[SPARK-26080][PYTHON] Skips Python resource limit on Windows in Python worker

## What changes were proposed in this pull request?

`resource` package is a Unix specific package. See https://docs.python.org/2/library/resource.html and https://docs.python.org/3/library/resource.html.

Note that we document Windows support:

> Spark runs on both Windows and UNIX-like systems (e.g. Linux, Mac OS).

This should be backported into branch-2.4 to restore Windows support in Spark 2.4.1.

## How was this patch tested?

Manually mocking the changed logics.

Closes #23055 from HyukjinKwon/SPARK-26080.

Lead-authored-by: hyukjinkwon <[email protected]>
Co-authored-by: Hyukjin Kwon <[email protected]>
Signed-off-by: Hyukjin Kwon <[email protected]>
(cherry picked from commit 9cda9a8)
Signed-off-by: Hyukjin Kwon <[email protected]>

Author: HyukjinKwon

docs/configuration.md

@@ -190,6 +190,8 @@ of the most common options to set are:
     and it is up to the application to avoid exceeding the overhead memory space
     shared with other non-JVM processes. When PySpark is run in YARN or Kubernetes, this memory
     is added to executor resource requests.
+
+    NOTE: Python memory usage may not be limited on platforms that do not support resource limiting, such as Windows.
   </td>
 </tr>
 <tr>

python/pyspark/worker.py

@@ -22,7 +22,12 @@
 import os
 import sys
 import time
-import resource
+# 'resource' is a Unix specific module.
+has_resource_module = True
+try:
+    import resource
+except ImportError:
+    has_resource_module = False
 import socket
 import traceback
 
@@ -268,9 +273,9 @@ def main(infile, outfile):
 
         # set up memory limits
         memory_limit_mb = int(os.environ.get('PYSPARK_EXECUTOR_MEMORY_MB', "-1"))
-        total_memory = resource.RLIMIT_AS
-        try:
-            if memory_limit_mb > 0:
+        if memory_limit_mb > 0 and has_resource_module:
+            total_memory = resource.RLIMIT_AS
+            try:
                 (soft_limit, hard_limit) = resource.getrlimit(total_memory)
                 msg = "Current mem limits: {0} of max {1}\n".format(soft_limit, hard_limit)
                 print(msg, file=sys.stderr)
@@ -283,9 +288,9 @@ def main(infile, outfile):
                     print(msg, file=sys.stderr)
                     resource.setrlimit(total_memory, (new_limit, new_limit))
 
-        except (resource.error, OSError, ValueError) as e:
-            # not all systems support resource limits, so warn instead of failing
-            print("WARN: Failed to set memory limit: {0}\n".format(e), file=sys.stderr)
+            except (resource.error, OSError, ValueError) as e:
+                # not all systems support resource limits, so warn instead of failing
+                print("WARN: Failed to set memory limit: {0}\n".format(e), file=sys.stderr)
 
         # initialize global state
         taskContext = None