diff --git a/absl/base/dynamic_annotations.h b/absl/base/dynamic_annotations.h
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+/*
+ *  Copyright 2017 The Abseil Authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+/* This file defines dynamic annotations for use with dynamic analysis
+   tool such as valgrind, PIN, etc.
+
+   Dynamic annotation is a source code annotation that affects
+   the generated code (that is, the annotation is not a comment).
+   Each such annotation is attached to a particular
+   instruction and/or to a particular object (address) in the program.
+
+   The annotations that should be used by users are macros in all upper-case
+   (e.g., ANNOTATE_THREAD_NAME).
+
+   Actual implementation of these macros may differ depending on the
+   dynamic analysis tool being used.
+
+   This file supports the following configurations:
+   - Dynamic Annotations enabled (with static thread-safety warnings disabled).
+     In this case, macros expand to functions implemented by Thread Sanitizer,
+     when building with TSan. When not provided an external implementation,
+     dynamic_annotations.cc provides no-op implementations.
+
+   - Static Clang thread-safety warnings enabled.
+     When building with a Clang compiler that supports thread-safety warnings,
+     a subset of annotations can be statically-checked at compile-time. We
+     expand these macros to static-inline functions that can be analyzed for
+     thread-safety, but afterwards elided when building the final binary.
+
+   - All annotations are disabled.
+     If neither Dynamic Annotations nor Clang thread-safety warnings are
+     enabled, then all annotation-macros expand to empty. */
+
+#ifndef ABSL_BASE_DYNAMIC_ANNOTATIONS_H_
+#define ABSL_BASE_DYNAMIC_ANNOTATIONS_H_
+
+#ifndef DYNAMIC_ANNOTATIONS_ENABLED
+# define DYNAMIC_ANNOTATIONS_ENABLED 0
+#endif
+
+#if DYNAMIC_ANNOTATIONS_ENABLED != 0
+
+  /* -------------------------------------------------------------
+     Annotations that suppress errors.  It is usually better to express the
+     program's synchronization using the other annotations, but these can
+     be used when all else fails. */
+
+  /* Report that we may have a benign race at "pointer", with size
+     "sizeof(*(pointer))". "pointer" must be a non-void* pointer.  Insert at the
+     point where "pointer" has been allocated, preferably close to the point
+     where the race happens.  See also ANNOTATE_BENIGN_RACE_STATIC. */
+  #define ANNOTATE_BENIGN_RACE(pointer, description) \
+    AnnotateBenignRaceSized(__FILE__, __LINE__, pointer, \
+                            sizeof(*(pointer)), description)
+
+  /* Same as ANNOTATE_BENIGN_RACE(address, description), but applies to
+     the memory range [address, address+size). */
+  #define ANNOTATE_BENIGN_RACE_SIZED(address, size, description) \
+    AnnotateBenignRaceSized(__FILE__, __LINE__, address, size, description)
+
+  /* Enable (enable!=0) or disable (enable==0) race detection for all threads.
+     This annotation could be useful if you want to skip expensive race analysis
+     during some period of program execution, e.g. during initialization. */
+  #define ANNOTATE_ENABLE_RACE_DETECTION(enable) \
+    AnnotateEnableRaceDetection(__FILE__, __LINE__, enable)
+
+  /* -------------------------------------------------------------
+     Annotations useful for debugging. */
+
+  /* Report the current thread name to a race detector. */
+  #define ANNOTATE_THREAD_NAME(name) \
+    AnnotateThreadName(__FILE__, __LINE__, name)
+
+  /* -------------------------------------------------------------
+     Annotations useful when implementing locks.  They are not
+     normally needed by modules that merely use locks.
+     The "lock" argument is a pointer to the lock object. */
+
+  /* Report that a lock has been created at address "lock". */
+  #define ANNOTATE_RWLOCK_CREATE(lock) \
+    AnnotateRWLockCreate(__FILE__, __LINE__, lock)
+
+  /* Report that a linker initialized lock has been created at address "lock".
