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authorGravatar Abseil Team <absl-team@google.com>2019-04-09 08:22:32 -0700
committerGravatar Shaindel Schwartz <shaindel@google.com>2019-04-09 13:34:52 -0400
commitdbae8764fbd429bf7d7745e24bcf73962177a7c0 (patch)
tree9e0b90d17192c02952632d619616f00ec4f68580 /absl/base/internal/cycleclock.cc
parent044da8a29c923506af0f0b46bc46f43c1e1300b5 (diff)
Export of internal Abseil changes.
-- 3f04cd3c25a99df91ff913977b8c5b343532db5d by Abseil Team <absl-team@google.com>: Stricter memory order constraints for CycleClock callback. PiperOrigin-RevId: 242670115 -- 216db48375306490f1722a11aaf33080939d9f2f by Abseil Team <absl-team@google.com>: internal/optional.h: move macro from types/optional.h ABSL_OPTIONAL_USE_INHERITING_CONSTRUCTORS is only used within this file. additionally check the macro with #ifdef rather than #if, fixes -Wundef warning: 'ABSL_OPTIONAL_USE_INHERITING_CONSTRUCTORS' is not defined, evaluates to 0 PiperOrigin-RevId: 242548205 -- fbe22e7d8dc5c0b3d43ac26297e97ddbaeab3d39 by Samuel Benzaquen <sbenza@google.com>: Implement %f natively for any input. It evaluates the input at runtime and allocates stack space accordingly. This removes a potential fallback into snprintf, improves performance, and removes all memory allocations in this formatting path. PiperOrigin-RevId: 242531736 -- 1458f9ba2a79ef0534e46527cd34770dee54164d by Greg Falcon <gfalcon@google.com>: Add explicit check for NVCC in compressed_tuple.h. NVCC claims to be MSVC, but does not implement this MSVC attribute. PiperOrigin-RevId: 242513453 GitOrigin-RevId: 3f04cd3c25a99df91ff913977b8c5b343532db5d Change-Id: I0742e8619c5248c7607961113e406486bc0e279b
Diffstat (limited to 'absl/base/internal/cycleclock.cc')
-rw-r--r--absl/base/internal/cycleclock.cc18
1 files changed, 16 insertions, 2 deletions
diff --git a/absl/base/internal/cycleclock.cc b/absl/base/internal/cycleclock.cc
index 4b553c29..e9844b71 100644
--- a/absl/base/internal/cycleclock.cc
+++ b/absl/base/internal/cycleclock.cc
@@ -55,10 +55,23 @@ static constexpr int32_t kShift = 2;
static constexpr double kFrequencyScale = 1.0 / (1 << kShift);
static std::atomic<CycleClockSourceFunc> cycle_clock_source;
+CycleClockSourceFunc LoadCycleClockSource() {
+ // Optimize for the common case (no callback) by first doing a relaxed load;
+ // this is significantly faster on non-x86 platforms.
+ if (cycle_clock_source.load(std::memory_order_relaxed) == nullptr) {
+ return nullptr;
+ }
+ // This corresponds to the store(std::memory_order_release) in
+ // CycleClockSource::Register, and makes sure that any updates made prior to
+ // registering the callback are visible to this thread before the callback is
+ // invoked.
+ return cycle_clock_source.load(std::memory_order_acquire);
+}
+
} // namespace
int64_t CycleClock::Now() {
- auto fn = cycle_clock_source.load(std::memory_order_relaxed);
+ auto fn = LoadCycleClockSource();
if (fn == nullptr) {
return base_internal::UnscaledCycleClock::Now() >> kShift;
}
@@ -70,7 +83,8 @@ double CycleClock::Frequency() {
}
void CycleClockSource::Register(CycleClockSourceFunc source) {
- cycle_clock_source.store(source, std::memory_order_relaxed);
+ // Corresponds to the load(std::memory_order_acquire) in LoadCycleClockSource.
+ cycle_clock_source.store(source, std::memory_order_release);
}
#else