public void SetState(LeakyBucketState bucketInfo)
{
//Shopify Plus customers have a bucket that is twice the size (80) so we resize the bucket capacity accordingly
//It is apparently possible to request the bucket size to be even larger
//https://ecommerce.shopify.com/c/shopify-apis-and-technology/t/what-is-the-default-api-call-limit-on-shopify-stores-407292
//Note that when the capacity doubles, the leak rate also doubles. So, not only can request bursts be larger, it is also possible to sustain a faster rate over the long term.
if (bucketInfo.Capacity > this._bucketCapacity)
{
lock (_semaphore)
{
if (bucketInfo.Capacity > this._bucketCapacity)
{
_semaphore.Release(bucketInfo.Capacity - this._bucketCapacity);
_bucketCapacity = bucketInfo.Capacity;
_leakRate = bucketInfo.Capacity / DEFAULT_BUCKET_CAPACITY;
}
}
}
//Corrects the grant capacity of the bucket based on the size returned by Shopify.
//Shopify may know that the remaining capacity is less than we think it is (for example if multiple programs are using that same token)
//Shopify may also think that the remaining capacity is more than we know, but we do not ever empty the bucket because Shopify is not
//considering requests that we know are already in flight.
int grantCapacity = this._bucketCapacity - bucketInfo.CurrentFillLevel;
while (_semaphore.CurrentCount > grantCapacity)
{
//We refill the virtual bucket accordingly.
_semaphore.Wait();
}
}
public async Task <RequestResult <T> > Run <T>(CloneableRequestMessage baseRequest, ExecuteRequestAsync <T> executeRequestAsync, CancellationToken cancellationToken)
{
var accessToken = GetAccessToken(baseRequest);
LeakyBucket bucket = null;
if (accessToken != null)
{
bucket = _shopAccessTokenToLeakyBucket.GetOrAdd(accessToken, _ => new LeakyBucket());
}
while (true)
{
var request = baseRequest.Clone();
if (accessToken != null)
{
await bucket.GrantAsync();
}
try
{
var fullResult = await executeRequestAsync(request);
var bucketState = LeakyBucketState.Get(fullResult.Response);
if (bucketState != null)
{
bucket?.SetState(bucketState);
}
return(fullResult);
}
catch (ShopifyRateLimitException ex) when(ex.Reason == ShopifyRateLimitReason.BucketFull || !_retryOnlyIfLeakyBucketFull)
{
//Only retry if breach caused by full bucket
//Other limits will bubble the exception because it's not clear how long the program should wait
//Even if there is a Retry-After header, we probably don't want the thread to sleep for potentially many hours
//
//An exception may still occur:
//-Shopify may have a slightly different algorithm
//-Shopify may change to a different algorithm in the future
//-There may be timing and latency delays
//-Multiple programs may use the same access token
//-Multiple instances of the same program may use the same access token
await Task.Delay(THROTTLE_DELAY, cancellationToken);
}
}
}