+   */
+#ifdef THREAD_SANITIZER
+  #define ANNOTATE_RWLOCK_CREATE_STATIC(lock) \
+    AnnotateRWLockCreateStatic(__FILE__, __LINE__, lock)
+#else
+  #define ANNOTATE_RWLOCK_CREATE_STATIC(lock) ANNOTATE_RWLOCK_CREATE(lock)
+#endif
+
+  /* Report that the lock at address "lock" is about to be destroyed. */
+  #define ANNOTATE_RWLOCK_DESTROY(lock) \
+    AnnotateRWLockDestroy(__FILE__, __LINE__, lock)
+
+  /* Report that the lock at address "lock" has been acquired.
+     is_w=1 for writer lock, is_w=0 for reader lock. */
+  #define ANNOTATE_RWLOCK_ACQUIRED(lock, is_w) \
+    AnnotateRWLockAcquired(__FILE__, __LINE__, lock, is_w)
+
+  /* Report that the lock at address "lock" is about to be released. */
+  #define ANNOTATE_RWLOCK_RELEASED(lock, is_w) \
+    AnnotateRWLockReleased(__FILE__, __LINE__, lock, is_w)
+
+#else  /* DYNAMIC_ANNOTATIONS_ENABLED == 0 */
+
+  #define ANNOTATE_RWLOCK_CREATE(lock) /* empty */
+  #define ANNOTATE_RWLOCK_CREATE_STATIC(lock) /* empty */
+  #define ANNOTATE_RWLOCK_DESTROY(lock) /* empty */
+  #define ANNOTATE_RWLOCK_ACQUIRED(lock, is_w) /* empty */
+  #define ANNOTATE_RWLOCK_RELEASED(lock, is_w) /* empty */
+  #define ANNOTATE_BENIGN_RACE(address, description) /* empty */
+  #define ANNOTATE_BENIGN_RACE_SIZED(address, size, description) /* empty */
+  #define ANNOTATE_THREAD_NAME(name) /* empty */
+  #define ANNOTATE_ENABLE_RACE_DETECTION(enable) /* empty */
+
+#endif  /* DYNAMIC_ANNOTATIONS_ENABLED */
+
+/* These annotations are also made available to LLVM's Memory Sanitizer */
+#if DYNAMIC_ANNOTATIONS_ENABLED == 1 || defined(MEMORY_SANITIZER)
+  #define ANNOTATE_MEMORY_IS_INITIALIZED(address, size) \
+    AnnotateMemoryIsInitialized(__FILE__, __LINE__, address, size)
+
+  #define ANNOTATE_MEMORY_IS_UNINITIALIZED(address, size) \
+    AnnotateMemoryIsUninitialized(__FILE__, __LINE__, address, size)
+#else
+  #define ANNOTATE_MEMORY_IS_INITIALIZED(address, size) /* empty */
+  #define ANNOTATE_MEMORY_IS_UNINITIALIZED(address, size) /* empty */
+#endif  /* DYNAMIC_ANNOTATIONS_ENABLED || MEMORY_SANITIZER */
+
+/* TODO(delesley) -- Replace __CLANG_SUPPORT_DYN_ANNOTATION__ with the
+   appropriate feature ID. */
+#if defined(__clang__) && (!defined(SWIG)) \
+    && defined(__CLANG_SUPPORT_DYN_ANNOTATION__)
+
+  #if DYNAMIC_ANNOTATIONS_ENABLED == 0
+    #define ANNOTALYSIS_ENABLED
+  #endif
+
+  /* When running in opt-mode, GCC will issue a warning, if these attributes are
+     compiled. Only include them when compiling using Clang. */
+  #define ATTRIBUTE_IGNORE_READS_BEGIN \
+      __attribute((exclusive_lock_function("*")))
+  #define ATTRIBUTE_IGNORE_READS_END \
+      __attribute((unlock_function("*")))
+#else
+  #define ATTRIBUTE_IGNORE_READS_BEGIN  /* empty */
+  #define ATTRIBUTE_IGNORE_READS_END  /* empty */
+#endif  /* defined(__clang__) && ... */
+
+#if (DYNAMIC_ANNOTATIONS_ENABLED != 0) || defined(ANNOTALYSIS_ENABLED)
+  #define ANNOTATIONS_ENABLED
+#endif
+
+#if (DYNAMIC_ANNOTATIONS_ENABLED != 0)
+
+  /* Request the analysis tool to ignore all reads in the current thread
+     until ANNOTATE_IGNORE_READS_END is called.
