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-// Copyright (c) 2007, Google Inc.
-// All rights reserved.
-// 
-// Redistribution and use in source and binary forms, with or without
-// modification, are permitted provided that the following conditions are
-// met:
-// 
-//     * Redistributions of source code must retain the above copyright
-// notice, this list of conditions and the following disclaimer.
-//     * Redistributions in binary form must reproduce the above
-// copyright notice, this list of conditions and the following disclaimer
-// in the documentation and/or other materials provided with the
-// distribution.
-//     * Neither the name of Google Inc. nor the names of its
-// contributors may be used to endorse or promote products derived from
-// this software without specific prior written permission.
-// 
-// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
-// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
-// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
-// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
-// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
-// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
-// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
-// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
-// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
-// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
-// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
-// 
-// ---
-// Author: Craig Silverstein.
-//
-// A simple mutex wrapper, supporting locks and read-write locks.
-// You should assume the locks are *not* re-entrant.
-//
-// To use: you should define the following macros in your configure.ac:
-//   ACX_PTHREAD
-//   AC_RWLOCK
-// The latter is defined in ../autoconf.
-//
-// This class is meant to be internal-only and should be wrapped by an
-// internal namespace.  Before you use this module, please give the
-// name of your internal namespace for this module.  Or, if you want
-// to expose it, you'll want to move it to the Google namespace.  We
-// cannot put this class in global namespace because there can be some
-// problems when we have multiple versions of Mutex in each shared object.
-//
-// NOTE: by default, we have #ifdef'ed out the TryLock() method.
-//       This is for two reasons:
-// 1) TryLock() under Windows is a bit annoying (it requires a
-//    #define to be defined very early).
-// 2) TryLock() is broken for NO_THREADS mode, at least in NDEBUG
-//    mode.
-// If you need TryLock(), and either these two caveats are not a
-// problem for you, or you're willing to work around them, then
-// feel free to #define GMUTEX_TRYLOCK, or to remove the #ifdefs
-// in the code below.
-//
-// CYGWIN NOTE: Cygwin support for rwlock seems to be buggy:
-//    http://www.cygwin.com/ml/cygwin/2008-12/msg00017.html
-// Because of that, we might as well use windows locks for
-// cygwin.  They seem to be more reliable than the cygwin pthreads layer.
-//
-// TRICKY IMPLEMENTATION NOTE:
-// This class is designed to be safe to use during
-// dynamic-initialization -- that is, by global constructors that are
-// run before main() starts.  The issue in this case is that
-// dynamic-initialization happens in an unpredictable order, and it
-// could be that someone else's dynamic initializer could call a
-// function that tries to acquire this mutex -- but that all happens
-// before this mutex's constructor has run.  (This can happen even if
-// the mutex and the function that uses the mutex are in the same .cc
-// file.)  Basically, because Mutex does non-trivial work in its
-// constructor, it's not, in the naive implementation, safe to use
-// before dynamic initialization has run on it.
-//
-// The solution used here is to pair the actual mutex primitive with a
-// bool that is set to true when the mutex is dynamically initialized.
-// (Before that it's false.)  Then we modify all mutex routines to
-// look at the bool, and not try to lock/unlock until the bool makes
-// it to true (which happens after the Mutex constructor has run.)
-//
-// This works because before main() starts -- particularly, during
-// dynamic initialization -- there are no threads, so a) it's ok that
-// the mutex operations are a no-op, since we don't need locking then
-// anyway; and b) we can be quite confident our bool won't change
-// state between a call to Lock() and a call to Unlock() (that would
-// require a global constructor in one translation unit to call Lock()
-// and another global constructor in another translation unit to call
-// Unlock() later, which is pretty perverse).
-//
-// That said, it's tricky, and can conceivably fail; it's safest to
-// avoid trying to acquire a mutex in a global constructor, if you
-// can.  One way it can fail is that a really smart compiler might
-// initialize the bool to true at static-initialization time (too
-// early) rather than at dynamic-initialization time.  To discourage
-// that, we set is_safe_ to true in code (not the constructor
-// colon-initializer) and set it to true via a function that always
-// evaluates to true, but that the compiler can't know always
-// evaluates to true.  This should be good enough.
