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# Simple advisory lock manager for PostgreSQL. When used on different database
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# it does not perform any locking. Rails (6) only implements advisory non-blocking
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# locking for migrations via Connection#get_advisory_lock which is not suitable
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# for application use. More information:
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#
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# https://www.postgresql.org/docs/current/explicit-locking.html
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# https://www.kostolansky.sk/posts/postgresql-advisory-locks/
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#
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module Foreman
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class AdvisoryLockManager
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class << self
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# Performs transaction-level advisory lock which is automaticaly released when the
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# built-in explicit transaction ends, or when the session ends.
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def with_transaction_lock(lock_name)
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if ActiveRecord::Base.connection.adapter_name == 'PostgreSQL'
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lock_id = generate_lock_id(lock_name)
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ActiveRecord::Base.transaction do
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Rails.logger.debug("Acquiring Advisory-Transaction-Lock '#{lock_name}' -> #{lock_id}")
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sql = ActiveRecord::Base.sanitize_sql("SELECT pg_advisory_xact_lock(#{lock_id})")
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ActiveRecord::Base.connection.execute(sql)
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yield
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end
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else
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yield
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end
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end
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# Performs session-level advisory lock which is automaticaly released when the block
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# returns. Does not create explicit transaction.
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def with_session_lock(lock_name)
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if ActiveRecord::Base.connection.adapter_name == 'PostgreSQL'
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begin
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lock_id = generate_lock_id(lock_name)
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Rails.logger.debug("Acquiring Advisory-Session-Lock '#{lock_name}' -> #{lock_id}")
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sql = ActiveRecord::Base.sanitize_sql("SELECT pg_advisory_lock(#{lock_id})")
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ActiveRecord::Base.connection.execute(sql)
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yield
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ensure
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sql = ActiveRecord::Base.sanitize_sql("SELECT pg_advisory_unlock(#{lock_id})")
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ActiveRecord::Base.connection.execute(sql)
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end
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else
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yield
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end
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end
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private
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# PostgreSQL requires signed 64 bit (BIGINT).
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def generate_lock_id(lock_name)
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Digest::SHA512.digest(lock_name).unpack1('q')
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end
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end
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end
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end
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