+     Useful to ignore intentional racey reads, while still checking
+     other reads and all writes.
+     See also ANNOTATE_UNPROTECTED_READ. */
+  #define ANNOTATE_IGNORE_READS_BEGIN() \
+    AnnotateIgnoreReadsBegin(__FILE__, __LINE__)
+
+  /* Stop ignoring reads. */
+  #define ANNOTATE_IGNORE_READS_END() \
+    AnnotateIgnoreReadsEnd(__FILE__, __LINE__)
+
+  /* Similar to ANNOTATE_IGNORE_READS_BEGIN, but ignore writes instead. */
+  #define ANNOTATE_IGNORE_WRITES_BEGIN() \
+    AnnotateIgnoreWritesBegin(__FILE__, __LINE__)
+
+  /* Stop ignoring writes. */
+  #define ANNOTATE_IGNORE_WRITES_END() \
+    AnnotateIgnoreWritesEnd(__FILE__, __LINE__)
+
+/* Clang provides limited support for static thread-safety analysis
+   through a feature called Annotalysis. We configure macro-definitions
+   according to whether Annotalysis support is available. */
+#elif defined(ANNOTALYSIS_ENABLED)
+
+  #define ANNOTATE_IGNORE_READS_BEGIN() \
+    StaticAnnotateIgnoreReadsBegin(__FILE__, __LINE__)
+
+  #define ANNOTATE_IGNORE_READS_END() \
+    StaticAnnotateIgnoreReadsEnd(__FILE__, __LINE__)
+
+  #define ANNOTATE_IGNORE_WRITES_BEGIN() \
+    StaticAnnotateIgnoreWritesBegin(__FILE__, __LINE__)
+
+  #define ANNOTATE_IGNORE_WRITES_END() \
+    StaticAnnotateIgnoreWritesEnd(__FILE__, __LINE__)
+
+#else
+  #define ANNOTATE_IGNORE_READS_BEGIN()  /* empty */
+  #define ANNOTATE_IGNORE_READS_END()  /* empty */
+  #define ANNOTATE_IGNORE_WRITES_BEGIN()  /* empty */
+  #define ANNOTATE_IGNORE_WRITES_END()  /* empty */
+#endif
+
+/* Implement the ANNOTATE_IGNORE_READS_AND_WRITES_* annotations using the more
+   primitive annotations defined above. */
+#if defined(ANNOTATIONS_ENABLED)
+
+  /* Start ignoring all memory accesses (both reads and writes). */
+  #define ANNOTATE_IGNORE_READS_AND_WRITES_BEGIN() \
+    do {                                           \
+      ANNOTATE_IGNORE_READS_BEGIN();               \
+      ANNOTATE_IGNORE_WRITES_BEGIN();              \
+    }while (0)
+
+  /* Stop ignoring both reads and writes. */
+  #define ANNOTATE_IGNORE_READS_AND_WRITES_END()   \
+    do {                                           \
+      ANNOTATE_IGNORE_WRITES_END();                \
+      ANNOTATE_IGNORE_READS_END();                 \
+    }while (0)
+
+#else
+  #define ANNOTATE_IGNORE_READS_AND_WRITES_BEGIN()  /* empty */
+  #define ANNOTATE_IGNORE_READS_AND_WRITES_END()  /* empty */
+#endif
+
+/* Use the macros above rather than using these functions directly. */
+#include <stddef.h>
+#ifdef __cplusplus
+extern "C" {
+#endif
+void AnnotateRWLockCreate(const char *file, int line,
+                          const volatile void *lock);
+void AnnotateRWLockCreateStatic(const char *file, int line,
+                          const volatile void *lock);
+void AnnotateRWLockDestroy(const char *file, int line,
+                           const volatile void *lock);
+void AnnotateRWLockAcquired(const char *file, int line,
+                            const volatile void *lock, long is_w);  /* NOLINT */
+void AnnotateRWLockReleased(const char *file, int line,
+                            const volatile void *lock, long is_w);  /* NOLINT */
