Reviewers: yurys, caseq,
Description:
Fix CPU profiler deadlock on Windows + AMD CPU.
Implement a lock free version of RolloverProtectedTickClock::Now
to eliminate a deadlock.
BUG=521420
LOG=Y
Please review this at https://codereview.chromium.org/1304873011/
Base URL: https://chromium.googlesource.com/v8/v8.git@master
Affected files (+13, -13 lines):
M src/base/platform/time.cc
Index: src/base/platform/time.cc
diff --git a/src/base/platform/time.cc b/src/base/platform/time.cc
index
7e4c8fc0ac902db962fa3b5a3337f1e876ebd561..1e01d9ac04e056fb64aa184df83e8048e53e73af
100644
--- a/src/base/platform/time.cc
+++ b/src/base/platform/time.cc
@@ -17,6 +17,7 @@
#include <ostream>
#if V8_OS_WIN
+#include "src/base/atomicops.h"
#include "src/base/lazy-instance.h"
#include "src/base/win32-headers.h"
#endif
@@ -434,36 +435,35 @@ class HighResolutionTickClock final : public
TickClock {
class RolloverProtectedTickClock final : public TickClock {
public:
- // We initialize rollover_ms_ to 1 to ensure that we will never
- // return 0 from TimeTicks::HighResolutionNow() and TimeTicks::Now()
below.
- RolloverProtectedTickClock() : last_seen_now_(0), rollover_ms_(1) {}
+ RolloverProtectedTickClock() : rollover_(0) {}
virtual ~RolloverProtectedTickClock() {}
int64_t Now() override {
- LockGuard<Mutex> lock_guard(&mutex_);
// We use timeGetTime() to implement TimeTicks::Now(), which rolls over
// every ~49.7 days. We try to track rollover ourselves, which works if
- // TimeTicks::Now() is called at least every 49 days.
+ // TimeTicks::Now() is called at least every 24 days.
// Note that we do not use GetTickCount() here, since timeGetTime()
gives
// more predictable delta values, as described here:
//
http://blogs.msdn.com/b/larryosterman/archive/2009/09/02/what-s-the-difference-between-gettickcount-and-timegettime.aspx
// timeGetTime() provides 1ms granularity when combined with
// timeBeginPeriod(). If the host application for V8 wants fast
timers, it
// can use timeBeginPeriod() to increase the resolution.
- DWORD now = timeGetTime();
- if (now < last_seen_now_) {
- rollover_ms_ += V8_INT64_C(0x100000000); // ~49.7 days.
+ // We use a lock-free version because the sampler thread calls it
+ // while having the rest of the world stopped, that could cause a
deadlock.
+ base::Atomic32 rollover = base::Acquire_Load(&rollover_);
+ base::Atomic32 now = static_cast<base::Atomic32>(timeGetTime());
+ if ((now >> 31) != (rollover & 1)) {
+ base::Release_CompareAndSwap(&rollover_, rollover, rollover + 1);
+ ++rollover;
}
- last_seen_now_ = now;
- return (now + rollover_ms_) * Time::kMicrosecondsPerMillisecond;
+ int64_t rollover_ms = static_cast<int64_t>(rollover) << 31;
+ return (rollover_ms | now) * Time::kMicrosecondsPerMillisecond;
}
bool IsHighResolution() override { return false; }
private:
- Mutex mutex_;
- DWORD last_seen_now_;
- int64_t rollover_ms_;
+ base::Atomic32 rollover_;
};
--
--
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