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bpo-25920: Remove socket.getaddrinfo() lock on macOS #20177

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Merged
merged 1 commit into from
May 28, 2020
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bpo-25920: Remove socket.getaddrinfo() lock on macOS #20177

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7 changes: 7 additions & 0 deletions Misc/NEWS.d/next/Library/2020-05-18-15-38-25.bpo-25920.PxrLY8.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,7 @@
On macOS, when building Python for macOS 10.4 and older, which wasn't the case
for python.org macOS installer, :func:`socket.getaddrinfo` no longer uses an
internal lock to prevent race conditions when calling ``getaddrinfo()`` which
is thread-safe since macOS 10.5. Python 3.9 requires macOS 10.6 or newer. The
internal lock caused random hang on fork when another thread was calling
:func:`socket.getaddrinfo`. The lock was also used on FreeBSD older than 5.3,
OpenBSD older than 201311 and NetBSD older than 4.
49 changes: 2 additions & 47 deletions Modules/socketmodule.c
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Original file line number Diff line number Diff line change
Expand Up @@ -197,43 +197,6 @@ if_indextoname(index) -- return the corresponding interface name\n\
# define USE_GETHOSTBYNAME_LOCK
#endif

/* To use __FreeBSD_version, __OpenBSD__, and __NetBSD_Version__ */
#ifdef HAVE_SYS_PARAM_H
#include <sys/param.h>
#endif
/* On systems on which getaddrinfo() is believed to not be thread-safe,
(this includes the getaddrinfo emulation) protect access with a lock.

getaddrinfo is thread-safe on Mac OS X 10.5 and later. Originally it was
a mix of code including an unsafe implementation from an old BSD's
libresolv. In 10.5 Apple reimplemented it as a safe IPC call to the
mDNSResponder process. 10.5 is the first be UNIX '03 certified, which
includes the requirement that getaddrinfo be thread-safe. See issue #25924.

It's thread-safe in OpenBSD starting with 5.4, released Nov 2013:
http://www.openbsd.org/plus54.html

It's thread-safe in NetBSD starting with 4.0, released Dec 2007:

http://cvsweb.netbsd.org/bsdweb.cgi/src/lib/libc/net/getaddrinfo.c.diff?r1=1.82&r2=1.83
*/
#if ((defined(__APPLE__) && \
MAC_OS_X_VERSION_MIN_REQUIRED < MAC_OS_X_VERSION_10_5) || \
(defined(__FreeBSD__) && __FreeBSD_version+0 < 503000) || \
(defined(__OpenBSD__) && OpenBSD+0 < 201311) || \
(defined(__NetBSD__) && __NetBSD_Version__+0 < 400000000) || \
!defined(HAVE_GETADDRINFO))
#define USE_GETADDRINFO_LOCK
#endif

#ifdef USE_GETADDRINFO_LOCK
#define ACQUIRE_GETADDRINFO_LOCK PyThread_acquire_lock(netdb_lock, 1);
#define RELEASE_GETADDRINFO_LOCK PyThread_release_lock(netdb_lock);
#else
#define ACQUIRE_GETADDRINFO_LOCK
#define RELEASE_GETADDRINFO_LOCK
#endif

#if defined(__APPLE__) || defined(__CYGWIN__) || defined(__NetBSD__)
# include <sys/ioctl.h>
#endif
Expand Down Expand Up @@ -1061,7 +1024,7 @@ new_sockobject(SOCKET_T fd, int family, int type, int proto)

/* Lock to allow python interpreter to continue, but only allow one
thread to be in gethostbyname or getaddrinfo */
#if defined(USE_GETHOSTBYNAME_LOCK) || defined(USE_GETADDRINFO_LOCK)
#if defined(USE_GETHOSTBYNAME_LOCK)
static PyThread_type_lock netdb_lock;
#endif

Expand All @@ -1086,14 +1049,12 @@ setipaddr(const char *name, struct sockaddr *addr_ret, size_t addr_ret_size, int
hints.ai_socktype = SOCK_DGRAM; /*dummy*/
hints.ai_flags = AI_PASSIVE;
Py_BEGIN_ALLOW_THREADS
ACQUIRE_GETADDRINFO_LOCK
error = getaddrinfo(NULL, "0", &hints, &res);
Py_END_ALLOW_THREADS
/* We assume that those thread-unsafe getaddrinfo() versions
*are* safe regarding their return value, ie. that a
subsequent call to getaddrinfo() does not destroy the
outcome of the first call. */
RELEASE_GETADDRINFO_LOCK
if (error) {
set_gaierror(error);
return -1;
Expand Down Expand Up @@ -1194,7 +1155,6 @@ setipaddr(const char *name, struct sockaddr *addr_ret, size_t addr_ret_size, int
memset(&hints, 0, sizeof(hints));
hints.ai_family = af;
Py_BEGIN_ALLOW_THREADS
ACQUIRE_GETADDRINFO_LOCK
error = getaddrinfo(name, NULL, &hints, &res);
#if defined(__digital__) && defined(__unix__)
if (error == EAI_NONAME && af == AF_UNSPEC) {
Expand All @@ -1205,7 +1165,6 @@ setipaddr(const char *name, struct sockaddr *addr_ret, size_t addr_ret_size, int
}
#endif
Py_END_ALLOW_THREADS
RELEASE_GETADDRINFO_LOCK /* see comment in setipaddr() */
if (error) {
set_gaierror(error);
return -1;
Expand Down Expand Up @@ -6563,10 +6522,8 @@ socket_getaddrinfo(PyObject *self, PyObject *args, PyObject* kwargs)
hints.ai_protocol = protocol;
hints.ai_flags = flags;
Py_BEGIN_ALLOW_THREADS
ACQUIRE_GETADDRINFO_LOCK
error = getaddrinfo(hptr, pptr, &hints, &res0);
Py_END_ALLOW_THREADS
RELEASE_GETADDRINFO_LOCK /* see comment in setipaddr() */
if (error) {
set_gaierror(error);
goto err;
Expand Down Expand Up @@ -6659,10 +6616,8 @@ socket_getnameinfo(PyObject *self, PyObject *args)
hints.ai_socktype = SOCK_DGRAM; /* make numeric port happy */
hints.ai_flags = AI_NUMERICHOST; /* don't do any name resolution */
Py_BEGIN_ALLOW_THREADS
ACQUIRE_GETADDRINFO_LOCK
error = getaddrinfo(hostp, pbuf, &hints, &res);
Py_END_ALLOW_THREADS
RELEASE_GETADDRINFO_LOCK /* see comment in setipaddr() */
if (error) {
set_gaierror(error);
goto fail;
Expand Down Expand Up @@ -8422,7 +8377,7 @@ PyInit__socket(void)
#endif /* _MSTCPIP_ */

/* Initialize gethostbyname lock */
#if defined(USE_GETHOSTBYNAME_LOCK) || defined(USE_GETADDRINFO_LOCK)
#if defined(USE_GETHOSTBYNAME_LOCK)
netdb_lock = PyThread_allocate_lock();
#endif

Expand Down