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diff --git a/src/third_party/re2/dist/util/mutex.h b/src/third_party/re2/dist/util/mutex.h
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+++ b/src/third_party/re2/dist/util/mutex.h
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+// Copyright 2007 The RE2 Authors.  All Rights Reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+#ifndef UTIL_MUTEX_H_
+#define UTIL_MUTEX_H_
+
+/*
+ * A simple mutex wrapper, supporting locks and read-write locks.
+ * You should assume the locks are *not* re-entrant.
+ */
+
+#ifdef _WIN32
+// Requires Windows Vista or Windows Server 2008 at minimum.
+#include <windows.h>
+#if defined(WINVER) && WINVER >= 0x0600
+#define MUTEX_IS_WIN32_SRWLOCK
+#endif
+#else
+#ifndef _POSIX_C_SOURCE
+#define _POSIX_C_SOURCE 200809L
+#endif
+#include <unistd.h>
+#if defined(_POSIX_READER_WRITER_LOCKS) && _POSIX_READER_WRITER_LOCKS > 0
+#define MUTEX_IS_PTHREAD_RWLOCK
+#endif
+#endif
+
+#if defined(MUTEX_IS_WIN32_SRWLOCK)
+typedef SRWLOCK MutexType;
+#elif defined(MUTEX_IS_PTHREAD_RWLOCK)
+#include <pthread.h>
+#include <stdlib.h>
+typedef pthread_rwlock_t MutexType;
+#else
+#include <mutex>
+typedef std::mutex MutexType;
+#endif
+
+namespace re2 {
+
+class Mutex {
+ public:
+  inline Mutex();
+  inline ~Mutex();
+  inline void Lock();    // Block if needed until free then acquire exclusively
+  inline void Unlock();  // Release a lock acquired via Lock()
+  // Note that on systems that don't support read-write locks, these may
+  // be implemented as synonyms to Lock() and Unlock().  So you can use
+  // these for efficiency, but don't use them anyplace where being able
+  // to do shared reads is necessary to avoid deadlock.
+  inline void ReaderLock();   // Block until free or shared then acquire a share
+  inline void ReaderUnlock(); // Release a read share of this Mutex
+  inline void WriterLock() { Lock(); }     // Acquire an exclusive lock
+  inline void WriterUnlock() { Unlock(); } // Release a lock from WriterLock()
+
+ private:
+  MutexType mutex_;
+
+  // Catch the error of writing Mutex when intending MutexLock.
+  Mutex(Mutex *ignored);
+
+  Mutex(const Mutex&) = delete;
+  Mutex& operator=(const Mutex&) = delete;
+};
+
+#if defined(MUTEX_IS_WIN32_SRWLOCK)
+
+Mutex::Mutex()             : mutex_(SRWLOCK_INIT) { }
+Mutex::~Mutex()            { }
+void Mutex::Lock()         { AcquireSRWLockExclusive(&mutex_); }
+void Mutex::Unlock()       { ReleaseSRWLockExclusive(&mutex_); }
+void Mutex::ReaderLock()   { AcquireSRWLockShared(&mutex_); }
+void Mutex::ReaderUnlock() { ReleaseSRWLockShared(&mutex_); }
+
+#elif defined(MUTEX_IS_PTHREAD_RWLOCK)
+
+#define SAFE_PTHREAD(fncall)    \
+  do {                          \
+    if ((fncall) != 0) abort(); \
+  } while (0)
+
+Mutex::Mutex()             { SAFE_PTHREAD(pthread_rwlock_init(&mutex_, NULL)); }
+Mutex::~Mutex()            { SAFE_PTHREAD(pthread_rwlock_destroy(&mutex_)); }
+void Mutex::Lock()         { SAFE_PTHREAD(pthread_rwlock_wrlock(&mutex_)); }
+void Mutex::Unlock()       { SAFE_PTHREAD(pthread_rwlock_unlock(&mutex_)); }
+void Mutex::ReaderLock()   { SAFE_PTHREAD(pthread_rwlock_rdlock(&mutex_)); }
+void Mutex::ReaderUnlock() { SAFE_PTHREAD(pthread_rwlock_unlock(&mutex_)); }
+
+#undef SAFE_PTHREAD
+
+#else
+
+Mutex::Mutex()             { }
+Mutex::~Mutex()            { }
+void Mutex::Lock()         { mutex_.lock(); }
+void Mutex::Unlock()       { mutex_.unlock(); }
+void Mutex::ReaderLock()   { Lock(); }  // C++11 doesn't have std::shared_mutex.
+void Mutex::ReaderUnlock() { Unlock(); }
+
+#endif
+
+// --------------------------------------------------------------------------
+// Some helper classes
+
+// MutexLock(mu) acquires mu when constructed and releases it when destroyed.
+class MutexLock {
+ public:
+  explicit MutexLock(Mutex *mu) : mu_(mu) { mu_->Lock(); }
+  ~MutexLock() { mu_->Unlock(); }
+ private:
+  Mutex * const mu_;
+
+  MutexLock(const MutexLock&) = delete;
+  MutexLock& operator=(const MutexLock&) = delete;
+};
+
+// ReaderMutexLock and WriterMutexLock do the same, for rwlocks
+class ReaderMutexLock {
+ public:
+  explicit ReaderMutexLock(Mutex *mu) : mu_(mu) { mu_->ReaderLock(); }
+  ~ReaderMutexLock() { mu_->ReaderUnlock(); }
+ private:
+  Mutex * const mu_;
+
+  ReaderMutexLock(const ReaderMutexLock&) = delete;
+  ReaderMutexLock& operator=(const ReaderMutexLock&) = delete;
+};
+
+class WriterMutexLock {
+ public:
+  explicit WriterMutexLock(Mutex *mu) : mu_(mu) { mu_->WriterLock(); }
+  ~WriterMutexLock() { mu_->WriterUnlock(); }
+ private:
+  Mutex * const mu_;
+
+  WriterMutexLock(const WriterMutexLock&) = delete;
+  WriterMutexLock& operator=(const WriterMutexLock&) = delete;
+};
+
+// Catch bug where variable name is omitted, e.g. MutexLock (&mu);
+#define MutexLock(x) static_assert(false, "MutexLock declaration missing variable name")
+#define ReaderMutexLock(x) static_assert(false, "ReaderMutexLock declaration missing variable name")
+#define WriterMutexLock(x) static_assert(false, "WriterMutexLock declaration missing variable name")
+
+}  // namespace re2
+
+#endif  // UTIL_MUTEX_H_