How to create a linux fifo "pipe" (or something), which does not block writer and reader?

Question

I created a fifo pipe

$ mkfifo pipename

Now if I write somthing into it, the command won't not return,

$ echo "foo" > pipename

until I read it:

$ cat < pipename 
foo

Also, also read command won't return until something is written to it.

Now, I would like to create a such a thing (actually, maybe this thing should not be considered to be a pipe, rather some sort of buffer) that

• reading command will return immediately, regardless of there is something in the pipe or not (if pipe is empty, then reading should return immediately with zero bytes)
• write command returns immediately

Thanks

Solution

Use a fifo, but write your own reader and writer. Open the fifo with O_NONBLOCK set, and open will return immediately if no other process has the other side open. Your write command will return immediately (as requested), but the data will be lost. If you want the data to persist, use a regular file.

Comments

[bpgergo]

Thanks. I want the data to persist until the box is up. Regular file writes data to disk, doesn't it? Is there a way to achieve the same in the memory?

[LiKao]

Yes, with a regular file the data is written to the disk. If you need some kind of buffering it is usually hard to make sure data is only stored in memory, but not on the disk (it might get swapped out). If you just are concerned about write/read cycles and speed, you could use a ramdisk (usually available under some directory on all distributions).

[hildogjr]

I want to use this to create a "virtual device". So I would like to create a FIFO with buffer.