From: Antonio Ospite Date: Wed, 3 Apr 2013 15:03:10 +0000 (+0200) Subject: Initial import X-Git-Url: https://git.ao2.it/experiments/double-buffering.git/commitdiff_plain/34c39b440bec3f548cb0d1ecb02cebe46d60db75?ds=inline Initial import --- 34c39b440bec3f548cb0d1ecb02cebe46d60db75 diff --git a/.gitignore b/.gitignore new file mode 100644 index 0000000..ccc5972 --- /dev/null +++ b/.gitignore @@ -0,0 +1,2 @@ +*.o +double-buffering diff --git a/Makefile b/Makefile new file mode 100644 index 0000000..66fc139 --- /dev/null +++ b/Makefile @@ -0,0 +1,44 @@ +CFLAGS = -std=c99 -pedantic -pedantic-errors -Wall -g3 -O2 -D_ANSI_SOURCE_ +CFLAGS += -fno-common \ + -Wall \ + -Wdeclaration-after-statement \ + -Wextra \ + -Wformat=2 \ + -Winit-self \ + -Winline \ + -Wpacked \ + -Wp,-D_FORTIFY_SOURCE=2 \ + -Wpointer-arith \ + -Wlarger-than-65500 \ + -Wmissing-declarations \ + -Wmissing-format-attribute \ + -Wmissing-noreturn \ + -Wmissing-prototypes \ + -Wnested-externs \ + -Wold-style-definition \ + -Wredundant-decls \ + -Wsign-compare \ + -Wstrict-aliasing=2 \ + -Wstrict-prototypes \ + -Wswitch-enum \ + -Wundef \ + -Wunreachable-code \ + -Wunsafe-loop-optimizations \ + -Wunused-but-set-variable \ + -Wwrite-strings + +# for usleep() +CFLAGS += -D_BSD_SOURCE + +# for clock_gettime() +CFLAGS += -D_POSIX_C_SOURCE=199309L + +LDLIBS += -lpthread -lrt + +double-buffering: double-buffering.o + +clean: + rm -rf *~ *.o *.jpg double-buffering + +test: double-buffering + valgrind --leak-check=full --show-reachable=yes ./double-buffering diff --git a/double-buffering.c b/double-buffering.c new file mode 100644 index 0000000..244d576 --- /dev/null +++ b/double-buffering.c @@ -0,0 +1,188 @@ +/* + * double-buffering - an example of double-buffering with pthreads + * + * Copyright (C) 2013 Antonio Ospite + * + * This program is free software: you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation, either version 3 of the License, or + * (at your option) any later version. + * + * This program 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 General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program. If not, see . + */ + +/* + * NOTE: the synchronization scheme used in this program assume that we want + * to consume ALL the buffer produced, exactly ONE time. + * + * In other cases when buffer skipping or buffer duplication in wanted the + * synchronization scheme can change. + */ + +#include +#include +#include +#include +#include +#include +#include + +#define BUFFER_SIZE 10 +#define MAXLEN 1024 + +/* + * The time spent by the producer and the consumer thread is quite predictable + * in this program, this may not be the case when some communication with + * actual hardware influences the production or consumption phase. + */ +#define PRODUCER_DELAY 50000 +#define CONSUMER_DELAY 20000 + +#define NUM_ITERATIONS 23 + +struct buffer { + int *data; + unsigned int size; +}; + +struct double_buffer_context { + struct buffer buffer[2]; + int back_buffer_index; + int font_buffer_is_consumable; + pthread_cond_t front_buffer_cond; + pthread_mutex_t mutex; +}; + +#define BACK_BUFFER(ctx) ((ctx)->buffer[(ctx)->back_buffer_index]) +#define FRONT_BUFFER(ctx) ((ctx)->buffer[(ctx)->back_buffer_index ^ 1]) +#define