wip: add SimpleLogRecordProcessor

Author: yuzurihaaa

Diff for: lib/src/sdk/logs/processors/simple_log_record_processor.dart

@@ -0,0 +1,49 @@
+// Copyright 2021-2022 Workiva.
+// Licensed under the Apache License, Version 2.0. Please see https://github.com/Workiva/opentelemetry-dart/blob/master/LICENSE for more information
+
+import 'dart:async';
+
+import 'package:logging/logging.dart' as logging;
+import 'package:meta/meta.dart';
+import 'package:opentelemetry/src/experimental_sdk.dart' as sdk;
+
+class SimpleLogRecordProcessor implements sdk.LogRecordProcessor {
+  final logger = logging.Logger('opentelemetry.sdk.logs.simplelogrecordprocessor');
+  final sdk.LogRecordExporter exporter;
+  bool _shutDownOnce = false;
+
+  @visibleForTesting
+  final exportsCompletion = <Completer>[];
+
+  SimpleLogRecordProcessor({required this.exporter});
+
+  bool _isForcedFlushed = false;
+
+  @override
+  void onEmit(sdk.ReadableLogRecord logRecord) {
+    if (_shutDownOnce) return;
+    final completer = Completer();
+    exportsCompletion.add(completer);
+    exporter.export([logRecord]).then((result) {
+      if (result.code != sdk.ExportResultCode.success) {
+        logger.shout('SimpleLogRecordProcessor: log record export failed', result.error, result.stackTrace);
+      }
+    }).whenComplete(() {
+      completer.complete();
+      if (_isForcedFlushed) return;
+      exportsCompletion.remove(completer);
+    });
+  }
+
+  @override
+  Future<void> forceFlush() async {
+    _isForcedFlushed = true;
+    await Future.forEach(exportsCompletion, (completer) => completer.future);
+  }
+
+  @override
+  Future<void> shutdown() async {
+    _shutDownOnce = true;
+    await exporter.shutdown();
+  }
+}