398 lines
14 KiB
C
398 lines
14 KiB
C
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// Copyright (c) 2006- Facebook
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// Distributed under the Thrift Software License
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//
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// See accompanying file LICENSE or visit the Thrift site at:
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// http://developers.facebook.com/thrift/
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#ifndef THRIFT_ASYNC_TEVENTBASE_H_
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#define THRIFT_ASYNC_TEVENTBASE_H_ 1
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#include "thrift/lib/cpp/Thrift.h"
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#include "thrift/lib/cpp/async/TAsyncTimeout.h"
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#include "thrift/lib/cpp/server/TServer.h"
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#include "thrift/lib/cpp/transport/TTransportUtils.h"
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#include "thrift/lib/cpp/concurrency/ThreadManager.h"
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#include <memory>
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#include <stack>
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#include <list>
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#include <queue>
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#include <cstdlib>
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#include <set>
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#include <utility>
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#include <boost/intrusive/list.hpp>
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#include <boost/utility.hpp>
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#include <tr1/functional>
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#include <event.h> // libevent
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#include <errno.h>
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#include <math.h>
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namespace apache { namespace thrift { namespace async {
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typedef std::tr1::function<void()> Cob;
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template <typename MessageT>
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class TNotificationQueue;
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/**
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* This class is a wrapper for all asynchronous I/O processing functionality
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* used in thrift.
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*
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* TEventBase provides a main loop that notifies TEventHandler callback objects
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* when I/O is ready on a file descriptor, and notifies TAsyncTimeout objects
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* when a specified timeout has expired. More complex, higher-level callback
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* mechanisms can then be built on top of TEventHandler and TAsyncTimeout.
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*
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* A TEventBase object can only drive an event loop for a single thread. To
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* take advantage of multiple CPU cores, most asynchronous I/O servers have one
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* thread per CPU, and use a separate TEventBase for each thread.
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*
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* In general, most TEventBase methods may only be called from the thread
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* running the TEventBase's loop. There are a few exceptions to this rule, for
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* methods that are explicitly intended to allow communication with a
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* TEventBase from other threads. When it is safe to call a method from
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* another thread it is explicitly listed in the method comments.
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*/
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class TEventBase : private boost::noncopyable {
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public:
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/**
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* A callback interface to use with runInLoop()
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*
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* Derive from this class if you need to delay some code execution until the
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* next iteration of the event loop. This allows you to schedule code to be
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* invoked from the top-level of the loop, after your immediate callers have
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* returned.
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*
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* If a LoopCallback object is destroyed while it is scheduled to be run in
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* the next loop iteration, it will automatically be cancelled.
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*/
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class LoopCallback {
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public:
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virtual ~LoopCallback() {}
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virtual void runLoopCallback() THRIFT_NOEXCEPT = 0;
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void cancelLoopCallback() {
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hook_.unlink();
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}
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bool isLoopCallbackScheduled() const {
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return hook_.is_linked();
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}
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private:
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typedef boost::intrusive::list_member_hook<
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boost::intrusive::link_mode<boost::intrusive::auto_unlink> > ListHook;
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ListHook hook_;
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typedef boost::intrusive::list<
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LoopCallback,
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boost::intrusive::member_hook<LoopCallback, ListHook,
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&LoopCallback::hook_>,
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boost::intrusive::constant_time_size<false> > List;
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// TEventBase needs access to LoopCallbackList (and therefore to hook_)
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friend class TEventBase;
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};
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/**
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* Create a new TEventBase object.
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*/
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TEventBase();
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/**
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* Create a new TEventBase object that will use the specified libevent
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* event_base object to drive the event loop.
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*
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* The TEventBase will take ownership of this event_base, and will call
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* event_base_free(evb) when the TEventBase is destroyed.
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*/
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explicit TEventBase(event_base* evb);
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~TEventBase();
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/**
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* Runs the event loop.
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*
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* loop() will loop waiting for I/O or timeouts and invoking TEventHandler
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* and TAsyncTimeout callbacks as their events become ready. loop() will
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* only return when there are no more events remaining to process, or after
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* terminateLoopSoon() has been called.
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*
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* loop() may be called again to restart event processing after a previous
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* call to loop() or loopForever() has returned.
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*
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* Returns true if the loop completed normally (if it processed all
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* outstanding requests, or if terminateLoopSoon() was called). If an error
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* occurs waiting for events, false will be returned.
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*/
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bool loop();
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/**
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* Runs the event loop.
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*
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* loopForever() behaves like loop(), except that it keeps running even if
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* when there are no more user-supplied TEventHandlers or TAsyncTimeouts
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* registered. It will only return after terminateLoopSoon() has been
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* called.
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*
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* This is useful for callers that want to wait for other threads to call
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* runInEventBaseThread(), even when there are no other scheduled events.
