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the kernel always uses non-private wake when walking the robust list when a thread or process exits, so it's not able to wake waiters listening with the private futex flag. this problem is solved by doing the equivalent in userspace as the last step of pthread_exit. care is taken to remove mutexes from the robust list before unlocking them so that the kernel will not attempt to access them again, possibly after another thread locks them. this removal code can treat the list as singly-linked, since no further code which would add or remove items is able to run at this point. moreover, the pending pointer is not needed since the mutexes being unlocked are all process-local; in the case of asynchronous process termination, they all cease to exist. since a process-local robust mutex cannot come into existence without a call to pthread_mutexattr_setrobust in the same process, the code for userspace robust list processing is put in that source file, and a weak alias to a dummy function is used to avoid pulling in this bloat as part of pthread_exit in static-linked programs.
musl libc
musl, pronounced like the word "mussel", is an MIT-licensed
implementation of the standard C library targetting the Linux syscall
API, suitable for use in a wide range of deployment environments. musl
offers efficient static and dynamic linking support, lightweight code
and low runtime overhead, strong fail-safe guarantees under correct
usage, and correctness in the sense of standards conformance and
safety. musl is built on the principle that these goals are best
achieved through simple code that is easy to understand and maintain.
The 1.1 release series for musl features coverage for all interfaces
defined in ISO C99 and POSIX 2008 base, along with a number of
non-standardized interfaces for compatibility with Linux, BSD, and
glibc functionality.
For basic installation instructions, see the included INSTALL file.
Information on full musl-targeted compiler toolchains, system
bootstrapping, and Linux distributions built on musl can be found on
the project website:
http://www.musl-libc.org/