'\"p
.\" aegis - project change supervisor
.\" Copyright (C) 1998, 2006-2008, 2010, 2012 Peter Miller
.\"
.\" This program is free software; you can redistribute it and/or modify
.\" it under the terms of the GNU General Public License as published by
.\" the Free Software Foundation; either version 3 of the License, or
.\" (at your option) any later version.
.\"
.\" This program is distributed in the hope that it will be useful,
.\" but WITHOUT ANY WARRANTY; without even the implied warranty of
.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
.\" General Public License for more details.
.\"
.\" You should have received a copy of the GNU General Public License
.\" along with this program. If not, see <http://www.gnu.org/licenses/>.
.\"
.nr PS 72
.nr VS 75000
.LP
.ad c
Recursive
.br
.ad l
.sp 0.3i
.nr PS 36
.nr VS 37
.XP
\(bu
Multiple makefiles
.br
.ps 16
.vs 17
.ft CW
.TS
tab(@);
l | l.
@prog: ../a/a.o b.o
@  cc -o prog ../a/a.o b.o
.sp 0.5
a.o: a.c a.h@a.o: \fIforce\fP
  cc -c a.c@  cd ../a;make a.o
.sp 0.5
a.c a.h: a.y@b.o: b.c ../a/a.h
  yacc -d a.y@  cc -c b.c
  \fImv \&...\fP
.TE
.XP
\(bu
Multiple graphs
.br
.ps 16
.vs 17
.sp 0.5
.PS
.ft CW
ellipseht = 0.4
ellipsewid = ellipseht * 2.5
down
A1: ellipse "prog"
move 3*ellipseht
C2: ellipse "a.h"
C3: ellipse "b.c" with .w at C2.e+(ellipseht,0)
B2: ellipse "b.o" with .c at 0.5<A1.s,C3.n>
B1: ellipse "a.o" with .c at (A1.c.x*2-B2.c.x,B2.c.y)
arrow from B1.n to A1.sw
arrow from B2.n to A1.se
arrow from C2.n to B2.sw
arrow from C3.n to B2.se
.\" -------------------------------------------
CC2: ellipse "a.h" with .e at C2.w-(ellipseht,0)
C1: ellipse "a.c" with .e at CC2.w-(ellipseht,0)
BB1: ellipse "a.o" with .e at B1.w-(ellipseht,0)
D1: ellipse "a.y" with .n at 0.5<C1.s,CC2.s>-(0,ellipseht)
arrow from C1.n to BB1.sw
arrow from CC2.n to BB1.se
arrow from D1.n to C1.se
arrow from D1.n to CC2.sw
.ft P
.PE
.bp
.nr PS 24
.nr VS 25
.XP
\(bu
Ignore the picky details, like \-I options.
And yacc files, \fIetc\fP.
.XP
\(bu
The first traditional fix:
building too much (\f(CWa.o\fP) every single time.
.XP
\(bu
The second traditional fix:
building too little (\f(CWa.h \(<- a.y\fP)
.XP
\(bu
The third traditional fix:
building more than once (not shown)
.XP
\(bu
If you read \f(CWliba.a\fP instead of \f(CWa.o\fP,
you can see how hard it may be to tell if
it is out of date.
.XP
\(bu
(Include) dependencies are nasty, they can multiply without you knowing
.br
\(dg and they are repaired in the \fIconsumer\fP,
but how does the producer know?
.br
\(dg remember \fBlarge\fP projects, with 100s of directories
.XP
\(bu
Make then performs two separate traversals of these graphs.
.br
\(dg To work properly, \fImake\fP needs the whole graph.
.br
\(dg To work properly, \fImake\fP needs to be free to choose its own order.
.\" vim: set ts=8 sw=4 et :