src/base/Lock.h

   1 /*
   2  * Copyright (C) 1996-2014 The Squid Software Foundation and contributors
   3  *
   4  * Squid software is distributed under GPLv2+ license and includes
   5  * contributions from numerous individuals and organizations.
   6  * Please see the COPYING and CONTRIBUTORS files for details.
   7  */
   8
   9 #ifndef SQUID_SRC_BASE_LOCK_H
  10 #define SQUID_SRC_BASE_LOCK_H
  11
  12 /**
  13  * This class provides a tracking counter and presents
  14  * lock(), unlock() and LockCount() accessors.
  15  *
  16  * All locks must be cleared with unlock() before this object
  17  * is destroyed.
  18  *
  19  * Accessors provided by this interface are not private,
  20  * to allow class hierarchies.
  21  *
  22  * Build with -DLOCKCOUNT_DEBUG flag to enable lock debugging.
  23  * It is disabled by default due to the cost of debug output.
  24  */
  25 class Lock
  26 {
  27 public:
  28     Lock():count_(0) {}
  29
  30     virtual ~Lock() { assert(count_ == 0); }
  31
  32     /// Register one lock / reference against this object.
  33     /// All locks must be cleared before it may be destroyed.
  34     void lock() const {
  35 #if defined(LOCKCOUNT_DEBUG)
  36         old_debug(0,1)("Incrementing this %p from count %u\n",this,count_);
  37 #endif
  38         ++count_;
  39     }
  40
  41     /// Clear one lock / reference against this object.
  42     /// All locks must be cleared before it may be destroyed.
  43     unsigned unlock() const {
  44 #if defined(LOCKCOUNT_DEBUG)
  45         old_debug(0,1)("Decrementing this %p from count %u\n",this,count_);
  46 #endif
  47         assert(count_ > 0);
  48         return --count_;
  49     }
  50
  51     /// Inspect the current count of references.
  52     unsigned LockCount() const { return count_; }
  53
  54 private:
  55     mutable unsigned count_; ///< number of references currently being tracked
  56 };
  57
  58 // For clarity we provide some aliases for the tracking mechanisms
  59 // using Lock so that we can easily see what type of smart pointers
  60 // are to be used for the child object.
  61 // NP: CbcPointer<> and RefCount<> pointers should be used consistently
  62 //     for any given child class type
  63
  64 /// The locking interface for use on Reference-Counted classes
  65 #define RefCountable virtual Lock
  66
  67 #endif /* SQUID_SRC_BASE_LOCK_H */
  68