Re: Atomic Reference Counting - Do you think this would be useful to Boost?
James Kanze wrote:
Chris Thomasson wrote:
I don't think the following contrived scenario is valid with
shared_ptr<...>. Please correct me if I am wrong:
(pseudo-code)
static shared_ptr<app> g_app(new app(...))
static shared_ptr<foo> g_foo;
void a_number_of_threads() {
for(...) {
// I don't think the following is atomic in current shared_ptr<...>:
shared_ptr<foo> l_foo(g_foo);
I can't see any reason why it should be. I can't imagine any
use where it wouldn't lead to a programming error later.
This is the reader-writer problem. One scenario is
void reader()
{
shared_ptr<foo> local( g_foo );
// use local to compute something
}
void writer()
{
shared_ptr<foo> local( g_foo );
shared_ptr<foo> next( new foo( *local ) );
local.reset();
next->update();
g_foo = next; // race here
}
One could put a fast reader-writer lock around g_foo, of course, but it
wouldn't be truly lock-free.
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