Class: ActiveRecord::Tenanted::Mutex::Ready

Inherits:
Object
  • Object
show all
Defined in:
lib/active_record/tenanted/mutex.rb

Overview

This flock-based mutex is intended to hold a lock while the tenant database is in the process of being created and migrated (i.e., "made ready").

The creation-and-migration time span is generally very short, and only happens once at the beginning of the database file's existence. We can take advantage of these characteristics to make sure the readiness check is cheap for the majority of the database's life.

  1. The lock file is created and an advisory lock is acquired before the database file is created.
  2. Once the database migration has been completed and the database is ready, the lock is released and the file is removed.

If the lock file exists, then a relatively expensive shared lock must be acquired to ensure the database is ready to use. However, if the lock file does not exist (the majority of the database's life!) then the readiness check is a cheap check for existing on the database file.

Class Method Summary collapse

Class Method Details

.lock(database_path) ⇒ Object 



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# File 'lib/active_record/tenanted/mutex.rb', line 26

def lock(database_path)
  path = lock_file_path(database_path)
  FileUtils.mkdir_p(File.dirname(path))

  # mode "w" to create the file if it does not exist.
  File.open(path, "w") do |f|
    f.flock(File::LOCK_EX) # blocking!
    yield
  ensure
    File.unlink(path)
  end
end

.lock_file_path(database_path) ⇒ Object 



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# File 'lib/active_record/tenanted/mutex.rb', line 59

def lock_file_path(database_path)
  database_path.to_s + ".ready_lock"
end

.locked?(database_path) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/active_record/tenanted/mutex.rb', line 39

def locked?(database_path)
  path = lock_file_path(database_path)

  if File.exist?(path)
    result = nil
    begin
      # mode "r" to avoid creating the file if it does not exist.
      File.open(path, "r") do |f|
        result = f.flock(File::LOCK_SH | File::LOCK_NB)
      end
      result != 0
    rescue Errno::ENOENT
      # the file was deleted between the existence check and the open
      false
    end
  else
    false
  end
end