-
-#ifndef GOOGLE_MUTEX_H_
-#define GOOGLE_MUTEX_H_
-
-#include "config.h"           // to figure out pthreads support
-
-#if defined(NO_THREADS)
-  typedef int MutexType;      // to keep a lock-count
-#elif defined(_WIN32) || defined(__CYGWIN32__) || defined(__CYGWIN64__)
-# ifndef WIN32_LEAN_AND_MEAN
-#  define WIN32_LEAN_AND_MEAN  // We only need minimal includes
-# endif
-# ifdef GMUTEX_TRYLOCK
-  // We need Windows NT or later for TryEnterCriticalSection().  If you
-  // don't need that functionality, you can remove these _WIN32_WINNT
-  // lines, and change TryLock() to assert(0) or something.
-#   ifndef _WIN32_WINNT
-#     define _WIN32_WINNT 0x0400
-#   endif
-# endif
-// To avoid macro definition of ERROR.
-# ifndef NOGDI
-#  define NOGDI
-# endif
-// To avoid macro definition of min/max.
-# ifndef NOMINMAX
-#  define NOMINMAX
-# endif
-# include <windows.h>
-  typedef CRITICAL_SECTION MutexType;
-#elif defined(HAVE_PTHREAD) && defined(HAVE_RWLOCK)
-  // Needed for pthread_rwlock_*.  If it causes problems, you could take it
-  // out, but then you'd have to unset HAVE_RWLOCK (at least on linux -- it
-  // *does* cause problems for FreeBSD, or MacOSX, but isn't needed
-  // for locking there.)
-# ifdef __linux__
-#   ifndef _XOPEN_SOURCE  // Some other header might have already set it for us.
-#     define _XOPEN_SOURCE 500  // may be needed to get the rwlock calls
-#   endif
-# endif
-# include <pthread.h>
-  typedef pthread_rwlock_t MutexType;
-#elif defined(HAVE_PTHREAD)
-# include <pthread.h>
-  typedef pthread_mutex_t MutexType;
-#else
-# error Need to implement mutex.h for your architecture, or #define NO_THREADS
-#endif
-
-// We need to include these header files after defining _XOPEN_SOURCE
-// as they may define the _XOPEN_SOURCE macro.
-#include <assert.h>
-#include <stdlib.h>      // for abort()
-
-#define MUTEX_NAMESPACE glog_internal_namespace_
-
-namespace MUTEX_NAMESPACE {
-
-class Mutex {
- public:
-  // Create a Mutex that is not held by anybody.  This constructor is
-  // typically used for Mutexes allocated on the heap or the stack.
-  // See below for a recommendation for constructing global Mutex
-  // objects.
-  inline Mutex();
-
-  // Destructor
-  inline ~Mutex();
-
-  inline void Lock();    // Block if needed until free then acquire exclusively
-  inline void Unlock();  // Release a lock acquired via Lock()
-#ifdef GMUTEX_TRYLOCK
-  inline bool TryLock(); // If free, Lock() and return true, else return false
-#endif
-  // 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()
-
-  // TODO(hamaji): Do nothing, implement correctly.
-  inline void AssertHeld() {}
-
- private:
-  MutexType mutex_;
-  // We want to make sure that the compiler sets is_safe_ to true only
-  // when we tell it to, and never makes assumptions is_safe_ is
-  // always true.  volatile is the most reliable way to do that.
-  volatile bool is_safe_;
-
-  inline void SetIsSafe() { is_safe_ = true; }
-
-  // Catch the error of writing Mutex when intending MutexLock.
-  Mutex(Mutex* /*ignored*/) {}
-  // Disallow "evil" constructors
-  Mutex(const Mutex&);
-  void operator=(const Mutex&);
-};
-
-// Now the implementation of Mutex for various systems
-#if defined(NO_THREADS)
-
-// When we don't have threads, we can be either reading or writing,
-// but not both.  We can have lots of readers at once (in no-threads
-// mode, that's most likely to happen in recursive function calls),
-// but only one writer.  We represent this by having mutex_ be -1 when
-// writing and a number > 0 when reading (and 0 when no lock is held).
-//
-// In debug mode, we assert these invariants, while in non-debug mode
-// we do nothing, for efficiency.  That's why everything is in an
-// assert.
-
-Mutex::Mutex() : mutex_(0) { }
-Mutex::~Mutex()            { assert(mutex_ == 0); }
-void Mutex::Lock()         { assert(--mutex_ == -1); }
-void Mutex::Unlock()       { assert(mutex_++ == -1); }
-#ifdef GMUTEX_TRYLOCK
-bool Mutex::TryLock()      { if (mutex_) return false; Lock(); return true; }
-#endif
-void Mutex::ReaderLock()   { assert(++mutex_ > 0); }
-void Mutex::ReaderUnlock() { assert(mutex_-- > 0); }
-
-#elif defined(_WIN32) || defined(__CYGWIN32__) || defined(__CYGWIN64__)
-
-Mutex::Mutex()             { InitializeCriticalSection(&mutex_); SetIsSafe(); }
-Mutex::~Mutex()            { DeleteCriticalSection(&mutex_); }
-void Mutex::Lock()         { if (is_safe_) EnterCriticalSection(&mutex_); }
-void Mutex::Unlock()       { if (is_safe_) LeaveCriticalSection(&mutex_); }
-#ifdef GMUTEX_TRYLOCK
-bool Mutex::TryLock()      { return is_safe_ ?
