用MPICH2运行并行程序，代码中的printf语句只有在所有进程都结束后才会打印出来么？

[von_karman]

能不能各进程一边运行，一边打印？
例如代码：
MPI_Init(&argc, &argv);
MPI_Comm_rank(MPI_COMM_WORLD,&myrank);
for(i=0;i<1e1;i++)
{
a=integration(0,1,1e-6,f);
printf("current %d %d %e\n",myrank,i,a);
}
MPI_Finalize();
其中，integration函数每调用一次需要约2s时间，每个进程运行时间大约20s，我的理解是，每个进程每2s就应该打印一次“进程号，循环次数”，所以进程号应该是杂乱无章的，可是用MPICH开启3个进程实际运行结果是这样：

current 0 0 3.141593e+000
current 0 1 3.141593e+000
current 0 2 3.141593e+000
current 0 3 3.141593e+000
current 0 4 3.141593e+000
current 0 5 3.141593e+000
current 0 6 3.141593e+000
current 0 7 3.141593e+000
current 0 8 3.141593e+000
current 0 9 3.141593e+000
current 2 0 3.141593e+000
current 2 1 3.141593e+000
current 2 2 3.141593e+000
current 2 3 3.141593e+000
current 2 4 3.141593e+000
current 2 5 3.141593e+000
current 2 6 3.141593e+000
current 2 7 3.141593e+000
current 2 8 3.141593e+000
current 2 9 3.141593e+000
current 1 0 3.141593e+000
current 1 1 3.141593e+000
current 1 2 3.141593e+000
current 1 3 3.141593e+000
current 1 4 3.141593e+000
current 1 5 3.141593e+000
current 1 6 3.141593e+000
current 1 7 3.141593e+000
current 1 8 3.141593e+000
current 1 9 3.141593e+000
请按任意键继续. . .

为什么呢？