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ReadPipeTO timeouts not working?

Hello all:

I am doing some work on the libusb project and also the hplip (hp ink jet driver project) and I have stumbled across something and need some expert opinion.

I am attempting to improve the recoverability of both of these applications (e.g. press cancel in the middle of a scan), and their general performance.

Since the communication is basically half-duplex, I am attempting to replace the asynchronous IO with synchronous IO in libusb.

What I have found is that during certain exchange sequences, ReadPipeTO with a timeout specified (45000ms) returns immediately with kIOReturnSuccess but a read size of 0.

How can this be? Could the printer be signaling a NAK, or some such thing, and ReadPipeTO is interpreting this as a valid read. How can I make ReadPipeTO continue to block until it really has some data, or the timeout expires?

I also changed it to use ReadPipeAsync with no improvement - the callback shows success with 0 bytes read.

The reads are on a bulk input pipe. Eventually the pipe does return some data, but until then the code basically hard spins looking for data. This causes two problems: performance - really drags down the cpu, and the timeout testing for real error conditions does not work properly (since the requests are handled as if they were read ok - just with no data).

Thanks,
Robert Engels

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