{"id":1197,"date":"2021-12-11T12:30:51","date_gmt":"2021-12-11T04:30:51","guid":{"rendered":"https:\/\/summid.icu\/?p=1197"},"modified":"2022-03-08T15:16:59","modified_gmt":"2022-03-08T07:16:59","slug":"dissecting-the-async-methods-in-c","status":"publish","type":"post","link":"https:\/\/summid.icu\/index.php\/2021\/12\/11\/dissecting-the-async-methods-in-c\/","title":{"rendered":"\u5256\u6790C#\u4e2d\u7684 async \u65b9\u6cd5"},"content":{"rendered":"

\u672c\u6587\u624b\u52a8\u7ffb\u8bd1\u81ea\uff1aDissecting the async methods in C#<\/a><\/p>\n

C#\u662f\u5f00\u53d1\u8005\u7684\u751f\u4ea7\u529b\u5229\u5668\uff0c\u5e76\u4e14\u5b83\u8fd8\u5728\u88ab\u4e0d\u65ad\u5730\u63a8\u52a8\u7740\u8fdb\u5316\uff0c\u53d8\u5f97\u66f4\u9002\u5408\u5f00\u53d1\u9ad8\u6027\u80fd\u5e94\u7528\u7a0b\u5e8f\uff0c\u8fd9\u66f4\u662f\u5f00\u53d1\u8005\u4eec\u559c\u95fb\u4e50\u89c1\u7684\u6d88\u606f\u3002<\/span><\/p>\n

\u4e3e\u4e2a\u4f8b\u5b50\uff1aC# 5 \u7ed9\u6211\u4eec\u5e26\u6765\u4e86 <\/span>async<\/code><\/span> \u5f02\u6b65\u65b9\u6cd5\uff0c\u5b83\u7684\u51fa\u73b0\u6807\u5fd7\u7740\u3010\u6b21\u4e16\u4ee3\u3011\u7684\u6765\u4e34\u2014\u2014\u5b83\u53ef\u4ee5\u5c06\u591a\u4e2a\u57fa\u4e8e <\/span>Task<\/code><\/span> \u7684\u64cd\u4f5c\u7ed3\u5408\u5230\u4e00\u8d77\uff0c\u4f7f\u4ee3\u7801\u7f16\u5199\u66f4\u52a0\u76f4\u89c2\u5bb9\u6613\u3002\u4f46 <\/span>async<\/code><\/span> \u4e5f\u5b58\u5728\u989d\u5916\u5f00\u9500\uff0c<\/span>Task<\/code><\/span> \u662f\u5f15\u7528\u7c7b\u578b\uff0c\u521b\u5efa <\/span>Task<\/code><\/span> \u5bf9\u8c61\u7684\u65f6\u5019\u4f1a\u5411\u5806\u533a\u7533\u8bf7\u5185\u5b58\uff0c\u5373\u4f7f <\/span>async<\/code><\/span>\u00a0\u4ee5\u540c\u6b65\u7684\u65b9\u5f0f\u8fd0\u884c\uff0c\u4e5f\u4f1a\u6709\u6027\u80fd\u5f00\u9500\u3002\u5230\u4e86C# 7\uff0c<\/span>async<\/code><\/span> \u65b9\u6cd5\u5f00\u59cb\u652f\u6301\u8fd4\u56de\u7c7b<\/span>Task<\/code><\/span> \uff08task-like\uff09\u7684\u7c7b\u578b\uff0c\u5982 <\/span>ValueTask<\/code><\/span> \uff0c\u6765\u51cf\u5c11\u7533\u8bf7\u5806\u5185\u5b58\u7684\u6b21\u6570\u6216\u5728\u67d0\u4e9b\u60c5\u51b5\u4e0b\u5b8c\u5168\u907f\u514d\u3002<\/span><\/p>\n

