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22 Wed, 19 Feb 2014 22:47:50 +0200 (EET)
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23 From: Tomi Ollila <tomi.ollila@iki.fi>
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24 To: Austin Clements <amdragon@MIT.EDU>
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25 Subject: Re: [PATCH 1/1] emacs: always write emacs/.eldeps when the target is
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27 In-Reply-To: <20140219195457.GD13537@mit.edu>
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28 References: <1390645309-2326-1-git-send-email-tomi.ollila@iki.fi>
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29 <20140213071026.GX4375@mit.edu> <m2sirn1nik.fsf@guru.guru-group.fi>
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30 <20140213074944.GY4375@mit.edu> <m2bny9ebvk.fsf@guru.guru-group.fi>
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31 <20140214215736.GD4375@mit.edu> <20140219195457.GD13537@mit.edu>
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36 !)g;OY^,BjTbr)Np:%c_o'jj,Z
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37 Date: Wed, 19 Feb 2014 22:47:49 +0200
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38 Message-ID: <m2iosade2y.fsf@guru.guru-group.fi>
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41 Cc: notmuch@notmuchmail.org
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56 On Wed, Feb 19 2014, Austin Clements <amdragon@MIT.EDU> wrote:
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58 > Quoth myself on Feb 14 at 4:58 pm:
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59 >> Quoth Tomi Ollila on Feb 14 at 9:24 pm:
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60 >> > On Thu, Feb 13 2014, Austin Clements <amdragon@MIT.EDU> wrote:
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62 >> > > Quoth Tomi Ollila on Feb 13 at 9:26 am:
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63 >> > >> On Thu, Feb 13 2014, Austin Clements <amdragon@MIT.EDU> wrote:
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65 >> > >> > Quoth Tomi Ollila on Jan 25 at 12:21 pm:
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66 >> > >> >> So that the target is newer than its prerequisites.
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68 >> > >> >> emacs/Makefile.local | 3 +--
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69 >> > >> >> 1 file changed, 1 insertion(+), 2 deletions(-)
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71 >> > >> >> diff --git a/emacs/Makefile.local b/emacs/Makefile.local
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72 >> > >> >> index 42bfbd9..d5d402e 100644
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73 >> > >> >> --- a/emacs/Makefile.local
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74 >> > >> >> +++ b/emacs/Makefile.local
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75 >> > >> >> @@ -32,8 +32,7 @@ emacs_bytecode = $(emacs_sources:.el=.elc)
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76 >> > >> >> ifeq ($(HAVE_EMACS),1)
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77 >> > >> >> $(dir)/.eldeps: $(dir)/Makefile.local $(dir)/make-deps.el $(emacs_sources)
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78 >> > >> >> $(call quiet,EMACS) --directory emacs -batch -l make-deps.el \
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79 >> > >> >> - -f batch-make-deps $(emacs_sources) > $@.tmp && \
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80 >> > >> >> - (cmp -s $@.tmp $@ || mv $@.tmp $@)
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81 >> > >> >> + -f batch-make-deps $(emacs_sources) > $@.tmp && mv $@.tmp $@
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82 >> > >> >> -include $(dir)/.eldeps
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84 >> > >> >> CLEAN+=$(dir)/.eldeps $(dir)/.eldeps.tmp
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86 >> > >> > Is this just so the rule doesn't get run again on the next make
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87 >> > >> > invocation (unless, of course, a dependent changed)?
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89 >> > >> Basically yes. I did multiple builds in rapid succession when developing
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90 >> > >> something and this thing confused me quite a lot in the beginning...
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92 >> > >> > Interestingly, if any of the dependents have changed, but in ways that
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93 >> > >> > don't affect .eldeps, this change will make the build more expensive
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94 >> > >> > because it will trigger a make restart after .eldeps is updated.
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96 >> > >> I wondered what was the reason for the recipe you've chosen here, has
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97 >> > >> it something to do with inodes or something ;) (and were going to ask
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98 >> > >> an alternative to touch (or even : > $@) the target...
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100 >> > >> ... but now I understand. E.g. change in notmuch-lib.el will cause *all*
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101 >> > >> .el files to be re-bytecompiled after this change.
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103 >> > > This is unrelated to the cmp in the recipe. A change in
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104 >> > > notmuch-lib.el *must* cause almost all .el files to be recompiled
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105 >> > > because they almost all require it and may use macros from it. If you
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106 >> > > touch, e.g., notmuch-hello.el, you'll see that very little is rebuilt
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107 >> > > (with or without this patch).
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109 >> > >> An alternative to this patch would be adding a message to the rule
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110 >> > >> which informs user to touch .eldeps to avoid re-doing .eldeps if
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111 >> > >> that irritates one :D
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113 >> > >> something like:
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115 >> > >> (cmp -s $@.tmp $@ && \
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116 >> > >> echo "touch $@ to avoid redoing this target" || mv $@.tmp $@)
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118 >> > > I think this patch is good as it is; I was just pointing out that the
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119 >> > > change also has a performance drawback in some situations. (Knowing
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120 >> > > make, there's probably *some* way to get the best of both worlds and
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121 >> > > it's probably really ugly.)
