远程变量声明如何工作?我已尝试使用Chapel language specification的第26.2.1节中所述的on子句扩充普通变量声明,但它似乎不起作用。例如,这行代码:
on Locales[1] var x: [0..10] real;
无法编译,错误为syntax error: near 'var'
。
答案 0 :(得分:5)
简而言之,语法已指定,但目前尚未实现。不幸的是,语言规范目前没有指出它是未来的功能。
感谢你指出这个问题。作为针对Chapel项目的GitHub问题,这个可以说是更好的,所以我创建了an issue to track the problem。
典型的解决方法是选择以下之一:
on
语句来达到预期的效果on
语句我将在此描述每一个。
首先,我们需要一个稍长的例子。假设您正在尝试写:
on Locales[1] var A: [0..10] real; // declare array stored on Locales[1]
A = 1; // on Locale 0, set every element of A to 1
writeln(A); // on Locale 0, print out the array
// print out the locale storing each element
for x in A {
write(x.locale.id, " ");
}
writeln();
使用嵌套on
语句编写它的等效方法是:
on Locales[1] {
var A: [0..10] real;
on Locales[0] {
A = 1;
writeln(A);
for x in A {
write(x.locale.id, " ");
}
writeln();
}
}
// result, when run on 2 locales:
// from printing array elements:
// 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
// from printing element locales:
// 1 1 1 1 1 1 1 1 1 1 1
请注意,在示例中,我们知道分配将在Locale 0上进行。如果我们不知道我们运行的Locale,我们可以在第一个on
之前将其保存到变量中(例如var fromLocale = here;
)并在第二个on
中使用该变量。
在某些情况下,使用on
语句指定变量的初始化位置而不更改声明的位置可能更方便。现在,这可以通过类实例来完成。请注意,这些不是垃圾回收 - 您需要使用Owned / Shared或确保调用delete
。
本着更简单回答问题的精神,我将展示一个名为delete
的版本。
class MyArrayWrapper {
var A: [0..10] real;
}
var myObject: MyArrayWrapper; // starts out as nil
on Locales[1] {
// set myObject to a new instance
// since we do that on Locales[1], it is allocated there
// and the contained array is stored there too.
myObject = new MyArrayWrapper();
}
myObject.A = 1;
writeln(myObject.A);
for x in myObject.A {
write(x.locale.id, " ");
}
writeln();
delete myObject;
// result, when run on 2 locales:
// from printing array elements:
// 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
// from printing element locales:
// 1 1 1 1 1 1 1 1 1 1 1
现在,我们如何使用分布式阵列实现相同的目标? 首先,考虑这个例子,它在运行Chapel程序的Locales之间分配11个元素。
use BlockDist;
const MyDom = {0..10}; // this domain represents the index set 0..10
// declare a Block-distributed index set 0..10
// by default, this is distributed over all available Locales
const MyBlockDistributedDomain = MyDom dmapped Block(boundingBox=MyDom);
// declare an Block-distributed array
var BlockDistributedA: [MyBlockDistributedDomain] real;
BlockDistributedA = 1;
writeln(BlockDistributedA);
for x in BlockDistributedA {
write(x.locale.id, " ");
}
writeln();
// result, when run on 2 locales:
// from printing array elements:
// 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
// from printing element locales:
// 0 0 0 0 0 0 1 1 1 1 1
将数组分布在可用的语言环境中,但该行为只是Block分发的默认行为。我们可以指定要与Block构造函数的参数一起使用的语言环境,如以下示例所示:
use BlockDist;
const MyDom = {0..10};
// This time, specify the target locales for the Block distribution to use.
// Here we pass in an anonymous array storing just Locales[1], so that
// the resulting array only stores elements on Locales[1].
const MyDistributedDomain = MyDom dmapped Block(boundingBox=MyDom,
targetLocales=[Locales[1]]);
var DistributedA: [MyDistributedDomain] real;
DistributedA = 1;
writeln(DistributedA);
for x in DistributedA {
write(x.locale.id, " ");
}
writeln();
// result, when run on 2 locales:
// from printing array elements:
// 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
// from printing element locales:
// 1 1 1 1 1 1 1 1 1 1 1