[Issue 23624] New: Race condition in test runner for DMD

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=23624

          Issue ID: 23624
           Summary: Race condition in test runner for DMD
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P1
         Component: tools
          Assignee: nobody at puremagic.com
          Reporter: tim.dlang at t-online.de

The test runner for DMD uses parallel foreach
(https://github.com/dlang/dmd/blob/deb039f5f6740d4df0f09226d4ee02c450f75658/compiler/test/run.d#L189):

        foreach (target; parallel(targets, 1))
        {
            log("run: %-(%s %)", target.args);
            int status = spawnProcess(target.args, env, Config.none,
scriptDir).wait;
            if (status != 0)
            {
                const string name = target.filename
                            ? target.normalizedTestName
                            : "`unit` tests";

                writeln(">>> TARGET FAILED: ", name);
                failedTargets ~= name;
            }
        }

Appending to failedTargets inside the loop body could be a race condition,
because parallel can run the loop body from different threads. This could
result in a wrong value for failedTargets or crash the test runner.

I don't know if this happens in practice, though.

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