在调用read在派生进程不工作（Linux下C） [英] Calling read in forked process not working (Linux C)
本文介绍了在调用read在派生进程不工作（Linux下C）的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
Ç初学者在这里。我试图从读我的 reducer_pipes 在 fork_reducer 方法，但是当我打电话读，下没什么<$ C $ C>读被执行。如果我不叫读它得到执行。读出方法不可能在打印任何错误消息。
C $ C $ç
的#include＆LT; SYS / wait.h＆GT;
＃包括LT＆;＆stdbool.h GT;
＃包括LT＆;＆stdio.h中GT;
＃包括LT＆;＆stdlib.h中GT;
＃包括LT＆;＆unistd.h中GT;
＃包括LT＆;＆string.h中GT;
＃包括LT＆;＆time.h中GT;
＃包括LT＆;＆errno.h中GT;的#define BUFFER_SIZE 1024
＃定义ALPHA_OFFSET 97
＃定义快报26const int的NUM_OF_MAPPERS = 4;
const int的NUM_OF_REDUCERS = 26;const int的PIPE_READ_END = 0;
const int的PIPE_WRITE_END = 1;
const int的PIPE_BUFFER_SIZE = 1000;INT mapper_pipes [4] [2];
诠释reducer_pipes [26] [2];无效pipe_wrapper（INT pipefd []）{
INT RET =管（pipefd）;
如果（RET == -1）{
PERROR（错误尝试创建管道时失败。）;
出口（EXIT_FAILURE）;
}
}无效create_mapper_pipes（无效）{
INT I;
对于（i = 0; I＆LT; NUM_OF_MAPPERS;我++）{
pipe_wrapper（mapper_pipes [I]）;
}
}无效create_reducer_pipes（无效）{
INT I;
对于（i = 0; I＆LT; NUM_OF_REDUCERS;我++）{
pipe_wrapper（reducer_pipes [I]）;
}
}//打印错误味精如果发生退出。否则，返回系统调用值。
INT print_if_err（INT syscall_val，为const char * syscall_name）{
如果（syscall_val℃，）{
PERROR（syscall_name）;
退出（错误）;
}其他{
//没有系统调用的错误，我们可以返回
返回syscall_val;
}
}无效send_chars_to_reducers（字符*线）{
的printf（send_chars_to_reducers阅读：％S \\ n \\ n，行）;
INT I;
INT ob_size = 2;
对于（i = 0; I＆LT;的strlen（线）;我++）{
如果（行[I]＆GT; = ALPHA_OFFSET和放大器;＆放大器;线[1] - ; ALPHA_OFFSET +字母）{
写（reducer_pipes [行[I] -ALPHA_OFFSET] [PIPE_WRITE_END]，线[I]，ob_size）;
}
}
}无效close_reducer_pipes（无效）{
INT I;
对于（i = 0; I＆LT; NUM_OF_REDUCERS;我++）{
关闭（reducer_pipes [I] [PIPE_WRITE_END]）;
关闭（reducer_pipes [I] [PIPE_READ_END]）;
}
}无效fork_mappers（无效）{
/ *向所有儿童有益的常量* /
烧焦IBUF [PIPE_BUFFER_SIZE] //输入管道缓冲区
INT RLEN = 0; INT I;
对于（i = 0; I＆LT; NUM_OF_MAPPERS;我++）{
将为pid_t mapper_pid = print_if_err（fork（）的叉）;
如果（mapper_pid == 0）{
诠释J;
为（J = 0; J＆LT; NUM_OF_MAPPERS; J ++）{
关闭（mapper_pipes [I] [PIPE_WRITE_END]）;
如果（J！=ⅰ）{
关闭（mapper_pipes [J] [PIPE_READ_END]）;
}
}
RLEN = print_if_err（读（mapper_pipes [I] [PIPE_READ_END]，IBUF，1000），读）;
send_chars_to_reducers（IBUF）;
close_reducer_pipes（）;
的printf（分叉映射％d个读：％S \\ n \\ n，我，IBUF）;
关闭（mapper_pipes [I] [PIPE_READ_END]）;
_exit（0）;
}
}
}无效fork_reducers（无效）{
的printf（HELLLOOOO从减速\\ n）;
烧焦IBUF [PIPE_BUFFER_SIZE] //输入管道缓冲区
INT RLEN = 0;
INT I;
对于（i = 0; I＆LT; NUM_OF_REDUCERS;我++）{
将为pid_t reducer_pid = print_if_err（fork（）的叉）;
如果（reducer_pid == 0）{
的printf（减速子\\ n的内部）;
