private async Task <bool> TryAcquireOrRenew(CancellationToken cancellationToken)
{
var l = config.Lock;
var leaderElectionRecord = new LeaderElectionRecord()
{
HolderIdentity = l.Identity,
LeaseDurationSeconds = config.LeaseDuration.Seconds,
AcquireTime = DateTime.UtcNow,
RenewTime = DateTime.UtcNow,
LeaderTransitions = 0,
};
// 1. obtain or create the ElectionRecord
LeaderElectionRecord oldLeaderElectionRecord = null;
try
{
oldLeaderElectionRecord = await l.GetAsync(cancellationToken).ConfigureAwait(false);
}
catch (HttpOperationException e)
{
if (e.Response.StatusCode != HttpStatusCode.NotFound)
{
return(false);
}
}
if (oldLeaderElectionRecord?.AcquireTime == null ||
oldLeaderElectionRecord?.RenewTime == null ||
oldLeaderElectionRecord?.HolderIdentity == null)
{
var created = await l.CreateAsync(leaderElectionRecord, cancellationToken).ConfigureAwait(false);
if (created)
{
observedRecord = leaderElectionRecord;
observedTime = DateTimeOffset.Now;
return(true);
}
return(false);
}
// 2. Record obtained, check the Identity & Time
if (!Equals(observedRecord, oldLeaderElectionRecord))
{
observedRecord = oldLeaderElectionRecord;
observedTime = DateTimeOffset.Now;
}
if (!string.IsNullOrEmpty(oldLeaderElectionRecord.HolderIdentity) &&
observedTime + config.LeaseDuration > DateTimeOffset.Now &&
!IsLeader())
{
// lock is held by %v and has not yet expired", oldLeaderElectionRecord.HolderIdentity
return(false);
}
// 3. We're going to try to update. The leaderElectionRecord is set to it's default
// here. Let's correct it before updating.
if (IsLeader())
{
leaderElectionRecord.AcquireTime = oldLeaderElectionRecord.AcquireTime;
leaderElectionRecord.LeaderTransitions = oldLeaderElectionRecord.LeaderTransitions;
}
else
{
leaderElectionRecord.LeaderTransitions = oldLeaderElectionRecord.LeaderTransitions + 1;
}
var updated = await l.UpdateAsync(leaderElectionRecord, cancellationToken).ConfigureAwait(false);
if (!updated)
{
return(false);
}
observedRecord = leaderElectionRecord;
observedTime = DateTimeOffset.Now;
return(true);
}
protected bool Equals(LeaderElectionRecord other)
{
return(HolderIdentity == other?.HolderIdentity && Nullable.Equals(AcquireTime, other.AcquireTime) && Nullable.Equals(RenewTime, other.RenewTime));
}