\u4e3a\u4e86\u7406\u89e3\u8fd9\u4e00\u5957\u8fd0\u884c\u673a\u5236\uff0c\u6211\u4eec\u9700\u8981\u6df1\u5165\u4e86\u89e3 <\/span>async<\/code><\/span> \u65b9\u6cd5\u662f\u5982\u4f55\u5b9e\u73b0\u7684\u3002<\/span><\/p>\n

\u4f46\u9996\u5148\uff0c\u6765\u770b\u770b\u4e00\u4e9b\u5173\u4e8e\u5386\u53f2\u7684\u5c0f\u59ff\u52bf\uff1a<\/span><\/p>\n

Task<\/code><\/span> \u548c <\/span>Task<T><\/code><\/span> \u7c7b\u4e8e <\/span>.NET 4.0<\/code><\/span> \u4e2d\u5f15\u5165\uff0c\u4ee5\u6211\u7684\u89c2\u70b9\u6765\u770b\uff0c\u5b83\u8ba9 <\/span>.NET<\/code><\/span> \u5728\u5f02\u6b65\u548c\u5e76\u884c\u7f16\u7a0b\u9886\u57df\u7684\u601d\u60f3\u4ea7\u751f\u4e86\u5de8\u5927\u8f6c\u53d8\uff0c\u5b83\u662f <\/span>async<\/code><\/span> \u548c <\/span>await<\/code><\/span> \u7684\u57fa\u77f3\u3002\u8ddf\u4ee5\u5f80\u7684\u5f02\u6b65\u7f16\u7a0b\u6a21\u5f0f\u4e0d\u4e00\u6837\uff0c\u6bd4\u5982 <\/span>.NET1.0<\/code><\/span> \u4e2d <\/span>BeginXXX\/EndXXX<\/code><\/span> \u6a21\u5f0f\uff08AKA<\/span>\u540c\u6b65\u7f16\u7a0b\u6a21\u578b<\/span><\/a><\/span>\uff09\u6216\u8005<\/span>\u57fa\u4e8e\u4e8b\u4ef6\u7684\u5f02\u6b65\u7f16\u7a0b\u6a21\u5f0f<\/span><\/a><\/span>\uff0c\u4f8b\u5982 <\/span>.NET2.0<\/code><\/span> \u4e2d \u7684 <\/span>BackgroundWorker<\/code><\/span> \u7c7b<\/span><\/a><\/span>\uff0c\u548c\u5b83\u4eec\u76f8\u6bd4 <\/span>Task<\/code><\/span> \u53ef\u4ee5\u4e92\u76f8\u7ec4\u5408\uff0c\u5408\u4f5c\u5b8c\u6210\u4efb\u52a1\u3002<\/span><\/p>\n