+void AnnotateBenignRace(const char *file, int line,
+                        const volatile void *address,
+                        const char *description);
+void AnnotateBenignRaceSized(const char *file, int line,
+                        const volatile void *address,
+                        size_t size,
+                        const char *description);
+void AnnotateThreadName(const char *file, int line,
+                        const char *name);
+void AnnotateEnableRaceDetection(const char *file, int line, int enable);
+void AnnotateMemoryIsInitialized(const char *file, int line,
+                                 const volatile void *mem, size_t size);
+void AnnotateMemoryIsUninitialized(const char *file, int line,
+                                   const volatile void *mem, size_t size);
+
+/* Annotations expand to these functions, when Dynamic Annotations are enabled.
+   These functions are either implemented as no-op calls, if no Sanitizer is
+   attached, or provided with externally-linked implementations by a library
+   like ThreadSanitizer. */
+void AnnotateIgnoreReadsBegin(const char *file, int line)
+    ATTRIBUTE_IGNORE_READS_BEGIN;
+void AnnotateIgnoreReadsEnd(const char *file, int line)
+    ATTRIBUTE_IGNORE_READS_END;
+void AnnotateIgnoreWritesBegin(const char *file, int line);
+void AnnotateIgnoreWritesEnd(const char *file, int line);
+
+#if defined(ANNOTALYSIS_ENABLED)
+/* When Annotalysis is enabled without Dynamic Annotations, the use of
+   static-inline functions allows the annotations to be read at compile-time,
+   while still letting the compiler elide the functions from the final build.
+
+   TODO(delesley) -- The exclusive lock here ignores writes as well, but
+   allows IGNORE_READS_AND_WRITES to work properly. */
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wunused-function"
+static inline void StaticAnnotateIgnoreReadsBegin(const char *file, int line)
+    ATTRIBUTE_IGNORE_READS_BEGIN { (void)file; (void)line; }
+static inline void StaticAnnotateIgnoreReadsEnd(const char *file, int line)
+    ATTRIBUTE_IGNORE_READS_END { (void)file; (void)line; }
+static inline void StaticAnnotateIgnoreWritesBegin(
+    const char *file, int line) { (void)file; (void)line; }
+static inline void StaticAnnotateIgnoreWritesEnd(
+    const char *file, int line) { (void)file; (void)line; }
+#pragma GCC diagnostic pop
+#endif
+
+/* Return non-zero value if running under valgrind.
+
+  If "valgrind.h" is included into dynamic_annotations.cc,
+  the regular valgrind mechanism will be used.
+  See http://valgrind.org/docs/manual/manual-core-adv.html about
+  RUNNING_ON_VALGRIND and other valgrind "client requests".
+  The file "valgrind.h" may be obtained by doing
+     svn co svn://svn.valgrind.org/valgrind/trunk/include
+
+  If for some reason you can't use "valgrind.h" or want to fake valgrind,
+  there are two ways to make this function return non-zero:
+    - Use environment variable: export RUNNING_ON_VALGRIND=1
+    - Make your tool intercept the function RunningOnValgrind() and
+      change its return value.
