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MXS-1392 Add reference count to MXS_POLL_DATA

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The polling mechanism can now optionally be used for managing
the lifetime of an object placed into the poll set.

If a MXS_POLL_DATA has a non-null 'free', then the reference count
of the data will be increased before calling the handler and
decreased after. In that case, if the reference count reaches 0,
the free function will be called.

Note that the reference counts of *all* MXS_POLL_DATAs returned
by 'epoll_wait' will be increased before the events are delivered
to the handlers individually for each MXS_POLL_DATA, and then once
all events have been delivered, the reference count of each
MXS_POLL_DATA will be decreased.

This ensure that if there are interdependencies between different
MXS_POLL_DATAs returned by one call to 'epoll_wait', the case that
an MXS_POLL_DATA is deleted before its events have been delivered
can be avoided by using the reference count for lifetime management.

In subsequent commits, the reference count will be taken into use
in the lifetime management of DCBs.
This commit is contained in:
Johan Wikman
2017-09-06 15:47:07 +03:00
parent daef8ad5d7
commit 7e17e2cd56
3 changed files with 90 additions and 27 deletions
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23
server/core/worker.cc
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@ -162,6 +162,8 @@ Worker::Worker(int id,
, m_shutdown_initiated(false)
{
MXS_POLL_DATA::handler = &Worker::epoll_instance_handler;
MXS_POLL_DATA::free = NULL;
MXS_POLL_DATA::refcount = 0;
MXS_POLL_DATA::thread.id = id;
}
@ -1139,6 +1141,15 @@ void Worker::poll_waitevents()
uint64_t cycle_start = hkheartbeat;
for (int i = 0; i < nfds; i++)
{
MXS_POLL_DATA *data = (MXS_POLL_DATA*)events[i].data.ptr;
if (data->free)
{
poll_inc_ref(data);
}
}
for (int i = 0; i < nfds; i++)
{
/** Calculate event queue statistics */
@ -1200,6 +1211,18 @@ void Worker::poll_waitevents()
m_statistics.maxexectime = MXS_MAX(m_statistics.maxexectime, qtime);
}
for (int i = 0; i < nfds; i++)
{
MXS_POLL_DATA *data = (MXS_POLL_DATA*)events[i].data.ptr;
if (data->free)
{
if (poll_dec_ref(data) == 1)
{
data->free(data);
}
}
}
dcb_process_idle_sessions(m_id);
m_state = ZPROCESSING;