Locales¶

A locale is a Chapel abstraction for a piece of a target architecture that has processing and storage capabilities. Generally speaking, the tasks running within a locale have roughly uniform access to values stored in the locale’s local memory and longer latencies for accessing the memories of other locales. As examples, a single shared memory machine would be defined as a single locale, while in a system consisting of a group of network-connected multicore nodes or SMPs each node would be defined as a locale.

Chapel provides several predefined methods on locales, as well as a few variables that describe the locales upon which a program is running.

class locale¶

locale is the abstract class from which the various implementations inherit. It specifies the required interface and implements part of it, but requires the rest to be provided by the corresponding concrete classes.

var numCores: int¶

This is the number of processors on this locale. The term cores here is a misnomer. The value is actually the number of instances of the CPU architecture, so for a locale with a multithreaded hardware architecture, it’s the number of threads. Also, only processors actually available to the program are in this count. If the OS has made some of them off-limits to the program, for example, those are not included.

var maxTaskPar: int¶

This is the maximum task concurrency that one can expect to achieve on this locale. The value comes from an estimate by the runtime tasking layer. Typically it is the number of physical processor cores available to the program. Creating more tasks than this will probably increase walltime rather than decrease it.

const callStackSize: size_t¶

callStackSize holds the size of a task stack on a given locale. Thus, here.callStackSize is the size of the call stack for any task on the current locale, including the caller.

proc id: int¶

Get the integer identifier for the top-level locale the current task is running on.

Returns:	locale number, in the range 0..numLocales-1
Return type:	int

proc name¶

Get the name of the top-level locale the current task is running on.

Returns:	locale name
Return type:	string

proc here¶

This returns the locale from which the call is made.

Returns:	current locale
Return type:	locale

config const numLocales: int¶

numLocales is the number of top-level (network connected) locales.

const LocaleSpace = {0..numLocales-1}¶

This is the domain over which the global Locales array is defined.

const Locales: [LocaleSpace] locale¶

The global Locales array contains an entry for each top-level locale. One of the most common code idioms in all of Chapel is the following, which spreads parallel tasks across the network-connected locales upon which the program is running:

coforall loc in Locales { on loc { ... } }