Issue #21455: Add a default backlog to socket.listen().
diff --git a/Doc/library/socket.rst b/Doc/library/socket.rst
index 1f5a8e0..3a9d611 100644
--- a/Doc/library/socket.rst
+++ b/Doc/library/socket.rst
@@ -906,12 +906,15 @@
On other platforms, the generic :func:`fcntl.fcntl` and :func:`fcntl.ioctl`
functions may be used; they accept a socket object as their first argument.
-.. method:: socket.listen(backlog)
+.. method:: socket.listen([backlog])
- Listen for connections made to the socket. The *backlog* argument specifies the
- maximum number of queued connections and should be at least 0; the maximum value
- is system-dependent (usually 5), the minimum value is forced to 0.
+ Enable a server to accept connections. If *backlog* is specified, it must
+ be at least 0 (if it is lower, it is set to 0); it specifies the number of
+ unaccepted connections that the system will allow before refusing new
+ connections. If not specified, a default reasonable value is chosen.
+ .. versionchanged:: 3.5
+ The *backlog* parameter is now optional.
.. method:: socket.makefile(mode='r', buffering=None, *, encoding=None, \
errors=None, newline=None)
diff --git a/Lib/test/test_socket.py b/Lib/test/test_socket.py
index aed10a7..86cbec7 100644
--- a/Lib/test/test_socket.py
+++ b/Lib/test/test_socket.py
@@ -1344,10 +1344,13 @@
def test_listen_backlog(self):
for backlog in 0, -1:
- srv = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+ with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as srv:
+ srv.bind((HOST, 0))
+ srv.listen(backlog)
+
+ with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as srv:
srv.bind((HOST, 0))
- srv.listen(backlog)
- srv.close()
+ srv.listen()
@support.cpython_only
def test_listen_backlog_overflow(self):
diff --git a/Misc/NEWS b/Misc/NEWS
index 79e1505..76006d9 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -84,6 +84,8 @@
Library
-------
+- Issue #21455: Add a default backlog to socket.listen().
+
- Issue #21525: Most Tkinter methods which accepted tuples now accept lists too.
- Issue #10744: Fix PEP 3118 format strings on ctypes objects with a nontrivial
diff --git a/Modules/socketmodule.c b/Modules/socketmodule.c
index d0149dd..5a2893c 100644
--- a/Modules/socketmodule.c
+++ b/Modules/socketmodule.c
@@ -121,7 +121,7 @@
getsockname() -- return local address\n\
getsockopt(level, optname[, buflen]) -- get socket options\n\
gettimeout() -- return timeout or None\n\
-listen(n) -- start listening for incoming connections\n\
+listen([n]) -- start listening for incoming connections\n\
recv(buflen[, flags]) -- receive data\n\
recv_into(buffer[, nbytes[, flags]]) -- receive data (into a buffer)\n\
recvfrom(buflen[, flags]) -- receive data and sender\'s address\n\
@@ -2534,14 +2534,16 @@
/* s.listen(n) method */
static PyObject *
-sock_listen(PySocketSockObject *s, PyObject *arg)
+sock_listen(PySocketSockObject *s, PyObject *args)
{
- int backlog;
+ /* We try to choose a default backlog high enough to avoid connection drops
+ * for common workloads, yet not too high to limit resource usage. */
+ int backlog = Py_MIN(SOMAXCONN, 128);
int res;
- backlog = _PyLong_AsInt(arg);
- if (backlog == -1 && PyErr_Occurred())
+ if (!PyArg_ParseTuple(args, "|i:listen", &backlog))
return NULL;
+
Py_BEGIN_ALLOW_THREADS
/* To avoid problems on systems that don't allow a negative backlog
* (which doesn't make sense anyway) we force a minimum value of 0. */
@@ -2556,12 +2558,12 @@
}
PyDoc_STRVAR(listen_doc,
-"listen(backlog)\n\
+"listen([backlog])\n\
\n\
-Enable a server to accept connections. The backlog argument must be at\n\
-least 0 (if it is lower, it is set to 0); it specifies the number of\n\
+Enable a server to accept connections. If backlog is specified, it must be\n\
+at least 0 (if it is lower, it is set to 0); it specifies the number of\n\
unaccepted connections that the system will allow before refusing new\n\
-connections.");
+connections. If not specified, a default reasonable value is chosen.");
/*
@@ -3795,7 +3797,7 @@
{"share", (PyCFunction)sock_share, METH_VARARGS,
sock_share_doc},
#endif
- {"listen", (PyCFunction)sock_listen, METH_O,
+ {"listen", (PyCFunction)sock_listen, METH_VARARGS,
listen_doc},
{"recv", (PyCFunction)sock_recv, METH_VARARGS,
recv_doc},