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      1 //===- llvm/Support/Mutex.h - Mutex Operating System Concept -----*- C++ -*-===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 //
     10 // This file declares the llvm::sys::Mutex class.
     11 //
     12 //===----------------------------------------------------------------------===//
     13 
     14 #ifndef LLVM_SUPPORT_MUTEX_H
     15 #define LLVM_SUPPORT_MUTEX_H
     16 
     17 #include "llvm/Support/Compiler.h"
     18 #include "llvm/Support/Threading.h"
     19 #include <cassert>
     20 
     21 namespace llvm
     22 {
     23   namespace sys
     24   {
     25     /// @brief Platform agnostic Mutex class.
     26     class MutexImpl
     27     {
     28     /// @name Constructors
     29     /// @{
     30     public:
     31 
     32       /// Initializes the lock but doesn't acquire it. if \p recursive is set
     33       /// to false, the lock will not be recursive which makes it cheaper but
     34       /// also more likely to deadlock (same thread can't acquire more than
     35       /// once).
     36       /// @brief Default Constructor.
     37       explicit MutexImpl(bool recursive = true);
     38 
     39       /// Releases and removes the lock
     40       /// @brief Destructor
     41       ~MutexImpl();
     42 
     43     /// @}
     44     /// @name Methods
     45     /// @{
     46     public:
     47 
     48       /// Attempts to unconditionally acquire the lock. If the lock is held by
     49       /// another thread, this method will wait until it can acquire the lock.
     50       /// @returns false if any kind of error occurs, true otherwise.
     51       /// @brief Unconditionally acquire the lock.
     52       bool acquire();
     53 
     54       /// Attempts to release the lock. If the lock is held by the current
     55       /// thread, the lock is released allowing other threads to acquire the
     56       /// lock.
     57       /// @returns false if any kind of error occurs, true otherwise.
     58       /// @brief Unconditionally release the lock.
     59       bool release();
     60 
     61       /// Attempts to acquire the lock without blocking. If the lock is not
     62       /// available, this function returns false quickly (without blocking). If
     63       /// the lock is available, it is acquired.
     64       /// @returns false if any kind of error occurs or the lock is not
     65       /// available, true otherwise.
     66       /// @brief Try to acquire the lock.
     67       bool tryacquire();
     68 
     69     //@}
     70     /// @name Platform Dependent Data
     71     /// @{
     72     private:
     73 #if defined(LLVM_ENABLE_THREADS) && LLVM_ENABLE_THREADS != 0
     74       void* data_; ///< We don't know what the data will be
     75 #endif
     76 
     77     /// @}
     78     /// @name Do Not Implement
     79     /// @{
     80     private:
     81       MutexImpl(const MutexImpl &) = delete;
     82       void operator=(const MutexImpl &) = delete;
     83     /// @}
     84     };
     85 
     86 
     87     /// SmartMutex - A mutex with a compile time constant parameter that
     88     /// indicates whether this mutex should become a no-op when we're not
     89     /// running in multithreaded mode.
     90     template<bool mt_only>
     91     class SmartMutex {
     92       MutexImpl impl;
     93       unsigned acquired;
     94       bool recursive;
     95     public:
     96       explicit SmartMutex(bool rec = true) :
     97         impl(rec), acquired(0), recursive(rec) { }
     98 
     99       bool lock() {
    100         if (!mt_only || llvm_is_multithreaded()) {
    101           return impl.acquire();
    102         } else {
    103           // Single-threaded debugging code.  This would be racy in
    104           // multithreaded mode, but provides not sanity checks in single
    105           // threaded mode.
    106           assert((recursive || acquired == 0) && "Lock already acquired!!");
    107           ++acquired;
    108           return true;
    109         }
    110       }
    111 
    112       bool unlock() {
    113         if (!mt_only || llvm_is_multithreaded()) {
    114           return impl.release();
    115         } else {
    116           // Single-threaded debugging code.  This would be racy in
    117           // multithreaded mode, but provides not sanity checks in single
    118           // threaded mode.
    119           assert(((recursive && acquired) || (acquired == 1)) &&
    120                  "Lock not acquired before release!");
    121           --acquired;
    122           return true;
    123         }
    124       }
    125 
    126       bool try_lock() {
    127         if (!mt_only || llvm_is_multithreaded())
    128           return impl.tryacquire();
    129         else return true;
    130       }
    131 
    132       private:
    133         SmartMutex(const SmartMutex<mt_only> & original);
    134         void operator=(const SmartMutex<mt_only> &);
    135     };
    136 
    137     /// Mutex - A standard, always enforced mutex.
    138     typedef SmartMutex<false> Mutex;
    139 
    140     template<bool mt_only>
    141     class SmartScopedLock  {
    142       SmartMutex<mt_only>& mtx;
    143 
    144     public:
    145       SmartScopedLock(SmartMutex<mt_only>& m) : mtx(m) {
    146         mtx.lock();
    147       }
    148 
    149       ~SmartScopedLock() {
    150         mtx.unlock();
    151       }
    152     };
    153 
    154     typedef SmartScopedLock<false> ScopedLock;
    155   }
    156 }
    157 
    158 #endif
    159