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/**
* Copyright (C) 2018-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program 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
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#pragma once
#include <functional>
#include <memory>
#include <string>
#include "mongo/base/disallow_copying.h"
#include "mongo/base/status.h"
#include "mongo/base/status_with.h"
#include "mongo/base/string_data.h"
#include "mongo/executor/remote_command_request.h"
#include "mongo/executor/remote_command_response.h"
#include "mongo/stdx/condition_variable.h"
#include "mongo/stdx/functional.h"
#include "mongo/transport/baton.h"
#include "mongo/util/future.h"
#include "mongo/util/time_support.h"
namespace mongo {
class BSONObjBuilder;
class OperationContext;
namespace executor {
struct ConnectionPoolStats;
/**
* Executor with notions of events and callbacks.
*
* Callbacks represent work to be performed by the executor.
* They may be scheduled by client threads or by other callbacks. Methods that
* schedule callbacks return a CallbackHandle if they are able to enqueue the callback in the
* appropriate work queue. Every CallbackHandle represents an invocation of a function that
* will happen before the executor goes out of scope. Calling cancel(CallbackHandle) schedules
* the specified callback to run with a flag indicating that it is "canceled," but it will run.
* Client threads may block waiting for a callback to execute by calling wait(CallbackHandle).
*
* Events are level-triggered and may only be signaled one time. Client threads and callbacks
* may schedule callbacks to be run by the executor after the event is signaled, and client
* threads may ask the executor to block them until after the event is signaled.
*
* If an event is unsignaled when shutdown is called, the executor will ensure that any threads
* blocked in waitForEvent() eventually return.
*/
class TaskExecutor {
MONGO_DISALLOW_COPYING(TaskExecutor);
public:
struct CallbackArgs;
struct RemoteCommandCallbackArgs;
class CallbackState;
class CallbackHandle;
class EventState;
class EventHandle;
using ResponseStatus = RemoteCommandResponse;
/**
* Type of a regular callback function.
*
* The status argument passed at invocation will have code ErrorCodes::CallbackCanceled if
* the callback was canceled for any reason (including shutdown). Otherwise, it should have
* Status::OK().
*/
using CallbackFn = unique_function<void(const CallbackArgs&)>;
/**
* Type of a callback from a request to run a command on a remote MongoDB node.
*
* The StatusWith<const BSONObj> will have ErrorCodes::CallbackCanceled if the callback was
* canceled. Otherwise, its status will represent any failure to execute the command.
* If the command executed and a response came back, then the status object will contain
* the BSONObj returned by the command, with the "ok" field indicating the success of the
* command in the usual way.
*/
using RemoteCommandCallbackFn = stdx::function<void(const RemoteCommandCallbackArgs&)>;
/**
* Destroys the task executor. Implicitly performs the equivalent of shutdown() and join()
* before returning, if necessary.
*/
virtual ~TaskExecutor();
/**
* Causes the executor to initialize its internal state (start threads if appropriate, create
* network sockets, etc). This method may be called at most once for the lifetime of an
* executor.
*/
virtual void startup() = 0;
/**
* Signals to the executor that it should shut down. This method may be called from within a
* callback. As such, this method must not block. After shutdown returns, attempts to schedule
* more tasks on the executor will return errors.
*
* It is legal to call this method multiple times. If the task executor goes out of scope
* before this method is called, the destructor performs this activity.
*/
virtual void shutdown() = 0;
/**
* Waits for the shutdown sequence initiated by a call to shutdown() to complete. Must not be
* called from within a callback.
*
* Unlike stdx::thread::join, this method may be called from any thread that wishes to wait for
* shutdown to complete.
*/
virtual void join() = 0;
/**
* Writes diagnostic information into "b".
*/
virtual void appendDiagnosticBSON(BSONObjBuilder* b) const = 0;
/**
* Gets the current time. Callbacks should use this method to read the system clock.
*/
virtual Date_t now() = 0;
/**
* Creates a new event. Returns a handle to the event, or ErrorCodes::ShutdownInProgress if
* makeEvent() fails because the executor is shutting down.
