module Rake # A Promise object represents a promise to do work (a chore) in the # future. The promise is created with a block and a list of # arguments for the block. Calling value will return the value of # the promised chore. # # Used by ThreadPool. # class Promise # :nodoc: all NOT_SET = Object.new.freeze # :nodoc: attr_accessor :recorder # Create a promise to do the chore specified by the block. def initialize(args, &block) @mutex = Mutex.new @result = NOT_SET @error = NOT_SET @args = args @block = block end # Return the value of this promise. # # If the promised chore is not yet complete, then do the work # synchronously. We will wait. def value unless complete? stat :sleeping_on, :item_id => object_id @mutex.synchronize do stat :has_lock_on, :item_id => object_id chore stat :releasing_lock_on, :item_id => object_id end end error? ? raise(@error) : @result end # If no one else is working this promise, go ahead and do the chore. def work stat :attempting_lock_on, :item_id => object_id if @mutex.try_lock stat :has_lock_on, :item_id => object_id chore stat :releasing_lock_on, :item_id => object_id @mutex.unlock else stat :bailed_on, :item_id => object_id end end private # Perform the chore promised def chore if complete? stat :found_completed, :item_id => object_id return end stat :will_execute, :item_id => object_id begin @result = @block.call(*@args) rescue Exception => e @error = e end stat :did_execute, :item_id => object_id discard end # Do we have a result for the promise def result? ! @result.equal?(NOT_SET) end # Did the promise throw an error def error? ! @error.equal?(NOT_SET) end # Are we done with the promise def complete? result? || error? end # free up these items for the GC def discard @args = nil @block = nil end # Record execution statistics if there is a recorder def stat(*args) @recorder.call(*args) if @recorder end end end