Question

I am using named pipes for IPC. At times the data sent between the process can be large and frequent. During these time I see lots of data loss. Are there any obvious problems in the code below that could cause this?

Thanks

#!/usr/bin/env groovy
import java.io.FileOutputStream;
def bytes = new File('/etc/passwd').bytes
def pipe = new File('/home/mohadib/pipe')
1000.times{
    def fos = new FileOutputStream(pipe)
    fos.write(bytes)
    fos.flush()
    fos.close()
}


#!/usr/bin/env groovy
import java.io.FileInputStream;
import java.io.ByteArrayOutputStream;

def pipe = new File('/home/mohadib/pipe')
def bos = new ByteArrayOutputStream()
def len = -1
byte[] buff = new byte[8192]
def i = 0
while(true)
{
    def fis = new FileInputStream(pipe)
    while((len = fis.read(buff)) != -1) bos.write(buff, 0, len)
    fis.close()
    bos.reset()
    i++
    println i
}

Answer 1

Named pipes lose their contents when the last process closes them. In your example, this can happen if the writer process does another iteration while the reader process is about to do fis.close(). No error is reported in this case.

A possible fix is to arrange that the reader process never closes the fifo. To get rid of the EOF condition when the last writer disconnects, open the fifo for writing, close the read end, reopen the read end and close the temporary write end.