fix benchmark and adjust periodic dump for perf

benchmark/wave_dump_benchmark.dart

@@ -14,14 +14,14 @@ import 'package:benchmark_harness/benchmark_harness.dart';
 import 'package:rohd/rohd.dart';
 
 class _ModuleToDump extends Module {
-  _ModuleToDump(Logic d) {
+  static const _numExtraOutputs = 50;
+
+  _ModuleToDump(Logic d, Logic clk) {
     d = addInput('d', d);
 
     final q = addOutput('q');
 
-    final clk = SimpleClockGenerator(10).clk;
-
-    for (var i = 0; i < 100; i++) {
+    for (var i = 0; i < _numExtraOutputs; i++) {
       addOutput('i$i') <= FlipFlop(clk, ~output('i$i')).q;
     }
 
@@ -31,32 +31,40 @@ class _ModuleToDump extends Module {
 
 class WaveDumpBenchmark extends AsyncBenchmarkBase {
   late _ModuleToDump _mod;
+  late Logic _clk;
+
+  static const _maxSimTime = 1000;
 
   static const _vcdTemporaryPath = 'tmp_test/wave_dump_benchmark.vcd';
 
   WaveDumpBenchmark() : super('WaveDump');
 
   @override
   Future<void> setup() async {
-    Simulator.setMaxSimTime(1000);
-
-    _mod = _ModuleToDump(Logic());
-    await _mod.build();
+    Simulator.setMaxSimTime(_maxSimTime);
   }
 
   @override
   Future<void> teardown() async {
-    File(_vcdTemporaryPath).deleteSync();
-    await Simulator.reset();
+    if (File(_vcdTemporaryPath).existsSync()) {
+      File(_vcdTemporaryPath).deleteSync();
+    }
   }
 
   @override
   Future<void> run() async {
+    _clk = SimpleClockGenerator(10).clk;
+    _mod = _ModuleToDump(Logic(), _clk);
+    await _mod.build();
+
     WaveDumper(_mod, outputPath: _vcdTemporaryPath);
 
     await Simulator.run();
 
+    assert(Simulator.time == _maxSimTime, 'sim should run through end');
+
     await Simulator.reset();
+    Simulator.setMaxSimTime(_maxSimTime);
   }
 }
 

lib/src/wave_dumper.dart

@@ -19,7 +19,8 @@ import 'package:rohd/src/utilities/uniquifier.dart';
 /// Outputs to vcd format at [outputPath].  [module] must be built prior to
 /// attaching the [WaveDumper].
 ///
-/// The waves will only dump to the file once the simulation has completed.
+/// The waves will only dump to the file periodically and then once the
+/// simulation has completed.
 class WaveDumper {
   /// The [Module] being dumped.
   final Module module;
@@ -87,15 +88,28 @@ class WaveDumper {
     });
   }
 
+  /// Number of characters in the buffer after which it will
+  /// write contents to the output file.
+  static const _fileBufferLimit = 100000;
+
   /// Buffers [contents] to be written to the output file.
-  void _writeToFile(String contents) {
+  void _writeToBuffer(String contents) {
     _fileBuffer.write(contents);
+
+    if (_fileBuffer.length > _fileBufferLimit) {
+      _writeToFile();
+    }
   }
 
-  /// Terminates the waveform dumping, including closing the file.
-  Future<void> _terminate() async {
+  /// Writes all pending items in the [_fileBuffer] to the file.
+  void _writeToFile() {
     _outFileSink.write(_fileBuffer.toString());
     _fileBuffer.clear();
+  }
+
+  /// Terminates the waveform dumping, including closing the file.
+  Future<void> _terminate() async {
+    _writeToFile();
     await _outFileSink.flush();
     await _outFileSink.close();
   }
@@ -142,7 +156,7 @@ class WaveDumper {
 \$end
 \$timescale $timescale \$end
 ''';
-    _writeToFile(header);
+    _writeToBuffer(header);
   }
 
   /// Writes the scope of the VCD, including signal and hierarchy declarations,
@@ -151,9 +165,9 @@ class WaveDumper {
     var scopeString = _computeScopeString(module);
     scopeString += '\$enddefinitions \$end\n';
     scopeString += '\$dumpvars\n';
-    _writeToFile(scopeString);
+    _writeToBuffer(scopeString);
     _signalToMarkerMap.keys.forEach(_writeSignalValueUpdate);
-    _writeToFile('\$end\n');
+    _writeToBuffer('\$end\n');
   }
 
   /// Generates the top of the scope string (signal and hierarchy definitions).
@@ -191,7 +205,7 @@ class WaveDumper {
   /// Writes the current timestamp to the VCD.
   void _captureTimestamp(int timestamp) {
     final timestampString = '#$timestamp\n';
-    _writeToFile(timestampString);
+    _writeToBuffer(timestampString);
 
     _changedLogicsThisTimestamp
       ..forEach(_writeSignalValueUpdate)
@@ -209,7 +223,7 @@ class WaveDumper {
         : signal.value.toString(includeWidth: false);
     final marker = _signalToMarkerMap[signal];
     final updateString = '$updateValue$marker\n';
-    _writeToFile(updateString);
+    _writeToBuffer(updateString);
   }
 }