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