blob: 992a84985d7287a5fb26dbab7905e8581b1d21f7 (
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
|
/*
* Copyright (C) 2018 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef NETUTILS_OPERATIONLIMITER_H
#define NETUTILS_OPERATIONLIMITER_H
#include <mutex>
#include <unordered_map>
#include <android-base/logging.h>
#include <android-base/thread_annotations.h>
namespace android {
namespace netdutils {
// Tracks the number of operations in progress on behalf of a particular key or
// ID, rejecting further attempts to start new operations after a configurable
// limit has been reached.
//
// The intended usage pattern is:
// OperationLimiter<UserId> connections_per_user;
// ...
// // Before opening a new connection
// if (!limiter.start(user)) {
// return error;
// } else {
// // open the connection
// // ...do some work...
// // close the connection
// limiter.finish(user);
// }
//
// This class is thread-safe.
template<typename KeyType>
class OperationLimiter {
public:
explicit OperationLimiter(int limit) : mLimitPerKey(limit) {}
~OperationLimiter() {
DCHECK(mCounters.empty())
<< "Destroying OperationLimiter with active operations";
}
// Returns false if |key| has reached the maximum number of concurrent
// operations, otherwise increments the counter and returns true.
//
// Note: each successful start(key) must be matched by exactly one call to
// finish(key).
bool start(KeyType key) EXCLUDES(mMutex) {
std::lock_guard lock(mMutex);
auto& cnt = mCounters[key]; // operator[] creates new entries as needed.
if (cnt >= mLimitPerKey) {
// Oh, no!
return false;
}
++cnt;
return true;
}
// Decrements the number of operations in progress accounted to |key|.
// See usage notes on start().
void finish(KeyType key) EXCLUDES(mMutex) {
std::lock_guard lock(mMutex);
auto it = mCounters.find(key);
if (it == mCounters.end()) {
LOG(FATAL_WITHOUT_ABORT) << "Decremented non-existent counter for key=" << key;
return;
}
auto& cnt = it->second;
--cnt;
if (cnt <= 0) {
// Cleanup counters once they drop down to zero.
mCounters.erase(it);
}
}
private:
// Protects access to the map below.
std::mutex mMutex;
// Tracks the number of outstanding queries by key.
std::unordered_map<KeyType, int> mCounters GUARDED_BY(mMutex);
// Maximum number of outstanding queries from a single key.
const int mLimitPerKey;
};
} // namespace netdutils
} // namespace android
#endif // NETUTILS_OPERATIONLIMITER_H
|
