semaphore_plus

Description:

semaphore plus

semaphore_plus #

Semaphore is a lightweight data type that is used for controlling the cooperative access to a common resource inside the isolate.
This package is a continuation of the original semaphore package which was marked as discontinued by it's author due to the personal reasons.
Examples: #
Semaphore example:
import 'dart:async';

import 'package:semaphore_plus/semaphore_plus.dart';

Future<void> main(List<String> args) async {
final maxCount = 3;
final running = <int>[];
var simultaneous = 0;
final sm = LocalSemaphore(maxCount);
final tasks = <Future>[];
for (var i = 0; i < 9; i++) {
tasks.add(Future(() async {
try {
await sm.acquire();
running.add(i);
if (simultaneous < running.length) {
simultaneous = running.length;
}

print('Start $i, running $running');
await _doWork(100);
running.remove(i);
print('End $i, running $running');
} finally {
sm.release();
}
}));
}

await Future.wait(tasks);
print('Max permits: $maxCount, max simultaneous runned: $simultaneous');
}

Future _doWork(int ms) {
// Simulate work
return Future.delayed(Duration(milliseconds: ms));
}

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Output:
Start 0, running [0]
Start 1, running [0, 1]
Start 2, running [0, 1, 2]
End 0, running [1, 2]
Start 3, running [1, 2, 3]
End 1, running [2, 3]
Start 4, running [2, 3, 4]
End 2, running [3, 4]
Start 5, running [3, 4, 5]
End 3, running [4, 5]
Start 6, running [4, 5, 6]
End 4, running [5, 6]
Start 7, running [5, 6, 7]
End 5, running [6, 7]
Start 8, running [6, 7, 8]
End 6, running [7, 8]
End 7, running [8]
End 8, running []
Max permits: 3, max simultaneous runned: 3
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Conditional variables example:
import 'dart:async';
import 'dart:collection';
import 'dart:math';
import 'package:semaphore_plus/lock.dart';
import 'package:semaphore_plus/condition_variable.dart';

Future<void> main() async {
await Future.wait([
_producer('one'),
_producer('two'),
_consumer('one'),
_consumer('two'),
_consumer('three'),
]);
}

final _cvEmpty = ConditionVariable(_lock);
final _cvFull = ConditionVariable(_lock);
final _lock = Lock();
final _queue = Queue<int>();
var counter = 0;

Future<void> _doWork(int max) async {
final milliseconds = Random().nextInt(max);
await Future.delayed(Duration(milliseconds: milliseconds));
}

Future<void> _producer(String id) async {
while (true) {
await lock(_lock, () async {
while (_queue.length >= 2) {
print('producer $id: wait $_queue');
await _cvFull.wait();
}

print('producer $id: $counter');
await _doWork(1000);
_queue.add(counter++);
await _cvEmpty.signal();
});
}
}

Future<void> _consumer(String id) async {
while (true) {
int number;
await lock(_lock, () async {
while (_queue.isEmpty) {
print('consumer $id: wait $_queue');
await _cvEmpty.wait();
}

number = _queue.removeFirst();
await _cvFull.signal();
});

print('consumer $id: $number');
await _doWork(1000);
print(number);
}
}

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