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37 Tue, 29 Nov 2011 13:03:51 -0800 (PST)
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38 From: Dmitry Kurochkin <dmitry.kurochkin@gmail.com>
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39 To: Tomi Ollila <tomi.ollila@iki.fi>, Tomi Ollila <tomi.ollila@iki.fi>,
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40 notmuch@notmuchmail.org
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41 Subject: Re: [PATCH 1/3] test: add functions to count how much times notmuch
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43 In-Reply-To: <yf6mxbfxezr.fsf@taco2.nixu.fi>
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44 References: <1322271878-32614-1-git-send-email-dmitry.kurochkin@gmail.com>
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47 <yf6aa7gj7w5.fsf@taco2.nixu.fi> <87hb1ovsz4.fsf@gmail.com>
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48 <yf6mxbfxezr.fsf@taco2.nixu.fi>
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50 (x86_64-pc-linux-gnu)
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51 Date: Wed, 30 Nov 2011 01:03:27 +0400
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71 On Tue, 29 Nov 2011 14:58:00 +0200, Tomi Ollila <tomi.ollila@iki.fi> wrote:
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74 > On Tue, 29 Nov 2011 01:26:39 +0400, Dmitry Kurochkin <dmitry.kurochkin@gmail.com> wrote:
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77 > > On Mon, 28 Nov 2011 22:42:50 +0200, Tomi Ollila <tomi.ollila@iki.fi> wrote:
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78 > > > On Mon, 28 Nov 2011 07:28:13 +0400, Dmitry Kurochkin <dmitry.kurochkin@gmail.com> wrote:
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80 > > > > +# Creates a script that counts how much time it is executed and calls
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81 > > > > +# notmuch. $notmuch_counter_command is set to the path to the
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82 > > > > +# generated script. Use notmuch_counter_value() function to get the
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83 > > > > +# current counter value.
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84 > > > > +notmuch_counter_reset () {
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85 > > > > + notmuch_counter_command="$TMP_DIRECTORY/notmuch_counter"
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86 > > > > + if [ ! -x "$notmuch_counter_command" ]; then
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87 > > > > + notmuch_counter_state_path="$TMP_DIRECTORY/notmuch_counter.state"
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88 > > > > + cat >"$notmuch_counter_command" <<EOF || return
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91 > > > > +count=\$(cat "$notmuch_counter_state_path")
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92 > > > > +echo -n \$(expr \$count + 1) > "$notmuch_counter_state_path"
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94 > > > > +exec notmuch "\$@"
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96 > > > > + chmod +x "$notmuch_counter_command" || return
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99 > > > > + echo -n 0 > "$notmuch_counter_state_path"
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102 > > > > +# Returns the current notmuch counter value.
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103 > > > > +notmuch_counter_value () {
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104 > > > > + if [ -r "$notmuch_counter_state_path" ]; then
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105 > > > > + count=$(cat "$notmuch_counter_state_path")
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109 > > > > + echo -n $count
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113 > > > Good work! It would be nice if the state file contained newline after
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114 > > > count number.
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116 > > I wonder why it is actually nice :) I do not have strong preference
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117 > > here. So a newline is added in v3. Also a newline is added to
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118 > > notmuch_counter_value() output for consistency.
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120 > It is nice when I enter cat /path/to/notmuch_counter from command
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121 > line and shell prompt is not appended at the end of the file contents
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122 > (but on next line :)
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125 > > > Also some optimizations could be done:
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128 > > (Would be nice if you send a diff, or a human-friendly description of
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131 > Ok, I'll try to do this according to your wishes next time.
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133 > > > cat >"$notmuch_counter_command" <<EOF || return
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136 > > > read count < "$notmuch_counter_state_path"
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138 > > Nice. Fixed in the new patch version.
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140 > > > echo \$((count + 1)) > "$notmuch_counter_state_path"
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143 > > I do not think this is really an optimization. And I find expr more
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144 > > clear than using $(()). I always have troubles remembering "random
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145 > > special char syntax" (yeah, not a Perl fan :)), prefer human friendly
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148 > The (posix) shell command language defines 'Arithmetic Expansion' in
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150 > http://pubs.opengroup.org/onlinepubs/007908799/xcu/chap2.html#tag_001_006_004
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152 > I.e. using format $(( expression )) makes shell doing the arithetic itself
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153 > instead of forking a process (or two!) to do so.
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156 I though expr was a builtin. Now I agree that it is better to replace
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157 it with $(()), even though I still prefer the expr syntax.
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159 > Normally in this case it is not so big deal (and still it isn't, but...)
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160 > In this particular case the shell wrapper counting notmuch launches and
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161 > exec'ing it the wrapper could do this without fork(2)ing a single time
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162 > (i.e. keep the process count unchanged compared to execing notmuch
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165 > Anyway, many opinions; as far as it works I'm fine with it :)
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167 > Now that you feel relaxed, check the results of some further
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168 > experimentation ;) :
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170 > excerpt from man strace:
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172 > -ff If the -o filename option is in effect, each processes
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173 > trace is written to filename.pid where pid is the
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174 > numeric process id of each process.
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176 > Executing rm -f forked.*; strace -ff -o forked bash -c 'echo $(( 5 + 5 ))'
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178 > will output '10' and create just one 'forked.<pid>' file
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180 > Executing rm -f forked.*; strace -ff -o forked bash -c 'echo $(expr 5 + 5)'
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182 > output 10 as expected, but there is now *3* forked.<pid> files !
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184 > bash does not optmize; it forks subshell to execute $(...) and then
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185 > there just works as usual (forks subshell to execute builtin expr))
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187 > Executing rm -f forked.*; strace -ff -o forked bash -c 'echo $(exec expr 5 + 5)'
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189 > (the added 'exec' takes off one fork -- just 2 forked.<pid> files appear).
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191 > I did the same tests using dash, ksh & zsh on linux system, and every one
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192 > of these managed to optimize one fork out in the above 3 fork case.
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195 Thanks for details.
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