*
* May be called by client threads or callbacks running in the executor.
*/
virtual StatusWith<EventHandle> makeEvent() = 0;
/**
* Signals the event, making waiting client threads and callbacks runnable.
*
* May be called up to one time per event.
*
* May be called by client threads or callbacks running in the executor.
*/
virtual void signalEvent(const EventHandle& event) = 0;
/**
* Schedules a callback, "work", to run after "event" is signaled. If "event"
* has already been signaled, marks "work" as immediately runnable.
*
* If "event" has yet to be signaled when "shutdown()" is called, "work" will
* be scheduled with a status of ErrorCodes::CallbackCanceled.
*
* May be called by client threads or callbacks running in the executor.
*/
virtual StatusWith<CallbackHandle> onEvent(const EventHandle& event, CallbackFn work) = 0;
/**
* Blocks the calling thread until "event" is signaled. Also returns if the event is never
* signaled but shutdown() is called on the executor.
*
* TODO(schwerin): Return ErrorCodes::ShutdownInProgress when shutdown() has been called so that
* the caller can know which of the two reasons led to this method returning.
*
* NOTE: Do not call from a callback running in the executor.
*/
virtual void waitForEvent(const EventHandle& event) = 0;
/**
* Same as waitForEvent without an OperationContext, but if the OperationContext gets
* interrupted, will return the kill code, or, if the the deadline passes, will return
* Status::OK with cv_status::timeout.
*/
virtual StatusWith<stdx::cv_status> waitForEvent(OperationContext* opCtx,
const EventHandle& event,
Date_t deadline = Date_t::max()) = 0;
/**
* Schedules "work" to be run by the executor ASAP.
*
* Returns a handle for waiting on or canceling the callback, or
* ErrorCodes::ShutdownInProgress.
*
* May be called by client threads or callbacks running in the executor.
*
* Contract: Implementations should guarantee that callback should be called *after* doing any
* processing related to the callback.
*/
virtual StatusWith<CallbackHandle> scheduleWork(CallbackFn work) = 0;
/**
* Schedules "work" to be run by the executor no sooner than "when".
*
* If "when" is <= now(), then it schedules the "work" to be run ASAP.
*
* Returns a handle for waiting on or canceling the callback, or
* ErrorCodes::ShutdownInProgress.
*
* May be called by client threads or callbacks running in the executor.
*
* Contract: Implementations should guarantee that callback should be called *after* doing any
* processing related to the callback.
*/
virtual StatusWith<CallbackHandle> scheduleWorkAt(Date_t when, CallbackFn work) = 0;
/**
* Schedules "cb" to be run by the executor with the result of executing the remote command
* described by "request".
*
* Returns a handle for waiting on or canceling the callback, or
* ErrorCodes::ShutdownInProgress.
*
* May be called by client threads or callbacks running in the executor.
*
* Contract: Implementations should guarantee that callback should be called *after* doing any
* processing related to the callback.
*/
virtual StatusWith<CallbackHandle> scheduleRemoteCommand(
const RemoteCommandRequest& request,
const RemoteCommandCallbackFn& cb,
const transport::BatonHandle& baton = nullptr) = 0;
/**
* If the callback referenced by "cbHandle" hasn't already executed, marks it as
* canceled and runnable.
*
* May be called by client threads or callbacks running in the executor.
*/
virtual void cancel(const CallbackHandle& cbHandle) = 0;
/**
* Blocks until the executor finishes running the callback referenced by "cbHandle".
*
* Because callbacks all run during shutdown if they weren't run beforehand, there is no need
* to indicate the reason for returning from wait(CallbackHandle). It is always that the
* callback ran.
*
* NOTE: Do not call from a callback running in the executor.
*
* Prefer the version that takes an OperationContext* to this version.
*/
virtual void wait(const CallbackHandle& cbHandle,
Interruptible* interruptible = Interruptible::notInterruptible()) = 0;
/**
* Appends information about the underlying network interface's connections to the given
* builder.
