[feat] tracking support tensorboard (#408)

Add tensorboard in Tracking backends.

The user can set the environment variable TENSORBOARD_DIR to specify the
TensorBoard log path.

verl/utils/tracking.py

@@ -22,7 +22,7 @@
 
 
 class Tracking(object):
-    supported_backend = ["wandb", "mlflow", "swanlab", "vemlp_wandb", "console"]
+    supported_backend = ["wandb", "mlflow", "swanlab", "vemlp_wandb", "tensorboard", "console"]
 
     def __init__(self, project_name, experiment_name, default_backend: Union[str, List[str]] = 'console', config=None):
         if isinstance(default_backend, str):
@@ -81,6 +81,9 @@ def __init__(self, project_name, experiment_name, default_backend: Union[str, Li
             )
             self.logger['vemlp_wandb'] = vemlp_wandb
 
+        if 'tensorboard' in default_backend:
+            self.logger['tensorboard'] = _TensorboardAdapter()
+
         if 'console' in default_backend:
             from verl.utils.logger.aggregate_logger import LocalLogger
             self.console_logger = LocalLogger(print_to_console=True)
@@ -98,6 +101,26 @@ def __del__(self):
             self.logger['swanlab'].finish()
         if 'vemlp_wandb' in self.logger:
             self.logger['vemlp_wandb'].finish(exit_code=0)
+        if 'tensorboard' in self.logger:
+            self.logger['tensorboard'].finish()
+
+
+class _TensorboardAdapter:
+
+    def __init__(self):
+        from torch.utils.tensorboard import SummaryWriter
+        import os
+        tensorboard_dir = os.environ.get("TENSORBOARD_DIR", "tensorboard_log")
+        os.makedirs(tensorboard_dir, exist_ok=True)
+        print(f"Saving tensorboard log to {tensorboard_dir}.")
+        self.writer = SummaryWriter(tensorboard_dir)
+
+    def log(self, data, step):
+        for key in data:
+            self.writer.add_scalar(key, data[key], step)
+
+    def finish(self):
+        self.writer.close()
 
 
 class _MlflowLoggingAdapter: