[misc] fix custom allreduce p2p cache file generation (#7853)

vllm/distributed/device_communicators/custom_all_reduce_utils.py

@@ -4,6 +4,7 @@ import os
 import pickle
 import subprocess
 import sys
+import tempfile
 from itertools import product
 from typing import Dict, List, Optional, Sequence
 
@@ -211,20 +212,27 @@ def gpu_p2p_access_check(src: int, tgt: int) -> bool:
         # However, `can_actually_p2p` requires spawn method.
         # The fix is, we use `subprocess` to call the function,
         # where we have `if __name__ == "__main__":` in this file.
-        input_bytes = pickle.dumps((batch_src, batch_tgt))
-        returned = subprocess.run([sys.executable, __file__],
-                                  input=input_bytes,
-                                  capture_output=True)
-        # check if the subprocess is successful
-        try:
-            returned.check_returncode()
-        except Exception as e:
-            # wrap raised exception to provide more information
-            raise RuntimeError(
-                f"Error happened when batch testing "
-                f"peer-to-peer access from {batch_src} to {batch_tgt}:\n"
-                f"{returned.stderr.decode()}") from e
-        result = pickle.loads(returned.stdout)
+
+        # use a temporary file to store the result
+        # we don't use the output of the subprocess directly,
+        # because the subprocess might produce logging output
+        with tempfile.NamedTemporaryFile() as output_file:
+            input_bytes = pickle.dumps(
+                (batch_src, batch_tgt, output_file.name))
+            returned = subprocess.run([sys.executable, __file__],
+                                      input=input_bytes,
+                                      capture_output=True)
+            # check if the subprocess is successful
+            try:
+                returned.check_returncode()
+            except Exception as e:
+                # wrap raised exception to provide more information
+                raise RuntimeError(
+                    f"Error happened when batch testing "
+                    f"peer-to-peer access from {batch_src} to {batch_tgt}:\n"
+                    f"{returned.stderr.decode()}") from e
+            with open(output_file.name, "rb") as f:
+                result = pickle.load(f)
         for _i, _j, r in zip(batch_src, batch_tgt, result):
             cache[f"{_i}->{_j}"] = r
         with open(path, "w") as f:
@@ -241,6 +249,7 @@ def gpu_p2p_access_check(src: int, tgt: int) -> bool:
 __all__ = ["gpu_p2p_access_check"]
 
 if __name__ == "__main__":
-    batch_src, batch_tgt = pickle.loads(sys.stdin.buffer.read())
+    batch_src, batch_tgt, output_file = pickle.loads(sys.stdin.buffer.read())
     result = can_actually_p2p(batch_src, batch_tgt)
-    sys.stdout.buffer.write(pickle.dumps(result))
+    with open(output_file, "wb") as f:
+        f.write(pickle.dumps(result))