Remove use of EM_PYTHON_MULTIPROCESSING environment variable. NFC (emscripten-core#19224)

This was added a fallback to pre-existing behaviour by was always
intended to be temporary.

Author: sbc100

ChangeLog.md

@@ -20,6 +20,8 @@ See docs/process.md for more on how version tagging works.
 
 3.1.37 (in development)
 -----------------------
+- The `EM_PYTHON_MULTIPROCESSING` environment variable no longer has any effect.
+  This was added a temporary fallback but should no longer be needed. (#19224)
 - The old reverse dependency system based on `tools/deps_info.py` has been
   removed and the existing `__deps` entries in JS library files can now be used
   to express JS-to-native dependencies.  As well being more precise, and

test/test_other.py

@@ -12032,12 +12032,6 @@ def test_output_name_collision(self):
     self.assertExists('hello_.wasm')
     self.assertContained('hello, world!', self.run_js('hello.wasm'))
 
-  def test_EM_PYTHON_MULTIPROCESSING(self):
-    with env_modify({'EM_PYTHON_MULTIPROCESSING': '1'}):
-      # wasm2js optimizations use multiprocessing to run multiple node
-      # invocations
-      self.run_process([EMCC, test_file('hello_world.c'), '-sWASM=0', '-O2'])
-
   def test_main_module_no_undefined(self):
     # Test that ERROR_ON_UNDEFINED_SYMBOLS works with MAIN_MODULE.
     self.do_runf(test_file('hello_world.c'), emcc_args=['-sMAIN_MODULE', '-sERROR_ON_UNDEFINED_SYMBOLS'])

tools/shared.py

@@ -51,8 +51,6 @@
 MINIMUM_NODE_VERSION = (10, 19, 0)
 EXPECTED_LLVM_VERSION = 17
 
-# Used only when EM_PYTHON_MULTIPROCESSING=1 env. var is set.
-multiprocessing_pool = None
 logger = logging.getLogger('shared')
 
 # warning about absolute-paths is disabled by default, and not enabled by -Wall
@@ -163,17 +161,6 @@ def run_multiple_processes(commands,
   if env is None:
     env = os.environ.copy()
 
-  # By default, avoid using Python multiprocessing library due to a large amount
-  # of bugs it has on Windows (#8013, #718, etc.)
-  # Use EM_PYTHON_MULTIPROCESSING=1 environment variable to enable it. It can be
-  # faster, but may not work on Windows.
-  if int(os.getenv('EM_PYTHON_MULTIPROCESSING', '0')):
-    import multiprocessing
-    global multiprocessing_pool
-    if not multiprocessing_pool:
-      multiprocessing_pool = multiprocessing.Pool(processes=cap_max_workers_in_pool(get_num_cores()))
-    return multiprocessing_pool.map(mp_run_process, [(cmd, env, route_stdout_to_temp_files_suffix) for cmd in commands], chunksize=1)
-
   std_outs = []
 
   # TODO: Experiment with registering a signal handler here to see if that helps with Ctrl-C locking up the command prompt