Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>It would appear that your problem happens when a request is queued up when another one is already waiting. Here's my take on your pseudo code:</p> <pre><code>using System; using System.Threading; using System.Threading.Tasks; namespace ThrottledAsync { class Program { static void Main(string[] args) { // Queue up multiple user actions // within a short interval. for (var i = 0; i &lt; 10; i++) { OnUserAction(); Thread.Sleep(10); } Console.ReadLine(); } private static int UserActionID; private static DateTime previousWaitStartTime; public static async void OnUserAction() { // Keep track of the operation ID. var userActionID = Interlocked.Increment(ref UserActionID); // Pseudo-code implementation. var timeUntilPreviousCallWillBeOrWasMade = 1000 - (int)(DateTime.Now.Subtract(previousWaitStartTime).TotalMilliseconds); Console.WriteLine( "{0:HH:mm:ss.ffff} - User action {1}: timeUntilPreviousCallWillBeOrWasMade = {2}.", DateTime.Now, userActionID, timeUntilPreviousCallWillBeOrWasMade); var timeToWaitBeforeThisCallShouldBeMade = Math.Max(0, timeUntilPreviousCallWillBeOrWasMade + 1000); Console.WriteLine( "{0:HH:mm:ss.ffff} - User action {1}: timeToWaitBeforeThisCallShouldBeMade = {2}.", DateTime.Now, userActionID, timeToWaitBeforeThisCallShouldBeMade); previousWaitStartTime = DateTime.Now; await Task.Delay(timeToWaitBeforeThisCallShouldBeMade); await MakeCallToWebService(userActionID); } private static async Task MakeCallToWebService(int userActionID) { // Simulate network delay. await Task.Delay(new Random().Next(5, 10)); Console.WriteLine("{0:HH:mm:ss.ffff} - User action {1}: web service call.", DateTime.Now, userActionID); } } } </code></pre> <p>And the output:</p> <pre><code>19:10:11.1366 - User action 1: timeUntilPreviousCallWillBeOrWasMade = -2147482648. 19:10:11.1416 - User action 1: timeToWaitBeforeThisCallShouldBeMade = 0. 19:10:11.1536 - User action 2: timeUntilPreviousCallWillBeOrWasMade = 988. 19:10:11.1536 - User action 2: timeToWaitBeforeThisCallShouldBeMade = 1988. 19:10:11.1586 - User action 1: web service call. 19:10:11.1646 - User action 3: timeUntilPreviousCallWillBeOrWasMade = 990. 19:10:11.1646 - User action 3: timeToWaitBeforeThisCallShouldBeMade = 1990. 19:10:11.1756 - User action 4: timeUntilPreviousCallWillBeOrWasMade = 990. 19:10:11.1756 - User action 4: timeToWaitBeforeThisCallShouldBeMade = 1990. 19:10:11.1866 - User action 5: timeUntilPreviousCallWillBeOrWasMade = 990. 19:10:11.1866 - User action 5: timeToWaitBeforeThisCallShouldBeMade = 1990. 19:10:11.1976 - User action 6: timeUntilPreviousCallWillBeOrWasMade = 990. 19:10:11.1986 - User action 6: timeToWaitBeforeThisCallShouldBeMade = 1990. 19:10:11.2086 - User action 7: timeUntilPreviousCallWillBeOrWasMade = 990. 19:10:11.2086 - User action 7: timeToWaitBeforeThisCallShouldBeMade = 1990. 19:10:11.2186 - User action 8: timeUntilPreviousCallWillBeOrWasMade = 990. 19:10:11.2196 - User action 8: timeToWaitBeforeThisCallShouldBeMade = 1990. 19:10:11.2296 - User action 9: timeUntilPreviousCallWillBeOrWasMade = 990. 19:10:11.2296 - User action 9: timeToWaitBeforeThisCallShouldBeMade = 1990. 19:10:11.2406 - User action 10: timeUntilPreviousCallWillBeOrWasMade = 990. 19:10:11.2406 - User action 10: timeToWaitBeforeThisCallShouldBeMade = 1990. 19:10:13.1567 - User action 2: web service call. 19:10:13.1717 - User action 3: web service call. 19:10:13.1877 - User action 5: web service call. 19:10:13.1877 - User action 4: web service call. 19:10:13.2107 - User action 6: web service call. 19:10:13.2187 - User action 7: web service call. 19:10:13.2187 - User action 8: web service call. 19:10:13.2357 - User action 9: web service call. 19:10:13.2537 - User action 10: web service call. </code></pre> <p>You should really be using the right tool for the job. How about a <code>SemaphoreSlim</code>?</p> <pre><code>using System; using System.Threading; using System.Threading.Tasks; namespace ThrottledAsync { class Program { static void Main(string[] args) { // Queue up simultaneous calls. MakeThrottledCall(); MakeThrottledCall(); MakeThrottledCall(); MakeThrottledCall(); Console.ReadLine(); } // Used to throttle our web service calls. // Max degree of parallelism: 1. private static readonly SemaphoreSlim WebServiceMutex = new SemaphoreSlim(1, 1); private static async void MakeThrottledCall() { // Wait for the previous call // (and delay task) to complete. await WebServiceMutex.WaitAsync(); try { await MakeCallToWebService(); // Report the completion of your web service call if necessary. // Delay for a bit before releasing the semaphore. await Task.Delay(1000); } finally { // Allow the next web service call to go through. WebServiceMutex.Release(); } } private static async Task MakeCallToWebService() { // Simulate network delay. await Task.Delay(new Random().Next(5, 10)); Console.WriteLine("WebServiceCall: {0:HH:mm:ss.ffff}", DateTime.Now); } } } </code></pre> <p>EDIT: <code>MakeThrottledCall</code> no longer returns <code>Task</code> as per svick's comment.</p>
    singulars
    1. This table or related slice is empty.
    1. POHow to use Task.Delay to control time spans between calls to a web service
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USKirill Shlenskiy
    1. USKirill Shlenskiy
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. POHow to use Task.Delay to control time spans between calls to a web service
      singulars
      1. PTQuestion
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTAcceptedByOriginator
    1. COI don't like your solution, because `MakeThrottledCall()` should complete (more precisely, the `Task` it returns should complete) right after `MakeCallToWebService()` completes, not a second later.
      singulars
      1. PO
      1. USsvick
    2. CO@svick, you are making a fair point. I don't have a nice solution to that - only ugly hackery such as a fire-and-forget call to `Task.Delay(1000).ContinueWith(_ => Semaphore.Release());` The described solution is not a widely applicable pattern for async throttling in general. However, it does address the specific situation described by the question (and you would note that the original `OnUserAction` is a `void`), so I'm sticking by it for now.
      singulars
      1. PO
      1. USKirill Shlenskiy
    3. COThanks for the suggested alternative solution, will try it out. However, your assumption about the time between subsequent calls to the web service is not correct. Since it is expressed as `Max(0, timeUntilPreviousCallWillBeOrWasMade + 1000ms)` the wait time for the latest invoked call will be at least 1000ms when the previous calls has not yet been made (and less than 1000ms when it already has been made). So the question remains, why is the time between subsequent calls sometimes less than 1000ms?
      singulars
      1. PO
      1. USChristian
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload