多进程COW问题求教

鸡丝拌面

The standard I/O library, however, is buffered. Recall from Section 5.12 that standard output is line buffered if it's connected to a terminal device; otherwise, it's fully buffered. When we run the program interactively, we get only a single copy of the printf line, because the standard output buffer is flushed by the newline. But when we redirect standard output to a file, we get two copies of the printf line. In this second case, the printf before the fork is called once, but the line remains in the buffer when fork is called. This buffer is then copied into the child when the parent's data space is copied to the child. Both the parent and the child now have a standard I/O buffer with this line in it. The second printf, right before the exit, just appends its data to the existing buffer. When each process terminates, its copy of the buffer is finally flushed.

鸡丝拌面

ps，lz给出的代码里不是腔调了“/* we don't flush stdout */”嘛。