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atomic ops

 
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kris



Joined: 27 Mar 2004
Posts: 1494
Location: South Pacific

PostPosted: Mon Oct 31, 2005 11:30 pm    Post subject: atomic ops Reply with quote

Hi Sean,

Can you identify the equivalent Ares atomic function for these two, please?

Code:
/** Compare expect to *ptr and if equal copy update to *ptr and return true;
 * Otherwise return false.
 * \param ptr the memory location to update
 * \param expect the expected value at *ptr
 * \param update the new value for *ptr
 * \return true if successful
 */
  static bool compareAndSet32(void* vptr, void* expect, void* update)
  {
    return compareAndSet32(vptr,cast(int)expect,cast(int)update);
  }

  // alternative declaration for data instead of pointers
  static bool compareAndSet32(void* vptr, int expect, int update)
  {
   asm
     {
      mov   EBX,update;
      mov   EAX,expect;
      mov   ECX,vptr;
      lock;
      cmpxchg   [ECX],EBX;
      setz   AL;
      }
  }
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sean



Joined: 24 Jun 2004
Posts: 609
Location: Bay Area, CA

PostPosted: Tue Nov 01, 2005 6:41 pm    Post subject: Reply with quote

They both would use the same function call:
Code:
bit atomicStoreIf!(T,msync.acq)( inout T val, T newval, T equalTo );
bit atomicStoreIf!(T,msync.rel)( inout T val, T newval, T equalTo );


Pick msync.acq or msync.rel as appropriate, and if you aren't sure, use msync.rel. There's actually no difference in the memory barriers used for acquire/release on storeIf, but I suspect there might be on other platforms.

Also, the Atomic struct is the generalized form of the above and is intended to be used when you have full control over the variable being manipulated. Usage is essentially the same:
Code:
Atomic!(int) atom;
atom.storeIf!(msync.rel)( newval, equalTo );


A compiler bug currently limits the use of these functions to either signed or unsigned per byte size(so you can't use atomic int and atomic uint at the same time).
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kris



Joined: 27 Mar 2004
Posts: 1494
Location: South Pacific

PostPosted: Tue Nov 01, 2005 8:25 pm    Post subject: Reply with quote

Thanks!
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