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*
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* loopForever() may be called again to restart event processing after a
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* previous call to loop() or loopForever() has returned.
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*
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* Throws a TLibraryException if an error occurs.
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*/
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void loopForever();
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/**
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* Causes the event loop to exit soon.
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*
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* This will cause an existing call to loop() or loopForever() to stop event
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* processing and return, even if there are still events remaining to be
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* processed.
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*
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* It is safe to call terminateLoopSoon() from another thread to cause loop()
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* to wake up and return in the TEventBase loop thread. terminateLoopSoon()
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* may also be called from the loop thread itself (for example, a
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* TEventHandler or TAsyncTimeout callback may call terminateLoopSoon() to
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* cause the loop to exit after the callback returns.)
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*
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* Note that the caller is responsible for ensuring that cleanup of all event
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* callbacks occurs properly. Since terminateLoopSoon() causes the loop to
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* exit even when there are pending events present, there may be remaining
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* callbacks present waiting to be invoked. If the loop is later restarted
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* pending events will continue to be processed normally, however if the
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* TEventBase is destroyed after calling terminateLoopSoon() it is the
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* caller's responsibility to ensure that cleanup happens properly even if
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* some outstanding events are never processed.
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*/
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void terminateLoopSoon();
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/**
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* Adds the given callback to a queue of things run after the current pass
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* through the event loop completes. Note that if this callback calls
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* runInLoop() the new callback won't be called until the main event loop
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* has gone through a cycle.
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*
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* This method may only be called from the TEventBase's thread. This
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* essentially allows an event handler to schedule an additional callback to
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* be invoked after it returns.
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*
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* Use runInEventBaseThread() to schedule functions from another thread.
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*/
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void runInLoop(LoopCallback* callback);
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/**
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* Convenience function to call runInLoop() with a tr1::function.
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*
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* This creates a LoopCallback object to wrap the tr1::function, and invoke
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* the tr1::function when the loop callback fires. This is slightly more
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* expensive than defining your own LoopCallback, but more convenient in
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* areas that aren't performance sensitive where you just want to use
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* tr1::bind. (tr1::bind is fairly slow on even by itself.)
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*
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* This method may only be called from the TEventBase's thread. This
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* essentially allows an event handler to schedule an additional callback to
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* be invoked after it returns.
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*
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* Use runInEventBaseThread() to schedule functions from another thread.
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*/
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void runInLoop(const Cob& c);
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/**
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* Run the specified function in the TEventBase's thread.
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*
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* This method is thread-safe, and may be called from another thread.
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*
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* If runInEventBaseThread() is called when the TEventBase loop is not
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* running, the function call will be delayed until the next time the loop is
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* started.
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*
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* If runInEventBaseThread() returns true the function has successfully been
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* scheduled to run in the loop thread. However, if the loop is terminated
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* (and never later restarted) before it has a chance to run the requested
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* function, the function may never be run at all. The caller is responsible
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* for handling this situation correctly if they may terminate the loop with
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* outstanding runInEventBaseThread() calls pending.
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*
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* If two calls to runInEventBaseThread() are made from the same thread, the
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* functions will always be run in the order that they were scheduled.
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* Ordering between functions scheduled from separate threads is not
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* guaranteed.
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*
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* @param fn The function to run. The function must not throw any
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* exceptions.
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* @param arg An argument to pass to the function.
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*
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* @return Returns true if the function was successfully scheduled, or false
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* if there was an error scheduling the function.
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*/
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template<typename T>
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bool runInEventBaseThread(void (*fn)(T*), T* arg) {
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return runInEventBaseThread(reinterpret_cast<void (*)(void*)>(fn),
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reinterpret_cast<void*>(arg));
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}
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bool runInEventBaseThread(void (*fn)(void*), void* arg);
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/**
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* Run the specified function in the TEventBase's thread
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*
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* This version of runInEventBaseThread() takes a tr1::function object.
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* Note that this is less efficient than the version that takes a plain
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* function pointer and void* argument, as it has to allocate memory to copy
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* the tr1::function object.
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*
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* If the TEventBase loop is terminated before it has a chance to run this
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* function, the allocated memory will be leaked. The caller is responsible
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* for ensuring that the TEventBase loop is not terminated before this
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* function can run.
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*
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* The function must not throw any exceptions.
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*/
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bool runInEventBaseThread(const std::tr1::function<void()>& fn);
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/**
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* Runs the given Cob at some time after the specified number of
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* milliseconds. (No guarantees exactly when.)
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*
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* @return true iff the cob was successfully registered.
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*/
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bool runAfterDelay(const Cob& c, int milliseconds);
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/**
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* Set the maximum desired latency in us and provide a callback which will be
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* called when that latency is exceeded.
