[lldb-dev] lldb hangs during reverse-connect if lldb-server dies

[Ted Woodward]

How about calling select() before accept() with a 5 second timeout. If we
get a timeout, clean up and return an error. If we don't get a timeout,
there's activity on the socket, so the normal path would handle any issues.

--
Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a
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-----Original Message-----
From: Greg Clayton [mailto:gclayton at apple.com] 
Sent: Wednesday, June 17, 2015 3:28 PM
To: Ted Woodward
Cc: lldb-dev at cs.uiuc.edu
Subject: Re: [lldb-dev] lldb hangs during reverse-connect if lldb-server
dies

We should implement a timeout of say 5 seconds (since this is a locally
spawned lldb-server) and also watch for the spawned lldb-server process to
be reaped. If the lldb-server gets reaped we need to cancel. Don't do any
fancy thread canceling (no pthread_cancel or anything like that) if you do
fix this, just have something locally connect to the socket and allow the
accept thread to exit normally.


> On Jun 17, 2015, at 11:32 AM, Ted Woodward <ted.woodward at codeaurora.org>
wrote:
> 
>  
> With reverse-connect, lldb gets a port from the OS, spawns a listen thread
using the port, and launches lldb-server/debugserver, telling it to connect
back to lldb. lldb with then join with the listen thread. The listen thread
calls accept() to wait for the server to connect back to it.
>  
> On Linux (and possibly other OSes), if lldb-server dies or quits before
connecting, lldb will hang. It sits waiting for accept() to return, but it
never will.
>  
> If the child dies, the listen thread should be killed, and an error
returned to the user.
>  
>  
> This is easily seen on Linux. Simply point to an alternate debugserver.
Set LLDB_DEBUGSERVER_PATH to something else, say /bin/ls. This will finish
and never connect back to lldb.
>  
> -> setenv LLDB_DEBUGSERVER_PATH /bin/ls bin/lldb /bin/ls
> (lldb) target create "/bin/ls"
> Current executable set to '/bin/ls' (x86_64).
> (lldb) r
>  
> <hang>
>  
> --
> Qualcomm Innovation Center, Inc.
> The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, 
> a Linux Foundation Collaborative Project
>  
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