Make HTTP connection attempt cancellable #472
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lgtm! |
alanmcgovern
approved these changes
Mar 7, 2017
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Task.Run only checks the CancellationToken before starting the task; after that point, the task itself is responsible for checking the token. Hence the complicated |
Contributor
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Which seems to be the problem here. I'm working on a better solution, will update the PR once it's ready. |
The `HttpURLConnection.ConnectAsync` API doesn't accept a `CancellationToken` instance and, thus, cannot be easily cancelled in a graceful manner. This limitation resulted in using the `Task.WhenAny` to make sure the connection attempt is aborted whenever the calling task is cancelled. This, however, led to a problem of unobserved exceptions should the cancellation occur before the connection attempt was successful. This commit wraps the synchronous `HttpURLConnection.Connect` call in a task that is passed the cancellation token, so that it can be gracefully cancelled when needed. The cancellation is done by registering a handler for when token is about to expire as Task.Run will check if cancellation was requested only before it runs the passed code, the rest is the code's responsibility. Since `URLConnection.Connect()` is asynchronous we abort it by calling `Disconnect()` on the instance which is a brutal but effective way to interrupt the connection attempt. Additionally, the diff makes sure to properly configure a few tasks for `await` Fixes https://bugzilla.xamarin.com/show_bug.cgi?id=51804
grendello
added a commit
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Mar 23, 2017
The `HttpURLConnection.ConnectAsync` API doesn't accept a `CancellationToken` instance and, thus, cannot be easily cancelled in a graceful manner. This limitation resulted in using the `Task.WhenAny` to make sure the connection attempt is aborted whenever the calling task is cancelled. This, however, led to a problem of unobserved exceptions should the cancellation occur before the connection attempt was successful. This commit wraps the synchronous `HttpURLConnection.Connect` call in a task that is passed the cancellation token, so that it can be gracefully cancelled when needed. The cancellation is done by registering a handler for when token is about to expire as Task.Run will check if cancellation was requested only before it runs the passed code, the rest is the code's responsibility. Since `URLConnection.Connect()` is asynchronous we abort it by calling `Disconnect()` on the instance which is a brutal but effective way to interrupt the connection attempt. Additionally, the diff makes sure to properly configure a few tasks for `await` Fixes https://bugzilla.xamarin.com/show_bug.cgi?id=51804
grendello
added a commit
to grendello/xamarin-android
that referenced
this pull request
Mar 23, 2017
The `HttpURLConnection.ConnectAsync` API doesn't accept a `CancellationToken` instance and, thus, cannot be easily cancelled in a graceful manner. This limitation resulted in using the `Task.WhenAny` to make sure the connection attempt is aborted whenever the calling task is cancelled. This, however, led to a problem of unobserved exceptions should the cancellation occur before the connection attempt was successful. This commit wraps the synchronous `HttpURLConnection.Connect` call in a task that is passed the cancellation token, so that it can be gracefully cancelled when needed. The cancellation is done by registering a handler for when token is about to expire as Task.Run will check if cancellation was requested only before it runs the passed code, the rest is the code's responsibility. Since `URLConnection.Connect()` is asynchronous we abort it by calling `Disconnect()` on the instance which is a brutal but effective way to interrupt the connection attempt. Additionally, the diff makes sure to properly configure a few tasks for `await` Fixes https://bugzilla.xamarin.com/show_bug.cgi?id=51804
jonpryor
pushed a commit
that referenced
this pull request
Mar 23, 2017
The `HttpURLConnection.ConnectAsync` API doesn't accept a `CancellationToken` instance and, thus, cannot be easily cancelled in a graceful manner. This limitation resulted in using the `Task.WhenAny` to make sure the connection attempt is aborted whenever the calling task is cancelled. This, however, led to a problem of unobserved exceptions should the cancellation occur before the connection attempt was successful. This commit wraps the synchronous `HttpURLConnection.Connect` call in a task that is passed the cancellation token, so that it can be gracefully cancelled when needed. The cancellation is done by registering a handler for when token is about to expire as Task.Run will check if cancellation was requested only before it runs the passed code, the rest is the code's responsibility. Since `URLConnection.Connect()` is asynchronous we abort it by calling `Disconnect()` on the instance which is a brutal but effective way to interrupt the connection attempt. Additionally, the diff makes sure to properly configure a few tasks for `await` Fixes: https://bugzilla.xamarin.com/show_bug.cgi?id=51804
grendello
added a commit
that referenced
this pull request
Mar 23, 2017
The `HttpURLConnection.ConnectAsync` API doesn't accept a `CancellationToken` instance and, thus, cannot be easily cancelled in a graceful manner. This limitation resulted in using the `Task.WhenAny` to make sure the connection attempt is aborted whenever the calling task is cancelled. This, however, led to a problem of unobserved exceptions should the cancellation occur before the connection attempt was successful. This commit wraps the synchronous `HttpURLConnection.Connect` call in a task that is passed the cancellation token, so that it can be gracefully cancelled when needed. The cancellation is done by registering a handler for when token is about to expire as Task.Run will check if cancellation was requested only before it runs the passed code, the rest is the code's responsibility. Since `URLConnection.Connect()` is asynchronous we abort it by calling `Disconnect()` on the instance which is a brutal but effective way to interrupt the connection attempt. Additionally, the diff makes sure to properly configure a few tasks for `await` Fixes https://bugzilla.xamarin.com/show_bug.cgi?id=51804
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The
HttpURLConnection.ConnectAsyncAPI doesn't accept aCancellationTokeninstance and, thus, cannot be easily cancelled in a graceful manner. This
limitation resulted in using the
Task.WhenAnyto make sure the connectionattempt is aborted whenever the calling task is cancelled. This, however, led to
a problem of unobserved exceptions should the cancellation occur before the
connection attempt was successful.
This commit wraps the synchronous
HttpURLConnection.Connectcall in a taskthat is passed the cancellation token, so that it can be gracefully cancelled
when needed.
Fixes https://bugzilla.xamarin.com/show_bug.cgi?id=51804