SWAP_BUFFERS(ctx) ((ctx)->back_buffer_index ^= 1) + +static void do_log(char *message) +{ + struct timespec now; + double timestamp; + + clock_gettime(CLOCK_MONOTONIC, &now); + timestamp = now.tv_sec + now.tv_nsec / 1000000000.0; + fprintf(stderr, "[%f] %s\n", timestamp, message); +} + +/* the consumer thread will only read from the front buffer */ +static void *consumer_cb(void *arg) +{ + struct double_buffer_context *ctx = (struct double_buffer_context *) arg; + unsigned int i; + + char message[MAXLEN]; + int len; + + while(1) { + pthread_mutex_lock(&ctx->mutex); + while (!ctx->font_buffer_is_consumable) { + pthread_cond_wait(&ctx->front_buffer_cond, &ctx->mutex); + } + pthread_mutex_unlock(&ctx->mutex); + + /* consume front buffer */ + len = snprintf(message, MAXLEN, "Consuming value: "); + for (i = 0; i < FRONT_BUFFER(ctx).size; i++) { + len += snprintf(message + len, MAXLEN - len, "%d ", FRONT_BUFFER(ctx).data[i]); + } + usleep(CONSUMER_DELAY); + do_log(message); + + pthread_mutex_lock(&ctx->mutex); + ctx->font_buffer_is_consumable = 0; + pthread_cond_signal(&ctx->front_buffer_cond); + pthread_mutex_unlock(&ctx->mutex); + } + + pthread_exit(0); + return (void *) 0; +} + +int main(void) +{ + int ret; + pthread_t consumer_tid; + struct double_buffer_context *ctx; + + unsigned int iterations; + unsigned int i; + + char message[MAXLEN]; + int len; + + ctx = malloc(sizeof(*ctx)); + if (ctx == NULL) { + perror("malloc"); + exit(EXIT_FAILURE); + } + memset(ctx, 0, sizeof(*ctx)); + + ctx->buffer[0].data = malloc(BUFFER_SIZE * sizeof(*ctx->buffer[0].data)); + ctx->buffer[0].size = BUFFER_SIZE; + ctx->buffer[1].data = malloc(BUFFER_SIZE * sizeof(*ctx->buffer[1].data)); + ctx->buffer[1].size = BUFFER_SIZE; + + ctx->back_buffer_index = 0; + ctx->font_buffer_is_consumable = 0; + pthread_mutex_init(&ctx->mutex, NULL); + pthread_cond_init(&ctx->front_buffer_cond, NULL); + + ret = pthread_create(&consumer_tid, NULL, consumer_cb, (void *)ctx); + if (ret != 0) + { + fprintf(stderr, "can't create thread: %s\n", strerror(ret)); + exit(1); + } + + /* fixed seed, always the same sequence */ + srand(0xa02); + iterations = NUM_ITERATIONS; + while (iterations--) { + /* produce: in the back buffer */ + len = snprintf(message, MAXLEN, "Producing value: "); + for (i = 0; i < BACK_BUFFER(ctx).size; i++) { + BACK_BUFFER(ctx).data[i] = rand(); + len += snprintf(message + len, MAXLEN - len, "%d ", BACK_BUFFER(ctx).data[i]); + } + usleep(PRODUCER_DELAY); + do_log(message); + + pthread_mutex_lock(&ctx->mutex); + while (ctx->font_buffer_is_consumable) { + pthread_cond_wait(&ctx->front_buffer_cond, &ctx->mutex); + } + + SWAP_BUFFERS(ctx); + + /* signal that the front buffer is ready to be consumed */ + ctx->font_buffer_is_consumable = 1; + pthread_cond_signal(&ctx->front_buffer_cond); + + pthread_mutex_unlock(&ctx->mutex); + } + + /* wait for the last consumer run before terminating the thread */ + pthread_mutex_lock(&ctx->mutex); + while (ctx->font_buffer_is_consumable) { + pthread_cond_wait(&ctx->front_buffer_cond, &ctx->mutex); + } + pthread_mutex_unlock(&ctx->mutex); + + pthread_cancel(consumer_tid); + pthread_join(consumer_tid, NULL); + + free(ctx->buffer[1].data); + free(ctx->buffer[0].data); + free(ctx); + + exit(0); +}