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author | Steven Knight <knight@baldmt.com> | 2008-08-09 18:23:26 (GMT) |
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committer | Steven Knight <knight@baldmt.com> | 2008-08-09 18:23:26 (GMT) |
commit | d0c5748eb01e8303b6221afad432cb908672c161 (patch) | |
tree | 962a16c94759f57f27387cb315e72a6a028aa443 /doc/user/sideeffect.in | |
parent | 2f5c0f667910c8c9db5e93842f5f6201409f704e (diff) | |
download | SCons-d0c5748eb01e8303b6221afad432cb908672c161.zip SCons-d0c5748eb01e8303b6221afad432cb908672c161.tar.gz SCons-d0c5748eb01e8303b6221afad432cb908672c161.tar.bz2 |
Merged revisions 3057-3059,3061-3264 via svnmerge from
http://scons.tigris.org/svn/scons/branches/core
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r3061 | stevenknight | 2008-06-10 10:06:24 -0700 (Tue, 10 Jun 2008) | 3 lines
Issue 2085: Fix man page indentation under Debian systems.
Also add escape characters to the beginnings of some necessary lines.
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r3063 | GregNoel | 2008-06-10 17:50:28 -0700 (Tue, 10 Jun 2008) | 1 line
Add David as a member; parametize input file
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r3064 | stevenknight | 2008-06-11 07:22:23 -0700 (Wed, 11 Jun 2008) | 3 lines
Issue 1973: Clarify the man page description of the SConscript(src_dir)
argument.
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r3065 | stevenknight | 2008-06-11 11:25:00 -0700 (Wed, 11 Jun 2008) | 3 lines
Issues 1974, 1999: document {Add,Get,Set}Option(). Reorganize the
section a little bit, other minor edits.
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r3066 | garyo | 2008-06-12 19:53:51 -0700 (Thu, 12 Jun 2008) | 1 line
Document GetBuildFailures in Users Guide. Closes issue #1989.
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r3067 | stevenknight | 2008-06-14 06:42:07 -0700 (Sat, 14 Jun 2008) | 2 lines
Fix build errors from undefined &GetBuildFailures; entity in doc.
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r3073 | garyo | 2008-06-14 18:40:20 -0700 (Sat, 14 Jun 2008) | 1 line
Fix issue #1538 (Handling of string argument in Action.Action). Includes test.
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r3074 | garyo | 2008-06-14 19:11:30 -0700 (Sat, 14 Jun 2008) | 1 line
doc: Trivial man page typo fix.
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r3075 | stevenknight | 2008-06-15 14:35:13 -0700 (Sun, 15 Jun 2008) | 3 lines
Add a test to make sure the env.RCS() applied to an individual file works
correctly when the checked-out copy is changed.
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r3076 | stevenknight | 2008-06-15 23:07:17 -0700 (Sun, 15 Jun 2008) | 2 lines
Issue 2025: User's Guide updates from Randall Spangler's review.
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r3078 | stevenknight | 2008-06-16 06:26:13 -0700 (Mon, 16 Jun 2008) | 2 lines
Issue 1990: Document the Requires() function in the Users's Guide.
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r3082 | stevenknight | 2008-06-16 19:31:00 -0700 (Mon, 16 Jun 2008) | 3 lines
Fix the second example in the AddMethod() chapter. Show the Windows
output generating a resource file. Other copyedits.
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r3083 | stevenknight | 2008-06-17 06:44:02 -0700 (Tue, 17 Jun 2008) | 2 lines
Fix misspelled entity: &Builders; => &Builder;s.
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r3084 | stevenknight | 2008-06-17 08:30:13 -0700 (Tue, 17 Jun 2008) | 3 lines
Issue 1588: - Document suggested use of the Viual C/C++ /FC option to fix
the ability to double-click on file names in compilation error messages.
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r3085 | stevenknight | 2008-06-17 08:50:33 -0700 (Tue, 17 Jun 2008) | 3 lines
Issue 1687: Document the need to use Clean() for any SideEffect()
files that must be explicitly removed when their targets are removed.
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r3086 | stevenknight | 2008-06-17 10:59:28 -0700 (Tue, 17 Jun 2008) | 2 lines
Typo fix in the new SideEffect() paragraph. (Gary Oberbrunner)
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r3088 | cournape | 2008-06-17 19:55:27 -0700 (Tue, 17 Jun 2008) | 3 lines
Initialized merge tracking via "svnmerge" with revisions "1-3087" from
http://scons.tigris.org/svn/scons/branches/vs_revamp
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r3094 | stevenknight | 2008-06-19 09:52:16 -0700 (Thu, 19 Jun 2008) | 3 lines
Change the User's Guide to use the new Variables object and its
associated function for controlling command-line build variables.
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r3115 | stevenknight | 2008-06-25 06:46:36 -0700 (Wed, 25 Jun 2008) | 2 lines
Issue 2072: end indentation after generated Builder text.
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r3116 | stevenknight | 2008-06-25 19:07:15 -0700 (Wed, 25 Jun 2008) | 2 lines
Reorganize the command-line arguments chapter.
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r3117 | stevenknight | 2008-06-25 19:13:58 -0700 (Wed, 25 Jun 2008) | 2 lines
Editing pass for formatting in the Glob() sections.
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r3118 | stevenknight | 2008-06-25 19:23:09 -0700 (Wed, 25 Jun 2008) | 3 lines
Wording changing: Preventing => Controlling, because the chapter
also talks about how to clean additional targets.
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r3119 | stevenknight | 2008-06-25 19:50:41 -0700 (Wed, 25 Jun 2008) | 2 lines
Fix missing </literal> tags, minor wording fix.
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r3120 | stevenknight | 2008-06-25 19:58:34 -0700 (Wed, 25 Jun 2008) | 2 lines
Add "the Default Function" to the appropriate subsection title.
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r3121 | stevenknight | 2008-06-26 08:33:43 -0700 (Thu, 26 Jun 2008) | 2 lines
Issue 1988: Document the Variables.UnknownVariables() method.
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r3122 | stevenknight | 2008-06-26 08:35:51 -0700 (Thu, 26 Jun 2008) | 3 lines
Remove comments listing some of the variables that have been
documented recently.
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r3123 | stevenknight | 2008-06-26 12:42:53 -0700 (Thu, 26 Jun 2008) | 2 lines
Issue 2118: Fix incorrectly swapped man page text. (Alexey Zezukin)
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r3124 | bdbaddog | 2008-06-26 21:23:46 -0700 (Thu, 26 Jun 2008) | 2 lines
Fix bug 2108 - duplicate text in description of interactive mode
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r3125 | stevenknight | 2008-06-27 21:54:56 -0700 (Fri, 27 Jun 2008) | 3 lines
Issue 1993: Document the $*COMSTR variables, the Progress() function,
and create a common "Controlling Build Output" chapter.
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r3126 | garyo | 2008-06-28 05:46:44 -0700 (Sat, 28 Jun 2008) | 1 line
Fix issue 2105; temporarily omit doc saying that SetOption can override user-created Options (until that is implemented).
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r3127 | stevenknight | 2008-06-28 07:29:18 -0700 (Sat, 28 Jun 2008) | 2 lines
Issue 1747: Explicitly document use of Node lists as input to Depends().
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r3128 | stevenknight | 2008-06-28 07:48:32 -0700 (Sat, 28 Jun 2008) | 6 lines
White space change: indent the construction environment sections
further to make way for combining this chapter with others to make
one big "Controlling Environments" chapter.
Also, get rid of some now-unnecessary doc from the old Cons classic
POD, that was taking up space here waiting to be documented.
