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POhow the system call read and write behave and why the threads cannot work?
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2012-03-10T09:24:28.163
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fifo.3 source code: <pre><code> #include <unistd.h> #include <stdlib.h> #include <stdio.h> #include <string.h> #include <fcntl.h> #include <limits.h> #include <sys/types.h> #include <sys/stat.h> #include <pthread.h> #include <time.h> #define FIFO_NAME "/tmp/my_fifo" #define BUFFER_SIZE PIPE_BUF //4096 #define TEN_MEG (1024 * 1024 * 1) void* thread_tick(void* arg) { int count =0; while(count < 4){ printf("hello, world!\n"); sleep(1); count++; } } void* thread_write(void* arg) { int pipe_fd; int res; int bytes_sent = 0; char buffer[BUFFER_SIZE ]; int count=0; if (access(FIFO_NAME, F_OK) == -1) { res = mkfifo(FIFO_NAME, 0777); if (res != 0) { fprintf(stderr, "Could not create fifo %s\n", FIFO_NAME); exit(EXIT_FAILURE); } } while(count < 10){ printf("write: Process %d opening FIFO O_WRONLY\n", getpid()); pipe_fd = open(FIFO_NAME, O_WRONLY); printf("write: Process %d result %d \n", getpid(), pipe_fd); if (pipe_fd != -1) { while(bytes_sent < TEN_MEG) { res = write(pipe_fd, buffer, BUFFER_SIZE); if (res == -1) { fprintf(stderr, "Write error on pipe\n"); exit(EXIT_FAILURE); } bytes_sent += res; } (void)close(pipe_fd); } else { exit(EXIT_FAILURE); } printf("write: Process %d finished , count =%d\n", getpid(),count); count++; } } void CreateThread(void* (*start_routine)(void*), void* arg,int stacksize, int priority) { pthread_t app_thread; pthread_attr_t thread_attr; int res; int max_priority; int min_priority; struct sched_param scheduling_value; res = pthread_attr_init(&thread_attr); if (res != 0) { perror("Attribute creation failed\n"); exit(EXIT_FAILURE); } res = pthread_attr_setdetachstate(&thread_attr, PTHREAD_CREATE_DETACHED); if (res != 0) { perror("Setting detached attribute failed"); exit(EXIT_FAILURE); } res = pthread_attr_setstacksize(&thread_attr, stacksize); if (res != 0) { perror("Set stack size failed\n"); exit(EXIT_FAILURE); } res = pthread_attr_setschedpolicy(&thread_attr, SCHED_RR); if (res != 0) { perror("Setting schedpolicy failed"); exit(EXIT_FAILURE); } max_priority = sched_get_priority_max(SCHED_RR); min_priority = sched_get_priority_min(SCHED_RR); scheduling_value.sched_priority = priority; res = pthread_attr_setschedparam(&thread_attr, &scheduling_value); if (res != 0) { perror("Setting schedpolicy failed"); exit(EXIT_FAILURE); } res = pthread_create(&app_thread, &thread_attr, (*start_routine), arg); if(res != 0){ perror("Thread creation failed\n"); exit(EXIT_FAILURE); } pthread_attr_destroy(&thread_attr); //res = pthread_join(app_thread ,0 ); //return app_thread; } int main() { CreateThread(thread_write, 0, 50000, 99); CreateThread(thread_tick, 0, 50000, 98); // pthread_join(w,0 ); // pthread_join(t ,0 ); return 0; } </code></pre> fifo.4 source code : <pre><code> #include <unistd.h> #include <stdlib.h> #include <stdio.h> #include <string.h> #include <fcntl.h> #include <limits.h> #include <sys/types.h> #include <sys/stat.h> #define FIFO_NAME "/tmp/my_fifo" #define BUFFER_SIZE PIPE_BUF //4096 int main() { int pipe_fd; int res; char buffer[BUFFER_SIZE ]; int bytes_read = 0; int count = 0; memset(buffer, '\0', sizeof(buffer)); while(count < 10){ printf("read: Process %d opening FIFO O_RDONLY\n", getpid()); pipe_fd = open(FIFO_NAME, O_RDONLY); printf("read: Process %d result %d\n", getpid(), pipe_fd); if (pipe_fd != -1) { do { res = read(pipe_fd, buffer, BUFFER_SIZE); bytes_read += res; } while (res > 0); (void)close(pipe_fd); } else { exit(EXIT_FAILURE); } printf("read: Process %d finished, %d bytes read , count =%d\n", getpid(), bytes_read,count); count++; } return 0; } </code></pre> this is the first time I post code on Stack overflow, so it is in a mess. Above are two C source code. fifo3.c has two thread and thread_write is to write data to named fifo. fifo4.c is to read data from named fifo. my question: 1) how does the read(pipe_fd, buffer, BUFFER_SIZE) behave when write() is writing data to fifo? If read() can not read data, SHOULD not read() return 0 and then exit, why read() would wait write() to finish write data??? of course, how does write() behave when read() is reading? 2) in fifo3.c , I create two threads, when I create them detached , the program can not run !!! but joinable, they could run correctly ！！I do not know why! In theory, they both could function right.
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how the system call read and write behave and why the threads cannot work?
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