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123 >> > Ah, now I understand, because emacs/Makefile.local includes emacs/.eldeps
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124 >> > when it notices mtime of emacs/.eldeps changes it restarts itself...
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126 >> > ... to compare with current behaviour:
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130 >> > $ touch emacs/notmuch.el
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134 >> > Use "make V=1" to see the verbose compile lines.
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135 >> > EMACS emacs/.eldeps
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136 >> > make: Nothing to be done for `all'.
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138 >> > Use "make V=1" to see the verbose compile lines.
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139 >> > EMACS emacs/.eldeps
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140 >> > make: Nothing to be done for `all'.
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142 >> > Use "make V=1" to see the verbose compile lines.
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143 >> > EMACS emacs/.eldeps
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144 >> > make: Nothing to be done for `all'.
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146 >> > It will rerun emacs -L emacs -batch -l make-deps.el -f batch-make-deps ...
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147 >> > over and over again...
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149 >> > I thought I figured out a solution involving .eldeps.stamp file but
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150 >> > that turned out to be no-go... (circular dependency netween .eldeps.stamp
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151 >> > and Makefile.local).
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153 >> > So, with this if one edits emacs/* files and keeps building byte-compiled
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154 >> > versions often, make will both run EMACS emacs/.eldeps and restarting
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155 >> > -- and when moving to edit other files both of the above stops. Without
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156 >> > this change after editing emacs/* files EMACS emacs/.eldeps will be
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157 >> > executed until it is touched or make clean executed (I wonder how make
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158 >> > handles rebuilding emacs/.eldeps while doing make clean ;)
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163 >> Here's a way that works, but it's more complicated than your patch and
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164 >> doesn't seem to perform any better:
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166 >> diff --git a/emacs/Makefile.local b/emacs/Makefile.local
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167 >> index 42bfbd9..8a1f1c2 100644
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168 >> --- a/emacs/Makefile.local
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169 >> +++ b/emacs/Makefile.local
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170 >> @@ -29,14 +29,28 @@ emacs_bytecode = $(emacs_sources:.el=.elc)
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171 >> # the byte compiler may load an old .elc file when processing a
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172 >> # "require" or we may fail to rebuild a .elc that depended on a macro
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173 >> # from an updated file.
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175 >> +# We do this in two rules. .eldeps is the "real" dependencies file
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176 >> +# and will be rebuilt if and only if a .el source file changes. We
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177 >> +# could include this directly, but then whenever a .el file changed
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178 >> +# (and .eldeps's mtime changed), make would restart immediately after
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179 >> +# the include below. To avoid this, we create a second file,
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180 >> +# .eldeps.x, that we only update when its *contents* differ from
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181 >> +# .eldeps. .eldeps will often have an mtime older than .eldeps.x (any
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182 >> +# .el file change that does not change dependencies will cause this),
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183 >> +# so the .eldeps.x rule will often run, but it executes quickly and
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184 >> +# quietly and will not trigger a make restart unless the dependencies
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185 >> +# actually change.
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187 > Here's a version of this comment that gets to the point directly:
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189 > # We could include .eldeps directly, but that would cause a make
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190 > # restart whenever any .el file was modified, even if dependencies
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191 > # didn't change, because the mtime of .eldeps will change. Instead,
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192 > # we include a second file, .eldeps.x, which we ensure always has the
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193 > # same content as .eldeps, but its mtime only changes when dependency
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194 > # information changes, in which case a make restart is necessary
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197 I think this behaviour is tolerable: instead of verbosely re-run emacs to
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198 re-create .eldeps every time just to see the new .eldeps is not going to be
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199 used we just silently re-run only lightweight cmp.
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204 >> ifeq ($(HAVE_EMACS),1)
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205 >> $(dir)/.eldeps: $(dir)/Makefile.local $(dir)/make-deps.el $(emacs_sources)
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206 >> $(call quiet,EMACS) --directory emacs -batch -l make-deps.el \
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207 >> -f batch-make-deps $(emacs_sources) > $@.tmp && \
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208 >> - (cmp -s $@.tmp $@ || mv $@.tmp $@)
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209 >> --include $(dir)/.eldeps
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211 >> +$(dir)/.eldeps.x: $(dir)/.eldeps
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212 >> + @cmp -s $^ $@ || cp $^ $@
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213 >> +-include $(dir)/.eldeps.x
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215 >> -CLEAN+=$(dir)/.eldeps $(dir)/.eldeps.tmp
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216 >> +CLEAN+=$(dir)/.eldeps $(dir)/.eldeps.tmp $(dir)/.eldeps.x
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218 >> ifeq ($(HAVE_EMACS),1)
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219 >> %.elc: %.el $(global_deps)
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220 > _______________________________________________
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