bpo-38630: Fix subprocess.Popen.send_signal() race condition (GH-16984)
On Unix, subprocess.Popen.send_signal() now polls the process status.
Polling reduces the risk of sending a signal to the wrong process if
the process completed, the Popen.returncode attribute is still None,
and the pid has been reassigned (recycled) to a new different
process.
diff --git a/Doc/library/subprocess.rst b/Doc/library/subprocess.rst
index f2e5463..7485748 100644
--- a/Doc/library/subprocess.rst
+++ b/Doc/library/subprocess.rst
@@ -774,6 +774,8 @@
Sends the signal *signal* to the child.
+ Do nothing if the process completed.
+
.. note::
On Windows, SIGTERM is an alias for :meth:`terminate`. CTRL_C_EVENT and