Hi,

This patch is an attempt to fix some potential race conditions with
accesses to shared data structures from multiple concurrent threads in
libgomp's OpenACC entry points. The main change is to move locking out
of lookup_host and lookup_dev in oacc-mem.c and into their callers
(which can then hold the locks for the whole operation that they are
performing).

Also missing locking has been added for gomp_acc_insert_pointer.

Tests look OK (with offloading to NVidia PTX).

OK? (For the gomp4 branch, maybe, if trunk's not suitable at the
moment?)

Thanks,

Julian

ChangeLog

    libgomp/
    * oacc-mem.c (lookup_host): Remove locking from function. Note
    locking requirement for caller in function comment.
    (lookup_dev): Likewise.
    (acc_free, acc_deviceptr, acc_hostptr, acc_is_present)
    (acc_map_data, acc_unmap_data, present_create_copy, delete_copyout)
    (update_dev_host, gomp_acc_insert_pointer, gomp_acc_remove_pointer):
    Add locking.