调用分叉进程中的读取不起作用（Linux C）
C初学者在这里。 我试图在fork_reducer方法中读取我的reducer_pipes ，但是当我调用read ， read下没有任何read被执行。 如果我不打电话给它，它会被执行。 read方法似乎不打印任何错误消息。
C代码
#include #include #include #include #include #include #include #include #define BUFFER_SIZE 1024 #define ALPHA_OFFSET 97 #define LETTERS 26 const int NUM_OF_MAPPERS = 4; const int NUM_OF_REDUCERS = 26; const int PIPE_READ_END = 0; const int PIPE_WRITE_END = 1; const int PIPE_BUFFER_SIZE = 1000; int mapper_pipes[4][2]; int reducer_pipes[26][2]; void pipe_wrapper(int pipefd[]) { int ret = pipe(pipefd); if (ret == -1) { perror("Error. Failed when trying to create pipes."); exit(EXIT_FAILURE); } } void create_mapper_pipes(void) { int i; for (i = 0; i < NUM_OF_MAPPERS; i++) { pipe_wrapper(mapper_pipes[i]); } } void create_reducer_pipes(void) { int i; for (i=0; i < NUM_OF_REDUCERS; i++) { pipe_wrapper(reducer_pipes[i]); } } // Prints an error msg and exits if one occurs. Else, returns the system call value. int print_if_err(int syscall_val, const char* syscall_name) { if (syscall_val < 0) { perror(syscall_name); exit(errno); } else { //No syscall error we can return return syscall_val; } } void send_chars_to_reducers(char * line) { printf("send_chars_to_reducers read: %s\n\n", line); int i; int ob_size = 2; for (i = 0; i = ALPHA_OFFSET && line[i] < ALPHA_OFFSET + LETTERS) { write(reducer_pipes[line[i]-ALPHA_OFFSET][PIPE_WRITE_END], line[i], ob_size); } } } void close_reducer_pipes(void) { int i; for (i = 0; i < NUM_OF_REDUCERS; i++) { close(reducer_pipes[i][PIPE_WRITE_END]); close(reducer_pipes[i][PIPE_READ_END]); } } void fork_mappers(void) { /* Constants useful to all children */ char ibuf[PIPE_BUFFER_SIZE]; // input pipe buffer int rlen = 0; int i; for (i=0; i<NUM_OF_MAPPERS; i++) { pid_t mapper_pid = print_if_err(fork(), "fork"); if (mapper_pid == 0) { int j; for (j=0; j < NUM_OF_MAPPERS; j++) { close(mapper_pipes[i][PIPE_WRITE_END]); if (j != i) { close(mapper_pipes[j][PIPE_READ_END]); } } rlen = print_if_err(read(mapper_pipes[i][PIPE_READ_END], ibuf, 1000), "read"); send_chars_to_reducers(ibuf); close_reducer_pipes(); printf("forked mapper%d read: %s\n\n", i, ibuf); close(mapper_pipes[i][PIPE_READ_END]); _exit(0); } } } void fork_reducers(void) { printf("HELLLOOOO FROM REDUCER\n"); char ibuf[PIPE_BUFFER_SIZE]; // input pipe buffer int rlen = 0; int i; for (i = 0; i 0) { printf("reducer #%d, read %s\n", i, ibuf); } } } } } void send_lines_to_mappers(void) { int wlen = 0; char obuf[PIPE_BUFFER_SIZE]; int ob_size; int count = 0; char buff[BUFFER_SIZE]; // a buffer for each line of the file FILE *input_file = fopen("input.txt", "r"); // read the input file line by line while(fgets(buff, BUFFER_SIZE, input_file) > 0) { printf("send_lines_to_mappers read: %s\n\n", buff); ob_size = sizeof buff; switch(count) { case 0 : write(mapper_pipes[0][PIPE_WRITE_END], buff, ob_size); close(mapper_pipes[0][PIPE_WRITE_END]); close(mapper_pipes[0][PIPE_READ_END]); break; case 1 : write(mapper_pipes[1][PIPE_WRITE_END], buff, ob_size); close(mapper_pipes[1][PIPE_WRITE_END]); close(mapper_pipes[1][PIPE_READ_END]); break; case 2 : write(mapper_pipes[2][PIPE_WRITE_END], buff, ob_size); close(mapper_pipes[2][PIPE_WRITE_END]); close(mapper_pipes[2][PIPE_READ_END]); break; case 3 : write(mapper_pipes[3][PIPE_WRITE_END], buff, ob_size); close(mapper_pipes[3][PIPE_WRITE_END]); close(mapper_pipes[3][PIPE_READ_END]); break; default : printf("you did something wrong in send_lines_to_mappers loop"); } count++; } fclose(input_file); } int main(void) { // Setup the mapper pipes create_mapper_pipes(); create_reducer_pipes(); fork_reducers(); fork_mappers(); send_lines_to_mappers(); return 0; }
您需要移动while (1)循环内部的read ：
while (1) { printf("hello from while reducer while loop"); rlen = print_if_err(read(reducer_pipes[i][PIPE_READ_END], ibuf, 1000), "read"); if (rlen > 0) { printf("reducer #%d, read %s\n", i, ibuf); } }