summaryrefslogtreecommitdiff
path: root/src/mongo/executor/task_executor.h
blob: a392f72b974d00a01c57776b5641db41af4ec912 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
/**
 *    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 <functional>
#include <memory>
#include <string>

#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/transport/baton.h"
#include "mongo/util/future.h"
#include "mongo/util/out_of_line_executor.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 : public OutOfLineExecutor {
    TaskExecutor(const TaskExecutor&) = delete;
    TaskExecutor& operator=(const TaskExecutor&) = delete;

public:
    struct CallbackArgs;
    struct RemoteCommandCallbackArgs;
    struct RemoteCommandOnAnyCallbackArgs;
    class CallbackState;
    class CallbackHandle;
    class EventState;
    class EventHandle;

    using ResponseStatus = RemoteCommandResponse;
    using ResponseOnAnyStatus = RemoteCommandOnAnyResponse;

    /**
     * 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 = std::function<void(const RemoteCommandCallbackArgs&)>;

    using RemoteCommandOnAnyCallbackFn = std::function<void(const RemoteCommandOnAnyCallbackArgs&)>;

    /**
     * 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.
     *
     * On success, returns a handle for waiting on or canceling the callback. The provided "work"
     * argument is moved from and invalid for use in the caller. On error, returns
     * ErrorCodes::ShutdownInProgress, and "work" is still valid. If you intend to call "work" after
     * error, make sure it is an actual CallbackFn, not a lambda or other value that implicitly
     * converts to CallbackFn, since such a value would be moved from and invalidated during
     * conversion with no way to recover it.
     *
     * 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;


    void schedule(OutOfLineExecutor::Task func) final override;

    /**
     * Schedules "work" to be run by the executor ASAP.
     *
     * On success, returns a handle for waiting on or canceling the callback. The provided "work"
     * argument is moved from and invalid for use in the caller. On error, returns
     * ErrorCodes::ShutdownInProgress, and "work" is still valid. If you intend to call "work" after
     * error, make sure it is an actual CallbackFn, not a lambda or other value that implicitly
     * converts to CallbackFn, since such a value would be moved from and invalidated during
     * conversion with no way to recover it.
     *
     * 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.
     *
     * On success, returns a handle for waiting on or canceling the callback. The provided "work"
     * argument is moved from and invalid for use in the caller. On error, returns
     * ErrorCodes::ShutdownInProgress, and "work" is still valid. If you intend to call "work" after
     * error, make sure it is an actual CallbackFn, not a lambda or other value that implicitly
     * converts to CallbackFn, since such a value would be moved from and invalidated during
     * conversion with no way to recover it.
     *
     * 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 BatonHandle& baton = nullptr);

    virtual StatusWith<CallbackHandle> scheduleRemoteCommandOnAny(
        const RemoteCommandRequestOnAny& request,
        const RemoteCommandOnAnyCallbackFn& cb,
        const 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 {
    CallbackState(const CallbackState&) = delete;
    CallbackState& operator=(const CallbackState&) = delete;

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 {
    EventState(const EventState&) = delete;
    EventState& operator=(const EventState&) = delete;

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 = nullptr);

    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);

    RemoteCommandCallbackArgs(const RemoteCommandOnAnyCallbackArgs& other, size_t idx);

    TaskExecutor* executor;
    CallbackHandle myHandle;
    RemoteCommandRequest request;
    ResponseStatus response;
};

struct TaskExecutor::RemoteCommandOnAnyCallbackArgs {
    RemoteCommandOnAnyCallbackArgs(TaskExecutor* theExecutor,
                                   const CallbackHandle& theHandle,
                                   const RemoteCommandRequestOnAny& theRequest,
                                   const ResponseOnAnyStatus& theResponse);

    TaskExecutor* executor;
    CallbackHandle myHandle;
    RemoteCommandRequestOnAny request;
    ResponseOnAnyStatus response;
};

}  // namespace executor
}  // namespace mongo