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/*
* 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>
#include "Experiments.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;
// ...
// int connectToSomeResource(int user) {
// if (!connections_per_user.start(user)) return TRY_AGAIN_LATER;
// // ...do expensive work here...
// connections_per_user.finish(user);
// }
//
// This class is thread-safe.
template <typename KeyType>
class OperationLimiter {
public:
OperationLimiter(int limitPerKey) : mLimitPerKey(limitPerKey) {}
~OperationLimiter() {
DCHECK(mCounters.empty()) << "Destroying OperationLimiter with active operations";
}
// Returns false if |key| has reached the maximum number of concurrent operations,
// or if the global limit has been reached. 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, int globalLimit = INT_MAX) EXCLUDES(mMutex) {
std::lock_guard lock(mMutex);
if (globalLimit < mLimitPerKey) {
LOG(ERROR) << "Misconfiguration on max_queries_global " << globalLimit;
globalLimit = INT_MAX;
}
if (mGlobalCounter >= globalLimit) {
// Oh, no!
LOG(ERROR) << "Query from " << key << " denied due to global limit: " << globalLimit;
return false;
}
auto& cnt = mCounters[key]; // operator[] creates new entries as needed.
if (cnt >= mLimitPerKey) {
// Oh, no!
LOG(ERROR) << "Query from " << key << " denied due to limit: " << mLimitPerKey;
return false;
}
++cnt;
++mGlobalCounter;
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);
--mGlobalCounter;
if (mGlobalCounter < 0) {
LOG(FATAL_WITHOUT_ABORT) << "Global operations counter going negative, this is a bug.";
return;
}
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);
int mGlobalCounter GUARDED_BY(mMutex) = 0;
// Maximum number of outstanding queries from a single key.
const int mLimitPerKey;
};
} // namespace netdutils
} // namespace android
#endif // NETUTILS_OPERATIONLIMITER_H
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