{"id":3183,"date":"2008-12-30T12:00:00","date_gmt":"2008-12-30T12:00:00","guid":{"rendered":"https:\/\/blogs.msdn.microsoft.com\/vbteam\/2008\/12\/30\/system-diagnostics-process-avoid-deadlocks-in-redirectstandardinputoutput-lucian-wischik\/"},"modified":"2024-07-05T13:34:12","modified_gmt":"2024-07-05T20:34:12","slug":"system-diagnostics-process-avoid-deadlocks-in-redirectstandardinputoutput-lucian-wischik","status":"publish","type":"post","link":"https:\/\/devblogs.microsoft.com\/vbteam\/system-diagnostics-process-avoid-deadlocks-in-redirectstandardinputoutput-lucian-wischik\/","title":{"rendered":"System.Diagnostics.Process: avoid deadlocks in RedirectStandardInput\/Output (Lucian Wischik)"},"content":{"rendered":"

It’s common that you want to launch an external process but supply input and capture the output. Here’s one attempt: <\/p>\n

‘ BAD CODE<\/span><\/p>\n

<\/span><\/p>\n

Using<\/span> p As<\/span> New<\/span> System.Diagnostics.Process<\/p>\n

<\/span><\/p>\n

    <\/span>p.StartInfo.FileName = “cat”<\/p>\n

<\/span><\/span><\/p>\n

    <\/span>p.StartInfo.UseShellExecute = False<\/p>\n

<\/span><\/span><\/p>\n

    <\/span>p.StartInfo.RedirectStandardOutput = True<\/p>\n

<\/span><\/span><\/p>\n

    <\/span>p.StartInfo.RedirectStandardInput = True<\/p>\n

<\/span><\/span><\/p>\n

    <\/span>p.Start()<\/p>\n

<\/span><\/p>\n

    <\/span>p.StandardInput.Write(“world”<\/span> & vbCrLf & “hello”<\/span>)<\/span><\/p>\n

<\/span><\/p>\n

    <\/span>p.StandardInput.Close()<\/p>\n

<\/span><\/p>\n

    <\/span>Dim<\/span> op = p.StandardOutput.ReadToEnd()<\/p>\n

<\/span><\/p>\n

    <\/span>p.WaitForExit()<\/p>\n

<\/span><\/p>\n

    <\/span>p.Close()<\/p>\n

<\/span><\/p>\n

    <\/span>Console.WriteLine(“OUTPUT:”<\/span>) : Console.WriteLine(op)<\/p>\n

<\/span><\/p>\n

End<\/span> Using<\/p>\n

<\/span><\/span><\/p>\n

This code has a deadlock bug in it. That’s because of the possibility that “p” needs to write to StandardOutput before it’s yet finished reading all of StandardInput: there won’t be anyone to read from StandardOutput, and it might fill up!<\/p>\n

The MSDN documentation<\/a> says that the answer is to use multiple threads. So here’s code that uses multiple threads to avoid the deadlock: http:\/\/blogs.msdn.com\/lucian\/archive\/2008\/12\/29\/system-diagnostics-process-redirect-standardinput-standardoutput-standarderror.aspx<\/a><\/p>\n

 <\/p>\n

<\/p>\n

<\/span> <\/p>\n

<\/span><\/p>\n","protected":false},"excerpt":{"rendered":"

It’s common that you want to launch an external process but supply input and capture the output. Here’s one attempt:  ‘ BAD CODE Using p As New System.Diagnostics.Process     p.StartInfo.FileName = “cat”     p.StartInfo.UseShellExecute = False     p.StartInfo.RedirectStandardOutput = True     p.StartInfo.RedirectStandardInput = True     p.Start()     p.StandardInput.Write(“world” & vbCrLf & “hello”)     p.StandardInput.Close()     Dim op = […]<\/p>\n","protected":false},"author":260,"featured_media":8818,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[192,195],"tags":[99],"class_list":["post-3183","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-featured","category-visual-basic","tag-lucian-wischik"],"acf":[],"blog_post_summary":"

It’s common that you want to launch an external process but supply input and capture the output. Here’s one attempt:  ‘ BAD CODE Using p As New System.Diagnostics.Process     p.StartInfo.FileName = “cat”     p.StartInfo.UseShellExecute = False     p.StartInfo.RedirectStandardOutput = True     p.StartInfo.RedirectStandardInput = True     p.Start()     p.StandardInput.Write(“world” & vbCrLf & “hello”)     p.StandardInput.Close()     Dim op = […]<\/p>\n","_links":{"self":[{"href":"https:\/\/devblogs.microsoft.com\/vbteam\/wp-json\/wp\/v2\/posts\/3183","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/devblogs.microsoft.com\/vbteam\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/devblogs.microsoft.com\/vbteam\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/vbteam\/wp-json\/wp\/v2\/users\/260"}],"replies":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/vbteam\/wp-json\/wp\/v2\/comments?post=3183"}],"version-history":[{"count":0,"href":"https:\/\/devblogs.microsoft.com\/vbteam\/wp-json\/wp\/v2\/posts\/3183\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/vbteam\/wp-json\/wp\/v2\/media\/8818"}],"wp:attachment":[{"href":"https:\/\/devblogs.microsoft.com\/vbteam\/wp-json\/wp\/v2\/media?parent=3183"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/vbteam\/wp-json\/wp\/v2\/categories?post=3183"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/vbteam\/wp-json\/wp\/v2\/tags?post=3183"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}