mirror of
git://sourceware.org/git/glibc.git
synced 2025-04-12 14:21:18 +08:00
5bc7f09005
The current timer_create SIGEV_THREAD implementation has some
downsides:
1. There is no way to report failure at thread creation when a
timer triggers. It means that it might occur unreported and with
missed events depending of the system load.
2. The backgroup thread also kept in backgroun even when there is no
more timers, consuming resources and also misleading memory
profile tools (BZ 29705).
3. There is a lot of metadata that required to be kept: a control
variable for helper thread creation, a list of active SIGEV_THREAD
timers, atfork handlers to cleanup the list.
4. timer_create does not propagate all thread attributes to the new
thread (BZ 27895).
5. Kernel might deliver in-flight events for a timer after it was
destroyed by timer_delete. The timer_helper_thread mechanism to
handle it does not cover all possible issue, which leads to
callbacks being wrong triggered (BZ 32833).
This new implementation moves the thread creation to timer_create, so
any failure is reported to the caller. Also, the same thread will
issues the multiple timers, thus there is no unreported missed events.
Also, avoiding parallel timer activation also avoid possible parallel
timer invocation to see the same overrun value.
To implement using SIGTIMER internally as SIGCANCEL, it requires to
mask out SIGCANCEL on thread creation. It essentially disable async
thread cancellation, but POSIX requires that SIGEV_THREAD is always
created in detached mode and cancelling detached thread s UB (glibc
check the internal tid, but the memory referenced by pthread_t might
not always be valid as the momento of pthread_cancel call).
And to avoid the need to recreate the thread for pthread_exit call
(and having possible unreported missed due failed thread creation),
the SIGEV_THREAD install a cleanup handler that reset all internal
thread state.
It also prevents the re-use issue when a newly-allocated timer has
in-flight event being delivered by the kernel (BZ 32833).
Performance-wise it see it uses less CPU timer for multiple thread
activation, although each thread now requires a sigwaitinfo which
generate more context-switches/page-faults (check comment 7 from
BZ 30558). I would expect that latency should improve, since it
avoid a thread creation for each timer expiration.
Checked on x86_64-linux-gnu and i686-linux-gnu.
This directory contains the sources of the GNU C Library. See the file "version.h" for what release version you have. The GNU C Library is the standard system C library for all GNU systems, and is an important part of what makes up a GNU system. It provides the system API for all programs written in C and C-compatible languages such as C++ and Objective C; the runtime facilities of other programming languages use the C library to access the underlying operating system. In GNU/Linux systems, the C library works with the Linux kernel to implement the operating system behavior seen by user applications. In GNU/Hurd systems, it works with a microkernel and Hurd servers. The GNU C Library implements much of the POSIX.1 functionality in the GNU/Hurd system, using configurations i[4567]86-*-gnu and x86_64-gnu. When working with Linux kernels, this version of the GNU C Library requires Linux kernel version 3.2 or later. Also note that the shared version of the libgcc_s library must be installed for the pthread library to work correctly. The GNU C Library supports these configurations for using Linux kernels: aarch64*-*-linux-gnu alpha*-*-linux-gnu arc*-*-linux-gnu arm-*-linux-gnueabi csky-*-linux-gnuabiv2 hppa-*-linux-gnu i[4567]86-*-linux-gnu x86_64-*-linux-gnu Can build either x86_64 or x32 loongarch64-*-linux-gnu Hardware floating point, LE only. m68k-*-linux-gnu microblaze*-*-linux-gnu mips-*-linux-gnu mips64-*-linux-gnu or1k-*-linux-gnu powerpc-*-linux-gnu Hardware or software floating point, BE only. powerpc64*-*-linux-gnu Big-endian and little-endian. s390-*-linux-gnu s390x-*-linux-gnu riscv32-*-linux-gnu riscv64-*-linux-gnu sh[34]-*-linux-gnu sparc*-*-linux-gnu sparc64*-*-linux-gnu If you are interested in doing a port, please contact the glibc maintainers; see https://www.gnu.org/software/libc/ for more information. See the file INSTALL to find out how to configure, build, and install the GNU C Library. You might also consider reading the WWW pages for the C library at https://www.gnu.org/software/libc/. The GNU C Library is (almost) completely documented by the Texinfo manual found in the `manual/' subdirectory. The manual is still being updated and contains some known errors and omissions; we regret that we do not have the resources to work on the manual as much as we would like. For corrections to the manual, please file a bug in the `manual' component, following the bug-reporting instructions below. Please be sure to check the manual in the current development sources to see if your problem has already been corrected. Please see https://www.gnu.org/software/libc/bugs.html for bug reporting information. We are now using the Bugzilla system to track all bug reports. This web page gives detailed information on how to report bugs properly. The GNU C Library is free software. See the file COPYING.LIB for copying conditions, and LICENSES for notices about a few contributions that require these additional notices to be distributed. License copyright years may be listed using range notation, e.g., 1996-2015, indicating that every year in the range, inclusive, is a copyrightable year that would otherwise be listed individually.