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电梯直达

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发表于 2017-01-02 10:26 |只看该作者 |倒序浏览

最近遇到这样的一个奇怪错误:

#include<stdio.h>
#include<unistd.h>
int main()
{
int* pi=new int(5);
int i=5;
pid_t id=vfork();
if(id>0)//father
{
      *pi=4;
      i=4;
      printf("father set i=%d, *pi=%d\n",i, *pi);
      sleep(2);
      printf("father get i=%d, *pi=%d\n",i, *pi);
      delete pi;
}
else//child
{
      sleep(1);
      printf("child get i=%d, *pi=%d\n",i, *pi);
      i=3;
      *pi=3;
      printf("child set i=%d, *pi=%d\n",i, *pi);
}
return 0;
}

用vfork的时候，我期待i和pi是被父子进程共享的，所以父进程改了值，子进程就能用到，运行这个程序:
$ g++ myvshare.cpp && ./a.out

child get i=5, *pi=5
child set i=3, *pi=3
father set i=4, *pi=4
father get i=4, *pi=4
*** Error in `./a.out': free(): invalid pointer: 0xb75f9000 ***
======= Backtrace: =========
/lib/i386-linux-gnu/libc.so.6(+0x67257)[0xb74ae257]
/lib/i386-linux-gnu/libc.so.6(+0x6d577)[0xb74b4577]
/lib/i386-linux-gnu/libc.so.6(+0x6dd31)[0xb74b4d31]
/usr/lib/i386-linux-gnu/libstdc++.so.6(_ZdlPv+0x18)[0xb766bd98]
./a.out[0x8048621]
/lib/i386-linux-gnu/libc.so.6(+0x15f2d4)[0xb75a62d4]
======= Memory map: ========
08048000-08049000 r-xp 00000000 08:01 1055312 /home/x/cpp/a.out
08049000-0804a000 r--p 00000000 08:01 1055312 /home/x/cpp/a.out
0804a000-0804b000 rw-p 00001000 08:01 1055312 /home/x/cpp/a.out
0859e000-085c3000 rw-p 00000000 00:00 0 [heap]
b7200000-b7221000 rw-p 00000000 00:00 0
b7221000-b7300000 ---p 00000000 00:00 0
b73d3000-b73d5000 rw-p 00000000 00:00 0
b73d5000-b73f1000 r-xp 00000000 08:01 1181015 /lib/i386-linux-gnu/libgcc_s.so.1
b73f1000-b73f2000 rw-p 0001b000 08:01 1181015 /lib/i386-linux-gnu/libgcc_s.so.1
b73f2000-b7445000 r-xp 00000000 08:01 1181047 /lib/i386-linux-gnu/libm-2.23.so
b7445000-b7446000 r--p 00052000 08:01 1181047 /lib/i386-linux-gnu/libm-2.23.so
b7446000-b7447000 rw-p 00053000 08:01 1181047 /lib/i386-linux-gnu/libm-2.23.so
b7447000-b75f6000 r-xp 00000000 08:01 1180977 /lib/i386-linux-gnu/libc-2.23.so
b75f6000-b75f7000 ---p 001af000 08:01 1180977 /lib/i386-linux-gnu/libc-2.23.so
b75f7000-b75f9000 r--p 001af000 08:01 1180977 /lib/i386-linux-gnu/libc-2.23.so
b75f9000-b75fa000 rw-p 001b1000 08:01 1180977 /lib/i386-linux-gnu/libc-2.23.so
b75fa000-b75fd000 rw-p 00000000 00:00 0
b75fd000-b776a000 r-xp 00000000 08:01 400094 /usr/lib/i386-linux-gnu/libstdc++.so.6.0.21
b776a000-b776b000 ---p 0016d000 08:01 400094 /usr/lib/i386-linux-gnu/libstdc++.so.6.0.21
b776b000-b7770000 r--p 0016d000 08:01 400094 /usr/lib/i386-linux-gnu/libstdc++.so.6.0.21
b7770000-b7771000 rw-p 00172000 08:01 400094 /usr/lib/i386-linux-gnu/libstdc++.so.6.0.21
b7771000-b7774000 rw-p 00000000 00:00 0
b7788000-b778b000 rw-p 00000000 00:00 0
b778b000-b778d000 r--p 00000000 00:00 0 [vvar]
b778d000-b778e000 r-xp 00000000 00:00 0 [vdso]
b778e000-b77b0000 r-xp 00000000 08:01 1180949 /lib/i386-linux-gnu/ld-2.23.so
b77b0000-b77b1000 rw-p 00000000 00:00 0
b77b1000-b77b2000 r--p 00022000 08:01 1180949 /lib/i386-linux-gnu/ld-2.23.so
b77b2000-b77b3000 rw-p 00023000 08:01 1180949 /lib/i386-linux-gnu/ld-2.23.so
bf9ca000-bf9eb000 rw-p 00000000 00:00 0 [stack]
Terminated (core dupm)