[Process] Process truncates output

[astephens25]

When a process generates large amounts of output in a short time, the Process component can potentially ignore information which is buffered for reading. This appears to be because each readStreams() call reads only the first 8192 bytes of the data in the buffer for a particular pipe. I would expect that (on termination at least) all the remaining data is read from a pipe before closing.

This issue is also present if a single call to getOutput() is issued after the loop terminates. This issue becomes intermittent if the usleep() in the while loop below is omitted as a race condition is created between termination of the process and performing the next read.

This will only be present when generating large amounts of output. For programs which output less data, the number of calls to updateStatus() over the process lifetime will be sufficient to read all the output.

Code to reproduce:

$process = new Process('cat /etc/services');

$process->start();

while ($process->isRunning()) {
    echo $process->getIncrementalOutput();
    usleep(100);
}

echo $process->getIncrementalOutput();

As an experiment, I modified the readStreams() call in the ProcessPipes class to read using the following code:

$read[$type] = '';
while (strlen($data = fread($pipe, 8192)) > 0) {
    $read[$type] .= $data;
}

After this modification I was no longer able to reproduce the issue. I have not done a thorough investigation as to whether there is additional impact from a change such as this.