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r3129 | cournape | 2008-06-29 01:56:30 -0700 (Sun, 29 Jun 2008) | 3 lines
Initialized merge tracking via "svnmerge" with revisions "1-3128" from
http://scons.tigris.org/svn/scons/branches/trygrep
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r3143 | stevenknight | 2008-07-02 10:29:39 -0700 (Wed, 02 Jul 2008) | 3 lines
Initialized merge tracking via "svnmerge" with revisions "1-3142" from
http://scons.tigris.org/svn/scons/branches/sgk_lookup
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r3181 | stevenknight | 2008-07-08 07:17:27 -0700 (Tue, 08 Jul 2008) | 4 lines
Reorganize the discussion of different environments into one chapter.
Document the SetDefault(), PrependUnique(), AppendUnique(),
PrependENVPath() and AppendENVPath() functions.
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r3182 | stevenknight | 2008-07-08 08:47:55 -0700 (Tue, 08 Jul 2008) | 2 lines
Issue 1998: Docment the ARGLIST variable in the User's Guide.
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r3194 | GregNoel | 2008-07-09 23:16:51 -0700 (Wed, 09 Jul 2008) | 1 line
remove unnecessary trailing spaces on lines
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r3204 | stevenknight | 2008-07-11 08:29:18 -0700 (Fri, 11 Jul 2008) | 2 lines
Issue 1853: Remove referenc to SCons.Util.CLVar from a doc example.
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r3206 | GregNoel | 2008-07-12 02:08:19 -0700 (Sat, 12 Jul 2008) | 1 line
Another go at describing VariantDir()
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r3213 | stevenknight | 2008-07-13 08:57:57 -0700 (Sun, 13 Jul 2008) | 3 lines
Set /branches/comments in svnmerge-integrated property to allow
merging changes in both directions.
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r3217 | stevenknight | 2008-07-16 06:52:44 -0700 (Wed, 16 Jul 2008) | 2 lines
Update the copyright year in the User's Guide.
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r3218 | stevenknight | 2008-07-16 07:08:52 -0700 (Wed, 16 Jul 2008) | 3 lines
Issue 1881: Add man page text clarifying the behavior of
Add{Pre,Post}Action() when multiple targets are specified.
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r3223 | stevenknight | 2008-07-18 08:18:45 -0700 (Fri, 18 Jul 2008) | 3 lines
Initialized merge tracking via "svnmerge" with revisions "1-3222" from
http://scons.tigris.org/svn/scons/branches/sgk_subst
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r3231 | stevenknight | 2008-07-22 01:58:11 -0700 (Tue, 22 Jul 2008) | 4 lines
Enhance MSVSProject() tests so they're runnable on any system, regardless
of whether Visual Studio is installed, or if it's even a Windows system
at all.
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r3237 | GregNoel | 2008-07-26 00:07:49 -0700 (Sat, 26 Jul 2008) | 1 line
Issue 1983: Document ParseConfig, MergeFlags, and ParseFlags for the Users' Guide
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r3238 | stevenknight | 2008-07-26 08:38:18 -0700 (Sat, 26 Jul 2008) | 3 lines
Follow-ons for building the User's Guide with Greg's recent additions
for MergeFlags() and ParseFlags().
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r3239 | stevenknight | 2008-07-26 09:52:40 -0700 (Sat, 26 Jul 2008) | 3 lines
Re-arrange some sections talking about creating construction environments
and fetching/expanding variables.
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r3240 | stevenknight | 2008-07-26 12:16:11 -0700 (Sat, 26 Jul 2008) | 2 lines
Stylistic editing of new {Merge,Parse}{Config,Flags} sections.
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r3241 | GregNoel | 2008-07-26 12:42:42 -0700 (Sat, 26 Jul 2008) | 1 line
Issue 1987: Document SideEffect for Users' Guide (incomplete)
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r3242 | stevenknight | 2008-07-26 13:27:56 -0700 (Sat, 26 Jul 2008) | 2 lines
Correct dumb XML mistakes in my last checkin.
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r3243 | stevenknight | 2008-07-26 13:34:05 -0700 (Sat, 26 Jul 2008) | 2 lines
One-character typo. Gah.
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r3244 | stevenknight | 2008-07-26 13:44:14 -0700 (Sat, 26 Jul 2008) | 2 lines
Issue 1977,1980: document the Exit() and Flatten() functions.
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r3245 | stevenknight | 2008-07-27 10:24:12 -0700 (Sun, 27 Jul 2008) | 14 lines
Updates to the new SideEffect section (kudos to Greg).
While working on this, Greg discovered a bug (issue #2154) that prevents
a SideEffect() file from being used as input to another builder call; it
makes the builder target not get build when run in paralle (e.g. -j2)...
:-( So this patch comments out that section of Greg's section.
This also contains my usual editing pass. In this case I changed some
of the examples and added a bunch of text to try to help clarify some
things that seemed important. I also added a closing paragraph warning
that SideEffect() really shouldn't be used as an alternative to specifying
multiple target files in a Builder call when a command builds more than
one file that you care about.
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r3246 | stevenknight | 2008-07-27 10:31:17 -0700 (Sun, 27 Jul 2008) | 2 lines
Proofreading edits of the MergeFlags() section. (Greg Noel)
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r3247 | stevenknight | 2008-07-27 11:17:27 -0700 (Sun, 27 Jul 2008) | 2 lines
Issue 1976: document ensure{Python,SCons}Version() in the User's Guide.
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r3249 | GregNoel | 2008-07-28 15:57:00 -0700 (Mon, 28 Jul 2008) | 1 line
Add svn-bisect script
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Diffstat (limited to 'doc/user/sideeffect.in')
-rw-r--r-- | doc/user/sideeffect.in | 216 |
1 files changed, 216 insertions, 0 deletions
diff --git a/doc/user/sideeffect.in b/doc/user/sideeffect.in new file mode 100644 index 0000000..cbeefae --- /dev/null +++ b/doc/user/sideeffect.in @@ -0,0 +1,216 @@ +<!-- + + __COPYRIGHT__ + + Permission is hereby granted, free of charge, to any person obtaining + a copy of this software and associated documentation files (the + "Software"), to deal in the Software without restriction, including + without limitation the rights to use, copy, modify, merge, publish, + distribute, sublicense, and/or sell copies of the Software, and to + permit persons to whom the Software is furnished to do so, subject to + the following conditions: + + The above copyright notice and this permission notice shall be included + in all copies or substantial portions of the Software. + + THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY + KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE + WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND + NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE + LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION + OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION + WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. + +--> + + <!-- + + <para> + + If &SCons; is unaware that a build step produces an extra file, + the &SideEffect; method can be used to identify it, + so that the file can be used as a dependency in subsequent build steps. + However, the primary use for the &SideEffect; method + is to prevent two build steps from simultaneously modifying the same file. + + </para> + + TODO: currently doesn't work due to issue #2154: + http://scons.tigris.org/issues/show_bug.cgi?id=2154 + + <para> + + If more than one build step creates or manipulates the same file, + it can cause unpleasant results if both build steps are run at the same time. + The shared file is declared as a side-effect of building the primary targets + and &SCons; will prevent the two build steps from running in parallel. + + </para> + + <para> + + In this example, the <filename>SConscript</filename> uses + &SideEffect; to inform &SCons; about the additional output file. + + </para> + + <scons_example name="SideEffectSimple"> + <file name="SConstruct" printme="1"> + env = Environment() + f2 = env.Command('file2', 'log', Copy('$TARGET', '$SOURCE')) + f1 = env.Command('file1', [], + 'echo >$TARGET data1; echo >log updated file1')) + env.SideEffect('log', env.Command('file1', [], + 'echo >$TARGET data1; echo >log updated