Task<\/code><\/span> \u5bf9\u8c61\u80fd\u591f\u5728\u5f53\u5b83\u8d1f\u8d23\u7684\u4efb\u52a1\u5b8c\u6210\u540e\uff0c\u5c06\u7ed3\u679c\u8fd4\u56de\u7ed9\u4f60\u3002\u8fd9\u91cc\u7684\u4efb\u52a1\u53ef\u4ee5\u662f IO \u64cd\u4f5c\uff0c\u6216\u8005\u8ba1\u7b97\u5bc6\u96c6\u578b\u4efb\u52a1\u3002\u4efb\u52a1\u7684\u5185\u5bb9\u4e0d\u91cd\u8981\uff0c\u91cd\u8981\u7684\u662f\u5b83\u8fd4\u56de\u7684\u7ed3\u679c\uff0c\u5b83\u662f\u81ea\u7ed9\u81ea\u8db3\u7684\uff0c\u4e14\u662f <\/span>Task<\/code><\/span> \u4e2d\u59a5\u59a5\u7684\u4e00\u7b49\u516c\u6c11\u2014\u2014\u8bd5\u60f3\uff0c\u4f60\u7684\u540e\u7eed\u5de5\u4f5c\u9700\u8981 <\/span>Task<\/code><\/span> \u6267\u884c\u7684\u7ed3\u679c\u624d\u80fd\u7ee7\u7eed\u5f00\u5c55\uff0c\u56e0\u6b64\u4f60\u5f97\u5148\u7b49\u5f85\u5b83\u5b8c\u6210\u5e76\u8fd4\u56de\u3002<\/span>Task<\/code><\/span> \u5bf9\u8c61\u662f\u63a5\u6536\u3010\u672a\u6765\u3011\u7ed3\u679c\u7684\u90ae\u7bb1\u2014\u2014\u5f53 <\/span>Task<\/code><\/span> \u5b8c\u6210\u5de5\u4f5c\u540e\uff0c\u5b83\u4f1a\u5c06\u7ed3\u679c\u4fdd\u5b58\u4e0b\u6765\uff0c\u653e\u8fdb <\/span>Result<\/code><\/span> \u5c5e\u6027\u4e2d\u3002\u4f60\u53ef\u4ee5\u5c06 <\/span>Task<\/code><\/span> \u5bf9\u8c61\u5b58\u653e\u5728\u67d0\u4e2a\u53d8\u91cf\u91cc\uff08\u6bd4\u5982\u6570\u7ec4\uff09\uff0c\u5c06\u5b83\u4f5c\u4e3a\u65b9\u6cd5\u7684\u8fd4\u56de\u503c\u8fd4\u56de\uff0c\u6216\u8005\u8fd8\u80fd\u5c06\u5b83\u4f5c\u4e3a\u53c2\u6570\u4f20\u9012\u7ed9\u5176\u4ed6\u65b9\u6cd5\u3002\u751a\u81f3\uff0c\u4f60\u53ef\u4ee5\u5c06\u4e24\u4e2a <\/span>Task<\/code><\/span> \u7ed3\u5408\u5728\u4e00\u8d77\uff0c\u5f62\u6210\u4e00\u4e2a\u65b0\u7684 <\/span>Task<\/code><\/span> \uff0c\u4f8b\u5982\u5f53\u524d\u7f6e\u4efb\u52a1\u5b8c\u6210\u540e\uff0c\u81ea\u52a8\u5f00\u542f\u65b0\u4efb\u52a1\uff0c\u6784\u6210\u4e00\u6761\u7b80\u5355\u7684\u5de5\u4f5c\u6d41\u6c34\u7ebf\u3002\u901a\u8fc7 <\/span>Task<\/code><\/span> \u5e93\u63d0\u4f9b\u7684\u65b9\u6cd5\uff0c\u4f60\u4e5f\u53ef\u4ee5\u51b3\u5b9a\u5f53\u67d0\u4e2a <\/span>Task<\/code><\/span> \u6267\u884c\u6210\u529f\u3001\u5931\u8d25\u6216\u8005\u88ab\u53d6\u6d88\u540e\uff0c\u540e\u7eed\u5e94\u8be5\u505a\u7684\u4e8b\u60c5\u3002<\/span><\/p>\n

