Export of internal Abseil changes

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5bd06440e700fefd6eadd577d7d69c51f15c63e0 by Abseil Team <absl-team@google.com>:

Add if-guard to futex.h so that it doesn't fail to parse for unsupported platforms

PiperOrigin-RevId: 336880375

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8b3d3bb4ad123fc9f648f0e397b2eddd88dc0c02 by Derek Mauro <dmauro@google.com>:

Fix race in AddressIsReadable file descriptors using stronger memory ordering

PiperOrigin-RevId: 336874423

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1d8bf23747009cca29129b80c2793bc91443dd55 by Derek Mauro <dmauro@google.com>:

Avoid -Wundef warnings on ABSL_HAVE_THREAD_LOCAL

PiperOrigin-RevId: 336792406

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562a480f029c600c1d3b1428da6a9b09e8952a74 by Derek Mauro <dmauro@google.com>:

Fix preprocessor condition for symbols __tsan_mutex_read_lock and
__tsan_mutex_try_lock

PiperOrigin-RevId: 336732571
GitOrigin-RevId: 5bd06440e700fefd6eadd577d7d69c51f15c63e0
Change-Id: Id9bb331baec74b9d80c7b228959a7739bc30e694

8 files changed, 28 insertions, 19 deletions

diff --git a/absl/base/internal/exponential_biased_test.cc b/absl/base/internal/exponential_biased_test.cc
index 90a482d2..075583ca 100644
--- a/absl/base/internal/exponential_biased_test.cc
+++ b/absl/base/internal/exponential_biased_test.cc
@@ -185,7 +185,7 @@ TEST(ExponentialBiasedTest, InitializationModes) {
   ABSL_CONST_INIT static ExponentialBiased eb_static;
   EXPECT_THAT(eb_static.GetSkipCount(2), Ge(0));
 
-#if ABSL_HAVE_THREAD_LOCAL
+#ifdef ABSL_HAVE_THREAD_LOCAL
   thread_local ExponentialBiased eb_thread;
   EXPECT_THAT(eb_thread.GetSkipCount(2), Ge(0));
 #endif
diff --git a/absl/base/internal/sysinfo.cc b/absl/base/internal/sysinfo.cc
index 349d9268..4a3b2050 100644
--- a/absl/base/internal/sysinfo.cc
+++ b/absl/base/internal/sysinfo.cc
@@ -426,7 +426,7 @@ pid_t GetTID() {
 // userspace construct) to avoid unnecessary system calls. Without this caching,
 // it can take roughly 98ns, while it takes roughly 1ns with this caching.
 pid_t GetCachedTID() {
-#if ABSL_HAVE_THREAD_LOCAL
+#ifdef ABSL_HAVE_THREAD_LOCAL
   static thread_local pid_t thread_id = GetTID();
   return thread_id;
 #else
diff --git a/absl/container/internal/raw_hash_set.cc b/absl/container/internal/raw_hash_set.cc
index 919ac074..2f744a6e 100644
--- a/absl/container/internal/raw_hash_set.cc
+++ b/absl/container/internal/raw_hash_set.cc
@@ -27,7 +27,7 @@ constexpr size_t Group::kWidth;
 
