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8040140: System.nanoTime() is slow and non-monotonic on OS X

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Reviewed-by: sspitsyn, shade, dholmes, acorn
This commit is contained in:
Staffan Larsen 2014-04-25 07:40:33 +02:00
parent a162ea836e
commit 0ef4fb7100
5 changed files with 76 additions and 61 deletions
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43
hotspot/src/os/bsd/vm/os_bsd.cpp
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@ -127,8 +127,12 @@
// global variables
julong os::Bsd::_physical_memory = 0;
#ifdef __APPLE__
mach_timebase_info_data_t os::Bsd::_timebase_info = {0, 0};
volatile uint64_t os::Bsd::_max_abstime = 0;
#else
int (*os::Bsd::_clock_gettime)(clockid_t, struct timespec *) = NULL;
#endif
pthread_t os::Bsd::_main_thread;
int os::Bsd::_page_size = -1;
@ -986,13 +990,15 @@ jlong os::javaTimeMillis() {
return jlong(time.tv_sec) * 1000 + jlong(time.tv_usec / 1000);
}
#ifndef __APPLE__
#ifndef CLOCK_MONOTONIC
#define CLOCK_MONOTONIC (1)
#endif
#endif
#ifdef __APPLE__
void os::Bsd::clock_init() {
// XXXDARWIN: Investigate replacement monotonic clock
mach_timebase_info(&_timebase_info);
}
#else
void os::Bsd::clock_init() {
@ -1007,10 +1013,39 @@ void os::Bsd::clock_init() {
#endif
#ifdef __APPLE__
jlong os::javaTimeNanos() {
const uint64_t tm = mach_absolute_time();
const uint64_t now = (tm * Bsd::_timebase_info.numer) / Bsd::_timebase_info.denom;
const uint64_t prev = Bsd::_max_abstime;
if (now <= prev) {
return prev; // same or retrograde time;
}
const uint64_t obsv = Atomic::cmpxchg(now, (volatile jlong*)&Bsd::_max_abstime, prev);
assert(obsv >= prev, "invariant"); // Monotonicity
// If the CAS succeeded then we're done and return "now".
// If the CAS failed and the observed value "obsv" is >= now then
// we should return "obsv". If the CAS failed and now > obsv > prv then
// some other thread raced this thread and installed a new value, in which case
// we could either (a) retry the entire operation, (b) retry trying to install now
// or (c) just return obsv. We use (c). No loop is required although in some cases
// we might discard a higher "now" value in deference to a slightly lower but freshly
// installed obsv value. That's entirely benign -- it admits no new orderings compared
// to (a) or (b) -- and greatly reduces coherence traffic.
// We might also condition (c) on the magnitude of the delta between obsv and now.
// Avoiding excessive CAS operations to hot RW locations is critical.
// See https://blogs.oracle.com/dave/entry/cas_and_cache_trivia_invalidate
return (prev == obsv) ? now : obsv;
}
#else // __APPLE__
jlong os::javaTimeNanos() {
if (os::supports_monotonic_clock()) {
struct timespec tp;
int status = Bsd::clock_gettime(CLOCK_MONOTONIC, &tp);
int status = Bsd::_clock_gettime(CLOCK_MONOTONIC, &tp);
assert(status == 0, "gettime error");
jlong result = jlong(tp.tv_sec) * (1000 * 1000 * 1000) + jlong(tp.tv_nsec);
return result;
@ -1023,6 +1058,8 @@ jlong os::javaTimeNanos() {
}
}
#endif // __APPLE__
void os::javaTimeNanos_info(jvmtiTimerInfo *info_ptr) {
if (os::supports_monotonic_clock()) {
info_ptr->max_value = ALL_64_BITS;