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请教register

请教register# Programming - 葵花宝典

e*e2007-10-24 07:10

1 楼

看到个题目：
implement a test-and-set: check if a register is 0 or not. If it is 0,
set it to 1, and return 0
请问应该从何下手？谢谢

c*g2007-10-24 07:10

2 楼

int TestAndSet(int* register)
{
int v;
v = Swap(register, 1);
return v!=0;
}
Swap() should be atomic.

【在 e*******e 的大作中提到】

: 看到个题目：
: implement a test-and-set: check if a register is 0 or not. If it is 0,
: set it to 1, and return 0
: 请问应该从何下手？谢谢

k*f2007-10-24 07:10

3 楼

要控制reg，只能上汇编了
有些reg你读不到的，也没法改的

【在 e*******e 的大作中提到】

: 看到个题目：
: implement a test-and-set: check if a register is 0 or not. If it is 0,
: set it to 1, and return 0
: 请问应该从何下手？谢谢

e*e2007-10-24 07:10

4 楼

register是keyword，在这里怎么能做Input variable呢？

【在 c*****g 的大作中提到】

: int TestAndSet(int* register)
: {
: int v;
: v = Swap(register, 1);
: return v!=0;
: }
: Swap() should be atomic.

c*g2007-10-24 07:10

5 楼

com'n, it's pseudo-code

【在 e*******e 的大作中提到】

: register是keyword，在这里怎么能做Input variable呢？

e*e2007-10-24 07:10

6 楼

那用register跟普通int变量有什么区别呢？

int TestAndSet(int* register)
{
int v;
v = Swap(register, 1);
return v!=0;
}
Swap() should be atomic.

【在 c*****g 的大作中提到】

: int TestAndSet(int* register)
: {
: int v;
: v = Swap(register, 1);
: return v!=0;
: }
: Swap() should be atomic.

m*e2007-10-24 07:10

7 楼

You need to learn assembly. This is highly arch-dependent. But usually there
is one instruction or prefix for exactly this purpose.

【在 e*******e 的大作中提到】

: 看到个题目：
: implement a test-and-set: check if a register is 0 or not. If it is 0,
: set it to 1, and return 0
: 请问应该从何下手？谢谢

m*t2007-10-24 07:10

8 楼

test and set is basic for thread synchronization. but yes, the underlying
implementation is hardware dependent. register variable is just a way of
telling compiler try to put this variable into register, compiler does not
guaranttee to honor such request.

j*r2007-10-24 07:10

9 楼

Pseudo code:
int register;
int testandset(){
int ret = register;
register = 1;
return ret;
}
int function(){
while( testandset() );
...
}
Actually, testandset is a hardware instruction which is used to implement
synchronous primitives. So it must be atomic.

【在 e*******e 的大作中提到】

: 看到个题目：
: implement a test-and-set: check if a register is 0 or not. If it is 0,
: set it to 1, and return 0
: 请问应该从何下手？谢谢