Azure WebJob 日志记录正在崩溃主机，我们该怎么办？

Question

我们正在使用 Azure 运行多个 WebJobs。我们的 WebJob 函数之一具有以下签名：

public static Task ProcessFileUploadedMessageAsync(
    [QueueTrigger("uploads")] FileUploadedMessage message,
    TextWriter logger,
    CancellationToken cancellationToken)

此函数正在监视队列中是否存在指示文件已上传的消息，然后触发文件数据的导入。请注意使用 TextWriter 作为第二个参数：这是由 WebJobs API 基础结构提供的。

我们的导入过程有点慢（在某些情况下，单个文件导入可能需要几个小时），因此我们会定期将消息写入日志（通过TextWriter）以跟踪我们的进度。不幸的是，我们较大的文件导致 WebJob 托管进程由于日志记录异常而终止。这是来自托管进程日志的示例堆栈跟踪：

[04/02/2016 03:44:59 > 660083: ERR ] 
[04/02/2016 03:45:00 > 660083: ERR ] Unhandled Exception: System.ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection.
[04/02/2016 03:45:00 > 660083: ERR ] Parameter name: chunkLength
[04/02/2016 03:45:00 > 660083: ERR ]    at System.Text.StringBuilder.ToString()
[04/02/2016 03:45:00 > 660083: ERR ]    at System.IO.StringWriter.ToString()
[04/02/2016 03:45:00 > 660083: ERR ]    at Microsoft.Azure.WebJobs.Host.Loggers.UpdateOutputLogCommand.<UpdateOutputBlob>d__10.MoveNext()
[04/02/2016 03:45:00 > 660083: ERR ] --- End of stack trace from previous location where exception was thrown ---
[04/02/2016 03:45:00 > 660083: ERR ]    at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
[04/02/2016 03:45:00 > 660083: ERR ]    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
[04/02/2016 03:45:00 > 660083: ERR ]    at Microsoft.Azure.WebJobs.Host.Loggers.UpdateOutputLogCommand.<TryExecuteAsync>d__3.MoveNext()
[04/02/2016 03:45:00 > 660083: ERR ] --- End of stack trace from previous location where exception was thrown ---
[04/02/2016 03:45:00 > 660083: ERR ]    at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
[04/02/2016 03:45:00 > 660083: ERR ]    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
[04/02/2016 03:45:00 > 660083: ERR ]    at Microsoft.Azure.WebJobs.Host.Timers.RecurrentTaskSeriesCommand.<ExecuteAsync>d__0.MoveNext()
[04/02/2016 03:45:00 > 660083: ERR ] --- End of stack trace from previous location where exception was thrown ---
[04/02/2016 03:45:00 > 660083: ERR ]    at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
[04/02/2016 03:45:00 > 660083: ERR ]    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
[04/02/2016 03:45:00 > 660083: ERR ]    at Microsoft.Azure.WebJobs.Host.Timers.TaskSeriesTimer.<RunAsync>d__d.MoveNext()
[04/02/2016 03:45:00 > 660083: ERR ] --- End of stack trace from previous location where exception was thrown ---
[04/02/2016 03:45:00 > 660083: ERR ]    at Microsoft.Azure.WebJobs.Host.Timers.BackgroundExceptionDispatcher.<>c__DisplayClass1.<Throw>b__0()
[04/02/2016 03:45:00 > 660083: ERR ]    at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
[04/02/2016 03:45:00 > 660083: ERR ]    at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
[04/02/2016 03:45:00 > 660083: ERR ]    at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
[04/02/2016 03:45:00 > 660083: ERR ]    at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
[04/02/2016 03:45:00 > 660083: ERR ]    at System.Threading.ThreadHelper.ThreadStart()
[04/02/2016 03:45:00 > 660083: SYS ERR ] Job failed due to exit code -532462766
[04/02/2016 03:45:01 > 660083: SYS INFO] Process went down, waiting for 0 seconds
[04/02/2016 03:45:01 > 660083: SYS INFO] Status changed to PendingRestart

主要问题是这个异常不是由我们的代码引发的，而是由 WebJobs API 中的某些东西引发的：

at Microsoft.Azure.WebJobs.Host.Loggers.UpdateOutputLogCommand.<UpdateOutputBlob>d__10.MoveNext()

我们尝试在对TextWriter 的调用周围放置try...catch 块，但这些都没有效果。似乎日志消息在某处缓冲，并通过单独的线程定期刷新到 Azure blob 存储。如果是这种情况，那么我们就无法捕获异常。

有没有其他人遇到过同样的问题，或者任何人都可以想到可能的解决方案或解决方法？

---

为了完整起见，以下是我们使用TextWriter 进行日志记录的方式：

await logger.WriteLineAsync("some text to log");

没有比这更复杂的了。

---

更新：好像这已被报告为issue #675 on the WebJobs SDK GitHub。

Answer 1

你应该在方法中添加async，就像这样：

public async static Task ProcessFileUploadedMessageAsync(...)

了解详情可以看this article