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Bug 3330205, 3362385 clock(3) SMP safety and epoch

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Change-Id: Ida1e4400489c8c19818c6af5640ab89942c8f712
This commit is contained in:
Glenn Kasten 2011-01-09 09:57:09 -08:00
parent eae3fb664e
commit 2cc0d38afb
1 changed files with 21 additions and 13 deletions
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34
libc/unistd/time.c
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@ -42,21 +42,29 @@ time(time_t *t)
return (tt.tv_sec); return (tt.tv_sec);
} }
// return monotonically increasing CPU time in ticks relative to unspecified epoch
static inline clock_t clock_now(void)
{
struct timespec tm;
clock_gettime( CLOCK_MONOTONIC, &tm);
return tm.tv_sec * CLOCKS_PER_SEC + (tm.tv_nsec * (CLOCKS_PER_SEC/1e9));
}
// initialized by the constructor below
static clock_t clock_start;
// called by dlopen when .so is loaded
__attribute__((constructor)) static void clock_crt0(void)
{
clock_start = clock_now();
}
// return elapsed CPU time in clock ticks, since start of program execution
// (spec says epoch is undefined, but glibc uses crt0 as epoch)
clock_t clock_t
clock(void) clock(void)
{ {
struct timespec tm; // note that if we are executing in a different thread than crt0, then the
static int clock_inited; // pthread_create that made us had a memory barrier so clock_start is defined
static clock_t clock_start; return clock_now() - clock_start;
clock_t now;
clock_gettime( CLOCK_MONOTONIC, &tm);
now = tm.tv_sec * CLOCKS_PER_SEC + (tm.tv_nsec * (CLOCKS_PER_SEC/1e9));
if (!clock_inited) {
clock_start = now;
clock_inited = 1;
}
return now - clock_start;
} }