messages work

packages/mutex/test/mutex_multiple_read_test.dart

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+// Test contributed by "Cat-sushi"
+// <https://github.com/hoylen/dart-mutex/issues/11>
+
+import 'dart:async';
+// import 'dart:io';
+
+import 'package:mutex/mutex.dart';
+import 'package:test/test.dart';
+
+//================================================================
+// For debug output
+//
+// Uncomment the "stdout.write" line in the [debugWrite] method to enable
+// debug output.
+
+int numReadAcquired = 0;
+int numReadReleased = 0;
+
+enum State { waitingToAcquire, acquired, released }
+
+const stateSymbol = <State, String>{
+  State.waitingToAcquire: '?',
+  State.acquired: '+',
+  State.released: '-'
+};
+
+var _outputCount = 0; // to manage line breaks
+
+void debugOutput(String id, State state) {
+  debugWrite('$id${stateSymbol[state]} ');
+
+  _outputCount++;
+  if (_outputCount % 10 == 0) {
+    debugWrite('\n');
+  }
+}
+
+void debugWrite(String str) {
+  // Uncomment to show what is happening
+  // stdout.write(str);
+}
+
+//================================================================
+
+Future<void> mySleep([int ms = 1000]) async {
+  await Future<void>.delayed(Duration(milliseconds: ms));
+}
+
+Future<void> sharedLoop1(ReadWriteMutex mutex, String symbol) async {
+  while (true) {
+    debugOutput(symbol, State.waitingToAcquire);
+
+    await mutex.protectRead(() async {
+      numReadAcquired++;
+      debugOutput(symbol, State.acquired);
+
+      await mySleep(100);
+    });
+    numReadReleased++;
+
+    debugOutput(symbol, State.released);
+  }
+}
+
+void main() {
+  group('exclusive lock tests', () {
+    test('test1', () async {
+      const numReadLoops = 5;
+
+      final mutex = ReadWriteMutex();
+
+      assert(numReadLoops < 26, 'too many read loops for lowercase letters');
+      debugWrite('Number of read loops: $numReadLoops\n');
+
+      for (var x = 0; x < numReadLoops; x++) {
+        final symbol = String.fromCharCode('a'.codeUnitAt(0) + x);
+        unawaited(sharedLoop1(mutex, symbol));
+        await mySleep(10);
+      }
+
+      await mySleep();
+
+      debugWrite('\nAbout to acquireWrite'
+          ' (reads: acquired=$numReadAcquired released=$numReadReleased'
+          ' outstanding=${numReadAcquired - numReadReleased})\n');
+      _outputCount = 0; // reset line break
+
+      const writeSymbol = 'W';
+
+      debugOutput(writeSymbol, State.waitingToAcquire);
+      await mutex.acquireWrite();
+      debugOutput(writeSymbol, State.acquired);
+      mutex.release();
+      debugOutput(writeSymbol, State.released);
+
+      debugWrite('\nWrite mutex released\n');
+      _outputCount = 0; // reset line break
+
+      expect('a', 'a');
+    });
+  });
+}