RE: [boost] shared_count

From: Yitzhak Sapir (ysapir_at_[hidden])
Date: 2002-02-12 13:52:14

It is hard for me to follow to what point you are in the discussion now.
However, I wish there were some portable library that implemented a wide
variety of atomic operations.  Test and Set could be implemented in the
context of some hypothetical atomic_bitset<N>, or atomic_bitvector<N>,
shared count as atomic_long, etc.  atomic_long could also provide for
atomic exchanges (via swap specializations).  In all these operations,
any O(machine word size) operation would be atomic.  And all of these
could be implemented using compare-exchange instructions, which are
available on quite a variety of multiprocessor CPU architectures.
STLPort already provides an implementation of atomic_increment/decrement
for Sparc machines (stlport/stl/_sparc_atomic.h) and many other CPUs
which provide "compare and exchange" could also be made to work within
this framework.  It would bridge the gap between the CPU-specific
instructions and the general concept which is rather portable.

I'm not sure if this was discussed already and considered too
error-prone.  But if not, and it's not to be considered error-prone, it
could be very useful for other purposes besides the current shared_count
of smart pointers.