Export of internal Abseil changes

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517dc7eba9878290fc93c6523dc6d6e2c49b8c1e by Abseil Team <absl-team@google.com>:

Handle 'nan' in HumanReadableInt::ToInt64.

PiperOrigin-RevId: 318121226

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4fa6103b46dbc1375d416810dba591ab4f4898d1 by Abseil Team <absl-team@google.com>:

Promote `float`s to `double`s before formatting.

This will bring StrFormat behavior more in line with that of sprintf.

PiperOrigin-RevId: 318091841

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e4083a4b64b077d8520ccd8e0ca90da24f4ea24d by Abseil Team <absl-team@google.com>:

Google-internal changes only.

PiperOrigin-RevId: 318069900

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ab24f60127db089bccaf5fb7d2d1967c76f34768 by Greg Falcon <gfalcon@google.com>:

Inclusive language fix: Stop using blacklist/whitelist terminology in Abseil.

PiperOrigin-RevId: 317925379

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52b56a27a773ea7c10ea8fd456ed606b9d778947 by Abseil Team <absl-team@google.com>:

Add test for floats and label tests for double properly.

PiperOrigin-RevId: 317916380

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0f405960ab5b34d673244fda8bb9141c8f5c1a4f by Abseil Team <absl-team@google.com>:

Remove the static initialization of global variables used by absl::Mutex
as requested by Chromium

PiperOrigin-RevId: 317911430

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ce8cb49d8f4f68950fd111682657ba57d5a09ca0 by Abseil Team <absl-team@google.com>:

Internal Change

PiperOrigin-RevId: 317864956

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a781948e09fb8406d21a494b2fa4f78edaf9c2ea by Abseil Team <absl-team@google.com>:

Swap ABSL_DLL / ABSL_INTERNAL_ATOMIC_HOOK_ATTRIBUTES order to fix clang-cl builds.

PiperOrigin-RevId: 317858053

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4ba197f0dd2cbf8f9b96cebffd878c8847d6ce8d by Gennadiy Rozental <rogeeff@google.com>:

Migrate use of annotation macros to ABSL namespaced names

PiperOrigin-RevId: 317792057
GitOrigin-RevId: 517dc7eba9878290fc93c6523dc6d6e2c49b8c1e
Change-Id: I1a0c04d01adbdc5106b68fd69c97c31f822e11dc

2 files changed, 40 insertions, 30 deletions

diff --git a/absl/synchronization/internal/per_thread_sem.h b/absl/synchronization/internal/per_thread_sem.h
index 8ab43915..2228b6e8 100644
--- a/absl/synchronization/internal/per_thread_sem.h
+++ b/absl/synchronization/internal/per_thread_sem.h
@@ -78,7 +78,7 @@ class PerThreadSem {
   // !t.has_timeout() => Wait(t) will return true.
   static inline bool Wait(KernelTimeout t);
 
-  // White-listed callers.
+  // Permitted callers.
   friend class PerThreadSemTest;
   friend class absl::Mutex;
   friend absl::base_internal::ThreadIdentity* CreateThreadIdentity();
diff --git a/absl/synchronization/mutex.cc b/absl/synchronization/mutex.cc
index 62fa8e9c..05f5c041 100644
--- a/absl/synchronization/mutex.cc
+++ b/absl/synchronization/mutex.cc
@@ -39,7 +39,6 @@
 #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"
@@ -59,6 +58,7 @@
 
 using absl::base_internal::CurrentThreadIdentityIfPresent;
 using absl::base_internal::PerThreadSynch;
+using absl::base_internal::SchedulingGuard;
 using absl::base_internal::ThreadIdentity;
 using absl::synchronization_internal::GetOrCreateCurrentThreadIdentity;
 using absl::synchronization_internal::GraphCycles;
@@ -86,6 +86,28 @@ 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;
@@ -122,22 +144,7 @@ void RegisterSymbolizer(bool (*fn)(const void *pc, char *out, int out_size)) {
   symbolizer.Store(fn);
 }
 
