[Boost-users] Re: boost::thread::joincausesassertion(pthreads)

From: Kevin Wheatley (hxpro_at_[hidden])
Date: 2005-03-23 10:01:54

Peter Dimov wrote:
> Kevin Wheatley reports that the assert( res == WAIT_OBJECT_0 ) is failing
> for him on Windows. Printing res (WAIT_FAILED) or GetLastError() ("invalid
> handle" would be my bet) won't give us much information as to whether the
> assert is failing due to double thread::join, thread::join on a
> default-constructed thread, or an internal error in Boost.Threads.

To me the most obvious thing missing is something like:

void thread::join()
{
    assert(m_joinable);
    int res = 0;

rest of function....

at the start of the function, that should catch some of the
programming errors across all platforms and at least says that the
assumption is that join is only valid on joinable threads (those
non-default constructed, not already joined threads). At least I think
we could all agree on that :-)

but then does this mean there should be a

bool thread::isJoinable() const { return m_joinable; }

function too? this may lead to lots of "if (thrd.isJoinable())
thrd.join();" which I'm personally not too happy of

else where in threads there are somethings which suggest code more
like:

void thread::join()
{
    assert(m_joinable);
    if (!m_joinable) return;
    int res = 0;

rest of function....

for instance this is effectively what goes on in
thread_group::remove_thread() withthe if clause after the assert, in
that function there is a comment which even indicates that it is
potentially unclear what the appropriate level of error this should
be.

Kevin

-- 
| Kevin Wheatley, Cinesite (Europe) Ltd | Nobody thinks this      |
| Senior Technology                     | My employer for certain |
| And Network Systems Architect         | Not even myself         |