public async Task AddOrGetExisting_InvalidatesCompletedResultsWhenExpirationOnCompletionSet()
{
string key = "key";
string value = "test";
//Configure so that tasks should be immediately removed from the cache the instant they complete.
var expirationPolicy = new TaskCacheItemPolicy {
ExpirationOnCompletion = true
};
var valueFactoryStarted = new ManualResetEvent(false);
var valueFactoryContinue = new ManualResetEvent(false);
Func <Task <TestValue> > valueFactory = () => {
return(Task.Factory.StartNew(() => {
valueFactoryStarted.Set();
valueFactoryContinue.WaitOne();
return new TestValue(value);
}));
};
//First assert that the value is not yet in the cache
Assert.False(_cache.Contains(key));
var cacheUserTask = _cache.AddOrGetExisting(key, valueFactory, expirationPolicy);
// Wait until the value get from cache is in the middle of the value generation.
// At this point, a Task that is running but not completed has been added to the cache.
valueFactoryStarted.WaitOne();
// While the value generation is still running, confirm that it is present in the cache.
Assert.True(_cache.Contains(key));
// Let value generation run to completion.
valueFactoryContinue.Set();
await cacheUserTask;
// Assert that the value has now been invalidated and removed from the cache
Assert.False(_cache.Contains(key));
}
public async Task <T> AddOrGetExisting <T>(string key, Func <Task <T> > valueFactory, TaskCacheItemPolicy policy = default)
{
var asyncLazyValue = _cache.GetOrCreate(key, entry => {
//Add a common expiration token which is used for clearing the cache
entry.AddExpirationToken(new CancellationChangeToken(_cts.Token));
//Customize expiration as per the policy
entry.AbsoluteExpiration = policy.AbsoluteExpiration;
entry.AbsoluteExpirationRelativeToNow = policy.AbsoluteExpirationRelativeToNow;
entry.SlidingExpiration = policy.SlidingExpiration;
return(new AsyncLazy <T>(
factory: () => !policy.ExpirationOnCompletion
? valueFactory()
: valueFactory()
.ContinueWith(task => {
//Add an expiration token which triggers when the Task has completed (succeeded/failed/cancelled)
entry.AddExpirationToken(new TaskChangeToken(task));
return task;
})
.Unwrap()
));
});
try {
var result = await asyncLazyValue.ConfigureAwait(false);
// The awaited Task has completed. Check that the task still is the same version
// that the cache returns (i.e. the awaited task has not been invalidated during the await).
if (_cache.TryGetValue(key, out var existingValue))
{
if (existingValue != asyncLazyValue)
{
// The awaited value is no more the most recent one.
// Get the most recent value with a recursive call.
return(await AddOrGetExisting(key, valueFactory, policy).ConfigureAwait(false));
}
}
return(result);
} catch (Exception) {
// Task object for the given key failed with exception. Remove the task from the cache.
_cache.Remove(key);
// Re throw the exception to be handled by the caller.
throw;
}
}