Task<\/code><\/span> \u5e93\uff08Task Parallel Library\uff09\u6539\u53d8\u4e86\u6211\u4eec\u5bf9\u3010\u5e76\u884c\u3011\u7684\u8ba4\u8bc6\uff0c\u5e76\u4e14C# 5\u5e26\u6765\u7684 <\/span>async<\/code><\/span> \u548c <\/span>await<\/code><\/span> \u8ba9\u5176\u53d1\u626c\u5149\u5927\u3002<\/span>async\/await<\/code><\/span> \u5c06 <\/span>Task<\/code><\/span> \u5bf9\u8c61\u4eec\u4e32\u8fde\u8d77\u6765\uff0c\u5e76\u4e14\u8ba9\u5f00\u53d1\u8005\u5728\u5e73\u65f6\u5e38\u89c1\u7684\u7ed3\u6784\u4e2d\u4f7f\u7528\u5b83\u4eec\uff0c\u5982 <\/span>try\/catch<\/code><\/span> \u3001<\/span>using<\/code><\/span> \u7b49\u7b49\u3002\u4f46\u7f8e\u4e2d\u4e0d\u8db3\u7684\u662f\uff0c<\/span>async\/await<\/code><\/span> \u6709\u81ea\u8eab\u5e26\u6765\u7684\u989d\u5916\u6027\u80fd\u5f00\u9500\u3002\u4e3a\u4e86\u7406\u89e3\u8fd9\u90e8\u5206\u5f00\u9500\u662f\u5982\u4f55\u9020\u6210\u7684\uff0c\u6211\u4eec\u9700\u8981\u5148\u4e86\u89e3\u5b83\u7684\u5de5\u4f5c\u539f\u7406\u3002<\/span><\/p>\n

\u4f60\u505a\u4e86\u4ec0\u4e48\uff01Async \u5173\u952e\u5b57<\/span><\/h2>\n

\u5e38\u89c4\u7684\u65b9\u6cd5\u53ea\u6709\u4e00\u4e2a\u5165\u53e3\u548c\u4e00\u4e2a\u51fa\u53e3\uff08\u53ef\u80fd\u5b58\u5728\u591a\u4e2a <\/span>return<\/code><\/span> \u5173\u952e\u5b57\uff0c\u4f46\u8fd0\u884c\u65f6\u53ea\u4f1a\u6709\u4e00\u4e2a\u6267\u884c\uff09\u3002\u4f46\u662f <\/span>async<\/code><\/span> \u65b9\u6cd5\u548c\u8fed\u4ee3\u5668\u65b9\u6cd5\uff08\u6709 <\/span>yield return<\/code><\/span> \u7684\u65b9\u6cd5\uff09\u662f\u4e0d\u4e00\u6837\u7684\u3002\u8fd9\u91cc\u6211\u4eec\u53ea\u8ba8\u8bba <\/span>async<\/code><\/span> \u65b9\u6cd5\uff0c\u5f53\u5b83\u88ab\u8c03\u7528\u540e\uff0c\u5176\u4f1a\u7acb\u5373\u8fd4\u56de\u7ed3\u679c\uff08<\/span>Task<\/code><\/span> \u6216 <\/span>Task<T><\/code><\/span>\uff09\u7ed9\u8c03\u7528\u8005\uff0c\u7136\u540e\u8c03\u7528\u8005\u53ef\u4ee5\u4f7f\u7528 <\/span>await<\/code><\/span> \u7b49\u5f85 <\/span>Task<\/code><\/span> \u5c06\u771f\u6b63\u7684\u7ed3\u679c\u8fd4\u56de\u56de\u6765\u3002<\/span><\/p>\n

\u4e3a\u4e86\u65b9\u4fbf\uff0c\u540e\u9762\u6211\u4eec\u5c06 <\/span>async<\/code><\/span> \u65b9\u6cd5\u5b9a\u4e49\u4e3a\u88ab <\/span>async<\/code><\/span> \u5173\u952e\u5b57\u6807\u8bb0\u7684\u7684\u65b9\u6cd5\u3002\u88ab <\/span>async<\/code><\/span> \u6807\u8bb0\u4e0d\u4ee3\u8868\u8be5\u65b9\u6cd5\u5c31\u4ee5\u5f02\u6b65\u7684\u65b9\u5f0f\u6267\u884c\uff0c\u5b83\u53ea\u662f\u505a\u4e2a\u6807\u8bb0\uff0c\u8ba9\u7f16\u8bd1\u5668\u5728\u9047\u5230\u8be5\u6807\u8bb0\u65f6\u5bf9 <\/span>async<\/code><\/span> \u65b9\u6cd5\u505a\u4e00\u4e9b\u7279\u6b8a\u7684\u5904\u7406\uff0c\u8fd9\u4e00\u70b9\u5f88\u91cd\u8981\uff0c\u4e0d\u8981\u5fd8\u8bb0\u5570\uff01<\/span><\/p>\n

