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

3 files changed, 17 insertions, 10 deletions

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