What is the best course of action when dealing with a delayed response?

Question

What is the best course of action when dealing with a delayed response?

In this scenario, we have two buttons that each call a method which processes image data:

var NUMBER_OF_IMAGE_REQUEST_RETRIES = 3;
var IMAGE_REQUEST_TIMEOUT = 3000;


processImage: function(image_data) {
    var main_response = $q.defer();
    var hash = getImageHash(image_data);

    var requestsCounter = -1;

    requestImage = function() {
      $http.post(apiUrl, {params: {data: hash},timeout: IMAGE_REQUEST_TIMEOUT})
       .then(function(response) {
           return main_response.resolve(response.data);
        }, function(error) {
        if (++requestsCounter < NUMBER_OF_IMAGE_REQUEST_RETRIES) {
          requestLabelsImage();
        } else {
          return main_response.reject();
        }
      });
    };

    requestLabelsImage();

    return main_response.promise;
}

When a user presses one button and then quickly presses another, the issue arises where the response from the server for the second button's action is received before the response for the first button's action. This leads to confusion as the client associates the response with the latest action rather than the correct sequence of events.

To address this problem:

One potential solution involves storing the hash value of the most recent image data processed by the server:

var oldhash = null;

processImage: function(image_data) {
    var main_response = $q.defer();
    var hash = getImageHash(image_data);
    oldhash = hash;

    var requestsCounter = -1;

    requestImage = function(hash) {
     if(hash === oldhash){

      $http.post(apiUrl, {params: {data: hash},timeout: IMAGE_REQUEST_TIMEOUT})
       .then(function(response) {
           return main_response.resolve(response.data);
        }, function(error) {
        if (++requestsCounter < NUMBER_OF_IMAGE_REQUEST_RETRIES) {
          requestLabelsImage(hash);
        } else {
          return main_response.reject();
        }
      });

    }
    else {
      main_response.reject();
    }
   }

    requestLabelsImage(hash);

    return main_response.promise;
}

This approach aims to ensure that the client always receives the response relevant to the latest user action by comparing the hash values of the image data being sent to the server.

javascript angularjs asynchronous

Answer 1

Answer №1

If you wish to ignore previous requests, here is a solution:

One approach is to maintain a repository of requests using an array or dictionary structure. Upon making a new request and storing it in the repository, you can call .abort() on any previous requests.

For those interested in using a dictionary, a helpful example can be found here. Although the topic may vary, below is a modified code snippet from that resource relevant to your scenario:

var _pendingRequests = {};

function abortPendingRequests(key) {
    if (_pendingRequests[key]) {
        _pendingRequests[key].abort();
    }
}

The choice of the `key` parameter is flexible. It could represent the category of action, constants, button names, or even URLs of requests based on your preference.

You can delve deeper into this concept by checking out this insightful explanation:

jquery abort() ajax request before sending another

Answer 2

If you wish to ignore previous requests, here is a solution:

One approach is to maintain a repository of requests using an array or dictionary structure. Upon making a new request and storing it in the repository, you can call .abort() on any previous requests.

For those interested in using a dictionary, a helpful example can be found here. Although the topic may vary, below is a modified code snippet from that resource relevant to your scenario:

var _pendingRequests = {};

function abortPendingRequests(key) {
    if (_pendingRequests[key]) {
        _pendingRequests[key].abort();
    }
}

The choice of the `key` parameter is flexible. It could represent the category of action, constants, button names, or even URLs of requests based on your preference.

You can delve deeper into this concept by checking out this insightful explanation:

jquery abort() ajax request before sending another

Answer 3

Answer №2

When designing a user interface that allows for initiating multiple actions, with the processing of those actions being mutually exclusive, it is advisable to utilize promises and keep track of active promises.

button1.addEventListener("click", function(evt) {
  startRunning( task1.start() );
});

button2.addEventListener("click", function(evt) {
  startRunning( task2.start() );
});

A task runner function like this can be used:

function startRunning( promise ) {
  while(runningTasks.length>0) {
    cancel( runningTasks.unshift() );
  });
  runningTasks.push( promise );
}

The cancel functionality can be sourced from frameworks like Angular's service.cancelRequest, or custom code can be written to handle promise cancellation effectively.

If promises are not currently in use, consider integrating them into your workflow. Alternatively, a manager object approach can be implemented:

button1.addEventListener("click", function(evt) { task1(); });

button2.addEventListener("click", function(evt) { task2(); });

Utilize the following manager object:

var manager = [];

function cancelAll() {
  while(manager.lenght>0) {
    var cancelfn = manager.unshift()
    cancelfn();
  }
  return true;
}

function task1() {
  var running = cancelAll();
  manager.push(function() { running = false; });
  asyncDo(something1, function(result) {
    if(!running) return;
    // Handle actual operations here
  });
}

function task1() {
  var running = cancelAll();
  manager.push(function() { running = false; });
  asyncDo(something2, function(result) {
    if(!running) return;
    // Handle actual operations here
  });
}

This setup allows for easy cancellation management across various tasks. For instance, cancelling XHR requests or stopping processes at different stages can be achieved efficiently.

Answer 4

When designing a user interface that allows for initiating multiple actions, with the processing of those actions being mutually exclusive, it is advisable to utilize promises and keep track of active promises.

button1.addEventListener("click", function(evt) {
  startRunning( task1.start() );
});

button2.addEventListener("click", function(evt) {
  startRunning( task2.start() );
});

A task runner function like this can be used:

function startRunning( promise ) {
  while(runningTasks.length>0) {
    cancel( runningTasks.unshift() );
  });
  runningTasks.push( promise );
}

The cancel functionality can be sourced from frameworks like Angular's service.cancelRequest, or custom code can be written to handle promise cancellation effectively.

If promises are not currently in use, consider integrating them into your workflow. Alternatively, a manager object approach can be implemented:

button1.addEventListener("click", function(evt) { task1(); });

button2.addEventListener("click", function(evt) { task2(); });

Utilize the following manager object:

var manager = [];

function cancelAll() {
  while(manager.lenght>0) {
    var cancelfn = manager.unshift()
    cancelfn();
  }
  return true;
}

function task1() {
  var running = cancelAll();
  manager.push(function() { running = false; });
  asyncDo(something1, function(result) {
    if(!running) return;
    // Handle actual operations here
  });
}

function task1() {
  var running = cancelAll();
  manager.push(function() { running = false; });
  asyncDo(something2, function(result) {
    if(!running) return;
    // Handle actual operations here
  });
}

This setup allows for easy cancellation management across various tasks. For instance, cancelling XHR requests or stopping processes at different stages can be achieved efficiently.

Answer 5

Answer №3

This scenario seems like a perfect fit for promises. Essentially, whenever there is a new request, the goal is to abort any existing promises. Although I'm not well-versed in AngularJS, these links that are specific to ng might offer guidance:

How to cancel a promise in AngularJS when switching routes

Guide to Canceling Promises in AngularJS

Answer 6

This scenario seems like a perfect fit for promises. Essentially, whenever there is a new request, the goal is to abort any existing promises. Although I'm not well-versed in AngularJS, these links that are specific to ng might offer guidance:

How to cancel a promise in AngularJS when switching routes

Guide to Canceling Promises in AngularJS

What is the best course of action when dealing with a delayed response?

Answer №1

Answer №2

Answer №3

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