fork函数实验总结
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针对fork函数难以理解，根据网上的解释，参考他人代码，做了如下实验，并附以实验分析
2 #include
3 #include
4 #include
5 #include
6 #include
7
8 int main ()
9 {
10 pid_t pc,pr;
11 pc=fork();
(gdb)
12
13 if (pc<0)
14 {
15 printf("error fork.\n");
16
17 }
18 else if (pc==0)
19 {
20 printf("this is pc=%d\n",getpid());
21 sleep(5);
(gdb)
22 printf("5 s over\n");
23 //exit(0);
24 }
25 pr=fork();
26 if (pr==0)
27 {
28 printf("this is pr =%d\n",getpid());
29 }
30
31 else if (pr>0&&pc>0)
(gdb)
32 printf("this is main =%d",getpid());
33
34
35
36
37
38 }
(gdb) b 12
Breakpoint 1 at 0x804849d: file /home/lsp/fork3.c, line 12.
(gdb) b 19
Breakpoint 2 at 0x80484b7: file /home/lsp/fork3.c, line 19.
(gdb) b 24
Breakpoint 3 at 0x80484e4: file /home/lsp/fork3.c, line 24.
(gdb) b 26
Breakpoint 4 at 0x80484ec: file /home/lsp/fork3.c, line 26.
(gdb) run
Starting program: /home/lsp/fork3
Detaching after fork from child process 13200. ---说明pc=fork（）函数已经建立子进程
this is pc=13200
Breakpoint 1, main () at /home/lsp/fork3.c:13
13 if (pc<0)
(gdb) 5 s over
this is pr =13201 --说明pc=fork（）进程13200启动了新的子进程pr 其pid=13201
next
Breakpoint 3, main () at /home/lsp/fork3.c:25
25 pr=fork(); --父进程停在pr=fork（）处，
(gdb) next
Detaching after fork from child process 13254.
this is pr =13254 --此处pr的pid=13254 与上一个pr=13201不同，这说明此处的pr是由main创建的
Breakpoint 4, main () at /home/lsp/fork3.c:26
26 if (pr==0)
(gdb) next
31 else if (pr>0&&pc>0)
(gdb) next
32 printf("this is main =%d",getpid());
(gdb) next
38 }
(gdb) next
0x00a6d5d6 in __libc_start_main () from /lib/libc.so.6
(gdb) next
Single stepping until exit from function __libc_start_main,
which has no line number information.
this is main =13199 ---main函数退出，器pid=13199
Program exited with code 023.
(gdb)
小结：这段代码总共有4个进程，pid分别为
13199--main这个父进程自身的pid
13200--main这个父进程建立的pc进程pid=13200
13201--pc这个子进程创建的子进程，即main的孙进程pr
13254--main这个父进程创建的子进程pr 此处的pr与上一处pc创建的不同，从其pid上可做区别。
这说明fork的工作原理：
1.pc=fork（）函数创建自身时复制了如下代码段
12
13 if (pc<0)
14 {
15 printf("error fork.\n");
16
17 }
18 else if (pc==0)
19 {
20 printf("this is pc=%d\n",getpid());
21 sleep(5);
(gdb)
22 printf("5 s over\n");
23 //exit(0);
24 }
25 pr=fork();
26 if (pr==0)
27 {
28 printf("this is pr =%d\n",getpid());
29 }
30
31 else if (pr>0&&pc>0)
(gdb)
32 printf("this is main =%d",getpid());
33
34
35
36
37
38 }
2.pr=fork（）函数创建自身时复制了如下代码段：
26 if (pr==0)
27 {
28 printf("this is pr =%d\n",getpid());
29 }