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Make the library fork safe and drop the mutex #50

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Aug 3, 2023
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Make the library fork safe and drop the mutex #50

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19 changes: 6 additions & 13 deletions lib/mini_mime.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -50,8 +50,6 @@ def binary?
end

class Db
LOCK = Mutex.new

def self.lookup_by_filename(filename)
extension = File.extname(filename)
return if extension.empty?
Expand All @@ -60,18 +58,14 @@ def self.lookup_by_filename(filename)
end

def self.lookup_by_extension(extension)
LOCK.synchronize do
@db ||= new
@db.lookup_by_extension(extension) ||
@db.lookup_by_extension(extension.downcase)
end
@db ||= new
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There is a small race condition here, that could lead to more than one DB to be instantiated, but only one will be kept so not sure if it's a big deal.

We could eagerly instantiate the db, and reset it when the paths are changed, but that would change the semantic a bit.

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@ikaronen-relex ikaronen-relex Aug 27, 2023 •
edited
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Looks OK to me, but I guess there could be a performance impact if a lot of threads try to init the DB at the same time (e.g. because they're all executing the same startup code in lockstep). A possible alternative to avoid multiple initialization could be the DCL-like idiom @db || MUTEX.synchronize { @db ||= new }. (I can submit a PR if you think that would be a good idea.)

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Yeah, that's a good idea. Not sure why I didn't think about it.

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@casperisfine PR here: #56

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Thanks, note that I'm not maintainer though, it's up to @SamSaffron to merge this or not.

@db.lookup_by_extension(extension) ||
@db.lookup_by_extension(extension.downcase)
end

def self.lookup_by_content_type(content_type)
LOCK.synchronize do
@db ||= new
@db.lookup_by_content_type(content_type)
end
@db ||= new
@db.lookup_by_content_type(content_type)
end

class Cache
Expand Down Expand Up @@ -146,8 +140,7 @@ def lookup_uncached(val)
end

def resolve(row)
@file.seek(row * @row_length)
Info.new(@file.readline)
Info.new(@file.pread(@row_length, row * @row_length).force_encoding(Encoding::UTF_8))
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Hum, I really sorry, I realized that some platforms (e.g. Windows) don't have pread.

I'll submit another PR to shim it for these.

end
end

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2 changes: 1 addition & 1 deletion test/fixtures/custom_content_type_mime.db
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@@ -1,2 +1,2 @@
liquid application/x-liquid 8bit
liquid application/x-liquid 8bit
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This padding was missing.

mp4 video/vnd.objectvideo quoted-printable
2 changes: 1 addition & 1 deletion test/fixtures/custom_ext_mime.db
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Original file line number Diff line number Diff line change
@@ -1,2 +1,2 @@
lua application/x-lua 8bit
lua application/x-lua 8bit
m4v video/vnd.objectvideo quoted-printable