ACE/ace/Null_Semaphore.h

   1 // -*- C++ -*-
   2
   3 //==========================================================================
   4 /**
   5  *  @file    Null_Semaphore.h
   6  *
   7  *   Moved from Synch.h.
   8  *
   9  *  @author Douglas C. Schmidt <d.schmidt@vanderbilt.edu>
  10  */
  11 //==========================================================================
  12
  13 #ifndef ACE_NULL_SEMAPHORE_H
  14 #define ACE_NULL_SEMAPHORE_H
  15 #include /**/ "ace/pre.h"
  16
  17 #include "ace/os_include/os_errno.h"
  18 #include "ace/os_include/sys/os_types.h"
  19
  20 #if !defined (ACE_LACKS_PRAGMA_ONCE)
  21 # pragma once
  22 #endif /* ACE_LACKS_PRAGMA_ONCE */
  23
  24 ACE_BEGIN_VERSIONED_NAMESPACE_DECL
  25
  26 class ACE_Time_Value;
  27
  28 /**
  29  * @class ACE_Null_Semaphore
  30  *
  31  * @brief Implement a do nothing ACE_Semaphore, i.e., all the methods are
  32  * no ops.
  33  *
  34  * Although the methods are no-ops, the return values are different for
  35  * the blocking as opposed to timed acquires.  The blocking version of
  36  * acquire() is often used to serialize access to a critical section,
  37  * whereas the timed version is often used to wait for another thread
  38  * to update some condition or change some shared state.  When using an
  39  * ACE_Null_Semaphore, however, there's no other thread involved to
  40  * change a state or condition (otherwise, a null semaphore would be
  41  * inappropriate).  Returning an error value signifies that the
  42  * state or condition has not been (and can't be) changed, which is
  43  * consistent with the behavior of the threaded case where a timeout
  44  * occurs before the state or condition is changed.
  45  */
  46 class ACE_Null_Semaphore
  47 {
  48 public:
  49   ACE_Null_Semaphore (unsigned int = 1,
  50                        int = 0,
  51                        const ACE_TCHAR * = 0,
  52                        void * = 0,
  53                        int = 0x7fffffff) {}
  54   ~ACE_Null_Semaphore (void) {}
  55   /// Return 0.
  56   int remove (void) {return 0;}
  57
  58   /// Return 0.
  59   int acquire (void) {return 0;}
  60
  61   /// Return -1 with @c errno == @c ETIME.
  62   int acquire (ACE_Time_Value &) {errno = ETIME; return -1;}
  63
  64   /// Return -1 with @c errno == @c ETIME.
  65   int acquire (ACE_Time_Value *) {errno = ETIME; return -1;}
  66
  67   /// Return 0.
  68   int tryacquire (void) {return 0;}
  69
  70   /// Return 0.
  71   int release (void) {return 0;}
  72
  73   /// Return 0.
  74   int release (size_t) {return 0;}
  75
  76   /// Return 0.
  77   int acquire_write (void) {return 0;}
  78
  79   /// Return 0.
  80   int tryacquire_write (void) {return 0;}
  81
  82   /// Return 0.
  83   int tryacquire_write_upgrade (void) {return 0;}
  84
  85   /// Return 0.
  86   int acquire_read (void) {return 0;}
  87
  88   /// Return 0.
  89   int tryacquire_read (void) {return 0;}
  90
  91   /// Dump the state of an object.
  92   void dump (void) const {}
  93
  94   /// Declare the dynamic allocation hooks.
  95   //ACE_ALLOC_HOOK_DECLARE;
  96 };
  97
  98 ACE_END_VERSIONED_NAMESPACE_DECL
  99
 100 #include /**/ "ace/post.h"
 101 #endif /* ACE_NULL_SEMAPHORE_H */