private bool TryBecomeConductor()
{
try {
_writeSeriesLocks.Add(_conductorLock, Pid);
} catch (ArgumentException) {
}
long conductorPid;
if (_writeSeriesLocks.TryGetValue(_conductorLock, out conductorPid))
{
if (conductorPid == Pid)
{
LogConductorPid(Pid);
return(true);
}
if (IsProcessAlive(conductorPid))
{
return(false);
}
// TODO need atomic CAS operations on dictionary, however in this case it is not very important, we should not open/close repos many times
_writeSeriesLocks[_conductorLock] = Pid;
LogConductorPid(Pid);
return(true);
}
throw new ApplicationException("Value must exist");
}
private async Task Upgrade <K, V>(UUID seriesId, PersistentSeries <K, V> series)
{
if (!series.IsWriter)
{
try {
_writeSeriesLocks.Add(seriesId, Pid);
series.IsWriter = true;
LogAcquireLock(seriesId, series.Version);
return;
} catch (ArgumentException) { }
}
while (true)
{
// wait if a writer from the same repo releases lock
var released = await series.LockReleaseEvent.WaitAsync(1000);
if (released)
{
try {
// TODO TryAdd atomic method
_writeSeriesLocks.Add(seriesId, Pid);
series.IsWriter = true;
LogAcquireLock(seriesId, series.Version);
break;
} catch (ArgumentException) {
Trace.WriteLine("Could not upgrade after lock release, some one jumped ahead of us");
}
}
else
{
int pid;
if (_writeSeriesLocks.TryGetValue(seriesId, out pid))
{
try {
Process.GetProcessById(pid & ((1 << 16) - 1));
Trace.TraceWarning("Tried to steal a lock but the owner process was alive.");
} catch (ArgumentException) {
// pid is not running anymore, steal lock
Trace.TraceWarning($"Current process {Pid} has stolen a lock left by a dead process {pid}. If you see this often then dispose SeriesRepository properly before application exit.");
_writeSeriesLocks[seriesId] = Pid;
series.IsWriter = true;
LogAcquireLock(seriesId, series.Version);
break;
}
}
}
}
}
