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Avoid possible redundant database initialization from multiple threads #56

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merged 2 commits into from
Aug 31, 2023
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Avoid possible redundant database initialization from multiple threads #56

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Avoid possible redundant database initialization from multiple threads
ikaronen-relex Aug 31, 2023
35e98f6
Silence "instance variable @db not initialized" warning
ikaronen-relex Aug 31, 2023
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14 changes: 9 additions & 5 deletions lib/mini_mime.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -50,6 +50,13 @@ def binary?
end

class Db
LOCK = Mutex.new
@db = nil

def self.db
@db || LOCK.synchronize { @db ||= new }
Comment on lines +54 to +57
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Suggested change
@db = nil
def self.db
@db || LOCK.synchronize { @db ||= new }
def self.db
@db ||= LOCK.synchronize { @db ||= new }

If you want to avoid the warning on older rubies. But both works I guess.

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@ikaronen-relex ikaronen-relex Aug 31, 2023 •
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Do you mean a different warning than the "instance variable not initialized" one? The @db = nil line above ought to avoid that one, or at least it did when I tested this on ruby 2.6.10p210.

(The double ||= would indeed work too, but I'd rather avoid that since it makes the already somewhat complicated idiom even more confusing for the unfamiliar reader.)

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Yeah, I meant alternative solution to that same warning.

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I am ok with the implementation, its a bit of hair splitting going one way vs the other.

end

def self.lookup_by_filename(filename)
extension = File.extname(filename)
return if extension.empty?
Expand All @@ -58,14 +65,11 @@ def self.lookup_by_filename(filename)
end

def self.lookup_by_extension(extension)
@db ||= new
@db.lookup_by_extension(extension) ||
@db.lookup_by_extension(extension.downcase)
db.lookup_by_extension(extension) || db.lookup_by_extension(extension.downcase)
end

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

class Cache
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