Unix Fork 异常行为

Question

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>

int function(void* dat){
    sleep(5);
    printf("Executed Child Process...\n");
    return 5;
}

void dupliFork(int *childpid, int *funcRet, int *func(void*), void* data){
    int id = fork();
    if(id==0) *funcRet = *func(data);
    else *childpid=id;
    printf("Returned dupliFork with id %d\n", id);
}

int main(void){
    int childpid=0, funcRet=0;
    dupliFork(&childpid, &funcRet, function, NULL);
    printf("Waiting for Child Process with id %d...\n", childpid);
    waitpid(childpid, NULL, 0);
    printf("Child Process Terminated with return value %d...\n", funcRet);
}

您好，我无法理解上述代码的工作原理... 执行上面的代码时，我得到输出：

Returned dupliFork with id 4941
Waiting for Child Process with id 4941...
Executed Child Process...
Child Process Terminated with return value 0..."

这非常令人沮丧，因为我期待以下输出：

Returned dupliFork with id 4941
Waiting for Child Process with id 4941...
Executed Child Process...
Returned dupliFork with id 0
Child Process Terminated with return value 5...

这令人沮丧，因为似乎在分叉之后，原始的 duplifork 功能完美运行。但是，它的副本调用另一个函数，并需要 return 值才能继续执行，从来没有那样做。有人可以向我解释一下实际上是什么吗发生在这里？提前谢谢你。

Answer 1

你的函数指针语法错误。

int *func(void*)

应该是：

int (*func)(void*)

和：

if(id==0) *funcRet = *func(data);

应该是：

if(id==0) *funcRet = func(data);

进行这些更改，您将得到类似于：

paul@horus:~/src/sandbox$ ./fork
Returned dupliFork with id 69707
Waiting for Child Process with id 69707...
Executed Child Process...
Returned dupliFork with id 0
Waiting for Child Process with id 0...
Child Process Terminated with return value 5...
Child Process Terminated with return value 0...
paul@horus:~/src/sandbox$

因为除了父进程之外，您还（可能错误地）拥有子进程 wait()。

Unix Fork 异常行为

Unix Fork Strange Behavior

c

unix

fork