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Locking overhead can be significant in some stdio operations that are common in single threaded applications. This patch adds the _IO_FLAGS2_NEED_LOCK flag to indicate if an _IO_FILE object needs to be locked and some of the stdio functions just jump to their _unlocked variant when not. The flag is set on all _IO_FILE objects when the first thread is created. A new GLIBC_PRIVATE libc symbol, _IO_enable_locks, was added to do this from libpthread. The optimization can be applied to more stdio functions, currently it is only applied to single flag check or single non-wide-char standard operations. The flag should probably be never set for files with _IO_USER_LOCK, but that's just a further optimization, not a correctness requirement. The optimization is valid in a single thread because stdio operations are non-as-safe (so lock state is not observable from a signal handler) and stdio locks are recursive (so lock state is not observable via deadlock). The optimization is not valid if a thread may be created while an stdio lock is taken and thus it should be disabled if any user code may run during an stdio operation (interposed malloc, printf hooks, etc). This makes the optimization more complicated for some stdio operations (e.g. printf), but those are bigger and thus less important to optimize so this patch does not try to do that. * libio/libio.h (_IO_FLAGS2_NEED_LOCK, _IO_need_lock): Define. * libio/libioP.h (_IO_enable_locks): Declare. * libio/Versions (_IO_enable_locks): New symbol. * libio/genops.c (_IO_enable_locks): Define. (_IO_old_init): Initialize flags2. * libio/feof.c.c (_IO_feof): Avoid locking when not needed. * libio/ferror.c (_IO_ferror): Likewise. * libio/fputc.c (fputc): Likewise. * libio/putc.c (_IO_putc): Likewise. * libio/getc.c (_IO_getc): Likewise. * libio/getchar.c (getchar): Likewise. * libio/ioungetc.c (_IO_ungetc): Likewise. * nptl/pthread_create.c (__pthread_create_2_1): Enable stdio locks. * libio/iofopncook.c (_IO_fopencookie): Enable locking for the file. * sysdeps/pthread/flockfile.c (__flockfile): Likewise. |
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| assert | ||
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| bits | ||
| catgets | ||
| conform | ||
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| dev | ||
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| malloc | ||
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| stdlib | ||
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| support | ||
| sysdeps | ||
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| configure | ||
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| CONFORMANCE | ||
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| Makeconfig | ||
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| Rules | ||
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| version.h | ||
| WUR-REPORT | ||
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. The current GNU/Hurd support requires out-of-tree patches that will eventually be incorporated into an official GNU C Library release. 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 arm-*-linux-gnueabi hppa-*-linux-gnu Not currently functional without patches. i[4567]86-*-linux-gnu x86_64-*-linux-gnu Can build either x86_64 or x32 ia64-*-linux-gnu m68k-*-linux-gnu microblaze*-*-linux-gnu mips-*-linux-gnu mips64-*-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 sh[34]-*-linux-gnu sparc*-*-linux-gnu sparc64*-*-linux-gnu tilegx-*-linux-gnu tilepro-*-linux-gnu If you are interested in doing a port, please contact the glibc maintainers; see http://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 http://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 http://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.