Avoid pidfile creation race #18
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Add support for getFdName() on Darwin using fcntl(F_GETPATH), as Darwin does not have /proc Signed-off-by: Alex Bligh <[email protected]>
Avoid a race on pidfile creation by creating the pidfile before the JSON is processed. Prior to this patch, the pidfile was created only after the JSON had been processed. This creates a race if the initiating process assumes the daemon is running if it the call to start the daemon has returned. This corrects the problem by not consuming the JSON (and thus preventing the parent from quitting) until the lock file has been created. Signed-off-by: Alex Bligh <[email protected]>
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Great work. Thank you very much! |
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This patch (on top of #17) avoids a race on pidfile creation by creating the pidfile before the JSON is processed.
Prior to this patch, the pidfile was created only after the JSON had been processed. This creates a race if the initiating process assumes the daemon is running if it the call to start the daemon has returned.
For instance, before the patch, this was happening around 50% of the time under OS-X:
This patch corrects the problem by not consuming the JSON (and thus preventing the parent from quitting) until the lock file has been created. As the parent now cannot quit until the child has consumed the JSON (or closed the FD by crashing), we know that the child will have created the PID file by the time the parent exits, so it safe for the called (step 6 in the above) to check for the PID file and determine the daemon is running (or at least was started).