1// Copyright (c) 2007, Google Inc. 2// All rights reserved. 3// 4// Redistribution and use in source and binary forms, with or without 5// modification, are permitted provided that the following conditions are 6// met: 7// 8// * Redistributions of source code must retain the above copyright 9// notice, this list of conditions and the following disclaimer. 10// * Redistributions in binary form must reproduce the above 11// copyright notice, this list of conditions and the following disclaimer 12// in the documentation and/or other materials provided with the 13// distribution. 14// * Neither the name of Google Inc. nor the names of its 15// contributors may be used to endorse or promote products derived from 16// this software without specific prior written permission. 17// 18// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 19// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 20// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 21// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 22// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 23// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 24// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 25// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 26// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 27// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 28// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 29// 30// --- 31// Author: Craig Silverstein. 32// 33// A simple mutex wrapper, supporting locks and read-write locks. 34// You should assume the locks are *not* re-entrant. 35// 36// To use: you should define the following macros in your configure.ac: 37// ACX_PTHREAD 38// AC_RWLOCK 39// The latter is defined in ../autoconf. 40// 41// This class is meant to be internal-only and should be wrapped by an 42// internal namespace. Before you use this module, please give the 43// name of your internal namespace for this module. Or, if you want 44// to expose it, you'll want to move it to the Google namespace. We 45// cannot put this class in global namespace because there can be some 46// problems when we have multiple versions of Mutex in each shared object. 47// 48// NOTE: TryLock() is broken for NO_THREADS mode, at least in NDEBUG 49// mode. 50// 51// CYGWIN NOTE: Cygwin support for rwlock seems to be buggy: 52// http://www.cygwin.com/ml/cygwin/2008-12/msg00017.html 53// Because of that, we might as well use windows locks for 54// cygwin. They seem to be more reliable than the cygwin pthreads layer. 55// 56// TRICKY IMPLEMENTATION NOTE: 57// This class is designed to be safe to use during 58// dynamic-initialization -- that is, by global constructors that are 59// run before main() starts. The issue in this case is that 60// dynamic-initialization happens in an unpredictable order, and it 61// could be that someone else's dynamic initializer could call a 62// function that tries to acquire this mutex -- but that all happens 63// before this mutex's constructor has run. (This can happen even if 64// the mutex and the function that uses the mutex are in the same .cc 65// file.) Basically, because Mutex does non-trivial work in its 66// constructor, it's not, in the naive implementation, safe to use 67// before dynamic initialization has run on it. 68// 69// The solution used here is to pair the actual mutex primitive with a 70// bool that is set to true when the mutex is dynamically initialized. 71// (Before that it's false.) Then we modify all mutex routines to 72// look at the bool, and not try to lock/unlock until the bool makes 73// it to true (which happens after the Mutex constructor has run.) 74// 75// This works because before main() starts -- particularly, during 76// dynamic initialization -- there are no threads, so a) it's ok that 77// the mutex operations are a no-op, since we don't need locking then 78// anyway; and b) we can be quite confident our bool won't change 79// state between a call to Lock() and a call to Unlock() (that would 80// require a global constructor in one translation unit to call Lock() 81// and another global constructor in another translation unit to call 82// Unlock() later, which is pretty perverse). 83// 84// That said, it's tricky, and can conceivably fail; it's safest to 85// avoid trying to acquire a mutex in a global constructor, if you 86// can. One way it can fail is that a really smart compiler might 87// initialize the bool to true at static-initialization time (too 88// early) rather than at dynamic-initialization time. To discourage 89// that, we set is_safe_ to true in code (not the constructor 90// colon-initializer) and set it to true via a function that always 91// evaluates to true, but that the compiler can't know always 92// evaluates to true. This should be good enough. 