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Wat happens if two applications try to listen to the same port?

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The second one that binds to the port will get an error saying something else is already listening on the port.

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Does the program check for itself if some other program is listening to the port? – Wintermute Mar 3 '11 at 20:33
The operating system does the check. – carson Mar 3 '11 at 20:41
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Unless they are spawned via tcpmux, the first application binds to the port and listens for connections to it, while the second one cannot bind and cannot listen.

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What is it that prevents the application from binding to the port? – Wintermute Mar 3 '11 at 20:36
When your application makes the relevant system call to "grab" the port, the operating system will "inform" it (via a relevant error code) that it is already taken. – adamo Mar 3 '11 at 21:17
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