 // Returns "random" seed.
 inline size_t RandomSeed() {
-#if ABSL_HAVE_THREAD_LOCAL
+#ifdef ABSL_HAVE_THREAD_LOCAL
   static thread_local size_t counter = 0;
   size_t value = ++counter;
 #else   // ABSL_HAVE_THREAD_LOCAL
diff --git a/absl/debugging/internal/address_is_readable.cc b/absl/debugging/internal/address_is_readable.cc
index 65376063..329c285f 100644
--- a/absl/debugging/internal/address_is_readable.cc
+++ b/absl/debugging/internal/address_is_readable.cc
@@ -68,6 +68,7 @@ static void Unpack(uint64_t x, int *pid, int *read_fd, int *write_fd) {
 // unimplemented.
 // This is a namespace-scoped variable for correct zero-initialization.
 static std::atomic<uint64_t> pid_and_fds;  // initially 0, an invalid pid.
+
 bool AddressIsReadable(const void *addr) {
   absl::base_internal::ErrnoSaver errno_saver;
   // We test whether a byte is readable by using write().  Normally, this would
@@ -86,7 +87,7 @@ bool AddressIsReadable(const void *addr) {
     int pid;
     int read_fd;
     int write_fd;
-    uint64_t local_pid_and_fds = pid_and_fds.load(std::memory_order_relaxed);
+    uint64_t local_pid_and_fds = pid_and_fds.load(std::memory_order_acquire);
     Unpack(local_pid_and_fds, &pid, &read_fd, &write_fd);
     while (current_pid != pid) {
       int p[2];
@@ -98,13 +99,13 @@ bool AddressIsReadable(const void *addr) {
       fcntl(p[1], F_SETFD, FD_CLOEXEC);
       uint64_t new_pid_and_fds = Pack(current_pid, p[0], p[1]);
       if (pid_and_fds.compare_exchange_strong(
-              local_pid_and_fds, new_pid_and_fds, std::memory_order_relaxed,
+              local_pid_and_fds, new_pid_and_fds, std::memory_order_release,
               std::memory_order_relaxed)) {
         local_pid_and_fds = new_pid_and_fds;  // fds exposed to other threads
       } else {  // fds not exposed to other threads; we can close them.
         close(p[0]);
         close(p[1]);
-        local_pid_and_fds = pid_and_fds.load(std::memory_order_relaxed);
+        local_pid_and_fds = pid_and_fds.load(std::memory_order_acquire);
       }
       Unpack(local_pid_and_fds, &pid, &read_fd, &write_fd);
     }
@@ -124,7 +125,7 @@ bool AddressIsReadable(const void *addr) {
       // If pid_and_fds contains the problematic file descriptors we just used,
       // this call will forget them, and the loop will try again.
       pid_and_fds.compare_exchange_strong(local_pid_and_fds, 0,
-                                          std::memory_order_relaxed,
+                                          std::memory_order_release,
                                           std::memory_order_relaxed);
     }
   } while (errno == EBADF);
diff --git a/absl/synchronization/internal/futex.h b/absl/synchronization/internal/futex.h
index 3539f491..06fbd6d0 100644
--- a/absl/synchronization/internal/futex.h
+++ b/absl/synchronization/internal/futex.h
@@ -38,6 +38,19 @@
 #include "absl/base/optimization.h"
 #include "absl/synchronization/internal/kernel_timeout.h"
 
+#ifdef ABSL_INTERNAL_HAVE_FUTEX
+#error ABSL_INTERNAL_HAVE_FUTEX may not be set on the command line
+#elif defined(__BIONIC__)
+// Bionic supports all the futex operations we need even when some of the futex
+// definitions are missing.
+#define ABSL_INTERNAL_HAVE_FUTEX
+#elif defined(__linux__) && defined(FUTEX_CLOCK_REALTIME)
+// FUTEX_CLOCK_REALTIME requires Linux >= 2.6.28.
+#define ABSL_INTERNAL_HAVE_FUTEX
+#endif
+
+#ifdef ABSL_INTERNAL_HAVE_FUTEX
+
 namespace absl {
 ABSL_NAMESPACE_BEGIN
 namespace synchronization_internal {
@@ -136,4 +149,6 @@ class Futex : public FutexImpl {};
 ABSL_NAMESPACE_END
 }  // namespace absl
 
