Make more tests run on Windows (#8446)

* Remove worker Wait() call due to SIGCHLD being ignored

* Port _pid_alive to Windows

* Show PID as well as TID in glog

* Update TensorFlow version for Python 3.8 on Windows

* Handle missing Pillow on Windows

* Work around dm-tree PermissionError on Windows

* Fix some lint errors on Windows with Python 3.8

* Simplify torch requirements

* Quiet git clean

* Handle finalizer issues

* Exit with the signal number

* Get rid of wget

* Fix some Windows compatibility issues with tests

Co-authored-by: Mehrdad <noreply@github.com>

python/ray/test_utils.py

@@ -1,4 +1,5 @@
 import asyncio
+import errno
 import json
 import fnmatch
 import os
@@ -12,6 +13,9 @@ import ray
 
 import psutil  # We must import psutil after ray because we bundle it with ray.
 
+if sys.platform == "win32":
+    import _winapi
+
 
 class RayTestTimeoutException(Exception):
     """Exception used to identify timeouts from test utilities."""
@@ -27,11 +31,24 @@ def _pid_alive(pid):
     Returns:
         This returns false if the process is dead. Otherwise, it returns true.
     """
+    no_such_process = errno.EINVAL if sys.platform == "win32" else errno.ESRCH
+    alive = True
     try:
-        os.kill(pid, 0)
-        return True
-    except OSError:
-        return False
+        if sys.platform == "win32":
+            SYNCHRONIZE = 0x00100000  # access mask defined in <winnt.h>
+            handle = _winapi.OpenProcess(SYNCHRONIZE, False, pid)
+            try:
+                alive = (_winapi.WaitForSingleObject(handle, 0) !=
+                         _winapi.WAIT_OBJECT_0)
+            finally:
+                _winapi.CloseHandle(handle)
+        else:
+            os.kill(pid, 0)
+    except OSError as ex:
+        if ex.errno != no_such_process:
+            raise
+        alive = False
+    return alive
 
 
 def wait_for_pid_to_exit(pid, timeout=20):