file1')) + </file> + </scons_example> + + <para> + + Even when run in parallel mode, &SCons; will run the two steps in order: + + </para> + + <scons_output example="SideEffectSimple"> + <scons_output_command>scons -Q --jobs=2</scons_output_command> + </scons_output> + + --> + + <para> + + Sometimes a program the you need to call + to build a target file + will also update another file, + such as a log file describing what the program + does while building the target. + For example, we the folowing configuration + would have &SCons; invoke a hypothetical + script named <application>build</application> + (in the local directory) + with command-line arguments that write + log information to a common + <filename>logfile.txt</filename> file: + + </para> + + <screen> + env = Environment() + env.Command('file1.out', 'file.in', + './build --log logfile.txt $SOURCE $TARGET') + env.Command('file2.out', 'file.in', + './build --log logfile.txt $SOURCE $TARGET') + <screen> + + <para> + + This can cause problems when running + the build in parallel if + &SCons; decides to update both targets + by running both program invocations at the same time. + The multiple program invocations + may interfere with each other + writing to the common log file, + leading at best to intermixed output in the log file, + and at worst to an actual failed build + (on a system like Windows, for example, + where only one process at a time can open the log file for writing). + + </para> + + <para> + + We can make sure that &SCons; does not + run these <application>build</application> + commands at the same time + by using the &SideEffect; function + to specify that updating + the <filename>logfile.txt</filename> file + is a side effect of building the specified + <filename>file1</filename> + and + <filename>file2</filename> + target files: + + </para> + + <scons_example name="SideEffectShared"> + <file name="SConstruct" printme="1"> + env = Environment() + f1 = env.Command('file1.out', 'file1.in', + './build --log logfile.txt $SOURCE $TARGET') + f2 = env.Command('file2.out', 'file2.in', + './build --log logfile.txt $SOURCE $TARGET') + env.SideEffect('logfile.txt', f1 + f2) + </file> + <file name="file1.in">file1.in</file> + <file name="file2.in">file2.in</file> + <file name="build" chmod="0755"> + cat + </file> + </scons_example> + + <para> + + </para> + + <para> + + This makes sure the the two + <application>./build</application> steps are run sequentially, + even withthe <filename>--jobs=2</filename> in the command line: + + </para> + + <scons_output example="SideEffectShared"> + <scons_output_command>scons -Q --jobs=2</scons_output_command> + </scons_output> + + <para> + + The &SideEffect; function can be called multiple + times for the same side-effect file. + Additionally, the name used as a &SideEffect; does not + even need to actually exist as a file on disk. + &SCons; will still make sure + that the relevant targets + will be executed sequentially, not in parallel: + + </para> + + <scons_example name="SideEffectParallel"> + <file name="SConstruct" printme="1"> + env = Environment() + f1 = env.Command('file1.out', [], 'echo >$TARGET data1') + env.SideEffect('not_really_updated', f1) + f2 = env.Command('file2.out', [], 'echo >$TARGET data2') + env.SideEffect('not_really_updated', f2) + </file> + </scons_example> + + <scons_output example="SideEffectParallel"> + <scons_output_command>scons -Q --jobs=2</scons_output_command> + </scons_output> + + <para> + + Note that it might be tempting to + use &SideEffect; for additional target files + that a command produces. + For example, versions the Microsoft Visual C/C++ compiler + produce a <filename>foo.ilk</filename> + alongside compiling <filename>foo.obj</filename> file. + Specifying <filename>foo.ilk</filename> as a + side-effect of <filename>foo.obj</filename> + is <emphasis>not</emphasis> a recommended use of &SideEffect;, + because &SCons; handle side-effect files + slightly differently in its analysis of the dependency graph. + When a command produces multiple output files, + they should be specified as multiple targets of + the call to the relevant builder function, + and the &SideEffect; function itself should really only be used + when it's important to ensure that commands are not executed in parallel, + such as when a "peripheral" file (such as a log file) + may actually updated by more than one command invocation. + + </para> |