sage.doctest: multiprocessing import fixes for pyodide

src/sage/doctest/external.py

@@ -30,15 +30,15 @@
 #                  http://www.gnu.org/licenses/
 #*****************************************************************************
 
-import multiprocessing
 import os
 
+
 # With OS X, Python 3.8 defaults to use 'spawn' instead of 'fork' in
 # multiprocessing, and Sage doctesting doesn't work with 'spawn'. See
 # trac #27754.
 if os.uname().sysname == 'Darwin':
+    import multiprocessing
     multiprocessing.set_start_method('fork', force=True)
-Array = multiprocessing.Array
 
 # Functions in this module whose name is of the form 'has_xxx' tests if the
 # software xxx is available to Sage.
@@ -428,7 +428,11 @@ def __init__(self):
         features.update(all_features())
         self._features = sorted(features, key=lambda feature: feature.name)
         self._indices = {feature.name: idx for idx, feature in enumerate(self._features)}
-        self._seen = Array('i', len(self._features)) # initialized to zeroes
+        try:
+            from multiprocessing import Array
+            self._seen = Array('i', len(self._features))  # initialized to zeroes
+        except ImportError:  # module '_multiprocessing' is removed in Pyodide due to browser limitations
+            self._seen = [0] * len(self._features)
 
     def __contains__(self, item):
         """

src/sage/doctest/forker.py

@@ -52,7 +52,6 @@
 import signal
 import linecache
 import hashlib
-import multiprocessing
 import warnings
 import re
 import errno
@@ -80,8 +79,17 @@
 # multiprocessing, and Sage doctesting doesn't work with 'spawn'. See
 # trac #27754.
 if os.uname().sysname == 'Darwin':
+    import multiprocessing
     multiprocessing.set_start_method('fork', force=True)
 
+try:
+    import multiprocessing
+    from multiprocessing import Process
+except ImportError:
+    multiprocessing = None
+    class Process:
+        pass
+
 
 def _sorted_dict_pprinter_factory(start, end):
     """
@@ -1457,7 +1465,7 @@ def report_failure(self, out, test, example, got, globs):
                 except KeyboardInterrupt:
                     # Assume this is a *real* interrupt. We need to
                     # escalate this to the master doctesting process.
-                    if not self.options.serial:
+                    if not self.options.serial and multiprocessing:
                         os.kill(os.getppid(), signal.SIGINT)
                     raise
                 finally:
@@ -1594,7 +1602,7 @@ def report_unexpected_exception(self, out, test, example, exc_info):
                 except KeyboardInterrupt:
                     # Assume this is a *real* interrupt. We need to
                     # escalate this to the master doctesting process.
-                    if not self.options.serial:
+                    if not self.options.serial and multiprocessing:
                         os.kill(os.getppid(), signal.SIGINT)
                     raise
                 finally:
@@ -2106,13 +2114,13 @@ def dispatch(self):
             sage -t .../sage/rings/big_oh.py
                 [... tests, ... s]
         """
-        if self.controller.options.serial:
+        if self.controller.options.serial or not multiprocessing:
             self.serial_dispatch()
         else:
             self.parallel_dispatch()
 
 
-class DocTestWorker(multiprocessing.Process):
+class DocTestWorker(Process):
     """
     The DocTestWorker process runs one :class:`DocTestTask` for a given
     source. It returns messages about doctest failures (or all tests if
@@ -2176,7 +2184,7 @@ def __init__(self, source, options, funclist=[], baseline=None):
                 cumulative wall time: ... seconds
             Features detected...
         """
-        multiprocessing.Process.__init__(self)
+        Process.__init__(self)
 
         self.source = source
         self.options = options

src/sage/parallel/multiprocessing_sage.py

@@ -11,7 +11,6 @@
 #                  https://www.gnu.org/licenses/
 ################################################################################
 
-from multiprocessing import Pool
 from functools import partial
 from sage.misc.fpickle import pickle_function, call_pickled_function
 from . import ncpus
@@ -67,6 +66,8 @@ def parallel_iter(processes, f, inputs):
         sage: v.sort(); v
         [(((2,), {}), 4), (((3,), {}), 6)]
     """
+    from multiprocessing import Pool
+
     if processes == 0:
         processes = ncpus.ncpus()
     p = Pool(processes)