-                                 TryEnterCriticalSection(&mutex_) != 0 : true; }
-#endif
-void Mutex::ReaderLock()   { Lock(); }      // we don't have read-write locks
-void Mutex::ReaderUnlock() { Unlock(); }
-
-#elif defined(HAVE_PTHREAD) && defined(HAVE_RWLOCK)
-
-#define SAFE_PTHREAD(fncall)  do {   /* run fncall if is_safe_ is true */  \
-  if (is_safe_ && fncall(&mutex_) != 0) abort();                           \
-} while (0)
-
-Mutex::Mutex() {
-  SetIsSafe();
-  if (is_safe_ && pthread_rwlock_init(&mutex_, NULL) != 0) abort();
-}
-Mutex::~Mutex()            { SAFE_PTHREAD(pthread_rwlock_destroy); }
-void Mutex::Lock()         { SAFE_PTHREAD(pthread_rwlock_wrlock); }
-void Mutex::Unlock()       { SAFE_PTHREAD(pthread_rwlock_unlock); }
-#ifdef GMUTEX_TRYLOCK
-bool Mutex::TryLock()      { return is_safe_ ?
-                                    pthread_rwlock_trywrlock(&mutex_) == 0 :
-                                    true; }
-#endif
-void Mutex::ReaderLock()   { SAFE_PTHREAD(pthread_rwlock_rdlock); }
-void Mutex::ReaderUnlock() { SAFE_PTHREAD(pthread_rwlock_unlock); }
-#undef SAFE_PTHREAD
-
-#elif defined(HAVE_PTHREAD)
-
-#define SAFE_PTHREAD(fncall)  do {   /* run fncall if is_safe_ is true */  \
-  if (is_safe_ && fncall(&mutex_) != 0) abort();                           \
-} while (0)
-
-Mutex::Mutex()             {
-  SetIsSafe();
-  if (is_safe_ && pthread_mutex_init(&mutex_, NULL) != 0) abort();
-}
-Mutex::~Mutex()            { SAFE_PTHREAD(pthread_mutex_destroy); }
-void Mutex::Lock()         { SAFE_PTHREAD(pthread_mutex_lock); }
-void Mutex::Unlock()       { SAFE_PTHREAD(pthread_mutex_unlock); }
-#ifdef GMUTEX_TRYLOCK
-bool Mutex::TryLock()      { return is_safe_ ?
-                                 pthread_mutex_trylock(&mutex_) == 0 : true; }
-#endif
-void Mutex::ReaderLock()   { Lock(); }
-void Mutex::ReaderUnlock() { Unlock(); }
-#undef SAFE_PTHREAD
-
-#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_;
-  // Disallow "evil" constructors
-  MutexLock(const MutexLock&);
-  void operator=(const MutexLock&);
-};
-
-// 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_;
-  // Disallow "evil" constructors
-  ReaderMutexLock(const ReaderMutexLock&);
-  void operator=(const ReaderMutexLock&);
-};
-
-class WriterMutexLock {
- public:
-  explicit WriterMutexLock(Mutex *mu) : mu_(mu) { mu_->WriterLock(); }
-  ~WriterMutexLock() { mu_->WriterUnlock(); }
- private:
-  Mutex * const mu_;
-  // Disallow "evil" constructors
-  WriterMutexLock(const WriterMutexLock&);
-  void operator=(const WriterMutexLock&);
-};
-
-// Catch bug where variable name is omitted, e.g. MutexLock (&mu);
-#define MutexLock(x) COMPILE_ASSERT(0, mutex_lock_decl_missing_var_name)
-#define ReaderMutexLock(x) COMPILE_ASSERT(0, rmutex_lock_decl_missing_var_name)
-#define WriterMutexLock(x) COMPILE_ASSERT(0, wmutex_lock_decl_missing_var_name)
-
-}  // namespace MUTEX_NAMESPACE
-
-using namespace MUTEX_NAMESPACE;
-
-#undef MUTEX_NAMESPACE
-
-#endif  /* #define GOOGLE_MUTEX_H__ */