System.IO.IOException: Write fault on path /[Unknown]

In the case of providing an invalid option to a cmd-line tool, I would except to receive the cmd’s exit code of 1 (in this case, running ffmpeg via Xamarin.Android), instead an IOException thrown.

FYI: When ffmpeg is provided the correct option(s) and/or a media file that it can transcode, MedallionShell works great on Xamarin.Android (thanks 😀 )

Example code:

var cmd = Command.Run(ffmpegPath, (new string[]
{
"-hide_banner",
"-some_invalid_option",
}), ((options) =>
{
	options.WorkingDirectory(workingDir);
}));
var tasks = new List<Task>
{
	cmd.Task,
	cmd.StandardOutput.PipeToAsync(stdOutCollection),
	cmd.StandardError.PipeToAsync(stdErrCollection)
};
Task.WaitAll(tasks.ToArray());
exitCode = cmd.Result.ExitCode;

Note: stdOutCollection/stdErrCollection are ObservableCollections

Exception/Stacktrace:

[MonoDroid] System.IO.IOException: Write fault on path /[Unknown]
[MonoDroid]   at System.IO.FileStream.WriteInternal (System.Byte[] src, System.Int32 offset, System.Int32 count) [0x00077] in <fa70666c4440451cb5ca34569f933bb4>:0 
[MonoDroid]   at System.IO.FileStream.Write (System.Byte[] array, System.Int32 offset, System.Int32 count) [0x00090] in <fa70666c4440451cb5ca34569f933bb4>:0 
[MonoDroid]   at System.IO.StreamWriter.Flush (System.Boolean flushStream, System.Boolean flushEncoder) [0x00042] in <fa70666c4440451cb5ca34569f933bb4>:0 
[MonoDroid]   at System.IO.StreamWriter.set_AutoFlush (System.Boolean value) [0x00010] in <fa70666c4440451cb5ca34569f933bb4>:0 
[MonoDroid]   at System.Diagnostics.Process.StartWithCreateProcess (System.Diagnostics.ProcessStartInfo startInfo) [0x00353] in <5a97d41d36694fb19855c17429527b10>:0 
[MonoDroid]   at System.Diagnostics.Process.Start () [0x0003a] in <5a97d41d36694fb19855c17429527b10>:0 
[MonoDroid]   at (wrapper remoting-invoke-with-check) System.Diagnostics.Process.Start()
[MonoDroid]   at Medallion.Shell.ProcessCommand..ctor (System.Diagnostics.ProcessStartInfo startInfo, System.Boolean throwOnError, System.Boolean disposeOnExit, System.TimeSpan timeout, System.Threading.CancellationToken cancellationToken, System.Text.Encoding standardInputEncoding) [0x0004a] in <dcb0641c39fd4991a9750bcbbb6f72ce>:0 
[MonoDroid]   at Medallion.Shell.Shell.Run (System.String executable, System.Collections.Generic.IEnumerable`1[T] arguments, System.Action`1[T] options) [0x000f6] in <dcb0641c39fd4991a9750bcbbb6f72ce>:0 
[MonoDroid]   at Medallion.Shell.Command.Run (System.String executable, System.Collections.Generic.IEnumerable`1[T] arguments, System.Action`1[T] options) [0x00005] in <dcb0641c39fd4991a9750bcbbb6f72ce>:0 
[MonoDroid]   at GifVideo.MainActivity+<>c__DisplayClass2_0.<OnCreate>b__4 () [0x00088] in /Volumes/Code/code/Projects/GifVideo/GifVideo/MainActivity.cs:72 
[MonoDroid]   at System.Threading.Tasks.Task.InnerInvoke () [0x0000f] in <fa70666c4440451cb5ca34569f933bb4>:0 
[MonoDroid]   at System.Threading.Tasks.Task.Execute () [0x00010] in <fa70666c4440451cb5ca34569f933bb4>:0 
[MonoDroid] --- End of stack trace from previous location where exception was thrown ---
[MonoDroid]   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in <fa70666c4440451cb5ca34569f933bb4>:0 
[MonoDroid]   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) [0x0003e] in <fa70666c4440451cb5ca34569f933bb4>:0 
[MonoDroid]   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) [0x00028] in <fa70666c4440451cb5ca34569f933bb4>:0 
[MonoDroid]   at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task task) [0x00008] in <fa70666c4440451cb5ca34569f933bb4>:0 
[MonoDroid]   at System.Runtime.CompilerServices.TaskAwaiter.GetResult () [0x00000] in <fa70666c4440451cb5ca34569f933bb4>:0 
[MonoDroid]   at GifVideo.MainActivity+<>c__DisplayClass2_0+<<OnCreate>b__2>d.MoveNext () [0x00048] in /Volumes/Code/code/Projects/GifVideo/GifVideo/MainActivity.cs:47 
[MonoDroid] --- End of stack trace from previous location where exception was thrown ---
[MonoDroid]   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in <fa70666c4440451cb5ca34569f933bb4>:0 
[MonoDroid]   at System.Runtime.CompilerServices.AsyncMethodBuilderCore+<>c.<ThrowAsync>b__6_0 (System.Object state) [0x00000] in <fa70666c4440451cb5ca34569f933bb4>:0 
[MonoDroid]   at Android.App.SyncContext+<>c__DisplayClass2_0.<Post>b__0 () [0x00000] in <f7bb669be1a3453caf7f53a12b803ea2>:0 
[MonoDroid]   at Java.Lang.Thread+RunnableImplementor.Run () [0x00008] in <f7bb669be1a3453caf7f53a12b803ea2>:0 
[MonoDroid]   at Java.Lang.IRunnableInvoker.n_Run (System.IntPtr jnienv, System.IntPtr native__this) [0x00008] in <f7bb669be1a3453caf7f53a12b803ea2>:0 
[MonoDroid]   at (wrapper dynamic-method) System.Object.c7921d6c-67df-4e70-810d-9325c40be88e(intptr,intptr)

[madelson]

Hi @sushihangover thanks for reporting this.

There is a mechanism in place that is supposed to guard against this, but right now it is only enabled on Mono. We detect Mono by doing:

Type.GetType("Mono.Runtime") != null

What do you get when running this check on Xamarin/Android? What version of Mono are you running?

EDIT

Looking more closely at the stack trace, it seems like this is actually failing inside Process.Start. This feels like a runtime bug to me, since it will leave the Process object in an inconsistent state with only some of the streams set up.

That said, I’m not against having MedallionShell work around this, since one of the library’s main goals is working around oddities in the Process API.

EDIT

I’ve tried to reproduce this using ffmpeg and Mono on Windows but I don’t see the error. Could be an OS difference around how processes start. Windows process start isn’t the fastest so maybe it just gets lucky and avoids this race condition.

[sushihangover]

https://github.com/mono/mono/issues/8417