Remove the |checked| variable because the invalid value of -1 for |flags| can be used to indicate the same condition. Also rename |flags| to |cpu_flags| because there are a local variable and a function parameter named |flags| in the same file.
Add a test program libavutil/tests/cpu_init.c to check whether the one-time initialization in av_get_cpu_flags() has data races. Co-author: Dmitry Vyukov of Google Signed-off-by: Wan-Teh Chang <w...@google.com> --- libavutil/Makefile | 1 + libavutil/cpu.c | 40 ++++++++++++++------------ libavutil/tests/cpu_init.c | 72 ++++++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 94 insertions(+), 19 deletions(-) create mode 100644 libavutil/tests/cpu_init.c diff --git a/libavutil/Makefile b/libavutil/Makefile index 0fa90fe..732961a 100644 --- a/libavutil/Makefile +++ b/libavutil/Makefile @@ -187,6 +187,7 @@ TESTPROGS = adler32 \ camellia \ color_utils \ cpu \ + cpu_init \ crc \ des \ dict \ diff --git a/libavutil/cpu.c b/libavutil/cpu.c index f5785fc..73317c4 100644 --- a/libavutil/cpu.c +++ b/libavutil/cpu.c @@ -44,7 +44,20 @@ #include <unistd.h> #endif -static int flags, checked; +static int cpu_flags = -1; + +static int get_cpu_flags(void) +{ + if (ARCH_AARCH64) + return ff_get_cpu_flags_aarch64(); + if (ARCH_ARM) + return ff_get_cpu_flags_arm(); + if (ARCH_PPC) + return ff_get_cpu_flags_ppc(); + if (ARCH_X86) + return ff_get_cpu_flags_x86(); + return 0; +} void av_force_cpu_flags(int arg){ if ( (arg & ( AV_CPU_FLAG_3DNOW | @@ -69,33 +82,22 @@ void av_force_cpu_flags(int arg){ arg |= AV_CPU_FLAG_MMX; } - flags = arg; - checked = arg != -1; + cpu_flags = arg; } int av_get_cpu_flags(void) { - if (checked) - return flags; - - if (ARCH_AARCH64) - flags = ff_get_cpu_flags_aarch64(); - if (ARCH_ARM) - flags = ff_get_cpu_flags_arm(); - if (ARCH_PPC) - flags = ff_get_cpu_flags_ppc(); - if (ARCH_X86) - flags = ff_get_cpu_flags_x86(); - - checked = 1; + int flags = cpu_flags; + if (flags == -1) { + flags = get_cpu_flags(); + cpu_flags = flags; + } return flags; } void av_set_cpu_flags_mask(int mask) { - checked = 0; - flags = av_get_cpu_flags() & mask; - checked = 1; + cpu_flags = get_cpu_flags() & mask; } int av_parse_cpu_flags(const char *s) diff --git a/libavutil/tests/cpu_init.c b/libavutil/tests/cpu_init.c new file mode 100644 index 0000000..5a5ecda --- /dev/null +++ b/libavutil/tests/cpu_init.c @@ -0,0 +1,72 @@ +/* + * This file is part of FFmpeg. + * + * FFmpeg is free software; you can redistribute it and/or + * modify it under the terms of the GNU Lesser General Public + * License as published by the Free Software Foundation; either + * version 2.1 of the License, or (at your option) any later version. + * + * FFmpeg is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + * Lesser General Public License for more details. + * + * You should have received a copy of the GNU Lesser General Public + * License along with FFmpeg; if not, write to the Free Software + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA + */ + +/* + * This test program tests whether the one-time initialization in + * av_get_cpu_flags() has data races. + */ + +#include <stdio.h> +#include <string.h> + +#include "config.h" + +#include "libavutil/cpu.h" +#include "libavutil/thread.h" + +#if HAVE_PTHREADS +static void *thread_main(void *arg) +{ + int *flags = arg; + + *flags = av_get_cpu_flags(); + return NULL; +} +#endif + + +int main(int argc, char **argv) +{ +#if HAVE_PTHREADS + int cpu_flags1; + int cpu_flags2; + int ret; + pthread_t thread1; + pthread_t thread2; + + if ((ret = pthread_create(&thread1, NULL, thread_main, &cpu_flags1))) { + fprintf(stderr, "pthread_create failed: %s.\n", strerror(ret)); + return 1; + } + if ((ret = pthread_create(&thread2, NULL, thread_main, &cpu_flags2))) { + fprintf(stderr, "pthread_create failed: %s.\n", strerror(ret)); + return 1; + } + pthread_join(thread1, NULL); + pthread_join(thread2, NULL); + + if (cpu_flags1 < 0) + return 2; + if (cpu_flags2 < 0) + return 2; + if (cpu_flags1 != cpu_flags2) + return 3; +#endif + + return 0; +} -- 2.8.0.rc3.226.g39d4020 _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel