一、简介
共享内存为在多个进程之间共享和传递数据提供了一种有效的方式。
但它本身并未提供同步机制。
在实际编程中,可以使用
信号量,
传递消息(使用管道或IPC消息),
生成信号,
条件变量,
等方法来提供读写之间的有效的同步机制。
本例程序使用信号量进行同步,
主要是因为它方便,使用广泛,且独立于进程。
本例程序实现了,
生产者进程:
每次读取YUV输入文件的一帧,
然后将其写到共享内存中。
消费者进程:
每次从共享内存中读到一帧,
处理后,
将其写到输出文件。
两个进程间使用信号量来保证同步处理每一帧。
本例程序很好地示范了共享内存和信号量的机制,
对于实际程序的开发很有意义。
二、生产者进程
common.h
用来设置一些测试用的基本参数。
- /*
- * \File
- * common.h
- */
- #ifndef __COMMON_H__
- #define __COMMON_H__
- #define TEST_FILE "coastguard_cif.yuv"
- #define OUTPUT_FILE "coastguard_cif_trsd.yuv"
- #define FYUV_WIDTH 352
- #define FYUV_HEIGHT 288
- #endif
共享内存相关的头文件。
shm_com.h
- /*
- * \File
- * shm_com.h
- * \Brief
- */
- #ifndef __SHM_COM_H__
- #define __SHM_COM_H__
- #define SHM_SEED 1001
- #define MAX_SHM_SIZE 2048*2048*3
- typedef struct shared_use_st
- {
- int end_flag; //用来标记进程间的内存共享是否结束: 0, 未结束; 1, 结束
- char shm_sp[MAX_SHM_SIZE]; //共享内存的空间
- }shared_use_st;
- #endif
信号量的头文件
semaphore.h
- /*
- * \File
- * semaphore.h
- * \Brief
- * semaphore operation
- */
- #ifndef __SEMAPHORE_H__
- #define __SEMAPHORE_H__
- #define SEM_SEED 1000
- union semun
- {
- int val;
- struct semid_ds *buf;
- unsigned short *array;
- };
- int set_semvalue(int sem_id, int value);
- void del_semvalue(int sem_id);
- int semaphore_p(int sem_id);
- int semaphore_v(int sem_id);
- #endif
帧处理的头文件
frame.h
- /*
- * \File
- * frame.h
- * \Brief
- *
- */
- #ifndef __FRAME_H__
- #define __FRAME_H__
- #include "shm_com.h"
- #define PIX_VALUE 1
- typedef enum
- {
- YUV420,
- YUV422,
- YUV444,
- RGB
- }frame_type_e;
- typedef struct
- {
- int frm_w; // width
- int frm_h; // height
- frame_type_e frm_type;
- int frm_size;
- char *frm_comps;
- }frame_t, *frame_p;
- int init_frame(frame_p frame, int width, int height, frame_type_e type);
- int free_frame(frame_p frame);
- int read_frame_from_file(frame_p frame, FILE* fp);
- int write_frame_into_file(FILE* fp, frame_p frame);
- int read_frame_from_shm(frame_p frame, shared_use_st* shm);
- int write_frame_into_shm(shared_use_st* shm, frame_p frame);
- int crop_frame(frame_p frame, int l_offset, int t_offset, int c_w, int c_h);
- #endif
生产者进程的基本流程:
打开输入文件并初始化帧;
创建并初始化共享内存和信号量;
然后每次读取一帧,
用信号量获取共享内存的权限后,
将读取的帧写入共享内存,
再释放共享内存的权限。
当处理完所有的帧后,
设置结束标志,
并释放相关的资源。
producer.c
- /*
- * \File
- * producer.c
- * \Brief
- * Test shared-memory and message-queue
- */
- #include <stdio.h>
- #include <stdlib.h>
- #include <string.h>
- #include <errno.h>
- #include <unistd.h>
- #include <sys/shm.h>
- #include <sys/sem.h>
- #include "common.h"
- #include "semaphore.h"
- #include "shm_com.h"
- #include "frame.h"
- int main(char argc, char* argv[])
- {
- FILE* fp_in = NULL;
- frame_t frame;
- int frame_cnt = 0;
- int sem_id; // semaphore id
- int shm_id; // shared-memory id
- void* shared_memory = (void*)0;
- shared_use_st* shared_stuff;
- /* Open input file */
- if ((fp_in = fopen(TEST_FILE, "rb")) < 0 )
- {
- printf("Open input file failed: %s\n", TEST_FILE);
- exit(EXIT_FAILURE);
- }
- /* Init frame */
- init_frame(&frame, FYUV_WIDTH, FYUV_HEIGHT, YUV420);
- printf("FRAME: w = %d, h = %d\n", frame.frm_w, frame.frm_h);
- /* Create and init semaphore */
- sem_id = semget((key_t)SEM_SEED, 1, 0666 | IPC_CREAT);
- if (sem_id == -1)
- {
- fprintf(stderr, "semget failed.\n");
- exit(EXIT_FAILURE);
- }
- /* Init shared-memory */
- shm_id = shmget((key_t)SHM_SEED, sizeof(struct shared_use_st), 0666 | IPC_CREAT);
- if (shm_id == -1)
- {
- fprintf(stderr, "shmget failed.\n");
- exit(EXIT_FAILURE);
- }
- shared_memory = shmat(shm_id, (void*)0, 0);
- if (shared_memory == (void*)-1)
- {
- fprintf(stderr, "shmat failed.\n");
- exit(EXIT_FAILURE);
- }
- shared_stuff = (struct shared_use_st*)shared_memory;
- shared_stuff->end_flag = 0;
- printf("FRAME_CNT: %d\n", frame_cnt);
- set_semvalue(sem_id, 1);
- while (read_frame_from_file(&frame, fp_in) == 0)
- {
- semaphore_p(sem_id);
- /* Write it into shared memory */
- write_frame_into_shm(shared_stuff, &frame);
- shared_stuff->end_flag = 0;
-
- semaphore_v(sem_id);
- frame_cnt++;
- printf("FRAME_CNT: %d\n", frame_cnt);
- }
- semaphore_p(sem_id);
- shared_stuff->end_flag = 1;
- semaphore_v(sem_id);
- /* over */
- printf("\nProducer over!\n");
- fclose(fp_in);
- free_frame(&frame);
- del_semvalue(sem_id);
- if (shmdt(shared_memory) == -1)
- {
- fprintf(stderr, "shmdt failed.\n");
- exit(EXIT_FAILURE);
- }
- exit(EXIT_SUCCESS);
- }
三、消费者进程
消费者进程的基本流程:
打开输出文件并初始化帧;
获取共享内存和信号量;
每次
得到共享内存的权限后,
从共享内存中读取一帧并获得结束标志
进行帧处理,
释放共享内存的权限。
直到结束标志为真。
最后释放相关的资源。
consumer.c
- /*
- * \File
- * consumer.c
- * \Brief
- *
- */
- #include <stdio.h>
- #include <stdlib.h>
- #include <string.h>
- #include <errno.h>
- #include <unistd.h>
- #include <sys/shm.h>
- #include <sys/sem.h>
- #include "common.h"
- #include "semaphore.h"
- #include "shm_com.h"
- #include "frame.h"
- int main(char argc, char *argv[])
- {
- FILE* fp_out = NULL;
- frame_t frame;
- int frame_cnt = 0;
- int sem_id; // semaphore id
- int shm_id; // shared-memory id
- void* shared_memory = (void*)0;
- shared_use_st* shared_stuff;
- int end_flag = 0;
- /* Open output file */
- if ((fp_out = fopen(OUTPUT_FILE, "wb")) < 0 )
- {
- printf("Open output file failed: %s\n", OUTPUT_FILE);
- exit(EXIT_FAILURE);
- }
- /* Init frame */
- init_frame(&frame, FYUV_WIDTH, FYUV_HEIGHT, YUV420);
- printf("FRAME: w = %d, h = %d\n", frame.frm_w, frame.frm_h);
- /* Create semaphore */
- sem_id = semget((key_t)SEM_SEED, 1, 0666 | IPC_CREAT);
- if (sem_id == -1)
- {
- fprintf(stderr, "semget failed.\n");
- exit(EXIT_FAILURE);
- }
- /* Init shared-memory */
- shm_id = shmget((key_t)SHM_SEED, sizeof(struct shared_use_st), 0666 | IPC_CREAT);
- if (shm_id == -1)
- {
- fprintf(stderr, "shmget failed.\n");
- exit(EXIT_FAILURE);
- }
- shared_memory = shmat(shm_id, (void*)0, 0);
- if (shared_memory == (void*)-1)
- {
- fprintf(stderr, "shmat failed.\n");
- exit(EXIT_FAILURE);
- }
- shared_stuff = (struct shared_use_st*)shared_memory;
- printf("FRAME_CNT: %d\n", frame_cnt);
- /*
- * 必须先置0,
- * 否则会因生产者进程的异常退出未释放信号量而导致程序出错
- */
- set_semvalue(sem_id, 0);
- do
- {
- semaphore_p(sem_id);
- /* Read frame from shared-memory */
- read_frame_from_shm(&frame, shared_stuff);
- end_flag = shared_stuff->end_flag;
- crop_frame(&frame, 10, 10, 40, 40);
- write_frame_into_file(fp_out, &frame);
- semaphore_v(sem_id);
- frame_cnt++;
- printf("FRAME_CNT: %d\n", frame_cnt);
- } while(!end_flag);
- /* Over */
- printf("\nConsumer over!\n");
- fclose(fp_out);
- free_frame(&frame);
- if (shmdt(shared_memory) == -1)
- {
- fprintf(stderr, "shmdt failed.\n");
- exit(EXIT_FAILURE);
- }
- exit(EXIT_SUCCESS);
- }
四、信号量函数和帧处理函数
信号量函数
semaphore.c
- /*
- * \File
- * semaphore.c
- * \Breif
- *
- */
- #include <stdio.h>
- #include <stdlib.h>
- #include <unistd.h>
- #include <sys/sem.h>
- #include "semaphore.h"
- /* init semaphore by semctl */
- int set_semvalue(int sem_id, int value)
- {
- union semun sem_union;
-
- sem_union.val = value;
- if (semctl(sem_id, 0, SETVAL, sem_union) == -1)
- return 1;
- return 0;
- }
- /* delete semaphore by sectl */
- void del_semvalue(int sem_id)
- {
- union semun sem_union;
- if (semctl(sem_id, 0, IPC_RMID, sem_union) == -1)
- fprintf(stderr, "Failed to delete semaphore\n");
- }
- /* P(v) */
- int semaphore_p(int sem_id)
- {
- struct sembuf sem_b;
- sem_b.sem_num = 0;
- sem_b.sem_op = -1; /* P(v) */
- sem_b.sem_flg = SEM_UNDO;
- if (semop(sem_id, &sem_b, 1) == -1)
- {
- fprintf(stderr, "semaphore_p failed\n");
- return 1;
- }
- return 0;
- }
- /* V(v) */
- int semaphore_v(int sem_id)
- {
- struct sembuf sem_b;
- sem_b.sem_num = 0;
- sem_b.sem_op = 1; // V(v)
- sem_b.sem_flg = SEM_UNDO;
- if (semop(sem_id, &sem_b, 1) == -1)
- {
- fprintf(stderr, "semaphore_v failed\n");
- return 1;
- }
- return 0;
- }
帧处理函数
frame.c
- /*
- * \File
- * frame.c
- */
- #include <stdio.h>
- #include <stdlib.h>
- #include <unistd.h>
- #include <memory.h>
- #include <assert.h>
- #include <errno.h>
- #include "frame.h"
- /*
- * \Brief
- * init frame
- */
- int init_frame(frame_p frame, int width, int height, frame_type_e type)
- {
- assert(frame != NULL);
-
- frame->frm_w = width;
- frame->frm_h = height;
- frame->frm_type = type;
- switch(frame->frm_type)
- {
- case YUV420:
- frame->frm_size = (frame->frm_w * frame->frm_h * 3) / 2;
- break;
- case YUV422:
- frame->frm_size = frame->frm_w * frame->frm_h * 2;
- break;
- case YUV444:
- frame->frm_size = frame->frm_w * frame->frm_h * 3;
- break;
- case RGB:
- frame->frm_size = frame->frm_w * frame->frm_h * 3;
- break;
- default:
- fprintf(stderr, "frame type is invalid.");
- return 1;
- }
- if ((frame->frm_comps = (char*)calloc(frame->frm_size, sizeof(char))) == NULL)
- {
- fprintf(stderr, "calloc failed.");
- return 1;
- }
- return 0;
- }
- /*
- * \Brief
- * init frame
- */
- int free_frame(frame_p frame)
- {
- assert(frame != NULL);
- free(frame->frm_comps);
- return 0;
- }
-
- /*
- * \Brief
- * read a frame from file
- */
- int read_frame_from_file(frame_p frame, FILE* fp)
- {
- int ret;
- assert(frame != NULL && fp != NULL);
- if (ret = (fread(frame->frm_comps, sizeof(char), frame->frm_size, fp))
- != frame->frm_size)
- {
- fprintf(stderr, "read_frame_from_file failed. %d\n", ret);
- return 1;
- }
- return 0;
- }
- /*
- * \Brief
- * write a frame into file
- */
- int write_frame_into_file(FILE* fp, frame_p frame)
- {
- assert(frame != NULL && fp != NULL);
- if (fwrite(frame->frm_comps, sizeof(char), frame->frm_size, fp)
- != frame->frm_size)
- {
- fprintf(stderr, "write_frame_into_file failed.\n");
- return 1;
- }
- return 0;
- }
- /*
- * \Brief
- * read a frame from shared-memory
- */
- int read_frame_from_shm(frame_p frame, shared_use_st* shm)
- {
- assert(frame != NULL && shm != NULL);
- memcpy((char*)frame->frm_comps, (char*)shm->shm_sp, frame->frm_size);
- return 0;
- }
- /*
- * \Brief
- * write a frame into shared-memory
- */
- int write_frame_into_shm(shared_use_st* shm, frame_p frame)
- {
- assert(frame != NULL && shm != NULL);
- memcpy((char*)shm->shm_sp, (char*)frame->frm_comps, frame->frm_size);
- return 0;
- }
- /*
- * \Brief
- * crop frame
- */
- int crop_frame(frame_p frame, int l_offset, int t_offset, int c_w, int c_h)
- {
- char* crop_loc;
- int index_h;
- assert(frame != NULL);
- if ((l_offset + c_w) > frame->frm_w)
- {
- printf("Crop width is out of range.\n");
- return 1;
- }
- if ((t_offset + c_h) > frame->frm_h)
- {
- printf("Crop height is out of range.\n");
- return 1;
- }
- crop_loc = frame->frm_comps + (t_offset * frame->frm_w) + l_offset;
- for (index_h = 0; index_h < c_h; index_h++)
- {
- memset(crop_loc, PIX_VALUE, c_w);
- crop_loc += frame->frm_w;
- }
- return 0;
- }
五、编译与运行
makefile.producer
- OBJECTS = producer.o semaphore.o frame.o
- CC = gcc
- CFLAG = -g -Wa
- producer : $(OBJECTS)
- $(CC) $(CFLAG) -o producer $(OBJECTS)
- producer.o: common.h semaphore.h frame.h shm_com.h
- semaphore.o:semaphore.h
- frame.o: frame.h
- .PHONY:clean
- clean:
- rm producer $(OBJECTS)
makefile.consumer
- OBJECTS = consumer.o semaphore.o frame.o
- CC = gcc
- CFLAG = -g -Wa
- consumer : $(OBJECTS)
- $(CC) $(CFLAG) -o consumer $(OBJECTS)
- consumer.o: common.h semaphore.h frame.h shm_com.h
- semaphore.o:semaphore.h
- frame.o:frame.h
- .PHONY:clean
- clean:
- rm consumer $(OBJECTS)
编译与运行:
- $make -f makefile.producer
- $make -f makefile.consumer
- $producer &
- $consumer
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