jeemyeong · March 2, 2021 00:55 · Apr 12, 2017 · Apr 12, 2017 · Apr 12, 2017 · Apr 12, 2017
diff --git a/README.org b/README.org
@@ -1,3 +1,5 @@
+* The Promise All Problem
+
 in case of processing a very large array e.g. =Promise.all(A_VERY_LARGE_ARRAY_OF_XHR_PROMISE)=
 
 which would probably blow you browser memory by trying to send all requests at the same time

diff --git a/README.org b/README.org
@@ -1,6 +1,6 @@
 in case of processing a very large array e.g. =Promise.all(A_VERY_LARGE_ARRAY_OF_XHR_PROMISE)=
 
-which would probably blow you browser memory by trying to send all request at the send time
+which would probably blow you browser memory by trying to send all requests at the same time
 
 solution is limit the concurrent of requests, and wrap promise in thunk
 
@@ -10,4 +10,4 @@ if set concurrent to 2, it will send request BLAH1 and BLAH2 at the same time
 
 if BLAH1 return response and resolved, will immediatly send request to BLAH3
 
-in this way promise sending at the same time always keep the limit 2 we just set before
+in this way promise sending at the same time always keep the limit 2 which we've just configed before
diff --git a/README.org b/README.org
@@ -0,0 +1,13 @@
+in case of processing a very large array e.g. =Promise.all(A_VERY_LARGE_ARRAY_OF_XHR_PROMISE)=
+
+which would probably blow you browser memory by trying to send all request at the send time
+
+solution is limit the concurrent of requests, and wrap promise in thunk
+
+=Promise.allConcurrent(2)([()=>fetch('BLAH1'), ()=>fetch('BLAH2'),...()=>fetch('BLAHN')])=
+
+if set concurrent to 2, it will send request BLAH1 and BLAH2 at the same time
+
+if BLAH1 return response and resolved, will immediatly send request to BLAH3
+
+in this way promise sending at the same time always keep the limit 2 we just set before
diff --git a/prelude-test.js b/prelude-test.js
@@ -15,7 +15,7 @@ describe('promiseAllStepN', function(){
         }, 1000)))
         tasks[2].returns(Promise.resolve(2))
 
-        return Promise.allStepN(2)(tasks).then(x=>console.log(x))
+        return Promise.allConcurrent(2)(tasks).then(x=>console.log(x))
       })
     })
   })
@@ -34,7 +34,7 @@ describe('promiseAllStepN', function(){
           resolve(1)
           done()
         }, 1000)))
-        return Promise.allStepN(2)(tasks).then(x=>console.log(x))
+        return Promise.allConcurrent(2)(tasks).then(x=>console.log(x))
       })
     })
   })

diff --git a/prelude.js b/prelude.js
@@ -25,4 +25,4 @@ function promiseAllStepN(n, list) {
     }
   })
 }
-Promise.allCucurrent = n => list =>  promiseAllStepN(n, list)
+Promise.allConcurrent = n => list =>  promiseAllStepN(n, list)
diff --git a/prelude-test.js b/prelude-test.js
@@ -0,0 +1,42 @@
+describe('promiseAllStepN', function(){
+  describe('3 tasks, and cucurrent is 2', function(){
+    let tasks;
+    beforeEach(function(){
+      tasks = range(3).map(x=>sinon.stub())
+    })
+    describe('1 is finish', function(){
+      it('will kickoff the third task', function(done){
+        tasks[0].returns(Promise.resolve(0))
+        let task2 = tasks[2]
+        tasks[1].returns(new Promise(resolve=>setTimeout(()=>{
+          expect(task2.called).to.be.equal(true)
+          resolve(1)
+          done()
+        }, 1000)))
+        tasks[2].returns(Promise.resolve(2))
+
+        return Promise.allStepN(2)(tasks).then(x=>console.log(x))
+      })
+    })
+  })
+
+  describe('10 tasks, and cucurrent is 3', function(){
+    let tasks;
+    beforeEach(function(){
+      tasks = range(10).map(x=>sinon.stub())
+    })
+    describe('1st is finish but 2nd stuck', function(){
+      it.only('final task will run before 2nd', function(done){
+        tasks.forEach((task,index) => task.returns(Promise.resolve(index)))
+        let task10 = tasks[9]
+        tasks[1].returns(new Promise(resolve=>setTimeout(()=>{
+          expect(task10.called).to.be.equal(true)
+          resolve(1)
+          done()
+        }, 1000)))
+        return Promise.allStepN(2)(tasks).then(x=>console.log(x))
+      })
+    })
+  })
+
+})
diff --git a/prelude.js b/prelude.js
@@ -0,0 +1,28 @@
+function promiseAllStepN(n, list) {
+  let tail = list.splice(n)
+  let head = list
+  let resolved = []
+  let processed = 0
+  return new Promise(resolve=>{
+    head.forEach(x=>{
+      let res = x()
+      resolved.push(res)
+      res.then(y=>{
+        runNext()
+        return y
+      })
+    })
+    function runNext(){
+      if(processed == tail.length){
+        resolve(Promise.all(resolved))
+      }else{
+        resolved.push(tail[processed]().then(x=>{
+          runNext()
+          return x
+        }))
+        processed++
+      }
+    }
+  })
+}
+Promise.allCucurrent = n => list =>  promiseAllStepN(n, list)
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