topic Re: send() function sleeping for tcp socket in Operating System - HP-UX

send() function sleeping for tcp socket

joeyu1201 — Wed, 30 Jun 2010 01:13:10 GMT

I have a tcp server application to generate reqeust and send to client. However, after startup a while, the application is blocked by send() function.

$ truss -p 10591
( Attached to process 10591 ("J_SMPP_Handler 127.0.0.1") [64-bit] )
send(5, 0x9ffffffffff97d60, 59, 0) [sleeping]

Why does send() being blocked?

Re: send() function sleeping for tcp socket

Steven Schweda — Wed, 30 Jun 2010 01:50:53 GMT

> I have a tcp server application [...]

Running on what, exactly? (_Who_ has
"truss"?)

Getting an accurate diagnosis of invisible
code running on a mystery system may be more
difficult than you seem to think.

Re: send() function sleeping for tcp socket

joeyu1201 — Wed, 30 Jun 2010 02:19:37 GMT

The application is running on IA64 11.31

Re: send() function sleeping for tcp socket

joeyu1201 — Wed, 30 Jun 2010 02:26:19 GMT

I call send with following parameter:
rc = send(fd, (char*)buffer, byte_to_send, 0);

Re: send() function sleeping for tcp socket

James R. Ferguson — Wed, 30 Jun 2010 05:17:13 GMT

Hi:

What does the return value of 'send()' contain? The manpages for 'send(2)' describe the various expectations including potential 'errno' indicators.

Regards!

...JRF...

Re: send() function sleeping for tcp socket

Matti_Kurkela — Wed, 30 Jun 2010 05:20:58 GMT

Maybe the client isn't reading from it's socket buffer for some reason.

As the client's receive buffer fills up, the client OS will automatically send TCP options to inform your server about the shrinking available space in the client's TCP receive window. Once the receive buffer has been completely filled, the TCP window size will also be reduced to zero.

At that point, the server knows it cannot send anything more to the client until the client processes the data already sent. As no more data can be sent, any further data will remain in the server socket's transmit buffer until the client sends another message telling it can receive more. Once the server socket's transmit buffer is 100% full, the send() function will start blocking.

From the send(2) man page:
----
If no buffer space is available to hold the data to be transmitted, send() blocks unless nonblocking mode is enabled.
----
... and if you had enabled nonblocking mode, the send() function would have failed with errno set to either EAGAIN or EWOULDBLOCK.

MK

Re: send() function sleeping for tcp socket

joeyu1201 — Wed, 30 Jun 2010 06:08:09 GMT

Can I know the remaining available TCP buffer of client/server side?
I used netstat to view the socket buffer, but there is accumulated data in socket buffer.

Re: send() function sleeping for tcp socket

joeyu1201 — Wed, 30 Jun 2010 10:03:46 GMT

sorry, should be no accumulated data in socket buffer