ACE/ace/Null_Semaphore.h

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