RLEN = print_if_err（读（reducer_pipes [I] [PIPE_READ_END]，IBUF，1000），读）;
而（1）{
的printf（你好，从而减速while循环）; 如果（RLEN大于0）{
的printf（减速＃％D，读％S \\ n，我，IBUF）;
} }
}
}
}无效send_lines_to_mappers（无效）{
INT WLEN = 0;
烧焦OBUF [PIPE_BUFFER_SIZE]
INT ob_size;
诠释计数= 0; 字符的buff [BUFFER_SIZE]; //为文件的每一行的缓冲区
FILE * INPUT_FILE =的fopen（input.txt的，R）;
//逐行读取输入文件行
而（与fgets（BUFF，BUFFER_SIZE，INPUT_FILE）0）{
的printf（send_lines_to_mappers阅读：％S \\ n \\ n，浅黄色）;
ob_size = sizeof的爱好者;
开关（计数）{
情况下0：
写（mapper_pipes [0] [PIPE_WRITE_END]，浅黄色，ob_size）;
关闭（mapper_pipes [0] [PIPE_WRITE_END]）;
关闭（mapper_pipes [0] [PIPE_READ_END]）;
打破;
情况1 ：
写（mapper_pipes [1] [PIPE_WRITE_END]，浅黄色，ob_size）;
关闭（mapper_pipes [1] [PIPE_WRITE_END]）;
关闭（mapper_pipes [1] [PIPE_READ_END]）;
打破;
案例2：
写（mapper_pipes [2] [PIPE_WRITE_END]，浅黄色，ob_size）;
关闭（mapper_pipes [2] [PIPE_WRITE_END]）;
关闭（mapper_pipes [2] [PIPE_READ_END]）;
打破;
案例3：
写（mapper_pipes [3] [PIPE_WRITE_END]，浅黄色，ob_size）;
关闭（mapper_pipes [3] [PIPE_WRITE_END]）;
关闭（mapper_pipes [3] [PIPE_READ_END]）;
打破;
默认情况下：
的printf（你做错了什么在send_lines_to_mappers回路）;
}
算上++;
}
FCLOSE（INPUT_FILE）;
}诠释主要（无效）{
//设置映射器管
create_mapper_pipes（）;
create_reducer_pipes（）;
fork_reducers（）;
fork_mappers（）;
send_lines_to_mappers（）; 返回0;
}
解决方案
您需要移动读里面的而（1）循环：
而（1）{
的printf（你好，从而减速while循环）; RLEN = print_if_err（读（reducer_pipes [I] [PIPE_READ_END]，IBUF，1000），读）;
如果（RLEN大于0）{
的printf（减速＃％D，读％S \\ n，我，IBUF）;
} }
C beginner here. I'm trying to read from my reducer_pipes in the fork_reducer method, but when I call read, nothing under the read gets executed. If I don't call read it does get executed. The read method does not appear to be printing any error messages.
C Code
#include <sys/wait.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <time.h>
#include <errno.h>
#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 < strlen(line); i++) {
if (line[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 < NUM_OF_REDUCERS; i++) {
pid_t reducer_pid = print_if_err(fork(), "fork");
if (reducer_pid == 0) {
printf("inside reducer child\n");
rlen = print_if_err(read(reducer_pipes[i][PIPE_READ_END], ibuf, 1000), "read");
while (1) {
printf("hello from while reducer while loop");
if (rlen > 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;
}
解决方案
You need to move the read inside of the while (1) loop:
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);
}
}
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