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22060f20ae
Make sentinel value configurable in `library/std/src/sys_common/thread_local_key.rs` This is an excerpt of a changeset for the QNX/Neutrino OS. To make the patch for QNX smaller and easier to review, I've extracted this change (which is OS independent). I would be surprised if no other OS is also affected. All this patch does is to define a `const` for a sentinel value instead of using it directly at several places. There are OSs that always return the lowest free value. The algorithm in `lazy_init` always avoids keys with the sentinel value. In affected OSs, this means that each call to `lazy_init` will always request two keys from the OS and returns/frees the first one (with sentinel value) immediately afterwards. By making the sentinel value configurable, affected OSs can use a different value than zero to prevent this performance issue. On QNX/Neutrino, it is planned to use a different sentinel value: ```rust // Define a sentinel value that is unlikely to be returned // as a TLS key (but it may be returned). #[cfg(not(target_os = "nto"))] const KEY_SENTVAL: usize = 0; // On QNX/Neutrino, 0 is always returned when currently not in use. // Using 0 would mean to always create two keys and remote the first // one (with value of 0) immediately afterwards. #[cfg(target_os = "nto")] const KEY_SENTVAL: usize = libc::PTHREAD_KEYS_MAX + 1; ``` It seems like no other OS defines `PTHREAD_KEYS_MAX` in Rusts libc, but `limits.h` on unix systems does. |
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| rtstartup | ||
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| stdarch@790411f93c | ||
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| unwind | ||