C prog: After append file, read still return 0

I've a new file, opened as read/write then 1 thread will receive from network and append binary data to that file, the other thread will read from the same file to process the binary data, but the read() always return 0, so I can't read the data, but if I using cat in command line to append data, then the program can read the data and process. I don't know why it can't开发者_运维技巧 notice the new data coming from network. I'm using open(), read(), and write() in this program.

Use a pipe instead of an HDD-file. Depending on your system (which you didnt tell us) there are only minor modifications to your code (which you didnt give us) to do that.

file operations are buffered. try flushing the stream?

Assuming that your read() and write() functions are the POSIX one, they share the file position, even if they are used in different threads. So your read after write was trying to read after the position at which write had written. Don't use file IO to communicate between threads. In most contexts, I'd not even use pipe or sockets for that (one context I'd use them is when the reading thread is using poll/select with other file descriptors) but simple shared memory and mutex.