\u6765\u770b\u770b\u4e0b\u9762\u7684 <\/span>async<\/code><\/span> \u65b9\u6cd5\uff1a<\/span><\/p>\n\n\n

class StockPrices\n{\n    private Dictionary<string, decimal> _stockPrices;\n    public async Task<decimal> GetStockPriceForAsync(string companyId)\n    {\n        await InitializeMapIfNeededAsync();\n        _stockPrices.TryGetValue(companyId, out var result);\n        return result;\n    }\n \n    private async Task InitializeMapIfNeededAsync()\n    {\n        if (_stockPrices != null)\n            return;\n \n        await Task.Delay(42);\n        \/\/ Getting the stock prices from the external source and cache in memory.\n        _stockPrices = new Dictionary<string, decimal> { { \"MSFT\", 42 } };\n    }\n}<\/code><\/pre>\n\n\n
GetStockPriceForAsync<\/code><\/span> \u65b9\u6cd5\u786e\u4fdd\u5b57\u5178 <\/span>_stockPrices<\/code><\/span> \u5728\u8fd4\u56de\u7ed3\u679c\u4e4b\u524d\u5df2\u88ab\u521d\u59cb\u5316\u3002<\/span><\/p>\n
\u4e3a\u4e86\u66f4\u597d\u5730\u7406\u89e3\u7f16\u8bd1\u5668\u7ed9\u4ee3\u7801\u65bd\u52a0\u4e86\u4ec0\u4e48\u9b54\u6cd5\uff0c\u6211\u4eec\u5148\u8bd5\u7740\u5c06\u4e0a\u9762\u7684\u4ee3\u7801\u624b\u52a8\u8f6c\u6362\u4e3a\u7f16\u8bd1\u5668\u4f18\u5316\u8fc7\u540e\u7684\u7248\u672c\u3002<\/span><\/p>\n
\u624b\u6495 async \u65b9\u6cd5<\/span><\/h2>\n
Task<\/code><\/span> \u7c7b\u5e93\u63d0\u4f9b\u4e24\u79cd\u65b9\u6cd5\u8ba9\u6211\u4eec\u521b\u5efa\u548c\u8fde\u63a5\uff1a<\/span>Task.ContinueWith<\/code><\/span> \u7528\u4e8e\u5728 <\/span>Task<\/code><\/span> \u5bf9\u8c61\u5b8c\u6210\u4efb\u52a1\u540e\u6307\u5b9a\u63a5\u4e0b\u6765\u7684\u4efb\u52a1\uff1b<\/span>TaskCompletionSource<T><\/code><\/span> \u7c7b\u7528\u4e8e\u624b\u52a8\u521b\u5efa <\/span>Task<\/code><\/span> \u5bf9\u8c61\u3002<\/span><\/p>\n\n\n
class GetStockPriceForAsync_StateMachine\n{\n    enum State { Start, Step1, }\n    private readonly StockPrices @this;\n    private readonly string _companyId;\n    private readonly TaskCompletionSource<decimal> _tcs;\n    private Task _initializeMapIfNeededTask;\n    private State _state = State.Start;\n \n    public GetStockPriceForAsync_StateMachine(StockPrices @this, string companyId)\n    {\n        this.@this = @this;\n        _companyId = companyId;\n    }\n \n    public void Start()\n    {\n        try\n        {\n            if (_state == State.Start)\n            {\n                \/\/ The code from the start of the method to the first 'await'.