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
|
/**
* Copyright (C) 2021-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 "mongo/base/status.h"
#include "mongo/util/cancellation.h"
#include "mongo/util/out_of_line_executor.h"
namespace mongo {
/**
* An executor supporting cancellation via a cancellation token. Given an existing
* OutOfLineExecutor "exec" and a cancellation token "token", you can create a CancelableExecutor
* using CancelableExecutor::make(exec, token). This executor will use "exec" to actually execute
* any scheduled work, but will refuse to run any work after "token" has been cancelled.
*
* Refusal to run work is similar to any other executor's refusal: the callback is still
* invoked, but with a non-OK status (the kCallbackCanceledErrorStatus defined below), and
* in a different execution context than the one maintained by the executor (see the
* class comment in out_of_line_executor.h for more details).
*
* Note: in cases where the CancelableExecutor will refuse to run a callback because it has been
* cancelled, and the backing executor refuses to do the work for some other reason (i.e. shutdown),
* the backing executor's error-status will be preferred and passed to the callback.
*
* This class can be used to manage ExecutorFuture chains; here's an example:
* ExecutorFuture(myExec)
* .then([] { return doThing1(); })
* .then([] { return doThing2(); })
* .thenRunOn(CancelableExecutor::make(myExec, myToken))
* .then([] { return doThing3(); })
* .thenRunOn(myExec)
* .then([] { return doThing4(); })
* .onError([](Status s) { return doThing5(s); })
* In this example, doThing1 and doThing2 will run on myExec; doThing3()
* will only run if myToken is not canceled when it is ready to run;
* doThing4() will only run if doThing3() runs and completes without error;
* doThing5 will run if doThing3() runs and errors _or_ if myToken was cancelled
* before doThing3() ran -- in which case the status s passed to doThing5() will be
* kCallbackCanceledErrorStatus.
*/
class CancelableExecutor : public OutOfLineExecutor {
public:
CancelableExecutor(ExecutorPtr exec, CancellationToken tok)
: _exec(std::move(exec)), _source(std::move(tok)) {}
CancelableExecutor(const CancelableExecutor&) = delete;
CancelableExecutor& operator=(const CancelableExecutor&) = delete;
CancelableExecutor(CancelableExecutor&&) = delete;
CancelableExecutor& operator=(CancelableExecutor&&) = delete;
/*
* This is the preferred way to get a CancelableExecutor, since the ExecutorFuture interface
* expects shared_ptrs to executors it receives in its constructor or .thenRunOn.
*/
static std::shared_ptr<CancelableExecutor> make(ExecutorPtr exec, CancellationToken token) {
return std::make_shared<CancelableExecutor>(std::move(exec), std::move(token));
}
void schedule(OutOfLineExecutor::Task func) override {
_exec->schedule([func = std::move(func), token = _source.token()](Status s) {
if (token.isCanceled() && s.isOK()) {
func({ErrorCodes::CallbackCanceled, "Callback Canceled"});
} else {
func(s);
}
});
}
private:
ExecutorPtr _exec;
CancellationSource _source;
};
} // namespace mongo
|
