src/ipc/ReadWriteLock.h

   1 #ifndef SQUID_IPC_READ_WRITE_LOCK_H
   2 #define SQUID_IPC_READ_WRITE_LOCK_H
   3
   4 #include "ipc/AtomicWord.h"
   5
   6 class StoreEntry;
   7
   8 namespace Ipc
   9 {
  10
  11 class ReadWriteLockStats;
  12
  13 /// an atomic readers-writer or shared-exclusive lock suitable for maps/tables
  14 class ReadWriteLock
  15 {
  16 public:
  17     // default constructor is OK because of shared memory zero-initialization
  18
  19     bool lockShared(); ///< lock for reading or return false
  20     bool lockExclusive(); ///< lock for modification or return false
  21     void unlockShared(); ///< undo successful sharedLock()
  22     void unlockExclusive(); ///< undo successful exclusiveLock()
  23     void switchExclusiveToShared(); ///< stop writing, start reading
  24
  25     /// adds approximate current stats to the supplied ones
  26     void updateStats(ReadWriteLockStats &stats) const;
  27
  28 public:
  29     mutable Atomic::Word readers; ///< number of users trying to read
  30     Atomic::Word writers; ///< number of writers trying to modify protected data
  31 };
  32
  33
  34 /// approximate stats of a set of ReadWriteLocks
  35 class ReadWriteLockStats
  36 {
  37 public:
  38     ReadWriteLockStats();
  39
  40     void dump(StoreEntry &e) const;
  41
  42     int count; ///< the total number of locks
  43     int readable; ///< number of locks locked for reading
  44     int writeable; ///< number of locks locked for writing
  45     int idle; ///< number of unlocked locks
  46     int readers; ///< sum of lock.readers
  47     int writers; ///< sum of lock.writers
  48 };
  49
  50 } // namespace Ipc
  51
  52 #endif /* SQUID_IPC_READ_WRITE_LOCK_H */