we have a use case where multiple clients are writing data to same socket which is receiver end.
 
Socket type used is SOCK_DGRAM
Operating System: QNX 7 
Platform: Qualcomm 6145 
setsockopt BUFFER_SIZE: 246000
 
We encountered no buffer exception in our code. Below is the syntax for pselect system call.. and we are using send/recv
 apis to send and received the data.

pselect((maxFd + 1), &mFdSet, NULL, NULL, NULL, NULL)
 
send(mFd,buffer,uiSize, MSG_WAITALL);
recv(fd, buffer,uiSize,MSG_WAITALL);
 
when multiple clients were trying to write the data, send api was returning "no buffer" exception.
 
when we checked in detail and added log before and after pselect system call, we observed that initially when we were 
pushing data before and after pselect prints were coming 

and then suddenly "after pselect" print stopped coming although data was being pushed from client side, after some time 
when socket buffer becomes full, clinets started getting "no buffer".

Hi Michael Schuster , 

I have provided the details. Is this sufficient for you to narrow down the issue. 
Please let us know . 

Thanks 
Sayooj Mandodi

We have verified that during issue scenario correct FD is being passed to pselect.
Same doubt was raised and when pselect was getting blocked we printed the FD and made sure its valid one .