How do I perform parallel compilation?

You can accomplish parallel compilation in one of two ways. The first involves GNU Make, the second involves DMAKE.

GNU Make:

To perform parallel compilation with GNU Make simply do two things:

o

Make sure your make file does not execute the make utility (again) from inside the make file.

On the GNU Make command line, specify '--jobs x', where 'x' is the maximum number of concurrent jobs you will allow GNU Make to execute. If you do not wish to have a maximum, then you may specify simply '--jobs' and GNU Make will execute as many jobs as possible at one time.

DMAKE:

The ini file comes in the dmake archive in a few different flavours. Take the file with the extension .msc and rename it to dmake.ini. Set an environment variable in config.sys

SET MAKESTARTUP=d:\COMPILER\DMAKE.INI

====== Makefile

CC=iccCOPTS=/Sm /Gt+ /Ti+ /O- /Gs+
CONLY=-c

LIBS=os2

INCS=psfax2.h

MAXPROCESS=2

all: psfax2.exe sendfax.exe

modem.obj:  modem.c $(INCS)
   $(CC) $(CONLY) $(COPTS) modem.c

psfax2.obj: psfax2.c $(INCS)
   $(CC) $(CONLY) $(COPTS) psfax2.c

psfax2.exe: psfax2.obj modem.obj
   link386 /ST:32768 /CO psfax2+modem;

sendfax.obj: sendfax.c $(INCS)
   $(CC) $(CONLY) $(COPTS) sendfax.c

sendfax.exe: sendfax.obj modem.obj
   link386 /ST:32768 /CO sendfax+modem;

====== End of makefile

Couple of gotchas. There is a bug in the MAXPROCESS handling of the copy I use. Set it to 1, and you get a typical make, ie one at a time. Set it to 2, and the thing launches 3 processes. Ie with more than 1, you actually get n+1 processes running.

Another caveat

xxx.yy: aaa.bbb
    command1
    command2
    command3

The above structure does not work. The reason is that all 3 commands will be spawned together in parallel sessions. To serialize them you must make up dependancies in the makefile. I ran into this becuase I have one makefile that completes every link stage by copying the result onto a network drive. I had to take all the links that previously had 2 commands, and break them into 2 blocks with the second being a dependancy of the remote file on the local file, and the copy command.

One more word of warning, dmake is not to pleased with those convoluted things that workframe spits out in the name of makefiles. You may have to do a significant amount of makefile editing, depending on how you makefile look now.

Provided that 3 simultaneous copies of your compiler doesn't push your machine into excessive swapping, the improvements in build speed are amazing. Before dmake I'd never seen a build actually top the cpu meter here, the process was always waiting for disk as it loaded compilers/headers etc. Now the compiler sits in ram and just gets re-used, and the headers are coming directly from cache all the time. Build time cut in half, and my cpu guage is pegged at 100% when a build is running.