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POFileUtils uptodate? issue in Ruby
 

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    <p>I use the uptodate? method in Ruby to determine if a file must be re-compiled/re-linked /re-generated etc. Sometimes the build framework I use is so fast at these steps that the output file and the prerequisite file have the exact same file modification timestamps. This causes the build framework to re-compile/re-link files unnecessarily.</p> <p>I compare timestamps for building like so -</p> <pre><code>compile_file(file) unless uptodate?(file, %W(#{dependencies})) </code></pre> <p>I looked up the source for uptodate? from <a href="http://www.ruby-doc.org/stdlib-1.9.3/libdoc/fileutils/rdoc/FileUtils.html#method-c-uptodate-3F" rel="nofollow">here</a> and it looks like this -</p> <pre><code>def uptodate?(new, old_list, options = nil) raise ArgumentError, 'uptodate? does not accept any option' if options return false unless File.exist?(new) new_time = File.mtime(new) old_list.each do |old| if File.exist?(old) return false unless new_time &gt; File.mtime(old) end end true end </code></pre> <p>As suspected, it returns false if the timestamps are equal. What's the most elegant way to get around this issue? I have tried running the framework on Linux and Windows and I have the same problem. From what I read <a href="https://github.com/joeyates/rake-builder#file-modification-time-resolutions" rel="nofollow">here</a> it's unlikely to be a file system specific file modification time resolution issue (since ext4 has a resolution of 1 microsecond).</p>
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    1. COThat code is weird, why accept options if you're going to raise an error when people provide them? And I don't understand the problem, if the build framework is so fast, then why does it matter if it occasionally recompiles a file? Unless you're saying that it recompiles the same file many times during the same build. If that's the case, then consider moving to a better tool. [Rake](http://jasonseifer.com/2010/04/06/rake-tutorial?again), for example, was built for this purpose, and deals with this via dependencies, so it wouldn't have such an issue.
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      1. USJoshua Cheek
    2. CO@JoshuaCheek That code is part of the FileUtils module in Ruby (i.e. it was not written by me!). I am using Rake but I suspect it would behave the same way even if I specified the file dependencies (I am guessing it uses uptodate? internally?). I don't want the build framework to recompile/re-link/run a unit test unnecessarily, because when you are TDD'ing it does matter!
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    3. COMan, there's some weird code in the stdlib O.o Anyway, the difference (If I understand correctly what you're doing) would be that Rake would check that file only one time e.g. it would compile it exactly once, this is because rake tasks are not like methods, but rather like dependencies. File a depends on c, File b depends on c. If you compile both a and b, then c will be compiled once for a, thus the dependency is satisfied for c.
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