Incoming TCP connection on iPhone iOS4 BG mode would fail over and over with EAGAIN error (thanks Bogdan Krakowski for the report)

[bennylp]

From accept() manual:
There may not always be a connection waiting after a SIGIO is delivered or select(2) or poll(2) return a readability event because the connection might have been removed by an asynchronous network error or another thread before accept() is called.

In iOS4, the problem is reproducible by putting the app to BG and locking the device, hence causing iOS4 to close all connections. When application is brought back to the FG, select() always returns a readability event while accept() always fails with EAGAIN error.

There was a report that the problem happened in Sun Solaris OS as well.

[ming]

(In [3316]) Fixed #1130
Since the problem may not be iOS4 specific, a general approach is adopted to fix the problem.

[ming]

To fix this, we create a counter and record the last error that we encountered from the accept() operation. If we get the same error, we increase the counter, otherwise the counter will be reset to zero. Once the counter reaches PJ_ACTIVESOCK_MAX_CONSECUTIVE_ACCEPT_ERROR, no further accept() operations will be called.