如何在C中按顺序执行子进程
我已经用C写了一个代码来计算文件中的行、字和字符。类似于如何在C中按顺序执行子进程,c,process,fork,C,Process,Fork,我已经用C写了一个代码来计算文件中的行、字和字符。类似于wc命令。代码如下，运行良好 #include <stdio.h> #include <string.h> #include <unistd.h> #include <errno.h> #include <string.h> #include <stdlib.h> char* concat(char *s1, char *s2) { char *result = ma
wc#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <stdlib.h>
char* concat(char *s1, char *s2)
{
char *result = malloc(strlen(s1)+strlen(s2)+1);
strcpy(result, s1);
strcat(result, s2);
return result;
}
int countLines(char *f){
FILE *file = fopen(f, "r");
int count = 0;
char ch;
while ((ch = fgetc(file)) != EOF){
if (ch == '\n')
count++;
}
return count;
}
int countWords(char *f){
char buffer[1];
FILE *file = fopen(f, "r");
int countW = 0;
enum states { WSP, WRD };
int state = WSP;
char last = ' ';
while (read(fileno(file),buffer,1) == 1 )
{
if ( buffer[0]== ' ' || buffer[0] == '\t' || buffer[0]=='\n' )
{
state = WSP;
}
else
{
if ( state == WSP )
{
countW++;
}
state = WRD;
}
last = buffer[0];
}
return countW;
}
int countChars(char *f){
FILE *file = fopen(f, "r");
int chars = 0;
char ch;
while ((ch = fgetc(file))){
if (ch == EOF) break;
chars++;
}
return chars;
}
int main(int argc, char** argv)
{
int lineCount = 0;
int wordCount = 0;
int charCount = 0;
int n = 3;
int i,status;
int pids[3];
char *theprogram = argv[0];
char *thefile = argv[1];
if ( argc !=2 )
{
printf( "Help: %s filename\n", argv[0]);
}
else{
FILE *file = fopen( argv[1], "r");
if(file == 0){
char *sub = concat(theprogram, ": ");
char *middle = concat(sub, thefile);
perror(middle);
}
else{
for (i = 0; i < n; i++) {
pids[i] = fork();
if ( pids[i] < 0) {
perror("fork");
exit(-1);
} else if (pids[i] == 0) {
if (i==0){
lineCount = countLines(argv[1]);
printf("This is child proccess %d, and the number of lines is %d\n", i+1, lineCount);
exit(0);
}
else if (i==1){
wordCount = countWords(argv[1]);
printf("This is child proccess %d, and the number of words is %d\n", i+1, wordCount);
exit(0);
}
else if (i==2){
charCount += countChars(argv[1]);
printf("This is child proccess %d, and the number of characters is %d\n", i+1, charCount);
exit(0);
}
}
}
for(i = 0; i < n; i++){
wait(NULL);
}
return 0;
}
}
}
第三个过程有时在第二个过程之前结束。如何防止这种情况发生？分叉的进程将与主线代码异步执行，因此如果希望它们按顺序执行，则需要使用某种标志。这可以是一个信号量、互斥量，或者在if条件中设置一个布尔值
您需要使用信号量或互斥量来保护易受影响的数据不受异步写入的影响，但这在本文中不是问题。分叉的进程将与主线代码异步执行，因此如果您希望它们按顺序发生，则需要使用某种标志。这可以是一个信号量、互斥量，或者在if条件中设置一个布尔值
您可能需要使用信号量或互斥来保护易受影响的数据不受异步写入的影响，但在这种情况下这不是问题。我认为您可以使用线程而不是进程，初始化一些全局变量并在子线程中分配变量值。控制父线程中的输出。我认为您可以使用线程而不是进程，初始化一些全局变量并在子线程中分配变量值。控制父线程中的输出。快速脏方法：
} else if (pids[i] == 0) {
usleep(i*1000); /* wait 1ms for child 1, 2ms for child 2,... */
if (i==0){
lineCount = countLines(argv[1]);
printf("This is child proccess %d, and the number of lines is %d\n", i+1, lineCount);
exit(0);
}
else if (i==1){
wordCount = countWords(argv[1]);
printf("This is child proccess %d, and the number of words is %d\n", i+1, wordCount);
exit(0);
}
else if (i==2){
charCount += countChars(argv[1]);
printf("This is child proccess %d, and the number of characters is %d\n", i+1, charCount);
exit(0);
}
}
另一种方法是让父进程创建三个UNIX套接字，并使用
select（） } else if (pids[i] == 0) {
usleep(i*1000); /* wait 1ms for child 1, 2ms for child 2,... */
if (i==0){
lineCount = countLines(argv[1]);
printf("This is child proccess %d, and the number of lines is %d\n", i+1, lineCount);
exit(0);
}
else if (i==1){
wordCount = countWords(argv[1]);
printf("This is child proccess %d, and the number of words is %d\n", i+1, wordCount);
exit(0);
}
else if (i==2){
charCount += countChars(argv[1]);
printf("This is child proccess %d, and the number of characters is %d\n", i+1, charCount);
exit(0);
}
}
另一种方法是让父进程创建三个UNIX套接字，并使用
select（）