93// 94// A related issue is code that could try to access the mutex 95// after it's been destroyed in the global destructors (because 96// the Mutex global destructor runs before some other global 97// destructor, that tries to acquire the mutex). The way we 98// deal with this is by taking a constructor arg that global 99// mutexes should pass in, that causes the destructor to do no 100// work. We still depend on the compiler not doing anything 101// weird to a Mutex's memory after it is destroyed, but for a 102// static global variable, that's pretty safe. 103 104#ifndef GOOGLE_MUTEX_H_ 105#define GOOGLE_MUTEX_H_ 106 107#include <config.h> 108 109#if defined(NO_THREADS) 110 typedef int MutexType; // to keep a lock-count 111#elif defined(_WIN32) || defined(__CYGWIN__) || defined(__CYGWIN32__) 112# ifndef WIN32_LEAN_AND_MEAN 113# define WIN32_LEAN_AND_MEAN // We only need minimal includes 114# endif 115 // We need Windows NT or later for TryEnterCriticalSection(). If you 116 // don't need that functionality, you can remove these _WIN32_WINNT 117 // lines, and change TryLock() to assert(0) or something. 118# ifndef _WIN32_WINNT 119# define _WIN32_WINNT 0x0400 120# endif 121# include <windows.h> 122 typedef CRITICAL_SECTION MutexType; 123#elif defined(HAVE_PTHREAD) && defined(HAVE_RWLOCK) 124 // Needed for pthread_rwlock_*. If it causes problems, you could take it 125 // out, but then you'd have to unset HAVE_RWLOCK (at least on linux -- it 126 // *does* cause problems for FreeBSD, or MacOSX, but isn't needed 127 // for locking there.) 128# ifdef __linux__ 129# define _XOPEN_SOURCE 500 // may be needed to get the rwlock calls 130# endif 131# include <pthread.h> 132 typedef pthread_rwlock_t MutexType; 133#elif defined(HAVE_PTHREAD) 134# include <pthread.h> 135 typedef pthread_mutex_t MutexType; 136#else 137# error Need to implement mutex.h for your architecture, or #define NO_THREADS 138#endif 139 140#include <assert.h> 141#include <stdlib.h> // for abort() 142 143#define MUTEX_NAMESPACE perftools_mutex_namespace 144 145namespace MUTEX_NAMESPACE { 146 147class Mutex { 148 public: 149 // This is used for the single-arg constructor 150 enum LinkerInitialized { LINKER_INITIALIZED }; 151 152 // Create a Mutex that is not held by anybody. This constructor is 153 // typically used for Mutexes allocated on the heap or the stack. 154 inline Mutex(); 155 // This constructor should be used for global, static Mutex objects. 156 // It inhibits work being done by the destructor, which makes it 157 // safer for code that tries to acqiure this mutex in their global 158 // destructor. 159 inline Mutex(LinkerInitialized); 160 161 // Destructor 162 inline ~Mutex(); 163 164 inline void Lock(); // Block if needed until free then acquire exclusively 165 inline void Unlock(); // Release a lock acquired via Lock() 166 inline bool TryLock(); // If free, Lock() and return true, else return false 167 // Note that on systems that don't support read-write locks, these may 168 // be implemented as synonyms to Lock() and Unlock(). So you can use 169 // these for efficiency, but don't use them anyplace where being able 170 // to do shared reads is necessary to avoid deadlock. 171 inline void ReaderLock(); // Block until free or shared then acquire a share 172 inline void ReaderUnlock(); // Release a read share of this Mutex 173 inline void WriterLock() { Lock(); } // Acquire an exclusive lock 174 inline void WriterUnlock() { Unlock(); } // Release a lock from WriterLock() 175 176 private: 177 MutexType mutex_; 178 // We want to make sure that the compiler sets is_safe_ to true only 179 // when we tell it to, and never makes assumptions is_safe_ is 180 // always true. volatile is the most reliable way to do that. 181 volatile bool is_safe_; 182 // This indicates which constructor was called. 183 bool destroy_; 184 185 inline void SetIsSafe() { is_safe_ = true; } 186 187 // Catch the error of writing Mutex when intending MutexLock. 188 Mutex(Mutex* /*ignored*/) {} 189 // Disallow "evil" constructors 190 Mutex(const Mutex&); 191 void operator=(const Mutex&); 192}; 193 194// Now the implementation of Mutex for various systems 195#if defined(NO_THREADS) 196 197// When we don't have threads, we can be either reading or writing, 198// but not both. We can have lots of readers at once (in no-threads 199// mode, that's most likely to happen in recursive function calls), 200// but only one writer. We represent this by having mutex_ be -1 when 201// writing and a number > 0 when reading (and 0 when no lock is held). 202// 203// In debug mode, we assert these invariants, while in non-debug mode 204// we do nothing, for efficiency. That's why everything is in an 205// assert. 