Re: Atomic set for double

From: Dorian Krause (
Date: Fri Feb 12 2010 - 03:09:22 PST

  • Next message: Paul H. Hargrove: "Re: Atomic set for double"
    > There are two functions for allocating a UPC lock (static definitions
    > are prohibited):
    >    upc_all_lock_alloc() is called collectively and all UPC threads
    > receive the same pointer
    >    upc_global_lock_alloc() is called by a single thread.
    > In Berkeley UPC we do allocate the locks from the UPC shared heap:
    >     In the case of the collective upc_all_lock_alloc() all such
    > allocations ARE from thread 0.
    >     In the case of the non-collective upc_global_lock_alloc() the
    > allocation is local to the calling thread.
    thanks a lot. Changing calls from upc_all_lock_alloc() to 
    upc_global_lock_alloc() indeed makes a difference (not in run-time, 
    though ...).
    Still I see that upc_lock_attempt and upc_lock require active 
    participation by the thread "hosting" a lock. To show what I mean, I 
    attached a test program which lets a master thread sleep and a slave 
    tries to acquire a lock. On my system (Opteron, ibv) I see the output:
    pvfs2-compute-2-13% upcrun -n 2 ./test_upc
    UPCR: UPC thread 0 of 2 on pvfs2-compute-2-13.local (process 0 of 2, 
    UPCR: UPC thread 1 of 2 on pvfs2-compute-2-13.local (process 1 of 2, 
      [0]: Done sleeping.
      [1]: Got the lock; took me 7.462001e-02
      [0]: Done sleeping.
      [1]: Got the lock; took me 1.491880e-01
    I don't quiet understand these results. Can't the lock simply be 
    implemented using e.g. bupc_atomic* functions without this "two-sided" 

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