From 17566573b2997e468cb4190c6853b1ebea125962 Mon Sep 17 00:00:00 2001 From: Paula Toth Date: Tue, 17 Mar 2020 12:59:21 -0700 Subject: [PATCH] [libc] Resolve race condition in sub-process test runner. Summary: There seems to be a race condition between the pipe closing and the child process death. Likely these two events are not atomic on some versions of linux. With the removal of `WNOHANG` we eliminate the race condition, however if the child closes the pipe intentionally then it could result in the test runner hanging. I find this situation less likely, where as I experience failures locally with this race condition rather consistently. Reviewers: sivachandra, abrachet Reviewed By: sivachandra, abrachet Subscribers: MaskRay, jfb, tschuett, libc-commits Tags: #libc-project Differential Revision: https://reviews.llvm.org/D76267 --- libc/utils/testutils/ExecuteFunctionUnix.cpp | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/libc/utils/testutils/ExecuteFunctionUnix.cpp b/libc/utils/testutils/ExecuteFunctionUnix.cpp index e920e50..1ddb24d 100644 --- a/libc/utils/testutils/ExecuteFunctionUnix.cpp +++ b/libc/utils/testutils/ExecuteFunctionUnix.cpp @@ -67,8 +67,12 @@ ProcessStatus invokeInSubprocess(FunctionCaller *Func, unsigned timeoutMS) { } int WStatus = 0; - int status = ::waitpid(Pid, &WStatus, WNOHANG); - assert(status == Pid && "wait call should not block here"); + // Wait on the pid of the subprocess here so it gets collected by the system + // and doesn't turn into a zombie. + pid_t status = ::waitpid(Pid, &WStatus, 0); + if (status == -1) + return ProcessStatus::Error("waitpid(2) failed"); + assert(status == Pid); (void)status; return {WStatus}; } -- 1.8.3.1