Use a temporary file during ReducerTest

[diego-plan9]

Fixes #37558

Use a temporary file instead of /dev/null in ReducerTest, to prevent the chance of unintended deletion when running as root. It seemed that there were no strong side-effects (running time?) by fixing it at the test level, compared to other solutions that involved modifying the behaviour of FileStore (for example, adding an optional flag to avoid auto-deleting the file upon destruction).

Please note this is my first contribution - I have done my best to read the contributing guide and checked for duplicate PRs with no luck, but apologies in advance for any oversights and lack of familiarity with the procedures.

[dr-ci]

💊 CI failures summary and remediations

As of commit e09fe4a (more details on the Dr. CI page):

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• 1/1 failures possibly* introduced in this PR
  • 1/1 non-CircleCI failure(s)

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Extra GitHub checks: 1 failed

• Failed: GitHub Actions - clang-tidy

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This comment has been revised 1 time.

[mrshenli]

Thanks for fixing! This LGTM. FileStore's dtor would delete the temporary file:

pytorch/torch/lib/c10d/FileStore.cpp

Lines 229 to 238 in d035d05

	FileStore::~FileStore() {
	// cleanup key will be different from all rest keys since all rest keys will
	// have a regular prefix.
	auto numFinishedWorker = addHelper(cleanupKey_, 1);
	// The last worker cleans up the file
	if (numFinishedWorker == numWorkers_) {
	// Best effort removal without checking the return
	std::remove(path_.c_str());
	}
	}

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[facebook-github-bot]

@mrshenli merged this pull request in 4d1df74.