Question

Possible Duplicate:
php exec command (or similar) to not wait for result
exec() waiting for a response in PHP

I have a php script that calls and runs a Matlab script. The result of the Matlab script is a .png image, which I would then like to load in php and send to a webpage. The php code I have is:

$matlabExe = '"C:\\Program Files\\MATLAB\\R2012a\\bin\\matlab.exe"';
$mFile = "'C:\\processSatData.m'";
$combine = '"run(' . $mFile . ');"';
$command = $matlabExe . ' -nodisplay -nosplash -nodesktop -r ' . $combine;

passthru($command);

$im = file_get_contents('C:\\habitat.png');
header('Content-type:image/png');
echo $im;

However, it appears that after sending the ‘passthru’ command, php does not wait for the Matlab script to finish running. Thus, if the image file does not exist before running the php code, then I get an error message.

Is there a way to make it so that the php code waits for the Matlab script to finish running before it attempts to load the image file?

Answer 1

passthru is not the main issue here .. but i guess as soon you have a response from your command the image is not written instantly but by a 3rd process

file_get_contents might also fail in this instance because .. The image might not be written once or in the process of writing which can result to file lock .. in any case you need to be sure you have a valid image before output is sent;

set_time_limit(0);
$timeout = 30; // sec
$output = 'C:\\habitat.png';
$matlabExe = '"C:\\Program Files\\MATLAB\\R2012a\\bin\\matlab.exe"';
$mFile = "'C:\\processSatData.m'";
$combine = '"run(' . $mFile . ');"';
$command = $matlabExe . ' -nodisplay -nosplash -nodesktop -r ' . $combine;

try {
    if (! @unlink($output) && is_file($output))
        throw new Exception("Unable to remove old file");

    passthru($command);

    $start = time();
    while ( true ) {
        // Check if file is readable
        if (is_file($output) && is_readable($output)) {
            $img = @imagecreatefrompng($output);
            // Check if Math Lab is has finished writing to image
            if ($img !== false) {
                header('Content-type:image/png');
                imagepng($img);
                break;
            }
        }

        // Check Timeout
        if ((time() - $start) > $timeout) {
            throw new Exception("Timeout Reached");
            break;
        }
    }
} catch ( Exception $e ) {
    echo $e->getMessage();
}