Common mistakes

FM is a low-level interface designed more for performance than for ease of use. Hence, there is very little error-checking code in the FM implementation. This makes it fairly easy for a programmer to make a simple mistake that introduces a race condition and/or causes a program to hang or crash. The following are some of the pitfalls to look out for while programming directly to the FM interface:

1. Forgetting to initialize handler ID variables before using them.
2. Terminating a receiver while a sender is still sending to it. This may occur when node A sends a large message to node B, node B's handler sets a termination flag and returns without touching any of the data, and node B's main code detects the termination flag and exits immediately. Meanwhile, node A is still trying to inject data into the network and, because FM guarantees delivery, will wait (forever) for acknowledgement from node B that the data was received correctly.
3. Sending more data with FM_send_piece() than was specified in FM_begin_message().
4. Receiving more data with FM_receive() than was sent by the remote process.

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