void ConnectionPool::quiesce_connections()
{
for (int ii = 0; ii < _num_connections; ii++)
{
quiesce_connection(ii);
}
}
void ConnectionPool::recycle_connections()
{
// The recycler periodically recycles the connections so that any new nodes
// in the upstream proxy cluster get used reasonably soon after they are
// active. To avoid mucking around with variable length waits, the
// algorithm waits for a fixed period (one second) then recycles connections
// that are due to be recycled.
while (!_terminated)
{
#ifdef UNIT_TEST
// A smaller pause here is much faster
sleep(0.1);
#else
sleep(1);
#endif
int now = time(NULL);
// Walk the vector of connections. This is safe to do without the lock
// because the vector is immutable.
for (size_t ii = 0; ii < _tp_hash.size(); ++ii)
{
if (_tp_hash[ii].tp == NULL)
{
// This slot is empty, so try to populate it now.
create_connection(ii);
}
else if ((_tp_hash[ii].connected) &&
(_tp_hash[ii].recycle_time != 0) &&
(now >= _tp_hash[ii].recycle_time))
{
// This slot is due to be recycled, so quiesce the existing
// connection and create a new one.
TRC_STATUS("Recycle TCP connection slot %d", ii);
quiesce_connection(ii);
create_connection(ii);
}
}
}
}
void ConnectionPool::recycle_connections()
{
// The recycler periodically recycles the connections so that any new nodes
// in the upstream proxy cluster get used reasonably soon after they are
// active. To avoid mucking around with variable length waits, the
// algorithm waits for a fixed period (one second) then recycles a
// number of connections.
//
// Logically the algorithm runs an independent trial for each hash slot
// with a success probability of (1/_recycle_period). For efficiency this
// is implemented by using a binomially distributed random number to find
// the number of successful trials, then selecting that number of hash slots
// at random.
//
// Currently the selection is done with replacement which raises the possibility
// that one connection may be recycled twice in the same schedule, but this
// should only introduce a small error in the recycling rate.
std::default_random_engine rand;
std::binomial_distribution<int> rbinomial(_num_connections, 1.0/_recycle_period);
while (!_terminated)
{
sleep(1);
int recycle = rbinomial(rand);
LOG_INFO("Recycling %d connections to %.*s:%d", recycle, _target.host.slen, _target.host.ptr, _target.port);
for (int ii = 0; ii < recycle; ++ii)
{
// Pick a hash slot at random, and quiesce the connection (if active).
int hash_slot = rand() % _num_connections;
quiesce_connection(hash_slot);
// Create a new connection for this hash slot.
create_connection(hash_slot);
}
int index = 0;
// Walk the hash table, attempting to fill in any gaps caused by transports failing.
//
// It is safe to walk the vector without the lock since:
//
// * The vector never changes size
// * We only care about the value of the entry being NULL (atomic check)
// * Only we can change a NULL value to a non-NULL value
// * If we just miss a change from non-NULL to NULL (a transport suddenly dies), we'll catch it in a second.
for (std::vector<tp_hash_slot>::iterator it = _tp_hash.begin();
it != _tp_hash.end();
++it)
{
if (it->tp == NULL)
{
create_connection(index);
}
index++;
}
}
}
