考虑这个替代代码,它可以更好地跟踪发生的事情:
#include <stdio.h>
#include <unistd.h>
int main(void)
{
int ret1 = fork();
int ret2 = fork();
int ret3 = fork();
int ret4 = fork();
if (ret4 == 0)
printf("one: (%d: %d, %d, %d, %d)\n", (int)getpid(), ret1, ret2, ret3, ret4);
else
printf("two: (%d: %d, %d, %d, %d)\n", (int)getpid(), ret1, ret2, ret3, ret4);
return 0;
}
向我们展示此变体的输出,我们可以看到哪些有效,哪些失败。
在看到替代输出后,我在我的 Mac 上得到了这个(其中 Isis JL:
是我的提示,rmk
是 make
的替代实现):
Isis JL: rmk fb && ./fb
/usr/bin/gcc -O3 -g -std=c99 -Wall -Wextra fb.c -o fb
two: (38068: 38069, 38070, 38071, 38072)
one: (38072: 38069, 38070, 38071, 0)
two: (38071: 38069, 38070, 0, 38075)
two: (38070: 38069, 0, 38074, 38077)
two: (38073: 0, 0, 38078, 38079)
two: (38069: 0, 38073, 38076, 38080)
one: (38075: 38069, 38070, 0, 0)
one: (38077: 38069, 0, 38074, 0)
Isis JL: two: (38074: 38069, 0, 0, 38081)
two: (38078: 0, 0, 0, 38082)
one: (38079: 0, 0, 38078, 0)
one: (38081: 38069, 0, 0, 0)
two: (38076: 0, 38073, 0, 38083)
one: (38080: 0, 38073, 38076, 0)
one: (38083: 0, 38073, 0, 0)
one: (38082: 0, 0, 0, 0)
Isis JL:
注意交错的提示——最后的空白行是我在输出完成后按回车键的地方。
假设:
ideone 上的输出在初始进程停止后未被捕获。
试试这个替代方案,它在退出之前等待 child 死亡:
#include <stdio.h>
#include <unistd.h>
#include <sys/wait.h>
int main(void)
{
int ret1 = fork();
int ret2 = fork();
int ret3 = fork();
int ret4 = fork();
if (ret4 == 0)
printf("one: (%d: %d, %d, %d, %d)\n", (int)getpid(), ret1, ret2, ret3, ret4);
else
printf("two: (%d: %d, %d, %d, %d)\n", (int)getpid(), ret1, ret2, ret3, ret4);
while (wait(0) > 0)
;
return 0;
}
再次在 Mac 上输出:
Isis JL: rmk fb && ./fb
/usr/bin/gcc -O3 -g -std=c99 -Wall -Wextra fb.c -o fb
two: (38111: 38112, 38113, 38114, 38115)
one: (38115: 38112, 38113, 38114, 0)
two: (38114: 38112, 38113, 0, 38119)
two: (38113: 38112, 0, 38117, 38121)
two: (38117: 38112, 0, 0, 38123)
one: (38119: 38112, 38113, 0, 0)
two: (38118: 0, 38116, 0, 38124)
one: (38121: 38112, 0, 38117, 0)
one: (38125: 0, 0, 38122, 0)
two: (38116: 0, 0, 38122, 38125)
two: (38122: 0, 0, 0, 38126)
two: (38112: 0, 38116, 38118, 38120)
one: (38120: 0, 38116, 38118, 0)
one: (38123: 38112, 0, 0, 0)
one: (38124: 0, 38116, 0, 0)
one: (38126: 0, 0, 0, 0)
Isis JL:
假设证明
只要你能证明任何事... http://ideone.com/zFoLn ...
这显示了所有 16 行输出。问题一定是“过早终止”。