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Dave Smith wrote:
> Frank Sorenson wrote:
>> How about opening the fifo read/write, which doesn't block:
>> # exec 4<> dave_fifo
>> # ls -alF /proc/$$/fd
>> ...
>> lrwx------ 1 sorenson sorenson 64 2009-04-09 18:14 4 -> /tmp/dave_fifo|
>>
>> Here's an example script:
>> #!/bin/bash
>>
>> exec 4<> /tmp/dave_fifo
>> (sleep 2 ; kill -SIGUSR1 $$ ; echo "I'm alive" >&4) &
>>
>> # Wait for the flag to get raised, or give up after a while:
>> read -t 5 -u 4 line
>> if [ $? -eq 0 ] ; then
>> echo "The child said: $line"
>> else
>> echo "Timed out waiting for child"
>> fi
>>
>
> Interesting idea. Doesn't this block my daemon process (a separate piece
> of C code) from opening the fifo for writing as well? My bash script
> reads from the fifo, but the C program writes to it (and is responsible
> for opening it for writing).
>
> --Dave
Not unless you're doing file locking to get exclusive access.
# cat dave_parent
#!/bin/bash
/tmp/dave_child &
child_pid=$!
exec 4<> /tmp/dave_fifo
echo "Parent $$ waiting for child $child_pid"
read -t 5 -u 4 line
if [ $? -eq 0 ] ; then
echo "The child said: $line"
else
echo "Timed out waiting for child"
fi
# cat dave_child
#!/bin/bash
exec 4<> /tmp/dave_fifo
sleep 2
echo "Dear $PPID, I'm alive. Love $$" >&4
./dave_parent
Parent 25732 waiting for child 25733
The child said: Dear 25732, I'm alive. Love 25733
Frank
- --
Frank Sorenson - KD7TZK
Linux Systems Engineer, DSS Engineering, UBS AG
[email protected]
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