4 Running programs

Once you have created an executable for a Mercury program, you can go ahead and execute it. You may however wish to specify certain options to the Mercury runtime system. The Mercury runtime accepts options via the MERCURY_OPTIONS environment variable. The most useful of these are the options that set the size of the stacks. (For the full list of available options, see Environment.)

When targeting Java or C#, and when targeting high level C (‘mmc --high-level-code’), stack management is the responsibility of the target language’s compiler. When targeting low level C (‘mmc’ without –high-level code), stack management is the responsibility of ‘mmc’ and of the C runtime system. This backend uses two stacks, the det stack and the nondet stack. With ‘mmc --stack-segments’, both of these stacks will grow and shrink automatically as needed. Without ‘--stack-segments’, their size is fixed at program start-up. The default size is 4096k times the word size (in bytes) for the det stack and 64k times the word size (in bytes) for the nondet stack, but these can be overridden with the ‘--detstack-size’ and ‘--nondetstack-size’ options, whose arguments are the desired sizes of the det and nondet stacks respectively, in units of kilobytes. On operating systems that provide the appropriate support, the Mercury runtime will ensure that stack overflow is trapped by the virtual memory system.

With conservative garbage collection (the default), the heap will start out with a zero size, and will be dynamically expanded as needed, When not using conservative garbage collection, the heap has a fixed size like the stacks. The default size is 8Mb times the word size (in bytes), but this can be overridden with the ‘--heap-size’ option.