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*/
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void setMaxLatency(int64_t maxLatency, const Cob& maxLatencyCob) {
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maxLatency_ = maxLatency;
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maxLatencyCob_ = maxLatencyCob;
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}
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/**
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* Set smoothing coefficient for loop load average; # of milliseconds
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* for exp(-1) (1/2.71828...) decay.
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*/
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void setLoadAvgMsec(uint32_t ms);
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/**
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* Get the average loop time in microseconds (an exponentially-smoothed ave)
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*/
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double getAvgLoopTime() const {
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return avgLoopTime_;
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}
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/**
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* Verify that current thread is the TEventBase thread, if the TEventBase is
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* running.
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*
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* This is primarily intended for debugging, to assert that functions that
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* register or unregister events are only ever invoked in the TEventBase's
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* thread.
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*/
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bool isInEventBaseThread() const {
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return !running_ || pthread_equal(loopThread_, pthread_self());
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}
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// --------- interface to underlying libevent base ------------
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// Avoid using these functions if possible. These functions are not
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// guaranteed to always be present if we ever provide alternative TEventBase
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// implementations that do not use libevent internally.
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event_base* getLibeventBase() const { return evb_; }
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static const char* getLibeventVersion() { return event_get_version(); }
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static const char* getLibeventMethod() { return event_get_method(); }
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private:
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// --------- libevent callbacks (not for client use) ------------
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/**
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* Called after a delay to break out of an idle event loop. We need to
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* use this instead of event_base_loopexit() since the latter installs
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* an event within libevent which is queued until it expires. Installing
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* our own timed event lets us delete it when another event causes the
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* loop to exit earlier..
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*/
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static void loopTimerCallback(int fd, short which, void* arg);
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static void runTr1FunctionPtr(std::tr1::function<void()>* fn);
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// small object used as a callback arg with enough info to execute the
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// appropriate client-provided Cob
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class CobTimeout : public TAsyncTimeout {
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public:
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CobTimeout(TEventBase* b, const Cob& c) : TAsyncTimeout(b), cob_(c) {}
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virtual void timeoutExpired() THRIFT_NOEXCEPT;
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private:
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Cob cob_;
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public:
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typedef boost::intrusive::list_member_hook<
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boost::intrusive::link_mode<boost::intrusive::auto_unlink> > ListHook;
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ListHook hook;
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typedef boost::intrusive::list<
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CobTimeout,
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boost::intrusive::member_hook<CobTimeout, ListHook, &CobTimeout::hook>,
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boost::intrusive::constant_time_size<false> > List;
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};
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typedef LoopCallback::List LoopCallbackList;
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class FunctionRunner;
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// executes any callbacks queued by runInLoop()
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void runLoopCallbacks();
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void initNotificationQueue();
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CobTimeout::List pendingCobTimeouts_;
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LoopCallbackList loopCallbacks_;
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// stop_ is set by terminateLoopSoon() and is used by the main loop
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// to determine if it should exit
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bool stop_;
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// running_ is set to true while loop() is running
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bool running_;
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// The ID of the thread running the main loop.
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// Only valid while running_ is true.
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pthread_t loopThread_;
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// pointer to underlying event_base class doing the heavy lifting
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event_base* evb_;
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// A notification queue for runInEventBaseThread() to use
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// to send function requests to the TEventBase thread.
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std::unique_ptr<TNotificationQueue<std::pair<void (*)(void*), void*>>> queue_;
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std::unique_ptr<FunctionRunner> fnRunner_;
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// limit for latency in microseconds (0 disables)
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int64_t maxLatency_;
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||
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|
|
||
|
|
// smoothed loop time used to invoke latency callbacks; differs from
|
||
|
|
// avgLoopTime_ in that it's scaled down after triggering a callback
|
||
|
|
// to reduce spamminess
|
||
|
|
double maxLatencyLoopTime_;
|
||
|
|
|
||
|
|
// exponentially-smoothed average loop time for latency-limiting
|
||
|
|
double avgLoopTime_;
|
||
|
|
|
||
|
|
// set to true if the event_base_loop(EVLOOP_ONCE) returned because
|
||
|
|
// the loop timeout fired, rather than because it found events to process
|
||
|
|
bool loopTimedOut_;
|
||
|
|
|
||
|
|
// factor used for exponential smoothing of load average
|
||
|
|
double expCoeff_;
|
||
|
|
|
||
|
|
// callback called when latency limit is exceeded
|
||
|
|
Cob maxLatencyCob_;
|
||
|
|
|
||
|
|
// we'll wait this long before running deferred callbacks if the event
|
||
|
|
// loop is idle.
|
||
|
|
static const int kDEFAULT_IDLE_WAIT_USEC = 20000; // 20ms
|
||
|
|
};
|
||
|
|
|
||
|
|
}}} // apache::thrift::async
|
||
|
|
|
||
|
|
#endif // #ifndef THRIFT_ASYNC_TEVENTBASE_H_
|