//------------------------------------------------------------------------------ /* This file is part of Beast: https://github.com/vinniefalco/Beast Copyright 2013, Vinnie Falco Permission to use, copy, modify, and/or distribute this software for any purpose with or without fee is hereby granted, provided that the above copyright notice and this permission notice appear in all copies. THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL , DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */ //============================================================================== #ifndef BEAST_THREADS_STOPPABLE_H_INCLUDED #define BEAST_THREADS_STOPPABLE_H_INCLUDED #include #include #include #include namespace beast { class RootStoppable; /** Provides an interface for starting and stopping. A common method of structuring server or peer to peer code is to isolate conceptual portions of functionality into individual classes, aggregated into some larger "application" or "core" object which holds all the parts. Frequently, these components are dependent on each other in unavoidably complex ways. They also often use threads and perform asynchronous i/o operations involving sockets or other operating system objects. The process of starting and stopping such a system can be complex. This interface provides a set of behaviors for ensuring that the start and stop of a composite application-style object is well defined. Upon the initialization of the composite object these steps are peformed: 1. Construct sub-components. These are all typically derived from Stoppable. There can be a deep hierarchy: Stoppable objects may themselves have Stoppable child objects. This captures the relationship of dependencies. 2. prepare() Because some components may depend on others, preparatory steps require that all objects be first constructed. The prepare step calls all Stoppable objects in the tree starting from the leaves and working up to the root. In this stage we are guaranteed that all objects have been constructed and are in a well-defined state. 3. onPrepare() This override is called for all Stoppable objects in the hierarchy during the prepare stage. Objects are called from the bottom up. It is guaranteed that all child Stoppable objects have already been prepared when this is called. 4. start() At this point all sub-components have been constructed and prepared, so it should be safe for them to be started. While some Stoppable objects may do nothing in their start function, others will start threads or call asynchronous i/o initiating functions like timers or sockets. 5. onStart() This override is called for all Stoppable objects in the hierarchy during the start stage. Objects are called from the bottom up. It is guaranteed that all child Stoppable objects have already been started when this is called. This is the sequence of events involved in stopping: 6. stopAsync() [optional] This notifies the root Stoppable and all its children that a stop is requested. 7. stop() This first calls stopAsync(), and then blocks on each child Stoppable in the in the tree from the bottom up, until the Stoppable indicates it has stopped. This will usually be called from the main thread of execution when some external signal indicates that the process should stop. For example, an RPC 'stop' command, or a SIGINT POSIX signal. 8. onStop() This override is called for the root Stoppable and all its children when stopAsync() is called. Derived classes should cancel pending I/O and timers, signal that threads should exit, queue cleanup jobs, and perform any other necessary final actions in preparation for exit. 9. onChildrenStopped() This override is called when all the children have stopped. This informs the Stoppable that there should not be any more dependents making calls into its member functions. A Stoppable that has no children will still have this function called. 10. stopped() The derived class calls this function to inform the Stoppable API that it has completed the stop. This unblocks the caller of stop(). For stoppables which are only considered stopped when all of their children have stopped, and their own internal logic indicates a stop, it will be necessary to perform special actions in onChildrenStopped(). The funtion areChildrenStopped() can be used after children have stopped, but before the Stoppable logic itself has stopped, to determine if the stoppable's logic is a true stop. Pseudo code for this process is as follows: @code // Returns `true` if derived logic has stopped. // // When the logic stops, logicProcessingStop() is no longer called. // If children are still active we need to wait until we get a // notification that the children have stopped. // bool logicHasStopped (); // Called when children have stopped void onChildrenStopped () { // We have stopped when the derived logic stops and children stop. if (logicHasStopped) stopped(); } // derived-specific logic that executes periodically void logicProcessingStep () { // process // ... // now see if we've stopped if (logicHasStopped() && areChildrenStopped()) stopped(); } @endcode Derived class that manage one or more threads should typically notify those threads in onStop that they should exit. In the thread function, when the last thread is about to exit it would call stopped(). @note A Stoppable may not be restarted. */ /** @{ */ class Stoppable { protected: Stoppable (char const* name, RootStoppable& root); public: /** Create the Stoppable. */ Stoppable (char const* name, Stoppable& parent); /** Destroy the Stoppable. */ virtual ~Stoppable (); /** Returns `true` if the stoppable should stop. */ bool isStopping () const; /** Returns `true` if the requested stop has completed. */ bool isStopped () const; /** Returns `true` if all children have stopped. */ bool areChildrenStopped () const; /** Called by derived classes to indicate that the stoppable has stopped. */ void stopped (); /** Override called during preparation. Since all other Stoppable objects in the tree have already been constructed, this provides an opportunity to perform initialization which depends on calling into other Stoppable objects. This call is made on the same thread that called prepare(). The default implementation does nothing. Guaranteed to only be called once. */ virtual void onPrepare (); /** Override called during start. */ virtual void onStart (); /** Override called when the stop notification is issued. The call is made on an unspecified, implementation-specific thread. onStop and onChildrenStopped will never be called concurrently, across all Stoppable objects descended from the same root, inclusive of the root. It is safe to call isStopping, isStopped, and areChildrenStopped from within this function; The values returned will always be valid and never change during the callback. The default implementation simply calls stopped(). This is applicable when the Stoppable has a trivial stop operation (or no stop operation), and we are merely using the Stoppable API to position it as a dependency of some parent service. Thread safety: May not block for long periods. Guaranteed only to be called once. Must be safe to call from any thread at any time. */ virtual void onStop (); /** Override called when all children have stopped. The call is made on an unspecified, implementation-specific thread. onStop and onChildrenStopped will never be called concurrently, across all Stoppable objects descended from the same root, inclusive of the root. It is safe to call isStopping, isStopped, and areChildrenStopped from within this function; The values returned will always be valid and never change during the callback. The default implementation does nothing. Thread safety: May not block for long periods. Guaranteed only to be called once. Must be safe to call from any thread at any time. */ virtual void onChildrenStopped (); private: friend class RootStoppable; struct Child; typedef LockFreeStack Children; struct Child : Children::Node { Child (Stoppable* stoppable_) : stoppable (stoppable_) { } Stoppable* stoppable; }; void prepareRecursive (); void startRecursive (); void stopAsyncRecursive (); void stopRecursive (Journal journal); protected: char const* m_name; RootStoppable& m_root; Child m_child; Atomic m_started; bool volatile m_stopped; bool volatile m_childrenStopped; Children m_children; WaitableEvent m_stoppedEvent; }; //------------------------------------------------------------------------------ class RootStoppable : public Stoppable { public: explicit RootStoppable (char const* name); ~RootStoppable (); bool isStopping() const; /** Prepare all contained Stoppable objects. This calls onPrepare for all Stoppable objects in the tree. Calls made after the first have no effect. Thread safety: May be called from any thread. */ void prepare (); /** Start all contained Stoppable objects. The default implementation does nothing. Calls made after the first have no effect. Thread safety: May be called from any thread. */ void start (); /** Notify a root stoppable and children to stop, and block until stopped. Has no effect if the stoppable was already notified. This blocks until the stoppable and all of its children have stopped. Undefined behavior results if stop() is called without a previous call to start(). Thread safety: Safe to call from any thread not associated with a Stoppable. */ void stop (Journal journal = Journal()); /** Notify a root stoppable and children to stop, without waiting. Has no effect if the stoppable was already notified. Thread safety: Safe to call from any thread at any time. */ void stopAsync (); private: Atomic m_prepared; Atomic m_calledStop; Atomic m_calledStopAsync; }; /** @} */ } #endif