src/base/Lock.h

   1 /*
   2  * Copyright (C) 1996-2023 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         debugs(0,1, "Incrementing this " << static_cast<void*>(this) << " from count " << count_);
  37 #endif
  38         assert(count_ < UINT32_MAX);
  39         ++count_;
  40     }
  41
  42     /// Clear one lock / reference against this object.
  43     /// All locks must be cleared before it may be destroyed.
  44     uint32_t unlock() const {
  45 #if defined(LOCKCOUNT_DEBUG)
  46         debugs(0,1, "Decrementing this " << static_cast<void*>(this) << " from count " << count_);
  47 #endif
  48         assert(count_ > 0);
  49         return --count_;
  50     }
  51
  52     /// Inspect the current count of references.
  53     uint32_t LockCount() const { return count_; }
  54
  55 private:
  56     mutable uint32_t count_; ///< number of references currently being tracked
  57 };
  58
  59 // For clarity we provide some aliases for the tracking mechanisms
  60 // using Lock so that we can easily see what type of smart pointers
  61 // are to be used for the child object.
  62 // NP: CbcPointer<> and RefCount<> pointers should be used consistently
  63 //     for any given child class type
  64
  65 /// The locking interface for use on Reference-Counted classes
  66 #define RefCountable virtual Lock
  67
  68 #endif /* SQUID_SRC_BASE_LOCK_H */
  69