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Use a condition variable to control busy threads in dispatch_apply test #93

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Merged
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Jun 27, 2016
Merged

Use a condition variable to control busy threads in dispatch_apply test #93

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19 changes: 8 additions & 11 deletions tests/dispatch_apply.c
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Original file line number Diff line number Diff line change
Expand Up @@ -37,15 +37,7 @@ static volatile int32_t busy_threads_started, busy_threads_finished;
/*
* Keep a thread busy, spinning on the CPU.
*/
#if TARGET_OS_EMBEDDED
// iPhone 4
#define ITERS_PER_SECOND 50000000UL
#elif __s390x__
#define ITERS_PER_SECOND 15000000000UL
#else
// On a 2.7 4-core i5 iMac12,2, one thread of this loop runs at ROUGHLY:
#define ITERS_PER_SECOND 1000000000UL
#endif
static volatile int all_done = 0;

/* Fiddling with j in the middle and hitting this global will hopefully keep
* the optimizer from cutting the whole thing out as dead code.
Expand All @@ -54,14 +46,16 @@ static volatile unsigned int busythread_useless;
void busythread(void *ignored)
{
(void)ignored;
uint64_t i = 0, j = 0;
/* prevent i and j been optimized out */
volatile uint64_t i = 0, j = 0;

OSAtomicIncrement32(&busy_threads_started);

for(i = 0; i < 2*ITERS_PER_SECOND; i++)
while(!all_done)
{
if(i == 500000) { j -= busythread_useless; }
j += i;
i += 1;
}

OSAtomicIncrement32(&busy_threads_finished);
Expand Down Expand Up @@ -109,6 +103,9 @@ void test_apply_contended(dispatch_queue_t dq)
test_long("contended: count", count, final);
test_long("contended: threads finished before apply", after, 0);

/* Release busy threads by setting all_done to 1 */
all_done = 1;

dispatch_group_wait(grp, DISPATCH_TIME_FOREVER);
dispatch_release(grp);

Expand Down