK_ACQUIRED) thelock->locked = 1;
status = pthread_mutex_unlock( &thelock->mut );
CHECK_STATUS_PTHREAD("pthread_mutex_unlock[1]");
}
if (success == PY_LOCK_ACQUIRED) thelock->locked = 1;
status = pthread_mutex_unlock( &thelock->mut );
CHECK_STATUS_PTHREAD("pthread_mutex_unlock[1]");

if (error) success = PY_LOCK_FAILURE;
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@vstinner vstinner Jun 26, 2017

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This code should be moved into the last if block. It seems like error is not used outside this if block.

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@pitrou pitrou Jun 26, 2017

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Actually, error is set by CHECK_STATUS_PTHREAD (yes, silly macro...).

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@vstinner vstinner Jun 26, 2017

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Ow, ignored my previous comment in that case :-)

dprintf(("PyThread_acquire_lock_timed(%p, %lld, %d) -> %d\n",
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