#357: implement process cpu_num() on Linux

4 files changed, 38 insertions, 0 deletions

diff --git a/docs/index.rst b/docs/index.rst
index 7fd79a1e..4f041675 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -1180,6 +1180,18 @@ Process class
 
     .. versionchanged:: 2.2.0 added support for FreeBSD
 
+  .. method:: cpu_num()
+
+    Return what CPU this process is currently running on.
+    The returned number should be ``<=`` :func:`psutil.cpu_count()` and
+    ``<= len(psutil.cpu_percent(percpu=True))``.
+    It may be used in conjunction with ``psutil.cpu_percent(percpu=True)`` to
+    observe the system workload distributed across multiple CPUs.
+
+    Availability: Linux
+
+    .. versionadded:: 5.1.0
+
   .. method:: memory_info()
 
     Return a namedtuple with variable fields depending on the platform
diff --git a/psutil/__init__.py b/psutil/__init__.py
index 3287a2c7..0ab33783 100644
--- a/psutil/__init__.py
+++ b/psutil/__init__.py
@@ -836,6 +836,18 @@ class Process(object):
             else:
                 self._proc.cpu_affinity_set(list(set(cpus)))
 
+    if hasattr(_psplatform.Process, "cpu_num"):
+
+        def cpu_num(self):
+            """Return what CPU this process is currently running on.
+            The returned number should be <= psutil.cpu_count()
+            and <= len(psutil.cpu_percent(percpu=True)).
+            It may be used in conjunction with
+            psutil.cpu_percent(percpu=True) to observe the system
+            workload distributed across CPUs.
+            """
+            return self._proc.cpu_num()
+
     # Linux, OSX and Windows only
     if hasattr(_psplatform.Process, "environ"):
 
diff --git a/psutil/_pslinux.py b/psutil/_pslinux.py
index 91fdae4f..c2c17a9a 100644
--- a/psutil/_pslinux.py
+++ b/psutil/_pslinux.py
@@ -1240,6 +1240,11 @@ class Process(object):
         return _common.pcputimes(utime, stime, children_utime, children_stime)
 
     @wrap_exceptions
+    def cpu_num(self):
+        """What CPU the process is on."""
+        return int(self._parse_stat_file()[37])
+
+    @wrap_exceptions
     def wait(self, timeout=None):
         try:
             return _psposix.wait_pid(self.pid, timeout)
diff --git a/psutil/tests/test_process.py b/psutil/tests/test_process.py
index b0176083..49aa4d86 100755
--- a/psutil/tests/test_process.py
+++ b/psutil/tests/test_process.py
@@ -281,6 +281,12 @@ class TestProcess(unittest.TestCase):
         if (max([kernel_time, ktime]) - min([kernel_time, ktime])) > 0.1:
             self.fail("expected: %s, found: %s" % (ktime, kernel_time))
 
+    @unittest.skipUnless(hasattr(psutil.Process, "cpu_num"),
+                         "platform not supported")
+    def test_cpu_num(self):
+        p = psutil.Process()
+        self.assertIn(p.cpu_num(), range(psutil.cpu_count()))
+
     def test_create_time(self):
         sproc = get_test_subprocess()
         now = time.time()
@@ -1728,6 +1734,9 @@ class TestFetchAllProcesses(unittest.TestCase):
         self.assertTrue(ret.user >= 0)
         self.assertTrue(ret.system >= 0)
 
+    def cpu_num(self, ret, proc):
+        self.assertIn(ret, range(psutil.cpu_count()))
+
     def memory_info(self, ret, proc):
         for name in ret._fields:
             self.assertGreaterEqual(getattr(ret, name), 0)