Bugs item #2871334, was opened at 2009-10-01 14:32
Message generated for change (Comment added) made by nobody
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Category: API
Group: None
Status: Open
Resolution: Invalid
Priority: 5
Private: No
Submitted By: Nobody/Anonymous (nobody)
Assigned to: Daniel Stenberg (bagder)
Summary: libssh2_session_startup may hang
Initial Comment:
Hi,
Our application has been hanging in libssh2_session_startup quite a long time.
It's probably a consequence of a
network issue (the connect() function worked so the network issue probablty
happened between these two functions)
The application has been not responding for more than 60 seconds, and it has
been restarted automatically by a monitor.
Fortunately a backtrace has been generated:
(gdb) bt
#0 0x00007ffeae99cce2 in select () from /lib/libc.so.6
#1 0x00007ffeaec3a458 in _libssh2_wait_socket (session=0x7ffea801a7d0) at
session.c:520
#2 0x00007ffeaec3ad46 in libssh2_session_startup (session=0x7ffea801a7d0,
sock=15) at session.c:687
I cannot see any timeout in the select(). The problem is we cannot control how
much time it may take. We
have used setsockopt to set a read/write timeout on the socket we pass to
libssh2, but the socket timeouts
have no effect with select.
So would it be possible to add an extra argument to libssh2_session_startup()
so that we can have
a timeout and we can just return and error instead of hanging. We are using
libssh2-1.2.
Thanks
----------------------------------------------------------------------
Comment By: Nobody/Anonymous (nobody)
Date: 2009-10-02 09:49
Message:
It's a good idea: I changed to the non-blocking mode and had to use loops
to retry while it returns EAGAIN, and it seems to work. It's just a bit
more complicated.
Anyway, the global timeout option will be great when it's implemented.
Thanks for your work on libssh2.
----------------------------------------------------------------------
Comment By: Daniel Stenberg (bagder)
Date: 2009-10-01 20:28
Message:
If non-blocking is an option, why can't you just use it for the
libssh2_session_startup() call too?
The select() done by libssh2 is there _only_ to provide the blocking API.
If you use it non-blocking the app does the select()ing...
----------------------------------------------------------------------
Comment By: Nobody/Anonymous (nobody)
Date: 2009-10-01 20:14
Message:
Thanks for your quick reply. That's right, a global timeout option would be
ideal. But I think it may be more important in that function, because in
other places the libssh2 the user program has a way to set a timeout:
1) the program does the connect() so it can do the setsockopt() to put a
timeout
2) for the standard libssh2_channel_read() and libssh2_channel_write()
functions we can use the non blocking mode using
libssh2_session_set_blocking()
The socket timeout is effective whenever libssh2 is doing a simple
read/write on the socket. It's really a problem there because libssh2 is
using a select() which makes the socket timeout option ineffective.
Thanks
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Comment By: Daniel Stenberg (bagder)
Date: 2009-10-01 18:04
Message:
This isn't a bug actually. It's simply so that the blocking interface for
libssh2 has no timeout anywhere, so all blocking functions do risk to
"hang" for a very long time if there's no network activity.
As the comment in _libssh2_wait_socket() says:
/* Note that this COULD be made to use a timeout that perhaps could
be
customizable by the app or something... */
but I think that rather than adding a timeout to a single function, it
should rather be something more generic so that all blocking functions
would get benefit from such a timeout.
----------------------------------------------------------------------
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