py3: Use os.cpu_count()

src/calibre/__init__.py

@@ -18,7 +18,7 @@ except EnvironmentError:
 
 from calibre.constants import (iswindows, isosx, islinux, isfrozen,
         isbsd, preferred_encoding, __appname__, __version__, __author__,
-        win32event, win32api, winerror, fcntl,
+        win32event, win32api, winerror, fcntl, ispy3,
         filesystem_encoding, plugins, config_dir)
 from calibre.startup import winutil, winutilerror
 from calibre.utils.icu import safe_chr
@@ -454,23 +454,30 @@ class CurrentDir(object):
 _ncpus = None
 
 
-def detect_ncpus():
+if ispy3:
-    """Detects the number of effective CPUs in the system"""
+    def detect_ncpus():
-    global _ncpus
+        global _ncpus
-    if _ncpus is None:
+        if _ncpus is None:
-        if iswindows:
+            _ncpus = max(1, os.cpu_count() or 1)
-            import win32api
+        return _ncpus
-            ans = win32api.GetSystemInfo()[5]
+else:
-        else:
+    def detect_ncpus():
-            import multiprocessing
+        """Detects the number of effective CPUs in the system"""
-            ans = -1
+        global _ncpus
-            try:
+        if _ncpus is None:
-                ans = multiprocessing.cpu_count()
+            if iswindows:
-            except Exception:
+                import win32api
-                from PyQt5.Qt import QThread
+                ans = win32api.GetSystemInfo()[5]
-                ans = QThread.idealThreadCount()
+            else:
-        _ncpus = max(1, ans)
+                import multiprocessing
-    return _ncpus
+                ans = -1
+                try:
+                    ans = multiprocessing.cpu_count()
+                except Exception:
+                    from PyQt5.Qt import QThread
+                    ans = QThread.idealThreadCount()
+            _ncpus = max(1, ans)
+        return _ncpus
 
 
 relpath = os.path.relpath