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authorGravatar Abseil Team <absl-team@google.com>2020-06-22 10:03:06 -0700
committerGravatar Mark Barolak <mbar@google.com>2020-06-22 14:04:24 -0400
commit10cb35e459f5ecca5b2ff107635da0bfa41011b4 (patch)
treed382b5929817af05d27c0e3e23c800c84e80e892 /absl/synchronization
parent4ccc0fce09836a25b474f4b1453146dae2c29f4d (diff)
Export of internal Abseil changes
-- b548087c24ae7c2c709e8040a118b5e312d18e2e by Derek Mauro <dmauro@google.com>: Remove the static initialization of global variables used by absl::Mutex as requested by Chromium PiperOrigin-RevId: 317676541 -- f198f5da1e966772efa978ba019bd23576899794 by Greg Miller <jgm@google.com>: fix: work around gcc-4.8 bug in disjunction See https://godbolt.org/z/i7-AmM for a repro of the bug. I realize that Abseil no longer supports gcc 4.8 officially (https://abseil.io/docs/cpp/platforms/platforms), but Cloud C++ still supports gcc 4.8 officially, and so it would be nice to get this simple fix in. fixes https://github.com/abseil/abseil-cpp/issues/718 PiperOrigin-RevId: 317484459 -- ed233f646530c6c0948213b643cc6919db1bee90 by Chris Kennelly <ckennelly@google.com>: Avoid determining the size of the duration unit at runtime. PiperOrigin-RevId: 317376300 -- 73d4011c17fcf747a990176924a7adc69d443533 by Greg Falcon <gfalcon@google.com>: Change spelling of internal detail from `Invoke`/`InvokeT` to `invoke`/`invoke_result_t`. This matches the spelling of the C++17 standard library names that perform the same operations. PiperOrigin-RevId: 317311527 GitOrigin-RevId: b548087c24ae7c2c709e8040a118b5e312d18e2e Change-Id: I131809ff0b92cfdb0d96dc94e94d9c6f751cb0ac
Diffstat (limited to 'absl/synchronization')
-rw-r--r--absl/synchronization/mutex.cc57
1 files changed, 27 insertions, 30 deletions
diff --git a/absl/synchronization/mutex.cc b/absl/synchronization/mutex.cc
index 1f8a696e..62fa8e9c 100644
--- a/absl/synchronization/mutex.cc
+++ b/absl/synchronization/mutex.cc
@@ -39,6 +39,7 @@
#include <thread> // NOLINT(build/c++11)
#include "absl/base/attributes.h"
+#include "absl/base/call_once.h"
#include "absl/base/config.h"
#include "absl/base/dynamic_annotations.h"
#include "absl/base/internal/atomic_hook.h"
@@ -85,28 +86,6 @@ ABSL_CONST_INIT std::atomic<OnDeadlockCycle> synch_deadlock_detection(
kDeadlockDetectionDefault);
ABSL_CONST_INIT std::atomic<bool> synch_check_invariants(false);
-// ------------------------------------------ spinlock support
-
-// Make sure read-only globals used in the Mutex code are contained on the
-// same cacheline and cacheline aligned to eliminate any false sharing with
-// other globals from this and other modules.
-static struct MutexGlobals {
- MutexGlobals() {
- // Find machine-specific data needed for Delay() and
- // TryAcquireWithSpinning(). This runs in the global constructor
- // sequence, and before that zeros are safe values.
- num_cpus = absl::base_internal::NumCPUs();
- spinloop_iterations = num_cpus > 1 ? 1500 : 0;
- }
- int num_cpus;
- int spinloop_iterations;
- // Pad this struct to a full cacheline to prevent false sharing.
- char padding[ABSL_CACHELINE_SIZE - 2 * sizeof(int)];
-} ABSL_CACHELINE_ALIGNED mutex_globals;
-static_assert(
- sizeof(MutexGlobals) == ABSL_CACHELINE_SIZE,
- "MutexGlobals must occupy an entire cacheline to prevent false sharing");
-
ABSL_INTERNAL_ATOMIC_HOOK_ATTRIBUTES
absl::base_internal::AtomicHook<void (*)(int64_t wait_cycles)>
submit_profile_data;
@@ -143,7 +122,22 @@ void RegisterSymbolizer(bool (*fn)(const void *pc, char *out, int out_size)) {
symbolizer.Store(fn);
}
-// spinlock delay on iteration c. Returns new c.
+struct ABSL_CACHELINE_ALIGNED MutexGlobals {
+ absl::once_flag once;
+ int num_cpus = 0;
+ int spinloop_iterations = 0;
+};
+
+static const MutexGlobals& GetMutexGlobals() {
+ ABSL_CONST_INIT static MutexGlobals data;
+ absl::base_internal::LowLevelCallOnce(&data.once, [&]() {
+ data.num_cpus = absl::base_internal::NumCPUs();
+ data.spinloop_iterations = data.num_cpus > 1 ? 1500 : 0;
+ });
+ return data;
+}
+
+// Spinlock delay on iteration c. Returns new c.
namespace {
enum DelayMode { AGGRESSIVE, GENTLE };
};
@@ -153,22 +147,25 @@ static int Delay(int32_t c, DelayMode mode) {
// gentle then spin only a few times before yielding. Aggressive spinning is
// used to ensure that an Unlock() call, which must get the spin lock for
// any thread to make progress gets it without undue delay.
- int32_t limit = (mutex_globals.num_cpus > 1) ?
- ((mode == AGGRESSIVE) ? 5000 : 250) : 0;
+ const int32_t limit =
+ GetMutexGlobals().num_cpus > 1 ? (mode == AGGRESSIVE ? 5000 : 250) : 0;
if (c < limit) {
- c++; // spin
+ // Spin.
+ c++;
} else {
ABSL_TSAN_MUTEX_PRE_DIVERT(nullptr, 0);
- if (c == limit) { // yield once
+ if (c == limit) {
+ // Yield once.
AbslInternalMutexYield();
c++;
- } else { // then wait
+ } else {
+ // Then wait.
absl::SleepFor(absl::Microseconds(10));
c = 0;
}
ABSL_TSAN_MUTEX_POST_DIVERT(nullptr, 0);
}
- return (c);
+ return c;
}
// --------------------------Generic atomic ops
@@ -1437,7 +1434,7 @@ void Mutex::AssertNotHeld() const {
// Attempt to acquire *mu, and return whether successful. The implementation
// may spin for a short while if the lock cannot be acquired immediately.
static bool TryAcquireWithSpinning(std::atomic<intptr_t>* mu) {
- int c = mutex_globals.spinloop_iterations;
+ int c = GetMutexGlobals().spinloop_iterations;
do { // do/while somewhat faster on AMD
intptr_t v = mu->load(std::memory_order_relaxed);
if ((v & (kMuReader|kMuEvent)) != 0) {