commit a10b00e890dccb6d4630be6461834360bce3cf81
author Octavian Purdila <tavip@google.com> Thu Oct 19 00:29:47 2023 +0000
committer CQ Bot Account <pigweed-scoped@luci-project-accounts.iam.gserviceaccount.com> Thu Oct 19 00:29:47 2023 +0000
tree 4289267f81cd7c95a1ce482b9b8c95410c431d3a
parent 2eb3273c02f1ab80d2d13017eda4549bd6394ccf

pw_emu: Fix pid file race condition

There is a race condition between writing and reading the pid file where
the reader can get an empty line:

======================================================================
ERROR: test_get_channel_addr (__main__.TestQemuChannelsTcp)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/local/google/home/tavip/src/pigweed/pw_emu/py/pw_emu/core.py", line 828, in _start_proc
    pid = int(file.readline())
ValueError: invalid literal for int() with base 10: ''

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "pw_emu/py/tests/qemu_test.py", line 79, in setUp
    self._emu.start(target='test-target', pause=True)
  File "/usr/local/google/home/tavip/src/pigweed/pw_emu/py/pw_emu/frontend.py", line 100, in start
    self._connector = self._launcher.start(
  File "/usr/local/google/home/tavip/src/pigweed/pw_emu/py/pw_emu/core.py", line 909, in start
    raise err
  File "/usr/local/google/home/tavip/src/pigweed/pw_emu/py/pw_emu/core.py", line 905, in start
    proc = self._start_proc(self._emu, cmd, foreground)
  File "/usr/local/google/home/tavip/src/pigweed/pw_emu/py/pw_emu/core.py", line 831, in _start_proc
    raise RunError(name, str(err))
pw_emu.core.RunError: error running `qemu`: invalid literal for int() with base 10:

To fix this race condition use a temporary file to write the pid than
rename that temporary file to the pid file.

Test: stress --cpu 512 --io 20 and run 1000 iterations of TestQemuChannelsTcp.test_get_channel_addr
Change-Id: I644027246a039b105de7da503af70f9e8d9e6980
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/176782
Commit-Queue: Octavian Purdila <tavip@google.com>
Reviewed-by: Armando Montanez <amontanez@google.com>