How many instances of a worker process (like the persistent Java compiler) may be launched if you use the 'worker' strategy. May be specified as [name=value] to give a different value per worker mnemonic. Takes an integer, or a keyword ("auto", "HOST_CPUS", "HOST_RAM"), optionally followed by an operation ([-|*]<float>) eg. "auto", "HOST_CPUS*.5". 'auto' calculates a reasonable default based on machine capacity. "=value" sets a default for unspecified mnemonics.