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Diffstat (limited to 'sdch/open-vcdiff/src/mutex.h')
| -rw-r--r-- | sdch/open-vcdiff/src/mutex.h | 303 |
1 files changed, 303 insertions, 0 deletions
diff --git a/sdch/open-vcdiff/src/mutex.h b/sdch/open-vcdiff/src/mutex.h new file mode 100644 index 0000000..eda1f4e --- /dev/null +++ b/sdch/open-vcdiff/src/mutex.h @@ -0,0 +1,303 @@ +// 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, so it's defined in the +// global namespace. If you want to expose it, you'll want to move +// it to the Google namespace. +// +// 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__) +# define WIN32_LEAN_AND_MEAN // We only need minimal includes +# 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 +# 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__ +# define _XOPEN_SOURCE 500 // may be needed to get the rwlock calls +# 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 + +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() + + 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. +#include <assert.h> + +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) + +#include <stdlib.h> // for abort() +#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) + +#include <stdlib.h> // for abort() +#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) + +#endif /* #define GOOGLE_MUTEX_H__ */ |