02-23-2010
I'm trying to achieve the following goals:
1. Only read the log files from disk once.
2. Only decompress the log files once.
3. Process the log files with multiple parallel processes.
4. wait for them all to complete
5. do something else.
The reason being is that disk io and decompression are expensive in comparison to log processing, so I only want to do them once. And running the processing in parallel leverages my quad core processor to further reduce run time.
I think I have what I need, but I'm open to any other suggestions for how to do this better.
With background jobs method you suggest I would have to :
1. create an array of 6 unique temporary pipe names
2. mkfifo for each of the 6 pipes
3. start sending the decompressed logs to 6 named pipes using tee
4. launch a the 6 processing pipelines in the background telling them to read from the named pipes.
5. Now I could use wait to wait for them all.
6. rm all the temporary pipes
7. continue my script
This would work too, but is this better than using 'tee >(cmd1) >(cmd2)...>(cmd6)' and waiting for them to echo something into one named pipe that I have to manually manage? At least 'tee' takes care of creating and destroying the named pipes for me.
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pipe(2) System Calls Manual pipe(2)
Name
pipe - create an interprocess channel
Syntax
include <limits.h> /*Definition of PIPE_MAX*/
pipe(fildes)
int fildes[2];
Arguments
fildes Passing an address as an array of two integers into the system call.
Description
The system call creates an I/O mechanism called a pipe. The file descriptors returned can be used in and operations. Their integer values
will be the two lowest available at the time of the function call. The O_NONBLOCK and FD_CLOEXEC flags will be clear on both file descrip-
tors.
When the pipe is written using the descriptor fildes[1], up to PIPE_MAX bytes of data are buffered before the writing process is suspended.
A read using the descriptor fildes[0] picks up the data.
It is assumed that after the pipe has been set up, two (or more) cooperating processes (created by subsequent calls) pass data through the
pipe with and calls.
The shell has a syntax to set up a linear array of processes connected by pipes.
For further information on how and calls behave with pipes, see the and reference pages.
A signal is generated if a write on a pipe with only one end is attempted.
Restrictions
Should more than 4096 bytes be necessary in any pipe among a loop of processes, deadlock may occur.
The underlying implementation of pipes is no longer socket based, but rather implemented through the file system. Any application that
needs socket functionality from pipes should use the system call.
Return Values
The function value zero is returned if the pipe was created; -1 if an error occurred.
Diagnostics
The call fails if:
[EMFILE] Too many descriptors are active.
[ENFILE] The system file table is full.
[EFAULT] The fildes buffer is in an invalid area of the process's address space.
Environment
Differs from the System V definition in that ENFILE is not a possible error condition.
See Also
sh(1), fork(2), read(2), socketpair(2), write(2)
pipe(2)