-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.
+// spinlock delay on iteration c.  Returns new c.
 namespace {
   enum DelayMode { AGGRESSIVE, GENTLE };
 };
@@ -147,25 +154,22 @@ 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.
-  const int32_t limit =
-      GetMutexGlobals().num_cpus > 1 ? (mode == AGGRESSIVE ? 5000 : 250) : 0;
+  int32_t limit = (mutex_globals.num_cpus > 1) ?
+      ((mode == AGGRESSIVE) ? 5000 : 250) : 0;
   if (c < limit) {
-    // Spin.
-    c++;
+    c++;               // spin
   } 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
@@ -1051,6 +1055,7 @@ static PerThreadSynch *DequeueAllWakeable(PerThreadSynch *head,
 // Try to remove thread s from the list of waiters on this mutex.
 // Does nothing if s is not on the waiter list.
 void Mutex::TryRemove(PerThreadSynch *s) {
+  SchedulingGuard::ScopedDisable disable_rescheduling;
   intptr_t v = mu_.load(std::memory_order_relaxed);
   // acquire spinlock & lock
   if ((v & (kMuWait | kMuSpin | kMuWriter | kMuReader)) == kMuWait &&
@@ -1434,7 +1439,7 @@ 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 = GetMutexGlobals().spinloop_iterations;
+  int c = mutex_globals.spinloop_iterations;
   do {  // do/while somewhat faster on AMD
     intptr_t v = mu->load(std::memory_order_relaxed);
     if ((v & (kMuReader|kMuEvent)) != 0) {
@@ -1811,9 +1816,9 @@ static inline bool EvalConditionIgnored(Mutex *mu, const Condition *cond) {
   // So we "divert" (which un-ignores both memory accesses and synchronization)
   // and then separately turn on ignores of memory accesses.
   ABSL_TSAN_MUTEX_PRE_DIVERT(mu, 0);
-  ANNOTATE_IGNORE_READS_AND_WRITES_BEGIN();
+  ABSL_ANNOTATE_IGNORE_READS_AND_WRITES_BEGIN();
   bool res = cond->Eval();
-  ANNOTATE_IGNORE_READS_AND_WRITES_END();
+  ABSL_ANNOTATE_IGNORE_READS_AND_WRITES_END();
   ABSL_TSAN_MUTEX_POST_DIVERT(mu, 0);
   static_cast<void>(mu);  // Prevent unused param warning in non-TSAN builds.
   return res;
@@ -1894,6 +1899,7 @@ static void CheckForMutexCorruption(intptr_t v, const char* label) {
 }
 
 void Mutex::LockSlowLoop(SynchWaitParams *waitp, int flags) {
+  SchedulingGuard::ScopedDisable disable_rescheduling;
   int c = 0;
   intptr_t v = mu_.load(std::memory_order_relaxed);
   if ((v & kMuEvent) != 0) {
@@ -2013,6 +2019,7 @@ void Mutex::LockSlowLoop(SynchWaitParams *waitp, int flags) {
 // or it is in the process of blocking on a condition variable; it must requeue
 // itself on the mutex/condvar to wait for its condition to become true.
 ABSL_ATTRIBUTE_NOINLINE void Mutex::UnlockSlow(SynchWaitParams *waitp) {
+  SchedulingGuard::ScopedDisable disable_rescheduling;
   intptr_t v = mu_.load(std::memory_order_relaxed);
   this->AssertReaderHeld();
   CheckForMutexCorruption(v, "Unlock");
@@ -2328,6 +2335,7 @@ void Mutex::Trans(MuHow how) {
 // It will later acquire the mutex with high probability.  Otherwise, we
 // enqueue thread w on this mutex.
 void Mutex::Fer(PerThreadSynch *w) {
+  SchedulingGuard::ScopedDisable disable_rescheduling;
   int c = 0;
   ABSL_RAW_CHECK(w->waitp->cond == nullptr,
                  "Mutex::Fer while waiting on Condition");
@@ -2426,6 +2434,7 @@ CondVar::~CondVar() {
 
 // Remove thread s from the list of waiters on this condition variable.
 void CondVar::Remove(PerThreadSynch *s) {
+  SchedulingGuard::ScopedDisable disable_rescheduling;
   intptr_t v;
   int c = 0;
   for (v = cv_.load(std::memory_order_relaxed);;
@@ -2586,6 +2595,7 @@ void CondVar::Wakeup(PerThreadSynch *w) {
 }
 
 void CondVar::Signal() {
+  SchedulingGuard::ScopedDisable disable_rescheduling;
   ABSL_TSAN_MUTEX_PRE_SIGNAL(nullptr, 0);
   intptr_t v;
   int c = 0;