*/
virtual void appendConnectionStats(ConnectionPoolStats* stats) const = 0;
protected:
// Retrieves the Callback from a given CallbackHandle
static CallbackState* getCallbackFromHandle(const CallbackHandle& cbHandle);
// Retrieves the Event from a given EventHandle
static EventState* getEventFromHandle(const EventHandle& eventHandle);
// Sets the given CallbackHandle to point to the given callback.
static void setCallbackForHandle(CallbackHandle* cbHandle,
std::shared_ptr<CallbackState> callback);
// Sets the given EventHandle to point to the given event.
static void setEventForHandle(EventHandle* eventHandle, std::shared_ptr<EventState> event);
TaskExecutor();
};
/**
* Class representing a scheduled callback and providing methods for interacting with it.
*/
class TaskExecutor::CallbackState {
MONGO_DISALLOW_COPYING(CallbackState);
public:
virtual ~CallbackState();
virtual void cancel() = 0;
virtual void waitForCompletion() = 0;
virtual bool isCanceled() const = 0;
protected:
CallbackState();
};
/**
* Handle to a CallbackState.
*/
class TaskExecutor::CallbackHandle {
friend class TaskExecutor;
public:
CallbackHandle();
// Exposed solely for testing.
explicit CallbackHandle(std::shared_ptr<CallbackState> cbData);
bool operator==(const CallbackHandle& other) const {
return _callback == other._callback;
}
bool operator!=(const CallbackHandle& other) const {
return !(*this == other);
}
bool isValid() const {
return _callback.get();
}
/**
* True if this handle is valid.
*/
explicit operator bool() const {
return isValid();
}
bool isCanceled() const {
return getCallback()->isCanceled();
}
template <typename H>
friend H AbslHashValue(H h, const CallbackHandle& handle) {
return H::combine(std::move(h), handle._callback);
}
private:
void setCallback(std::shared_ptr<CallbackState> callback) {
_callback = callback;
}
CallbackState* getCallback() const {
return _callback.get();
}
std::shared_ptr<CallbackState> _callback;
};
/**
* Class representing a scheduled event and providing methods for interacting with it.
*/
class TaskExecutor::EventState {
MONGO_DISALLOW_COPYING(EventState);
public:
virtual ~EventState();
virtual void signal() = 0;
virtual void waitUntilSignaled() = 0;
virtual bool isSignaled() = 0;
protected:
EventState();
};
/**
* Handle to an EventState.
*/
class TaskExecutor::EventHandle {
friend class TaskExecutor;
public:
EventHandle();
explicit EventHandle(std::shared_ptr<EventState> event);
bool operator==(const EventHandle& other) const {
return _event == other._event;
}
bool operator!=(const EventHandle& other) const {
return !(*this == other);
}
bool isValid() const {
return _event.get();
}
/**
* True if this event handle is valid.
*/
explicit operator bool() const {
return isValid();
}
private:
void setEvent(std::shared_ptr<EventState> event) {
_event = event;
}
EventState* getEvent() const {
return _event.get();
}
std::shared_ptr<EventState> _event;
};
/**
* Argument passed to all callbacks scheduled via a TaskExecutor.
*/
struct TaskExecutor::CallbackArgs {
CallbackArgs(TaskExecutor* theExecutor,
CallbackHandle theHandle,
Status theStatus,
OperationContext* opCtx = NULL);
TaskExecutor* executor;
CallbackHandle myHandle;
Status status;
OperationContext* opCtx;
};
/**
* Argument passed to all remote command callbacks scheduled via a TaskExecutor.
*/
struct TaskExecutor::RemoteCommandCallbackArgs {
RemoteCommandCallbackArgs(TaskExecutor* theExecutor,
const CallbackHandle& theHandle,
const RemoteCommandRequest& theRequest,
const ResponseStatus& theResponse);
TaskExecutor* executor;
CallbackHandle myHandle;
RemoteCommandRequest request;
ResponseStatus response;
};
} // namespace executor
} // namespace mongo
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