/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */ /************************************************************************* * * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * Copyright 2000, 2010 Oracle and/or its affiliates. * * OpenOffice.org - a multi-platform office productivity suite * * This file is part of OpenOffice.org. * * OpenOffice.org is free software: you can redistribute it and/or modify * it under the terms of the GNU Lesser General Public License version 3 * only, as published by the Free Software Foundation. * * OpenOffice.org is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU Lesser General Public License version 3 for more details * (a copy is included in the LICENSE file that accompanied this code). * * You should have received a copy of the GNU Lesser General Public License * version 3 along with OpenOffice.org. If not, see * * for a copy of the LGPLv3 License. * ************************************************************************/ #ifndef _RTL_UNLOAD_H_ #define _RTL_UNLOAD_H_ #include #include #include #include ///@HTML /** @file The API enables an effective way of unloading libraries in a centralized way. The mechanism ensures that used libraries are not unloaded. This prevents crashes if library code is being used after unloading the library. The unloading mechanism currently only works with libraries which contain UNO services. A library cannot be unloaded if one of the following conditions apply
  • An instance is still referenced
  • A module has been loaded without registering it
  • The service manager has created a one instance service
  • A service instance has been added to an UNO context
Notification Mechanism The API provides a notification mechanism. Clients can use it to do clean up, such as releasing cached references, in order to allow modules to be unloaded. As long as someone holds a reference to an object whose housing module supports unloading the module cannot be unloaded.

Because of the inherent danger of crashing the application by using this API all instances which control threads should be registered listeners. On notification they have to ensure that their threads assume a safe state, that is, they run outside of modules which could be unloaded and do not jump back into module code as a result of a finished function call. In other words, there must not be an address of the module on the thread's stack.

Since current operating systems lack APIs in respect to controlling the position of threads within libraries, it would be a major effort to comply with that recommendation. The best and most efficient way of handling the unloading scenario is to let all threads, except for the main thread, die in case of a notification.

Use this API with great care because it might crash the application. See the respective documentation (Library Unloading) on the udk.openoffice.org web site. */ /** A library which supports unloading has to implement and export a function called component_canUnload.

If the function returns sal_True then the module can be safely unloaded. That is the case when there are no external references to code within the library. In case a module houses UNO components then the function must return sal_False after the first factory has been handed out. The function then continues to return sal_False as long as there is at least one object (factory or service instance) which originated from the module.

Libraries which not only contain UNO components (or none at all) have to provide a means to control whether they can be unloaded or not, e.g. However, there is no concept yet.

The argument pTime is an optional out-parameter. If the return value is sal_True then pTime reflects a point in time since when the module could have been unloaded. Since that time the function would have continually returned sal_True up to the present. The value of pTime is important for the decision as to a module will be unloaded. When someone initiates the unloading of modules by calling rtl_unloadUnusedModules then the caller can specify a time span with the effect that only those modules are unloaded which are unused at least for that amount of time. If component_canUnload does not fill in pTime then the module is unloaded immediately.

component_canUnload is implicitly called by rtl_unloadUnusedModules . There is no need to call the function directly. */ #define COMPONENT_CANUNLOAD "component_canUnload" typedef sal_Bool (SAL_CALL * component_canUnloadFunc)( TimeValue* pTime); /** C-interface for a module reference counting */ #ifdef __cplusplus extern "C" { #endif /** By registering a module, one declares that a module supports the unloading mechanism. One registers a module by calling this function.

A module can only be unloaded from memory when it has been registered as many times as it has been loaded. The reason is that a library can be "loaded" several times by osl_loadModule within the same process. The function will then return the same module handle because the library will effectively only be loaded once. To remove the library from memory it is necessary to call osl_unloadModule as often as osl_loadModule was called. The function rtl_unloadUnusedModules calls osl_unloadModule for a module as many times as it was registered. If, for example, a module has been registered one time less then osl_loadModule has been called and the module can be unloaded then it needs a call to rtl_unloadUnusedModules and an explicit call to osl_unloadModule to remove the module from memory.

A module must be registered every time it has been loaded otherwise the unloading mechanism is not effective.

Before a module is registered, one has to make sure that the module is in a state that prevents it from being unloaded. In other words, component_canUnload must return sal_False. Assuming that component_canUnload returns sal_True and it is registered regardless, then a call to rtl_unloadUnusedModules causes the module to be unloaded. This unloading can be set off by a different thread and the thread which registered the module is "unaware" of this. Then when the first thread tries to obtain a factory or calls another function in the module, the application will crash, because the module has been unloaded before. Therefore one has to ensure that the module cannot be unloaded before it is registered. This is simply done by obtaining a factory from the module. As long as a factory or some other object, which has been created by the factory, is alive, the component_canUnload function will return sal_False.

Loading and registering have to be in this order:

  • load a library (osl_loadModule)
  • get the component_getFactory function and get a factory
  • register the module (rtl_registerModuleForUnloading
Usually the service manager is used to obtain an instance of a service. The service manager registers all modules which support the unloading mechanism. When the service manager is used to get service instances than one does not have to bother about registering. @param module a module handle as is obtained by osl_loadModule @return sal_True - the module could be registered for unloading, sal_False otherwise */ SAL_DLLPUBLIC sal_Bool SAL_CALL rtl_registerModuleForUnloading( oslModule module); /** The function revokes the registration of a module. By calling the function for a previously registered module one prevents the module from being unloaded by this unloading mechanism. However, in order to completely unregister the module it is necessary to call the function as often as the module has been registered.

rtl_unloadUnusedModules unregisters the modules which it unloads. Therefore there is no need to call this function unless one means to prevent the unloading of a module. @param module a module handle as is obtained by osl_loadModule */ SAL_DLLPUBLIC void SAL_CALL rtl_unregisterModuleForUnloading( oslModule module); /** This function sets off the unloading mechanism. At first it notifies the unloading listeners in order to give them a chance to do cleanup and get their threads in a safe state. Then all registered modules are asked if they can be unloaded. That is, the function calls component_canUnload on every registered module. If sal_True is returned then osl_unloadModule is called for the belonging module as often as it is registered.

