Merge "Add an optional global limit to OperationLimiter" am: 5bf80bee2d (3319d5f1) · Commits · e / os / android_packages_modules_DnsResolver

OperationLimiter.h

+28 −11

Original line number	Diff line number	Diff line
		@@ -33,39 +33,44 @@ namespace netdutils {
		// 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);
		// 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:
		explicit OperationLimiter(int limit) : mLimitPerKey(limit) {}
		OperationLimiter(int limitPerKey, int globalLimit = INT_MAX)
		: mLimitPerKey(limitPerKey), mGlobalLimit(globalLimit) {}

		~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.
		// 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) EXCLUDES(mMutex) {
		std::lock_guard lock(mMutex);

		if (mGlobalCounter >= mGlobalLimit) {
		// Oh, no!
		return false;
		}

		auto& cnt = mCounters[key]; // operator[] creates new entries as needed.
		if (cnt >= mLimitPerKey) {
		// Oh, no!
		return false;
		}

		++cnt;
		++mGlobalCounter;
		return true;
		}

		@@ -73,6 +78,13 @@ class OperationLimiter {
		// 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;
		@@ -93,8 +105,13 @@ class OperationLimiter {
		// 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;

		// Maximum number of outstanding queries, globally.
		const int mGlobalLimit;
		};

		} // namespace netdutils