[GraphBolt][CUDA] Use deque instead of Queue for Bufferer.

python/dgl/graphbolt/dataloader.py

@@ -1,6 +1,6 @@
 """Graph Bolt DataLoaders"""
 
-from queue import Queue
+from collections import deque
 
 import torch
 import torch.utils.data
@@ -69,18 +69,18 @@ def __init__(self, datapipe, buffer_size=1):
             raise ValueError(
                 "'buffer_size' is required to be a positive integer."
             )
-        self.buffer = Queue(buffer_size)
+        self.buffer = deque(maxlen=buffer_size)
 
     def __iter__(self):
         for data in self.datapipe:
-            if not self.buffer.full():
-                self.buffer.put(data)
+            if len(self.buffer) < self.buffer.maxlen:
+                self.buffer.append(data)
             else:
-                return_data = self.buffer.get()
-                self.buffer.put(data)
+                return_data = self.buffer.popleft()
+                self.buffer.append(data)
                 yield return_data
-        while not self.buffer.empty():
-            yield self.buffer.get()
+        while len(self.buffer) > 0:
+            yield self.buffer.popleft()
 
 
 class Awaiter(dp.iter.IterDataPipe):