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musl/src/thread/pthread_barrier_wait.c

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initial check-in, version 0.5.0
2011-02-12 00:22:29 -05:00
#include "pthread_impl.h"
completely new barrier implementation, addressing major correctness issues the previous implementation had at least 2 problems: 1. the case where additional threads reached the barrier before the first wave was finished leaving the barrier was untested and seemed not to be working. 2. threads leaving the barrier continued to access memory within the barrier object after other threads had successfully returned from pthread_barrier_wait. this could lead to memory corruption or crashes if the barrier object had automatic storage in one of the waiting threads and went out of scope before all threads finished returning, or if one thread unmapped the memory in which the barrier object lived. the new implementation avoids both problems by making the barrier state essentially local to the first thread which enters the barrier wait, and forces that thread to be the last to return.
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struct instance
{
int count;
int last;
int waiters;
int finished;
};
initial check-in, version 0.5.0
2011-02-12 00:22:29 -05:00
int pthread_barrier_wait(pthread_barrier_t *b)
{
completely new barrier implementation, addressing major correctness issues the previous implementation had at least 2 problems: 1. the case where additional threads reached the barrier before the first wave was finished leaving the barrier was untested and seemed not to be working. 2. threads leaving the barrier continued to access memory within the barrier object after other threads had successfully returned from pthread_barrier_wait. this could lead to memory corruption or crashes if the barrier object had automatic storage in one of the waiting threads and went out of scope before all threads finished returning, or if one thread unmapped the memory in which the barrier object lived. the new implementation avoids both problems by making the barrier state essentially local to the first thread which enters the barrier wait, and forces that thread to be the last to return.
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int limit = b->_b_limit;
struct instance *inst;
initial check-in, version 0.5.0
2011-02-12 00:22:29 -05:00
/* Trivial case: count was set at 1 */
completely new barrier implementation, addressing major correctness issues the previous implementation had at least 2 problems: 1. the case where additional threads reached the barrier before the first wave was finished leaving the barrier was untested and seemed not to be working. 2. threads leaving the barrier continued to access memory within the barrier object after other threads had successfully returned from pthread_barrier_wait. this could lead to memory corruption or crashes if the barrier object had automatic storage in one of the waiting threads and went out of scope before all threads finished returning, or if one thread unmapped the memory in which the barrier object lived. the new implementation avoids both problems by making the barrier state essentially local to the first thread which enters the barrier wait, and forces that thread to be the last to return.
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if (!limit) return PTHREAD_BARRIER_SERIAL_THREAD;
initial check-in, version 0.5.0
2011-02-12 00:22:29 -05:00
completely new barrier implementation, addressing major correctness issues the previous implementation had at least 2 problems: 1. the case where additional threads reached the barrier before the first wave was finished leaving the barrier was untested and seemed not to be working. 2. threads leaving the barrier continued to access memory within the barrier object after other threads had successfully returned from pthread_barrier_wait. this could lead to memory corruption or crashes if the barrier object had automatic storage in one of the waiting threads and went out of scope before all threads finished returning, or if one thread unmapped the memory in which the barrier object lived. the new implementation avoids both problems by making the barrier state essentially local to the first thread which enters the barrier wait, and forces that thread to be the last to return.
2011-05-06 20:00:59 -04:00
/* Otherwise we need a lock on the barrier object */
while (a_swap(&b->_b_lock, 1))
__wait(&b->_b_lock, &b->_b_waiters, 1, 0);
inst = b->_b_inst;
initial check-in, version 0.5.0
2011-02-12 00:22:29 -05:00
completely new barrier implementation, addressing major correctness issues the previous implementation had at least 2 problems: 1. the case where additional threads reached the barrier before the first wave was finished leaving the barrier was untested and seemed not to be working. 2. threads leaving the barrier continued to access memory within the barrier object after other threads had successfully returned from pthread_barrier_wait. this could lead to memory corruption or crashes if the barrier object had automatic storage in one of the waiting threads and went out of scope before all threads finished returning, or if one thread unmapped the memory in which the barrier object lived. the new implementation avoids both problems by making the barrier state essentially local to the first thread which enters the barrier wait, and forces that thread to be the last to return.
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/* First thread to enter the barrier becomes the "instance owner" */
if (!inst) {
struct instance new_inst = { 0 };
int spins = 10000;
b->_b_inst = inst = &new_inst;
a_store(&b->_b_lock, 0);
if (b->_b_waiters) __wake(&b->_b_lock, 1, 0);
while (spins-- && !inst->finished)
a_spin();
a_inc(&inst->finished);
while (inst->finished == 1)
__syscall(SYS_futex, &inst->finished, FUTEX_WAIT,1,0);
initial check-in, version 0.5.0
2011-02-12 00:22:29 -05:00
return PTHREAD_BARRIER_SERIAL_THREAD;
}
completely new barrier implementation, addressing major correctness issues the previous implementation had at least 2 problems: 1. the case where additional threads reached the barrier before the first wave was finished leaving the barrier was untested and seemed not to be working. 2. threads leaving the barrier continued to access memory within the barrier object after other threads had successfully returned from pthread_barrier_wait. this could lead to memory corruption or crashes if the barrier object had automatic storage in one of the waiting threads and went out of scope before all threads finished returning, or if one thread unmapped the memory in which the barrier object lived. the new implementation avoids both problems by making the barrier state essentially local to the first thread which enters the barrier wait, and forces that thread to be the last to return.
2011-05-06 20:00:59 -04:00
/* Last thread to enter the barrier wakes all non-instance-owners */
if (++inst->count == limit) {
b->_b_inst = 0;
a_store(&b->_b_lock, 0);
if (b->_b_waiters) __wake(&b->_b_lock, 1, 0);
a_store(&inst->last, 1);
if (inst->waiters)
__wake(&inst->last, -1, 0);
} else {
a_store(&b->_b_lock, 0);
if (b->_b_waiters) __wake(&b->_b_lock, 1, 0);
__wait(&inst->last, &inst->waiters, 0, 0);
}
initial check-in, version 0.5.0
2011-02-12 00:22:29 -05:00
completely new barrier implementation, addressing major correctness issues the previous implementation had at least 2 problems: 1. the case where additional threads reached the barrier before the first wave was finished leaving the barrier was untested and seemed not to be working. 2. threads leaving the barrier continued to access memory within the barrier object after other threads had successfully returned from pthread_barrier_wait. this could lead to memory corruption or crashes if the barrier object had automatic storage in one of the waiting threads and went out of scope before all threads finished returning, or if one thread unmapped the memory in which the barrier object lived. the new implementation avoids both problems by making the barrier state essentially local to the first thread which enters the barrier wait, and forces that thread to be the last to return.
2011-05-06 20:00:59 -04:00
/* Last thread to exit the barrier wakes the instance owner */
if (a_fetch_add(&inst->count,-1)==1 && a_fetch_add(&inst->finished,1))
__wake(&inst->finished, 1, 0);
initial check-in, version 0.5.0
2011-02-12 00:22:29 -05:00
return 0;
}
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