ACE/ace/Dynamic_Service_Dependency.h

   1 // -*- C++ -*-
   2
   3 //=============================================================================
   4 /**
   5  *  @file    Dynamic_Service_Dependency.h
   6  *
   7  *  @author Iliyan Jeliazkov <iliyan@ociweb.com>
   8  */
   9 //=============================================================================
  10
  11 #ifndef ACE_DYNAMIC_SERVICE_DEPENDENCY_H
  12 #define ACE_DYNAMIC_SERVICE_DEPENDENCY_H
  13
  14 #include /**/ "ace/pre.h"
  15
  16
  17 #if !defined (ACE_LACKS_PRAGMA_ONCE)
  18 # pragma once
  19 #endif /* ACE_LACKS_PRAGMA_ONCE */
  20
  21 #include "ace/Dynamic_Service_Base.h"
  22 #include "ace/Service_Object.h"
  23 #include "ace/DLL.h"
  24
  25 ACE_BEGIN_VERSIONED_NAMESPACE_DECL
  26
  27 /**
  28  * @class ACE_Dynamic_Service_Dependency
  29  *
  30  * @brief Provides a way to declare dependency on specific service,
  31  * thus helping to avoid order of initialization issues with instances
  32  * of an objects whose implementation code resides in dynamically loaded
  33  * services.
  34  *
  35  * It is disastrous to have dynamically loadable services create and give away
  36  * ownership of objects and then ending up being unloaded before all those
  37  * instances have been deleted. Normally the code for such objects classes
  38  * resides within the TEXT segment of the DLL, which implements the service.
  39  * If a service gets removed, its DLL may be unmapped from memory and then
  40  * any attempt to invoke a method on the said objects will cause SEGV.
  41  *
  42  * Such instances must contain a member of ACE_Dynamic_Service_Dependency
  43  * initialized with the service they depend on.
  44  * ACE_Dynamic_Service_Dependency's constructor and destructor are
  45  * "magical" - they work by maintaining the underlying dynamic service's
  46  * DLL reference count.
  47  */
  48 class ACE_Export ACE_Dynamic_Service_Dependency
  49 {
  50 public:
  51   ACE_Dynamic_Service_Dependency  (const ACE_Service_Gestalt *cfg,
  52                                    const ACE_TCHAR *principal);
  53   ACE_Dynamic_Service_Dependency  (const ACE_TCHAR *principal);
  54   ~ACE_Dynamic_Service_Dependency (void);
  55
  56 private:
  57   void init (const ACE_Service_Gestalt *cfg, const ACE_TCHAR *principal);
  58
  59 private:
  60   ACE_DLL tracker_;
  61 };
  62
  63 ACE_END_VERSIONED_NAMESPACE_DECL
  64
  65
  66 #include /**/ "ace/post.h"
  67
  68 #endif /* ACE_DYNAMIC_SERVICE_DEPENDENCY_H */