+#endif  // ABSL_INTERNAL_HAVE_FUTEX
+
 #endif  // ABSL_SYNCHRONIZATION_INTERNAL_FUTEX_H_
diff --git a/absl/synchronization/internal/waiter.cc b/absl/synchronization/internal/waiter.cc
index c51855b0..2123be60 100644
--- a/absl/synchronization/internal/waiter.cc
+++ b/absl/synchronization/internal/waiter.cc
@@ -48,10 +48,6 @@
 #include "absl/base/optimization.h"
 #include "absl/synchronization/internal/kernel_timeout.h"
 
-#if ABSL_WAITER_MODE == ABSL_WAITER_MODE_FUTEX
-#include "absl/synchronization/internal/futex.h"
-#endif
-
 
 namespace absl {
 ABSL_NAMESPACE_BEGIN
diff --git a/absl/synchronization/internal/waiter.h b/absl/synchronization/internal/waiter.h
index 887f9b1b..be3df180 100644
--- a/absl/synchronization/internal/waiter.h
+++ b/absl/synchronization/internal/waiter.h
@@ -36,6 +36,7 @@
 #include <cstdint>
 
 #include "absl/base/internal/thread_identity.h"
+#include "absl/synchronization/internal/futex.h"
 #include "absl/synchronization/internal/kernel_timeout.h"
 
 // May be chosen at compile time via -DABSL_FORCE_WAITER_MODE=<index>
@@ -48,12 +49,7 @@
 #define ABSL_WAITER_MODE ABSL_FORCE_WAITER_MODE
 #elif defined(_WIN32) && _WIN32_WINNT >= _WIN32_WINNT_VISTA
 #define ABSL_WAITER_MODE ABSL_WAITER_MODE_WIN32
-#elif defined(__BIONIC__)
-// Bionic supports all the futex operations we need even when some of the futex
-// definitions are missing.
-#define ABSL_WAITER_MODE ABSL_WAITER_MODE_FUTEX
-#elif defined(__linux__) && defined(FUTEX_CLOCK_REALTIME)
-// FUTEX_CLOCK_REALTIME requires Linux >= 2.6.28.
+#elif defined(ABSL_INTERNAL_HAVE_FUTEX)
 #define ABSL_WAITER_MODE ABSL_WAITER_MODE_FUTEX
 #elif defined(ABSL_HAVE_SEMAPHORE_H)
 #define ABSL_WAITER_MODE ABSL_WAITER_MODE_SEM
diff --git a/absl/synchronization/mutex.cc b/absl/synchronization/mutex.cc
index 63f09408..9e01393c 100644
--- a/absl/synchronization/mutex.cc
+++ b/absl/synchronization/mutex.cc
@@ -50,6 +50,7 @@
 #include "absl/base/internal/spinlock.h"
 #include "absl/base/internal/sysinfo.h"
 #include "absl/base/internal/thread_identity.h"
+#include "absl/base/internal/tsan_mutex_interface.h"
 #include "absl/base/port.h"
 #include "absl/debugging/stacktrace.h"
 #include "absl/debugging/symbolize.h"
@@ -705,7 +706,7 @@ static constexpr bool kDebugMode = false;
 static constexpr bool kDebugMode = true;
 #endif
 
-#ifdef ABSL_HAVE_THREAD_SANITIZER
+#ifdef ABSL_INTERNAL_HAVE_TSAN_INTERFACE
 static unsigned TsanFlags(Mutex::MuHow how) {
   return how == kShared ? __tsan_mutex_read_lock : 0;
 }
@@ -1767,7 +1768,7 @@ static inline bool EvalConditionAnnotated(const Condition *cond, Mutex *mu,
   // All memory accesses are ignored inside of mutex operations + for unlock
   // operation tsan considers that we've already released the mutex.
   bool res = false;
-#ifdef ABSL_HAVE_THREAD_SANITIZER
+#ifdef ABSL_INTERNAL_HAVE_TSAN_INTERFACE
   const int flags = read_lock ? __tsan_mutex_read_lock : 0;
   const int tryflags = flags | (trylock ? __tsan_mutex_try_lock : 0);
 #endif