On 04/05/2015 01:45 PM, Alexey Izbyshev wrote:
Hello!I've hit a strange problem that I reduced to the following test case: * Run several python processes in parallel that spin in the following loop: while True: if os.path.isfile(fname): with open(fname, 'rb') as f: f.read() break * Then, run another process that creates a temporary file and then renames it to the name than other processes are expecting * Now, some of the reading processes occasionally fail with "Permission denied" OSError I was able to reproduce it on two Windows 7 64-bit machines. It seems when the file appears on the filesystem it is still unavailable to reading, but I have no idea how it can happen. Both source and destination files are in the same directory, and the destination doesn't exist before calling os.rename. Everything I could find indicates that os.rename should be atomic under this conditions even on Windows, so nobody should be able to observe the destination in unaccessible state. I know that I can workaround this problem by removing useless os.path.isfile() check and wrapping open() with try-except, but I'd like to know the root cause of the problem. Please share you thoughts. The test case is attached, the main file is test.bat. Python is expected to be in PATH. Stderr of readers is redirected to *.log. You may need to run several times to hit the issue. Alexey Izbyshev, research assistant, ISP RAS
The attachment is missing; please just include it inline, after reducing it to a reasonably minimal sample.
My guess is that the process that does the os.rename is not closing the original file before renaming it. So even though the rename is atomic, the file is still locked by the first process.
-- DaveA -- https://mail.python.org/mailman/listinfo/python-list
