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40 id 1WEQlr-0007tC-LY; Fri, 14 Feb 2014 16:58:09 -0500
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41 Date: Fri, 14 Feb 2014 16:58:07 -0500
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42 From: Austin Clements <amdragon@MIT.EDU>
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43 To: Tomi Ollila <tomi.ollila@iki.fi>
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44 Subject: Re: [PATCH 1/1] emacs: always write emacs/.eldeps when the target is
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46 Message-ID: <20140214215736.GD4375@mit.edu>
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47 References: <1390645309-2326-1-git-send-email-tomi.ollila@iki.fi>
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48 <20140213071026.GX4375@mit.edu> <m2sirn1nik.fsf@guru.guru-group.fi>
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49 <20140213074944.GY4375@mit.edu> <m2bny9ebvk.fsf@guru.guru-group.fi>
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82 X-List-Received-Date: Fri, 14 Feb 2014 21:58:22 -0000
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84 Quoth Tomi Ollila on Feb 14 at 9:24 pm:
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85 > On Thu, Feb 13 2014, Austin Clements <amdragon@MIT.EDU> wrote:
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87 > > Quoth Tomi Ollila on Feb 13 at 9:26 am:
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88 > >> On Thu, Feb 13 2014, Austin Clements <amdragon@MIT.EDU> wrote:
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90 > >> > Quoth Tomi Ollila on Jan 25 at 12:21 pm:
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91 > >> >> So that the target is newer than its prerequisites.
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93 > >> >> emacs/Makefile.local | 3 +--
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94 > >> >> 1 file changed, 1 insertion(+), 2 deletions(-)
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96 > >> >> diff --git a/emacs/Makefile.local b/emacs/Makefile.local
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97 > >> >> index 42bfbd9..d5d402e 100644
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98 > >> >> --- a/emacs/Makefile.local
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99 > >> >> +++ b/emacs/Makefile.local
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100 > >> >> @@ -32,8 +32,7 @@ emacs_bytecode = $(emacs_sources:.el=.elc)
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101 > >> >> ifeq ($(HAVE_EMACS),1)
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102 > >> >> $(dir)/.eldeps: $(dir)/Makefile.local $(dir)/make-deps.el $(emacs_sources)
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103 > >> >> $(call quiet,EMACS) --directory emacs -batch -l make-deps.el \
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104 > >> >> - -f batch-make-deps $(emacs_sources) > $@.tmp && \
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105 > >> >> - (cmp -s $@.tmp $@ || mv $@.tmp $@)
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106 > >> >> + -f batch-make-deps $(emacs_sources) > $@.tmp && mv $@.tmp $@
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107 > >> >> -include $(dir)/.eldeps
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109 > >> >> CLEAN+=$(dir)/.eldeps $(dir)/.eldeps.tmp
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111 > >> > Is this just so the rule doesn't get run again on the next make
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112 > >> > invocation (unless, of course, a dependent changed)?
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114 > >> Basically yes. I did multiple builds in rapid succession when developing
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115 > >> something and this thing confused me quite a lot in the beginning...
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117 > >> > Interestingly, if any of the dependents have changed, but in ways that
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118 > >> > don't affect .eldeps, this change will make the build more expensive
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119 > >> > because it will trigger a make restart after .eldeps is updated.
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121 > >> I wondered what was the reason for the recipe you've chosen here, has
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122 > >> it something to do with inodes or something ;) (and were going to ask
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123 > >> an alternative to touch (or even : > $@) the target...
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125 > >> ... but now I understand. E.g. change in notmuch-lib.el will cause *all*
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126 > >> .el files to be re-bytecompiled after this change.
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128 > > This is unrelated to the cmp in the recipe. A change in
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129 > > notmuch-lib.el *must* cause almost all .el files to be recompiled
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130 > > because they almost all require it and may use macros from it. If you
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131 > > touch, e.g., notmuch-hello.el, you'll see that very little is rebuilt
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132 > > (with or without this patch).
