# HG changeset patch

# User Charles-François Natali <cf.natali@gmail.com>

# Date 1455316761 0

# Node ID d3662c088db8fb2c89f754031f18b1543419fed9

# Parent  5715a6d9ff12053e81f7ad75268ac059b079b351

Issue #24303: Fix random EEXIST upon multiprocessing semaphores creation with

Linux PID namespaces enabled.

diff --git a/Modules/_multiprocessing/semaphore.c b/Modules/_multiprocessing/semaphore.c

--- a/Modules/_multiprocessing/semaphore.c

+++ b/Modules/_multiprocessing/semaphore.c

@@ -429,7 +429,7 @@ semlock_new(PyTypeObject *type, PyObject

     int kind, maxvalue, value;

     PyObject *result;

     static char *kwlist[] = {"kind", "value", "maxvalue", NULL};

-    static int counter = 0;

+    int try = 0;

     if (!PyArg_ParseTupleAndKeywords(args, kwds, "iii", kwlist,

                                      &kind, &value, &maxvalue))

@@ -440,10 +440,18 @@ semlock_new(PyTypeObject *type, PyObject

         return NULL;

     }

-    PyOS_snprintf(buffer, sizeof(buffer), "/mp%ld-%d", (long)getpid(), counter++);

+    /* Create a semaphore with a unique name. The bytes returned by

+     * _PyOS_URandom() are treated as unsigned long to ensure that the filename

+     * is valid (no special characters). */

+    do {

+        unsigned long suffix;

+        _PyOS_URandom((char *)&suffix, sizeof(suffix));

+        PyOS_snprintf(buffer, sizeof(buffer), "/mp%ld-%lu", (long)getpid(),

+                      suffix);

+        SEM_CLEAR_ERROR();

+        handle = SEM_CREATE(buffer, value, maxvalue);

+    } while ((handle == SEM_FAILED) && (errno == EEXIST) && (++try < 100));

-    SEM_CLEAR_ERROR();

-    handle = SEM_CREATE(buffer, value, maxvalue);

     /* On Windows we should fail if GetLastError()==ERROR_ALREADY_EXISTS */

     if (handle == SEM_FAILED || SEM_GET_LAST_ERROR() != 0)

         goto failure;