issue pywinauto#852: re-work Application.cpu_usage for Linux platform

pywinauto/linux/application.py

@@ -39,6 +39,7 @@
 
 from ..backend import registry
 from ..base_application import AppStartError, ProcessNotFoundError, AppNotConnected, BaseApplication
+from ..timings import Timings  # noqa: E402
 
 
 class Application(BaseApplication):
@@ -120,13 +121,32 @@ def cpu_usage(self, interval=None):
         if not self.process:
             raise AppNotConnected("Please use start or connect before trying "
                                   "anything else")
-        if interval:
-            time.sleep(interval)
+        proc_pid_stat = "/proc/{}/stat".format(self.process)
+        def read_cpu_info():
+            with open(proc_pid_stat, 'r') as s:
+                pid_info = s.read().split()
+            with open("/proc/stat") as s:
+                info = s.read().split()
+            # return a tuple as following:
+            # pid utime, pid stime, total utime, total stime
+            return (int(pid_info[13]), int(pid_info[14]), int(info[1]), int(info[3]))
+
         try:
-            proc_info = subprocess.check_output(["ps", "-p", str(self.process), "-o", "%cpu"], universal_newlines=True)
-            proc_info = proc_info.split("\n")
-            return float(proc_info[1])
-        except Exception:
+            before = read_cpu_info()
+            if not interval:
+                interval = Timings.cpu_usage_interval
+            time.sleep(interval)
+            after = read_cpu_info()
+            pid_time = (after[0] - before[0]) + (after[1] - before[1])
+            sys_time = (after[2] - before[2]) + (after[3] - before[3])
+            if not sys_time:
+                res = 0.0
+            else:
+                res = 100.0 * (float(pid_time) / float(sys_time))
+            #print("linux app cpu usage: ", res)
+            return res
+
+        except IOError:
             raise ProcessNotFoundError()
 
     def kill(self, soft=False):

pywinauto/unittests/test_application_linux.py

@@ -6,10 +6,13 @@
 import time
 
 sys.path.append(".")
-from pywinauto.linux.application import Application, AppStartError, AppNotConnected
 from pywinauto.application import WindowSpecification  # noqa: E402
 if sys.platform.startswith('linux'):
     from pywinauto.controls import atspiwrapper  # register atspi backend
+    from pywinauto.linux.application import Application  # noqa: E402
+    from pywinauto.linux.application import AppStartError  # noqa: E402
+    from pywinauto.linux.application import AppNotConnected  # noqa: E402
+    from pywinauto.linux.application import ProcessNotFoundError  # noqa: E402
 
 app_name = r"gtk_example.py"
 
@@ -77,10 +80,19 @@ def test_connect_by_path(self):
             self.app.connect(path=_test_app())
             self.assertEqual(self.app.process, self.subprocess_app.pid)
 
-        def test_get_cpu_usage(self):
+        def test_cpu_usage(self):
             self.app.start(_test_app())
-            time.sleep(1)
-            self.assertGreater(self.app.cpu_usage(), 0)
+            self.assertGreater(self.app.cpu_usage(0.1), 0)
+            self.app.wait_cpu_usage_lower(threshold=0.1, timeout=2.9, usage_interval=0.2)
+            # default timings
+            self.assertEqual(self.app.cpu_usage(), 0)
+
+            # non-existing process
+            self.app.kill()
+            self.assertRaises(ProcessNotFoundError, self.app.cpu_usage, 7.8)
+
+            # not connected or not started app
+            self.assertRaises(AppNotConnected, Application().cpu_usage, 12.3)
 
         def test_is_process_running(self):
             self.app.start(_test_app())