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134 > >> An alternative to this patch would be adding a message to the rule
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135 > >> which informs user to touch .eldeps to avoid re-doing .eldeps if
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136 > >> that irritates one :D
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138 > >> something like:
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140 > >> (cmp -s $@.tmp $@ && \
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141 > >> echo "touch $@ to avoid redoing this target" || mv $@.tmp $@)
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143 > > I think this patch is good as it is; I was just pointing out that the
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144 > > change also has a performance drawback in some situations. (Knowing
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145 > > make, there's probably *some* way to get the best of both worlds and
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146 > > it's probably really ugly.)
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148 > Ah, now I understand, because emacs/Makefile.local includes emacs/.eldeps
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149 > when it notices mtime of emacs/.eldeps changes it restarts itself...
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151 > ... to compare with current behaviour:
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155 > $ touch emacs/notmuch.el
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159 > Use "make V=1" to see the verbose compile lines.
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160 > EMACS emacs/.eldeps
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161 > make: Nothing to be done for `all'.
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163 > Use "make V=1" to see the verbose compile lines.
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164 > EMACS emacs/.eldeps
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165 > make: Nothing to be done for `all'.
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167 > Use "make V=1" to see the verbose compile lines.
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168 > EMACS emacs/.eldeps
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169 > make: Nothing to be done for `all'.
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171 > It will rerun emacs -L emacs -batch -l make-deps.el -f batch-make-deps ...
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172 > over and over again...
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174 > I thought I figured out a solution involving .eldeps.stamp file but
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175 > that turned out to be no-go... (circular dependency netween .eldeps.stamp
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176 > and Makefile.local).
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178 > So, with this if one edits emacs/* files and keeps building byte-compiled
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179 > versions often, make will both run EMACS emacs/.eldeps and restarting
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180 > -- and when moving to edit other files both of the above stops. Without
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181 > this change after editing emacs/* files EMACS emacs/.eldeps will be
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182 > executed until it is touched or make clean executed (I wonder how make
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183 > handles rebuilding emacs/.eldeps while doing make clean ;)
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188 Here's a way that works, but it's more complicated than your patch and
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189 doesn't seem to perform any better:
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191 diff --git a/emacs/Makefile.local b/emacs/Makefile.local
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192 index 42bfbd9..8a1f1c2 100644
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193 --- a/emacs/Makefile.local
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194 +++ b/emacs/Makefile.local
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195 @@ -29,14 +29,28 @@ emacs_bytecode = $(emacs_sources:.el=.elc)
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196 # the byte compiler may load an old .elc file when processing a
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197 # "require" or we may fail to rebuild a .elc that depended on a macro
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198 # from an updated file.
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200 +# We do this in two rules. .eldeps is the "real" dependencies file
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201 +# and will be rebuilt if and only if a .el source file changes. We
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202 +# could include this directly, but then whenever a .el file changed
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203 +# (and .eldeps's mtime changed), make would restart immediately after
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204 +# the include below. To avoid this, we create a second file,
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205 +# .eldeps.x, that we only update when its *contents* differ from
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206 +# .eldeps. .eldeps will often have an mtime older than .eldeps.x (any
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207 +# .el file change that does not change dependencies will cause this),
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208 +# so the .eldeps.x rule will often run, but it executes quickly and
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209 +# quietly and will not trigger a make restart unless the dependencies
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210 +# actually change.
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211 ifeq ($(HAVE_EMACS),1)
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212 $(dir)/.eldeps: $(dir)/Makefile.local $(dir)/make-deps.el $(emacs_sources)
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213 $(call quiet,EMACS) --directory emacs -batch -l make-deps.el \
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214 -f batch-make-deps $(emacs_sources) > $@.tmp && \
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215 - (cmp -s $@.tmp $@ || mv $@.tmp $@)
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216 --include $(dir)/.eldeps
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218 +$(dir)/.eldeps.x: $(dir)/.eldeps
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219 + @cmp -s $^ $@ || cp $^ $@
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220 +-include $(dir)/.eldeps.x
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222 -CLEAN+=$(dir)/.eldeps $(dir)/.eldeps.tmp
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223 +CLEAN+=$(dir)/.eldeps $(dir)/.eldeps.tmp $(dir)/.eldeps.x
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225 ifeq ($(HAVE_EMACS),1)
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226 %.elc: %.el $(global_deps)
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