\n \n                if (string.IsNullOrEmpty(_companyId))\n                    throw new ArgumentNullException();\n \n                _initializeMapIfNeededTask = @this.InitializeMapIfNeeded();\n \n                \/\/ Update state and schedule continuation\n                _state = State.Step1;\n                _initializeMapIfNeededTask.ContinueWith(_ => Start());\n            }\n            else if (_state == State.Step1)\n            {\n                \/\/ Need to check the error and the cancel case first\n                if (_initializeMapIfNeededTask.Status == TaskStatus.Canceled)\n                    _tcs.SetCanceled();\n                else if (_initializeMapIfNeededTask.Status == TaskStatus.Faulted)\n                    _tcs.SetException(_initializeMapIfNeededTask.Exception.InnerException);\n                else\n                {\n                    \/\/ The code between first await and the rest of the method\n \n                    @this._store.TryGetValue(_companyId, out var result);\n                    _tcs.SetResult(result);\n                }\n            }\n        }\n        catch (Exception e)\n        {\n            _tcs.SetException(e);\n        }\n    }\n \n    public Task<decimal> Task => _tcs.Task;\n}\n \npublic Task<decimal> GetStockPriceForAsync(string companyId)\n{\n    var stateMachine = new GetStockPriceForAsync_StateMachine(this, companyId);\n    stateMachine.Start();\n    return stateMachine.Task;\n}<\/code><\/pre>\n\n\n
\u4ee3\u7801\u6bd4\u8f83\u5197\u957f\uff0c\u4f46\u5e76\u4e0d\u592a\u590d\u6742\u3002\u4e4b\u524d <\/span>GetStockPriceForAsync<\/code><\/span> \u65b9\u6cd5\u7684\u6240\u6709\u903b\u8f91\u90fd\u79fb\u52a8\u5230\u4e86 <\/span>GetStockPriceForAsync_StateMachine.Start<\/code><\/span> \u65b9\u6cd5\u91cc\u4e86\uff0c\u8be5\u65b9\u6cd5\u91c7\u53d6\u4e86\u3010\u7eed\u4f53\u4f20\u9012\u98ce\u683c\u6765\u7f16\u5199\u3011\uff08<\/span>continuation-pass style<\/span><\/a><\/span>)\u3002\u5f02\u6b65\u7b97\u6cd5\uff0c\u5927\u81f4\u4e0a\u662f\u6839\u636e <\/span>await<\/code><\/span> \u8fb9\u754c\u5c06\u539f\u65b9\u6cd5\u62c6\u5206\uff0c\u6784\u5efa\u6210\u4e00\u4e2a\u72b6\u6001\u673a\u3002\u7b2c\u4e00\u4e2a\u533a\u5757\u662f\u4ece\u65b9\u6cd5\u5f00\u59cb\u5230\u7b2c\u4e00\u4e2a <\/span>await<\/code><\/span> \u5173\u952e\u5b57\u7684\u90e8\u5206\uff1b\u7b2c\u4e8c\u4e2a\u533a\u5757\u662f\u4ece\u7b2c\u4e00\u4e2a <\/span>await<\/code><\/span> \u5f00\u59cb\u5230\u7b2c\u4e8c\u4e2a <\/span>await<\/code><\/span> \u90e8\u5206\uff1b\u7531\u6b64\u53ef\u89c1\uff0c\u7b2c\u4e09\u4e2a\u533a\u5757\u5c31\u662f\u4ece\u7b2c\u4e8c\u4e2a <\/span>await<\/code><\/span> \u5f00\u59cb\uff0c\u5230\u7b2c\u4e09\u4e2a <\/span>await<\/code><\/span> \u6216\u5230\u65b9\u6cd5\u7ed3\u675f\uff08\u82e5\u540e\u7eed\u6ca1\u6709 <\/span>await<\/code><\/span> \u5173\u952e\u5b57\uff09\uff1b\u7406\u89e3\u5230\u8fd9\u91cc\u5c31\u6bd4\u8f83\u7b80\u5355\u4e86\uff0c<\/span>await<\/code><\/span> \u5173\u952e\u5b57\u5c06\u65b9\u6cd5\u5206\u5272\u6210\u4e0d\u540c\u7684\u90e8\u5206\u3002<\/span><\/p>\n\n\n
\/\/ Step 1 of the generated state machine:\n \nif (string.IsNullOrEmpty(_companyId)) throw new ArgumentNullException();\n_initializeMapIfNeededTask = @this.InitializeMapIfNeeded();<\/code><\/pre>\n\n\n
\u6bcf\u4e2a\u88ab\u7b49\u5f85\u7684 <\/span>Task<\/code><\/span> \u5bf9\u8c61\u73b0\u5728\u53d8\u6210\u4e86\u72b6\u6001\u673a\u7684\u6210\u5458\u5b57\u6bb5\uff0c\u800c\u4e14 <\/span>Start<\/code><\/span> \u65b9\u6cd5\u5c06\u81ea\u5df1\u7533\u8bf7\u4e3a <\/span>Task<\/code><\/span> \u5bf9\u8c61\u7684\u540e\u7eed\u4efb\u52a1\uff1a<\/span><\/p>\n\n\n
_state = State.Step1;\n_initializeMapIfNeededTask.ContinueWith(_ => Start());<\/code><\/pre>\n\n\n
\u7136\u540e\u518d\u770b\uff0c\u5f53 <\/span>Task<\/code><\/span> \u5bf9\u8c61\u5de5\u4f5c\u5b8c\u6bd5\uff0c<\/span>Start<\/code><\/span> \u65b9\u6cd5\u4f1a\u88ab\u91cd\u65b0\u8c03\u7528\uff0c<\/span>_state<\/code><\/span> \u5b57\u6bb5\u5c06\u88ab\u518d\u6b21\u5224\u65ad\uff0c\u4ee5\u786e\u8ba4\u73b0\u5728\u8fdb\u884c\u5230\u4e86\u54ea\u4e00\u6b65\u3002\u4e4b\u540e\u7684\u903b\u8f91\u5c06\u5224\u65ad <\/span>Task<\/code><\/span> \u662f\u5426\u6267\u884c\u6210\u529f\u3001\u88ab\u53d6\u6d88\u6216\u8005\u5931\u8d25\u3002\u4e4b\u540e\uff0c\u72b6\u6001\u673a\u5c06\u8fd0\u884c\u81f3\u4e0b\u4e00\u72b6\u6001\uff0c\u6267\u884c\u4e0b\u4e00\u4e2a\u533a\u5757\u7684\u4ee3\u7801\u3002\u5f53\u6240\u6709\u4efb\u52a1\u90fd\u6267\u884c\u5b8c\u6bd5\u540e\uff0c\u72b6\u6001\u673a\u4f1a\u8bbe\u7f6e <\/span>TaskCompletionSorce<T><\/code><\/span> \u5bf9\u8c61\u7684\u7ed3\u679c\uff08\u8fd9\u91cc\u7684\u7ed3\u679c\u4e3a <\/span>Task<\/code><\/span> \u5bf9\u8c61\uff09\uff0c\u5e76\u4e14 <\/span>GetStockPriceForAsync<\/code><\/span> \u65b9\u6cd5\u4f1a\u5c06\u4f5c\u4e3a\u7ed3\u679c\u7684 <\/span>Task<\/code><\/span> \u8fd4\u56de\u3002 <\/span><\/p>\n\n\n
\/\/ The code between first await and the rest of the method\n \n@this._stockPrices.TryGetValue(_companyId, out var result);\n_tcs.SetResult(result); \/\/ The caller gets the result back<\/code><\/pre>\n\n\n
\u4e0a\u9762\u7684\u5b9e\u73b0\u65b9\u5f0f\u6709\u4e00\u4e9b\u81f4\u547d\u7f3a\u70b9\uff1a<\/span><\/p>\n