The following issue has been SUBMITTED. ====================================================================== https://austingroupbugs.net/view.php?id=1845 ====================================================================== Reported By: ralfjung Assigned To: ====================================================================== Project: 1003.1(2024)/Issue8 Issue ID: 1845 Category: System Interfaces Type: Clarification Requested Severity: Editorial Priority: normal Status: New Name: Ralf Jung Organization: User Reference: Section: exit Page Number: unknown Line Number: unknown Interp Status: --- Final Accepted Text: ====================================================================== Date Submitted: 2024-07-22 16:38 UTC Last Modified: 2024-07-22 16:38 UTC ====================================================================== Summary: Status of the thread-safety of exit is confusing Description: exit is not listed as a thread-unsafe function. It hence seems reasonable to assume that one can call exit concurrently from multiple threads. However, this leads to a SEGFAULT in glibc (https://sourceware.org/bugzilla/show_bug.cgi?id=31997), and the argument of the glibc developers is that their implementation is permitted because the standard says
"If a process calls the exit() function more than once, or calls the quick_exit() function in addition to the exit() function, the behavior is undefined." This is taken directly from the C standard. However, this wording has been in the C standard for a long time, even before there were threads, so it was likely meant to rule out calls to exit from within the atexit handlers. The problem with the glibc interpretation of this wording is that it becomes nearly impossible to call "exit" in a concurrent program, since there is no way to to be sure that there is no other thread (managed by some other library) that may call "exit" at the same time. (This is a particular problem for Rust where being sure that things are safe is a key premise of the language, see https://github.com/rust-lang/rust/issues/126600.) Desired Action: I hope POSIX could clarify that concurrent calls to "exit" are allowed (atexit handlers may run concurrently, which can cause problems, but the concurrent exit calls by themselves cannot be the source of UB). ====================================================================== Issue History Date Modified Username Field Change ====================================================================== 2024-07-22 16:38 ralfjung New Issue 2024-07-22 16:38 ralfjung Name => Ralf Jung 2024-07-22 16:38 ralfjung Section => exit 2024-07-22 16:38 ralfjung Page Number => unknown 2024-07-22 16:38 ralfjung Line Number => unknown ======================================================================
