Method: Simple::SQL::Connection#lock!

Defined in:
lib/simple/sql/connection/lock.rb

#lock!(key, key2 = nil, timeout: nil) ⇒ Object

Acquire an advisory lock.

This uses the pg_*_xact_lock locks - that once acquired, cannot be released, but will release automatically once the transaction ends. This is safer than the pg_advisory_lock group of functions.

For ease of use the key argument can also be a string - in which case we use a hash function to derive a key value. Usage example:

Simple::SQL.lock! "products", 12
Simple::SQL.ask "UPDATE products SET ... WHERE id=12"

Note that passing in a timeout value sets timeouts for all lock! invocations in this transaction.



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# File 'lib/simple/sql/connection/lock.rb', line 41

def lock!(key, key2 = nil, timeout: nil)
  unless in_transaction?
    raise "You cannot use lock! outside of a transaction"
  end

  if key.is_a?(String)
    # calculate a 31 bit checksum < 0
    key = Digest::CRC32.hexdigest(key).to_i(16) # get a 32-bit stable checksum
    key &= ~0x80000000 # reset bit 31
    key = -key # make it negative
  end

  # shorten key, key2 to the allowed number of bits
  if key2
    key  = apply_bitmask(key, MASK_31_BITS)
    key2 = apply_bitmask(key2, MASK_31_BITS)
  else
    key  = apply_bitmask(key, MASK_63_BITS)
  end

  if timeout
    lock_w_timeout(key, key2, timeout)
  else
    lock_wo_timeout(key, key2)
  end
end