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
|
/**
* Copyright (C) 2018 MongoDB Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* 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
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* 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 GNU Affero General 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 <memory>
#include "mongo/stdx/functional.h"
#include "mongo/transport/transport_layer.h"
#include "mongo/util/future.h"
#include "mongo/util/time_support.h"
namespace mongo {
class OperationContext;
namespace transport {
class TransportLayer;
class Session;
class ReactorTimer;
/**
* A Baton is basically a networking reactor, with limited functionality and no forward progress
* guarantees. Rather than asynchronously running tasks through one, the baton records the intent
* of those tasks and defers waiting and execution to a later call to run();
*
* Baton's provide a mechanism to allow consumers of a transport layer to execute IO themselves,
* rather than having this occur on another thread. This can improve performance by minimizing
* context switches, as well as improving the readability of stack traces by grounding async
* execution on top of a regular client call stack.
*/
class Baton {
public:
virtual ~Baton() = default;
/**
* Detaches a baton from an associated opCtx.
*/
virtual void detach() = 0;
/**
* Executes a callback on the baton via schedule. Returns a future which will execute on the
* baton runner.
*/
template <typename Callback>
Future<FutureContinuationResult<Callback>> execute(Callback&& cb) {
Promise<FutureContinuationResult<Callback>> promise;
auto future = promise.getFuture();
schedule([ cb = std::forward<Callback>(cb), sp = promise.share() ]() mutable {
sp.setWith(std::move(cb));
});
return future;
}
/**
* Executes a callback on the baton.
*/
virtual void schedule(stdx::function<void()> func) = 0;
/**
* Adds a session, returning a future which activates on read/write-ability of the session.
*/
enum class Type {
In,
Out,
};
virtual Future<void> addSession(Session& session, Type type) = 0;
/**
* Adds a timer, returning a future which activates after a duration.
*/
virtual Future<void> waitFor(const ReactorTimer& timer, Milliseconds timeout) = 0;
/**
* Adds a timer, returning a future which activates after a deadline.
*/
virtual Future<void> waitUntil(const ReactorTimer& timer, Date_t expiration) = 0;
/**
* Cancels waiting on a session.
*
* Returns true if the session was in the baton to be cancelled.
*/
virtual bool cancelSession(Session& session) = 0;
/**
* Cancels waiting on a timer
*
* Returns true if the timer was in the baton to be cancelled.
*/
virtual bool cancelTimer(const ReactorTimer& timer) = 0;
/**
* Runs the baton. This blocks, waiting for networking events or timeouts, and fulfills
* promises and executes scheduled work.
*
* Returns false if the optional deadline has passed
*/
virtual bool run(OperationContext* opCtx, boost::optional<Date_t> deadline) = 0;
};
using BatonHandle = std::shared_ptr<Baton>;
} // namespace transport
} // namespace mongo
|
