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Diffstat (limited to 'doc/user/depends.in')
| -rw-r--r-- | doc/user/depends.in | 61 |
1 files changed, 57 insertions, 4 deletions
diff --git a/doc/user/depends.in b/doc/user/depends.in index 69bb242..190670c 100644 --- a/doc/user/depends.in +++ b/doc/user/depends.in @@ -1,6 +1,6 @@ <!-- - Copyright (c) 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010 The SCons Foundation + Copyright (c) 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 The SCons Foundation Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the @@ -386,7 +386,7 @@ <para> - So configured, &SCons will still behave like + So configured, &SCons; will still behave like it does when using <literal>Decider('MD5')</literal>: </para> @@ -487,7 +487,7 @@ only its section of the input file. However, since the input file may contain a lot of data, we want to open the input file only if its timestamp has changed. - This could done with a custom + This could be done with a custom &Decider; function that might look something like this: </para> @@ -591,6 +591,59 @@ </para> + <para> + + Another thing to look out for, is the fact that the three + attributes above may not be present at the time of the first run. + Without any prior build, no targets got created and no + <filename>.sconsign</filename> DB file exists yet. + So, it is recommended to always check whether the + <varname>prev_ni</varname> attribute in question is available. + + </para> + + <para> + + We finally present a small example for a + <varname>csig</varname>-based decider function. Note how the + signature information for the <varname>dependency</varname> file + has to get initialized via <function>get_csig</function> + during each function call (this is mandatory!). + + </para> + + <sconstruct> + env = Environment() + + def config_file_decider(dependency, target, prev_ni): + import os.path + + # We always have to init the .csig value... + dep_csig = dependency.get_csig() + # .csig may not exist, because no target was built yet... + if 'csig' not in dir(prev_ni): + return True + # Target file may not exist yet + if not os.path.exists(str(target.abspath)): + return True + if dep_csig != prev_ni.csig: + # Some change on source file => update installed one + return True + return False + + def update_file(): + f = open("test.txt","a") + f.write("some line\n") + f.close() + + update_file() + + # Activate our own decider function + env.Decider(config_file_decider) + + env.Install("install","test.txt") + </sconstruct> + </section> <section> @@ -861,7 +914,7 @@ </section> - <section> + <section id="sect-implicit-dependencies"> <title>Implicit Dependencies: The &cv-CPPPATH; Construction Variable</title> <para> |