如何在PCF上托管的python CGI文件中刷新STDOUT？

Question

Due to Apache gateway timeouts, and a desire to display more information to the end user, I'd like to be able to flush STDOUT on a python CGI script hosted on PCF, essentially giving updates on the status of the script.

I have tried enabling the -u tag in python (#!/usr/python -u at head of my script), sys.stdout.flush() command, and even using subprocess.call to execute a perl script that is set to flush to STDOUT that prints some progress text ($| = 1; at beginning of perl script). Furthermore, I've double checked that I'm not using any Apache modules that would require buffering (no mod_deflate, for example). Finally, I'll mention that executing a standard perl CGI rather than a python CGI allows for the STDOUT flushing, so I figure it must be something with my python/Apache/PCF configuration.

I'm fresh out of ideas here, and would like some advice.

With any of these above methods, I would have thought stdout would flush. But, none of them have worked!

Thanks in advance for any assisstance.

Answer 1

You can disable buffering using something like this in your Python2 code:

    # set stdout as non-buffered
    if hasattr(sys.stdout, 'fileno'):
         fileno = sys.stdout.fileno()
         tmp_fd = os.dup(fileno)
         sys.stdout.close()
         os.dup2(tmp_fd, fileno)
         os.close(tmp_fd)
         sys.stdout = os.fdopen(fileno, "w", 0)

That is reopening sys.stdout with no buffer (ie the 0 as third arg). After you do that, anything writing to sys.stdout should not be buffered.