commit f1c59929c3c180ac283334c2b3c901ac8c82f6b1
Author: Timo Kaufmann <timokau@zoho.com>
Date:   Sat Oct 20 20:07:41 2018 +0200

    Revert "Something related to the sphinxbuild seems to be leaking memory"
    
    This reverts commit 7d85dc796c58c3de57401bc22d3587b94e205091.

diff --git a/src/sage_setup/docbuild/__init__.py b/src/sage_setup/docbuild/__init__.py
index 0b24b1a60b..084c3f89d7 100644
--- a/src/sage_setup/docbuild/__init__.py
+++ b/src/sage_setup/docbuild/__init__.py
@@ -265,29 +265,35 @@ class DocBuilder(object):
     # import the customized builder for object.inv files
     inventory = builder_helper('inventory')
 
-def build_many(target, args):
-    # Pool() uses an actual fork() to run each new instance. This is important
-    # for performance reasons, i.e., don't use a forkserver when it becomes
-    # available with Python 3: Here, sage is already initialized which is quite
-    # costly, with a forkserver we would have to reinitialize it for every
-    # document we build. At the same time, don't serialize this by taking the
-    # pool (and thus the call to fork()) out completely: The call to Sphinx
-    # leaks memory, so we need to build each document in its own process to
-    # control the RAM usage.
-    from multiprocessing import Pool
-    pool = Pool(NUM_THREADS, maxtasksperchild=1)
-    # map_async handles KeyboardInterrupt correctly. Plain map and
-    # apply_async does not, so don't use it.
-    x = pool.map_async(target, args, 1)
-    try:
-        ret = x.get(99999)
-        pool.close()
-        pool.join()
-    except Exception:
-        pool.terminate()
-        if ABORT_ON_ERROR:
-            raise
-    return ret
+if NUM_THREADS > 1:
+    def build_many(target, args):
+        from multiprocessing import Pool
+        pool = Pool(NUM_THREADS, maxtasksperchild=1)
+        # map_async handles KeyboardInterrupt correctly. Plain map and
+        # apply_async does not, so don't use it.
+        x = pool.map_async(target, args, 1)
+        try:
+            ret = x.get(99999)
+            pool.close()
+            pool.join()
+        except Exception:
+            pool.terminate()
+            if ABORT_ON_ERROR:
+                raise
+        return ret
+else:
+    def build_many(target, args):
+        results = []
+
+        for arg in args:
+            try:
+                results.append(target(arg))
+            except Exception:
+                if ABORT_ON_ERROR:
+                    raise
+
+        return results
+
 
 ##########################################
 #      Parallel Building Ref Manual      #