//------------------------------------------------------------------------------ /* 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_CORE_STOPPABLE_H_INCLUDED #define BEAST_CORE_STOPPABLE_H_INCLUDED /** Provides an interface for stopping. This is the sequence of events involved in stopping: 1. stopAsync() [optional] This notifies the root Stoppable and all its children that a stop is requested. 2. 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. 3. 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. 4. 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. 5. 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 { public: /** Create the stoppable. A stoppable without a parent is a root stoppable. @param name A name used in log output. @param parent Optional parent of this stoppable. */ /** @{ */ Stoppable (char const* name, Stoppable& parent); explicit Stoppable (char const* name, Stoppable* parent = nullptr); /** @} */ /** Destroy the stoppable. Undefined behavior results if the object is not stopped first. Stoppable objects should not be created and destroyed dynamically during the process lifetime. Rather, the set of stoppables should be static and well-defined after initialization. If the set of domain-specific objects which need to stop is dynamic, use a single parent Stoppable to manage those objects. For example, make an HTTP server implementation a Stoppable, rather than each of its active connections. */ virtual ~Stoppable (); /** 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. @param stream An optional Journal::Stream on which to log progress. Thread safety: Safe to call from any thread not associated with a Stoppable. */ void stop (Journal::Stream stream = Journal::Stream()); /** 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 (); /** Returns `true` if the stoppable should stop. Call from the derived class to determine if a long-running operation should be canceled. This is not appropriate for either threads, or asynchronous I/O. For threads, use the thread-specific facilities available to inform the thread that it should exit. For asynchronous I/O, cancel all pending operations inside the onStop override. @see onStop Thread safety: Safe to call from any thread at any time. */ bool isStopping (); /** Returns `true` if the stoppable has completed its stop. Thread safety: Safe to call from any thread at any time. */ bool isStopped (); /** Returns `true` if all children have stopped. For stoppables without children, this returns `true` immediately after a stop notification is received. Thread safety: Safe to call from any thread at any time. */ bool areChildrenStopped (); /** Called by derived classes to indicate that the stoppable has stopped. The derived class must call this either after isStopping returns `true`, or when onStop is called, or else the call to stop will never unblock. Thread safety: Safe to call from any thread at any time. */ void stopped (); /** 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: struct Child; typedef LockFreeStack Children; struct Child : Children::Node { Child (Stoppable* stoppable_) : stoppable (stoppable_) { } Stoppable* stoppable; }; void stopAsyncRecursive (); void stopRecursive (Journal::Stream stream); char const* m_name; bool m_root; Child m_child; Children m_children; // Flag that we called stop. This is for diagnostics. bool m_calledStop; // Atomic flag to make sure we only call stopAsync once. Atomic m_calledStopAsync; // Flag that this service stopped. Never goes back to false. bool volatile m_stopped; // Flag that all children have stopped (recursive). Never goes back to false. bool volatile m_childrenStopped; // stop() blocks on this event until stopped() is called. WaitableEvent m_stoppedEvent; }; #endif