206 207Mutex::Mutex() : mutex_(0) { } 208Mutex::Mutex(Mutex::LinkerInitialized) : mutex_(0) { } 209Mutex::~Mutex() { assert(mutex_ == 0); } 210void Mutex::Lock() { assert(--mutex_ == -1); } 211void Mutex::Unlock() { assert(mutex_++ == -1); } 212bool Mutex::TryLock() { if (mutex_) return false; Lock(); return true; } 213void Mutex::ReaderLock() { assert(++mutex_ > 0); } 214void Mutex::ReaderUnlock() { assert(mutex_-- > 0); } 215 216#elif defined(_WIN32) || defined(__CYGWIN__) || defined(__CYGWIN32__) 217 218Mutex::Mutex() : destroy_(true) { 219 InitializeCriticalSection(&mutex_); 220 SetIsSafe(); 221} 222Mutex::Mutex(LinkerInitialized) : destroy_(false) { 223 InitializeCriticalSection(&mutex_); 224 SetIsSafe(); 225} 226Mutex::~Mutex() { if (destroy_) DeleteCriticalSection(&mutex_); } 227void Mutex::Lock() { if (is_safe_) EnterCriticalSection(&mutex_); } 228void Mutex::Unlock() { if (is_safe_) LeaveCriticalSection(&mutex_); } 229bool Mutex::TryLock() { return is_safe_ ? 230 TryEnterCriticalSection(&mutex_) != 0 : true; } 231void Mutex::ReaderLock() { Lock(); } // we don't have read-write locks 232void Mutex::ReaderUnlock() { Unlock(); } 233 234#elif defined(HAVE_PTHREAD) && defined(HAVE_RWLOCK) 235 236#define SAFE_PTHREAD(fncall) do { /* run fncall if is_safe_ is true */ \ 237 if (is_safe_ && fncall(&mutex_) != 0) abort(); \ 238} while (0) 239 240Mutex::Mutex() : destroy_(true) { 241 SetIsSafe(); 242 if (is_safe_ && pthread_rwlock_init(&mutex_, NULL) != 0) abort(); 243} 244Mutex::Mutex(Mutex::LinkerInitialized) : destroy_(false) { 245 SetIsSafe(); 246 if (is_safe_ && pthread_rwlock_init(&mutex_, NULL) != 0) abort(); 247} 248Mutex::~Mutex() { if (destroy_) SAFE_PTHREAD(pthread_rwlock_destroy); } 249void Mutex::Lock() { SAFE_PTHREAD(pthread_rwlock_wrlock); } 250void Mutex::Unlock() { SAFE_PTHREAD(pthread_rwlock_unlock); } 251bool Mutex::TryLock() { return is_safe_ ? 252 pthread_rwlock_trywrlock(&mutex_) == 0 : true; } 253void Mutex::ReaderLock() { SAFE_PTHREAD(pthread_rwlock_rdlock); } 254void Mutex::ReaderUnlock() { SAFE_PTHREAD(pthread_rwlock_unlock); } 255#undef SAFE_PTHREAD 256 257#elif defined(HAVE_PTHREAD) 258 259#define SAFE_PTHREAD(fncall) do { /* run fncall if is_safe_ is true */ \ 260 if (is_safe_ && fncall(&mutex_) != 0) abort(); \ 261} while (0) 262 263Mutex::Mutex() : destroy_(true) { 264 SetIsSafe(); 265 if (is_safe_ && pthread_mutex_init(&mutex_, NULL) != 0) abort(); 266} 267Mutex::Mutex(Mutex::LinkerInitialized) : destroy_(false) { 268 SetIsSafe(); 269 if (is_safe_ && pthread_mutex_init(&mutex_, NULL) != 0) abort(); 270} 271Mutex::~Mutex() { if (destroy_) SAFE_PTHREAD(pthread_mutex_destroy); } 272void Mutex::Lock() { SAFE_PTHREAD(pthread_mutex_lock); } 273void Mutex::Unlock() { SAFE_PTHREAD(pthread_mutex_unlock); } 274bool Mutex::TryLock() { return is_safe_ ? 275 pthread_mutex_trylock(&mutex_) == 0 : true; } 276void Mutex::ReaderLock() { Lock(); } 277void Mutex::ReaderUnlock() { Unlock(); } 278#undef SAFE_PTHREAD 279 280#endif 281 282// -------------------------------------------------------------------------- 283// Some helper classes 284 285// MutexLock(mu) acquires mu when constructed and releases it when destroyed. 286class MutexLock { 287 public: 288 explicit MutexLock(Mutex *mu) : mu_(mu) { mu_->Lock(); } 289 ~MutexLock() { mu_->Unlock(); } 290 private: 291 Mutex * const mu_; 292 // Disallow "evil" constructors 293 MutexLock(const MutexLock&); 294 void operator=(const MutexLock&); 295}; 296 297// ReaderMutexLock and WriterMutexLock do the same, for rwlocks 298class ReaderMutexLock { 299 public: 300 explicit ReaderMutexLock(Mutex *mu) : mu_(mu) { mu_->ReaderLock(); } 301 ~ReaderMutexLock() { mu_->ReaderUnlock(); } 302 private: 303 Mutex * const mu_; 304 // Disallow "evil" constructors 305 ReaderMutexLock(const ReaderMutexLock&); 306 void operator=(const ReaderMutexLock&); 307}; 308 309class WriterMutexLock { 310 public: 311 explicit WriterMutexLock(Mutex *mu) : mu_(mu) { mu_->WriterLock(); } 312 ~WriterMutexLock() { mu_->WriterUnlock(); } 313 private: 314 Mutex * const mu_; 315 // Disallow "evil" constructors 316 WriterMutexLock(const WriterMutexLock&); 317 void operator=(const WriterMutexLock&); 318}; 319 320// Catch bug where variable name is omitted, e.g. MutexLock (&mu); 321#define MutexLock(x) COMPILE_ASSERT(0, mutex_lock_decl_missing_var_name) 322#define ReaderMutexLock(x) COMPILE_ASSERT(0, rmutex_lock_decl_missing_var_name) 323#define WriterMutexLock(x) COMPILE_ASSERT(0, wmutex_lock_decl_missing_var_name) 324 325} // namespace MUTEX_NAMESPACE 326 327using namespace MUTEX_NAMESPACE; 328 329#undef MUTEX_NAMESPACE 330 331#endif /* #define GOOGLE_SIMPLE_MUTEX_H_ */ 332