Issue #18756: os.urandom() now uses a lazily-opened persistent file descriptor, so as to avoid using many file descriptors when run in parallel from multiple threads.

1 files changed, 42 insertions, 13 deletions

diff --git a/Python/random.c b/Python/random.c
index 8cf2fef..1d470c7 100644
--- a/Python/random.c
+++ b/Python/random.c
@@ -90,6 +90,7 @@ vms_urandom(unsigned char *buffer, Py_ssize_t size, int raise)
 
 
 #if !defined(MS_WINDOWS) && !defined(__VMS)
+static int urandom_fd = -1;
 
 /* Read size bytes from /dev/urandom into buffer.
    Call Py_FatalError() on error. */
@@ -133,18 +134,30 @@ dev_urandom_python(char *buffer, Py_ssize_t size)
     if (size <= 0)
         return 0;
 
-    Py_BEGIN_ALLOW_THREADS
-    fd = _Py_open("/dev/urandom", O_RDONLY);
-    Py_END_ALLOW_THREADS
-    if (fd < 0)
-    {
-        if (errno == ENOENT || errno == ENXIO ||
-            errno == ENODEV || errno == EACCES)
-            PyErr_SetString(PyExc_NotImplementedError,
-                            "/dev/urandom (or equivalent) not found");
+    if (urandom_fd >= 0)
+        fd = urandom_fd;
+    else {
+        Py_BEGIN_ALLOW_THREADS
+        fd = _Py_open("/dev/urandom", O_RDONLY);
+        Py_END_ALLOW_THREADS
+        if (fd < 0)
+        {
+            if (errno == ENOENT || errno == ENXIO ||
+                errno == ENODEV || errno == EACCES)
+                PyErr_SetString(PyExc_NotImplementedError,
+                                "/dev/urandom (or equivalent) not found");
+            else
+                PyErr_SetFromErrno(PyExc_OSError);
+            return -1;
+        }
+        if (urandom_fd >= 0) {
+            /* urandom_fd was initialized by another thread while we were
+               not holding the GIL, keep it. */
+            close(fd);
+            fd = urandom_fd;
+        }
         else
-            PyErr_SetFromErrno(PyExc_OSError);
-        return -1;
+            urandom_fd = fd;
     }
 
     Py_BEGIN_ALLOW_THREADS
@@ -168,12 +181,20 @@ dev_urandom_python(char *buffer, Py_ssize_t size)
             PyErr_Format(PyExc_RuntimeError,
                          "Failed to read %zi bytes from /dev/urandom",
                          size);
-        close(fd);
         return -1;
     }
-    close(fd);
     return 0;
 }
+
+static void
+dev_urandom_close(void)
+{
+    if (urandom_fd >= 0) {
+        close(urandom_fd);
+        urandom_fd = -1;
+    }
+}
+
 #endif /* !defined(MS_WINDOWS) && !defined(__VMS) */
 
 /* Fill buffer with pseudo-random bytes generated by a linear congruent
@@ -271,3 +292,11 @@ _PyRandom_Init(void)
 #endif
     }
 }
+
+void
+_PyRandom_Fini(void)
+{
+#if !defined(MS_WINDOWS) && !defined(__VMS)
+    dev_urandom_close();
+#endif
+}