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musl - an implementation of the standard library for Linux-based systems
dd8f02b7dc
with these changes, in a program that has not created any threads besides the main thread and that has not called f[try]lockfile, getc performs indistinguishably from getc_unlocked. this was measured on several i386 and x86_64 models, and should hold on other archs too simply by the properties of the code generation. the case where the caller already holds the lock (via flockfile) is improved significantly as well (40-60% reduction in time on machines tested) and the case where locking is needed is improved somewhat (roughly 10%). the key technique used here is forcing the non-hot path out-of-line and enabling it to be a tail call. a static noinline function (conditional on __GNUC__) is used rather than the extern hiddens used elsewhere for this purpose, so that the compiler can choose non-default calling conventions, making it possible to tail-call to a callee that takes more arguments than the caller on archs where arguments are passed on the stack or must have space reserved on the stack for spilling the. the tid could just be reloaded via the thread pointer in locking_getc, but that would be ridiculously expensive on some archs where thread pointer load requires a trap or syscall. |
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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/