Why "No buffer space available"?

[Medialy <medialy@gmail.com>]

Hi,
I have written a program to log the nat behavior. the program works
well when traffic is low. But when the traffic reaches 1Gb, program
always error.
According to the previous discussions about this problem, I even set
the recv buffer size to 50MB and the error still exists.
For every callback, format the data and then put it into the queue
directly.  The formating of data causes less then 1 second for 0.65
million records.
Errors always occurs  when there are less than 10 log records.
Is anyone who can help?
Thanks.

Setting:
    Redhat Enterprise Linux 5
    libnetfilter_conntrack-0.0.100
    libnfnetlink-1.0.0
    recv buffer size: 50MB
    nfct_open(CONNTRACK, NF_NETLINK_CONNTRACK_NEW|NF_NETLINK_CONNTRACK_DESTROY)
    1Gb nat traffic, 0.65 million records per minute
    circular queue size: 1 million

Error:
    nfct_catch error: No buffer space available

Program Structure:
    Callback:
        lock;
        if log number > MAX_LOG_NUM:
            discard
        else:
            put log in circular queue
            log number += 1
        unlock

    Thread 2:
        lock;
        if log number >0 :
            get lock number
        unlock
        process log data in circular queue
        lock
        log number = log number - log number processed
        unlock