A call to osl_unloadModule does not guarantee that the module is unloaded even if its component_canUnload function returns sal_True.

The optional in-parameter libUnused specifies a period of time which a library must be unused in order to qualify for being unloaded. By using this argument one can counter the multithreading problem as described further above. It is in the responsibility of the user of this function to provide a timespan big enough to ensure that all threads are out of modules (see component_canUnload).

The service managers which have been created by functions such as createRegistryServiceFactory (declared in cppuhelper/servicefactory.hxx) are registered listeners and release the references to factories on notification. @param libUnused span of time that a module must be unused to be unloaded. the argument is optional. */ SAL_DLLPUBLIC void SAL_CALL rtl_unloadUnusedModules( TimeValue* libUnused); /** rtl_addUnloadingListener takes an argument of this type. @param id - The value that has been passed as second argument to rtl_addUnloadingListener */ typedef void (SAL_CALL *rtl_unloadingListenerFunc)(void* id); /** The function registered an unloading listener. The callback argument is a function which is called when the unloading procedure has been initiated by a call to rtl_unloadUnusedLibraries. The second argument is used to distinguish between different listener instances and may be NULL. It will be passed as argument when the callback function is being called. The return value identifies the registered listener and will be used for removing the listener later on. If the same listener is added more then once then every registration is treated as if made for a different listener. That is, a different cookie is returned and the callback function will be called as many times as it has been registered. @param callback - a function that is called to notify listeners. @param this - a value to distinguish different listener instances @return identifier which is used in rtl_removeUnloadingListener */ SAL_DLLPUBLIC sal_Int32 SAL_CALL rtl_addUnloadingListener( rtl_unloadingListenerFunc callback, void* _this); /** Listeners (the callback functions) must be unregistered before the listener code becomes invalid. That is, if a module contains listener code, namely callback functions of type rtl_unloadingListenerFunc, then those functions must not be registered when component_canUnload returns sal_True. @param cookie is an identifier as returned by rtl_addUnloadingListener function. */ SAL_DLLPUBLIC void SAL_CALL rtl_removeUnloadingListener( sal_Int32 cookie ); /** Pointers to rtl_ModuleCount are passed as arguments to the default factory creator functions: createSingleComponentFactory, createSingleFactory, createOneInstanceFactory. The factory implementation is calling rtl_ModuleCount.acquire when it is being constructed and it is calling rtl_ModuleCount.release. The implementations of acquire and release should influence the return value of component_canUnload in a way that it returns sal_False after acquire has been called. That is the module will not be unloaded once a default factory has been created. A call to release may cause component_canUnload to return sal_False, but only if there are no object alive which originated from the module. These objects are factory instances and the service instances which have been created by these factories.

It is not necessary to synchronize acquire and release as a whole. Simply sychronize the access to a counter variable, e.g. the rtl_moduleCount_release implementation:

extern "C" void rtl_moduleCount_acquire(rtl_ModuleCount * that )
{
    rtl_StandardModuleCount* pMod= (rtl_StandardModuleCount*)that;
    osl_incrementInterlockedCount( &pMod->counter);
}
The SAL library offers functions that can be used for acquire and release. See struct _rtl_StandardModuleCount. */ typedef struct _rtl_ModuleCount { void ( SAL_CALL * acquire ) ( struct _rtl_ModuleCount * that ); void ( SAL_CALL * release ) ( struct _rtl_ModuleCount * that ); }rtl_ModuleCount; #define MODULE_COUNT_INIT \ { {rtl_moduleCount_acquire,rtl_moduleCount_release}, rtl_moduleCount_canUnload, 0, {0, 0}} /** This struct can be used to implement the unloading mechanism. To make a UNO library unloadable create one global instance of this struct in the module. To initialize it one uses the MODULE_COUNT_INIT macro.
rtl_StandardModuleCount globalModuleCount= MODULE_COUNT_INIT
; */ typedef struct _rtl_StandardModuleCount { rtl_ModuleCount modCnt; sal_Bool ( *canUnload ) ( struct _rtl_StandardModuleCount* a, TimeValue* libUnused); oslInterlockedCount counter; TimeValue unusedSince; } rtl_StandardModuleCount; /** Default implementation for rtl_ModuleCount.acquire. Use this function along with rtl_StandardModuleCount. */ SAL_DLLPUBLIC void rtl_moduleCount_acquire(rtl_ModuleCount * that ); /** Default implementation for rtl_ModuleCount.release. Use this function along with rtl_StandardModuleCount. */ SAL_DLLPUBLIC void rtl_moduleCount_release( rtl_ModuleCount * that ); /** Default implementation for component_canUnload. Use this function along with rtl_StandardModuleCount. */ SAL_DLLPUBLIC sal_Bool rtl_moduleCount_canUnload( rtl_StandardModuleCount * that, TimeValue* libUnused); #ifdef __cplusplus } #endif #endif /* vim:set shiftwidth=4 softtabstop=4 expandtab: */