Update async_executor.md

doc/fluid/design/async_executor/async_executor.md

@@ -4,43 +4,44 @@ There are many deep learning applications that use sparse features as inputs, su
 
 ## User Interface Design
 ``` python
-import paddle.fluid as fluid
-
-
-
-startup_program = fluid.default_startup_program()
-main_program = fluid.default_main_program()
-
-filelist = "filelist.txt"
-train_dataset = fluid.datasets.MyFeeder(filelist, 
-                                        transforms.Transform([
-                                        transforms.tokenize()]))
-
-train_loader = fluid.data.DataLoader(
-               train_dataset, batch_size=args.batch_size, shuffle=(train_sampler is None),
-               num_workers=args.workers, pin_memory=True, sampler=train_sampler)
-
-cur_block = fluid.default_main_program().current_block()
-abs_input_var = cur_block.create_var(name='abs_input',
-                                     shape=[-1, 32, 32],
-                                     dtype='float32')
-abs_output_var = cur_block.create_var(name='abs_output',
-                                     shape=[-1, 32, 32],
-                                     dtype='float32')
-
-op_desc = cur_block.desc.append_op()
-abs_op = Operator(block=cur_block, desc=op_desc, type='abs',
-                  inputs={'X': [abs_input_var]}, outputs={'Out': [abs_output_var]})
-
-for i, (slots, label) in enumerate(train_loader):
-    paddle.async_executor(feed_list=[slots, label],
-                          startup_program=startup_program, 
-                          main_program=main_program,
-                          fetch_list=[abs_output_var], 
-                          fetch_iter=10)
-    # do something on fetch list    
-
-
+def train_loop():
+    filelist = ["file%d.txt" % i for i in range(10)]
+    dataset = MultiSlotDataset()
+    dataset.set_batch_size(128)
+    # input text data
+    data = fluid.layers.data(name="words", shape=[1], dtype="int64", lod_level=1)
+    # label data
+    label = fluid.layers.data(name="label", shape=[1], dtype="int64")
+
+    avg_cost, acc, prediction = bow_net(data, label)
+    sgd_optimizer = fluid.optimizer.Adagrad(learning_rate=0.002)
+    opt_ops, weight_and_grad = sgd_optimizer.minimize(avg_cost)
+
+    for w in weight_and_grad[0]:
+        reduce(lambda x * y, 1, w.shape)
+
+    varnames = [var.name for var in weight_and_grad[0]]
+    dataset.set_field_name([data.name, label.name])
+    startup_program = fluid.default_startup_program()
+    main_program = fluid.default_main_program()
+    infer_prog = get_infer_prog([data.name, label.name], [acc, predict])
+
+    place = fluid.CPUPlace()
+    executor = fluid.AsyncExecutor()
+    executor.run_startup_program(startup_program)
+    epochs = 10
+    for i in range(epochs):
+        acc_val = executor.run(
+            program=main_program, # make sure this can be changed during iteration
+            reader=dataset, # make sure this can be changed during iteration
+            filelist=filelist, # this can be changed during iteration
+            thread=thread_num, # make sure this can be changed during iteration
+            fetch=[acc]) # how to define fetch, and what kind of things to return here
+        print("accuracy %f" % acc_val)
+        executor.save_model(infer_prog, "epoch%d.model" % i)
+
+    # todo: 
+    # inference to be added, should loadup a program and a global scope
 ```
 ## Difference between async_executor and other executors
 async_executor is mainly designed for cpu training scenarios where data throughputs are high and the computation part of training is not intensive compared with GPU trained models such as resnet-50. Since data throughputs ability is very important in async_executor, we have to design very fast data IO modules to handle very large scale data reading. Another different key aspect is that memory is not a problem in cpu training scenarios given 128G or 256G RAW in modern server. 
@@ -52,13 +53,23 @@ to be discussed.
 
 ## Inside Structure of Async Executor
 ``` c++
-void AsyncExecutor::RunFromFiles(const std::vector<std::string> & files,
-                                 const int thread_num) {
+void AsyncExecutor::RunFromFiles(
+    const ProgramDesc& main_program,
+    const std::vector<std::string> & files,
+    const int thread_num) {
+  // todo: remove fluid related interface
   root_scope_->DropKids();
   std::vector<std::thread> threads;
   threads.resize(thread_num);
 
-  // prepare readers
+  /*
+    reader: 
+    1) each thread has a reader, reader will read input data and 
+    put it into input queue
+    2) each reader has a Next() iterface, that can fetch an instance
+    from the input queue
+   */
+  // todo: should be factory method for creating datafeed
   std::vector<std::shared_ptr<DataFeed> > readers;
   readers.resize(thread_num);
   for (auto& reader : readers) {
@@ -89,7 +100,6 @@ void AsyncExecutor::RunFromFiles(const std::vector<std::string> & files,
   }
   // fetch variables in scope 0, and return
 }
-
 ```
 
 ## How to print variable information during execution