Add callbacks (#7315)

* Add `on_train_start()` callback

* Update

* Update

train.py

@@ -66,6 +66,7 @@ def train(hyp, opt, device, callbacks):  # hyp is path/to/hyp.yaml or hyp dictio
     save_dir, epochs, batch_size, weights, single_cls, evolve, data, cfg, resume, noval, nosave, workers, freeze = \
         Path(opt.save_dir), opt.epochs, opt.batch_size, opt.weights, opt.single_cls, opt.evolve, opt.data, opt.cfg, \
         opt.resume, opt.noval, opt.nosave, opt.workers, opt.freeze
+    callbacks.run('on_pretrain_routine_start')
 
     # Directories
     w = save_dir / 'weights'  # weights dir
@@ -291,11 +292,13 @@ def train(hyp, opt, device, callbacks):  # hyp is path/to/hyp.yaml or hyp dictio
     scaler = amp.GradScaler(enabled=cuda)
     stopper = EarlyStopping(patience=opt.patience)
     compute_loss = ComputeLoss(model)  # init loss class
+    callbacks.run('on_train_start')
     LOGGER.info(f'Image sizes {imgsz} train, {imgsz} val\n'
                 f'Using {train_loader.num_workers * WORLD_SIZE} dataloader workers\n'
                 f"Logging results to {colorstr('bold', save_dir)}\n"
                 f'Starting training for {epochs} epochs...')
     for epoch in range(start_epoch, epochs):  # epoch ------------------------------------------------------------------
+        callbacks.run('on_train_epoch_start')
         model.train()
 
         # Update image weights (optional, single-GPU only)
@@ -317,6 +320,7 @@ def train(hyp, opt, device, callbacks):  # hyp is path/to/hyp.yaml or hyp dictio
             pbar = tqdm(pbar, total=nb, bar_format='{l_bar}{bar:10}{r_bar}{bar:-10b}')  # progress bar
         optimizer.zero_grad()
         for i, (imgs, targets, paths, _) in pbar:  # batch -------------------------------------------------------------
+            callbacks.run('on_train_batch_start')
             ni = i + nb * epoch  # number integrated batches (since train start)
             imgs = imgs.to(device, non_blocking=True).float() / 255  # uint8 to float32, 0-255 to 0.0-1.0
 

utils/loggers/__init__.py

@@ -84,6 +84,10 @@ class Loggers():
         else:
             self.wandb = None
 
+    def on_train_start(self):
+        # Callback runs on train start
+        pass
+
     def on_pretrain_routine_end(self):
         # Callback runs on pre-train routine end
         paths = self.save_dir.glob('*labels*.jpg')  # training labels

val.py

@@ -188,8 +188,10 @@ def run(
     dt, p, r, f1, mp, mr, map50, map = [0.0, 0.0, 0.0], 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0
     loss = torch.zeros(3, device=device)
     jdict, stats, ap, ap_class = [], [], [], []
+    callbacks.run('on_val_start')
     pbar = tqdm(dataloader, desc=s, bar_format='{l_bar}{bar:10}{r_bar}{bar:-10b}')  # progress bar
     for batch_i, (im, targets, paths, shapes) in enumerate(pbar):
+        callbacks.run('on_val_batch_start')
         t1 = time_sync()
         if cuda:
             im = im.to(device, non_blocking=True)
@@ -260,6 +262,8 @@ def run(
             f = save_dir / f'val_batch{batch_i}_pred.jpg'  # predictions
             Thread(target=plot_images, args=(im, output_to_target(out), paths, f, names), daemon=True).start()
 
+        callbacks.run('on_val_batch_end')
+
     # Compute metrics
     stats = [np.concatenate(x, 0) for x in zip(*stats)]  # to numpy
     if len(stats) and stats[0].any():