#687: [Linux] pid_exists() no longer returns True if passed a process thread ID

5 files changed, 56 insertions, 13 deletions

diff --git a/HISTORY.rst b/HISTORY.rst
index 94feab8e..92413ec1 100644
--- a/HISTORY.rst
+++ b/HISTORY.rst
@@ -3,8 +3,12 @@
 5.0.2
 =====
 
+*XXXX-XX-XX*
+
 **Bug fixes**
 
+- 687_: [Linux] pid_exists() no longer returns True if passed a process thread
+  ID.
 - 948_: cannot install psutil with PYTHONOPTIMIZE=2.
 
 
diff --git a/docs/index.rst b/docs/index.rst
index 3aed8094..022c6a6b 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -738,10 +738,12 @@ Process class
 
 .. class:: Process(pid=None)
 
-  Represents an OS process with the given *pid*. If *pid* is omitted current
-  process *pid* (`os.getpid() <http://docs.python.org/library/os.html#os.getpid>`__)
-  is used.
+  Represents an OS process with the given *pid*.
+  If *pid* is omitted current process *pid*
+  (`os.getpid() <http://docs.python.org/library/os.html#os.getpid>`__) is used.
   Raise :class:`NoSuchProcess` if *pid* does not exist.
+  On Linux *pid* can also refer to a thread ID (the *id* field returned by
+  :meth:`threads` method).
   When accessing methods of this class always be  prepared to catch
   :class:`NoSuchProcess`, :class:`ZombieProcess` and :class:`AccessDenied`
   exceptions.
diff --git a/psutil/_pslinux.py b/psutil/_pslinux.py
index 91fdae4f..fe2f459d 100644
--- a/psutil/_pslinux.py
+++ b/psutil/_pslinux.py
@@ -1070,8 +1070,32 @@ def pids():
 
 
 def pid_exists(pid):
-    """Check For the existence of a unix pid."""
-    return _psposix.pid_exists(pid)
+    """Check for the existence of a unix PID."""
+    if not _psposix.pid_exists(pid):
+        return False
+    else:
+        # Linux's apparently does not distinguish between PIDs and TIDs
+        # (thread IDs).
+        # listdir("/proc") won't show any TID (only PIDs) but
+        # os.stat("/proc/{tid}") will succeed if {tid} exists.
+        # os.kill() can also be passed a TID. This is quite confusing.
+        # In here we want to enforce this distinction and support PIDs
+        # only, see:
+        # https://github.com/giampaolo/psutil/issues/687
+        try:
+            # Note: already checked that this is faster than using a
+            # regular expr. Also (a lot) faster than doing
+            # 'return pid in pids()'
+            with open_binary("%s/%s/status" % (get_procfs_path(), pid)) as f:
+                for line in f:
+                    if line.startswith(b"Tgid:"):
+                        tgid = int(line.split()[1])
+                        # If tgid and pid are the same then we're
+                        # dealing with a process PID.
+                        return tgid == pid
+                raise ValueError("'Tgid' line not found")
+        except (EnvironmentError, ValueError):
+            return pid in pids()
 
 
 def wrap_exceptions(fun):
diff --git a/psutil/tests/test_linux.py b/psutil/tests/test_linux.py
index 871cb74e..028a41d9 100755
--- a/psutil/tests/test_linux.py
+++ b/psutil/tests/test_linux.py
@@ -40,6 +40,7 @@ from psutil.tests import safe_rmpath
 from psutil.tests import sh
 from psutil.tests import skip_on_not_implemented
 from psutil.tests import TESTFN
+from psutil.tests import ThreadTask
 from psutil.tests import TRAVIS
 from psutil.tests import unittest
 from psutil.tests import which
@@ -1004,6 +1005,24 @@ class TestMisc(unittest.TestCase):
             importlib.reload(psutil._pslinux)
             importlib.reload(psutil)
 
+    def test_issue_687(self):
+        # In case of thread ID:
+        # - pid_exists() is supposed to return False
+        # - Process(tid) is supposed to work
+        # - pids() should not return the TID
+        # See: https://github.com/giampaolo/psutil/issues/687
+        t = ThreadTask()
+        t.start()
+        try:
+            p = psutil.Process()
+            tid = p.threads()[1].id
+            assert not psutil.pid_exists(tid), tid
+            pt = psutil.Process(tid)
+            pt.as_dict()
+            self.assertNotIn(tid, psutil.pids())
+        finally:
+            t.stop()
+
 
 # =====================================================================
 # test process
diff --git a/psutil/tests/test_process.py b/psutil/tests/test_process.py
index 50e0cc74..d25f4474 100755
--- a/psutil/tests/test_process.py
+++ b/psutil/tests/test_process.py
@@ -501,10 +501,8 @@ class TestProcess(unittest.TestCase):
         try:
             step2 = p.num_threads()
             self.assertEqual(step2, step1 + 1)
-            thread.stop()
         finally:
-            if thread._running:
-                thread.stop()
+            thread.stop()
 
     @unittest.skipUnless(WINDOWS, 'WINDOWS only')
     def test_num_handles(self):
@@ -524,7 +522,6 @@ class TestProcess(unittest.TestCase):
 
         thread = ThreadTask()
         thread.start()
-
         try:
             step2 = p.threads()
             self.assertEqual(len(step2), len(step1) + 1)
@@ -536,11 +533,8 @@ class TestProcess(unittest.TestCase):
             self.assertEqual(athread.id, athread[0])
             self.assertEqual(athread.user_time, athread[1])
             self.assertEqual(athread.system_time, athread[2])
-            # test num threads
-            thread.stop()
         finally:
-            if thread._running:
-                thread.stop()
+            thread.stop()
 
     @retry_before_failing()
     # see: https://travis-ci.org/giampaolo/psutil/jobs/111842553