+ */
+int RunningOnValgrind(void);
+
+/* ValgrindSlowdown returns:
+    * 1.0, if (RunningOnValgrind() == 0)
+    * 50.0, if (RunningOnValgrind() != 0 && getenv("VALGRIND_SLOWDOWN") == NULL)
+    * atof(getenv("VALGRIND_SLOWDOWN")) otherwise
+   This function can be used to scale timeout values:
+   EXAMPLE:
+   for (;;) {
+     DoExpensiveBackgroundTask();
+     SleepForSeconds(5 * ValgrindSlowdown());
+   }
+ */
+double ValgrindSlowdown(void);
+
+#ifdef __cplusplus
+}
+#endif
+
+/* ANNOTATE_UNPROTECTED_READ is the preferred way to annotate racey reads.
+
+     Instead of doing
+        ANNOTATE_IGNORE_READS_BEGIN();
+        ... = x;
+        ANNOTATE_IGNORE_READS_END();
+     one can use
+        ... = ANNOTATE_UNPROTECTED_READ(x); */
+#if defined(__cplusplus) && defined(ANNOTATIONS_ENABLED)
+template <typename T>
+inline T ANNOTATE_UNPROTECTED_READ(const volatile T &x) { /* NOLINT */
+  ANNOTATE_IGNORE_READS_BEGIN();
+  T res = x;
+  ANNOTATE_IGNORE_READS_END();
+  return res;
+  }
+#else
+  #define ANNOTATE_UNPROTECTED_READ(x) (x)
+#endif
+
+#if DYNAMIC_ANNOTATIONS_ENABLED != 0 && defined(__cplusplus)
+  /* Apply ANNOTATE_BENIGN_RACE_SIZED to a static variable. */
+  #define ANNOTATE_BENIGN_RACE_STATIC(static_var, description)        \
+    namespace {                                                       \
+      class static_var ## _annotator {                                \
+       public:                                                        \
+        static_var ## _annotator() {                                  \
+          ANNOTATE_BENIGN_RACE_SIZED(&static_var,                     \
+                                      sizeof(static_var),             \
+            # static_var ": " description);                           \
+        }                                                             \
+      };                                                              \
+      static static_var ## _annotator the ## static_var ## _annotator;\
+    }  // namespace
+#else /* DYNAMIC_ANNOTATIONS_ENABLED == 0 */
+  #define ANNOTATE_BENIGN_RACE_STATIC(static_var, description)  /* empty */
+#endif /* DYNAMIC_ANNOTATIONS_ENABLED */
+
+#ifdef ADDRESS_SANITIZER
+/* Describe the current state of a contiguous container such as e.g.
+ * std::vector or std::string. For more details see
+ * sanitizer/common_interface_defs.h, which is provided by the compiler. */
+#include <sanitizer/common_interface_defs.h>
+#define ANNOTATE_CONTIGUOUS_CONTAINER(beg, end, old_mid, new_mid) \
+  __sanitizer_annotate_contiguous_container(beg, end, old_mid, new_mid)
+#define ADDRESS_SANITIZER_REDZONE(name)         \
+  struct { char x[8] __attribute__ ((aligned (8))); } name
+#else
+#define ANNOTATE_CONTIGUOUS_CONTAINER(beg, end, old_mid, new_mid)
+#define ADDRESS_SANITIZER_REDZONE(name) static_assert(true, "")
+#endif  // ADDRESS_SANITIZER
+
+/* Undefine the macros intended only in this file. */
+#undef ANNOTALYSIS_ENABLED
+#undef ANNOTATIONS_ENABLED
+#undef ATTRIBUTE_IGNORE_READS_BEGIN
+#undef ATTRIBUTE_IGNORE_READS_END
+
+#endif  /* ABSL_BASE_DYNAMIC_ANNOTATIONS_H_ */