[Python-checkins] bpo-39794: Add --without-decimal-contextvar (#18702)

Stefan Krah webhook-mailer at python.org
Sat Feb 29 13:43:51 EST 2020

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---

https://github.com/python/cpython/commit/815280eb160af637e1347213659f9236adf78f80
commit: 815280eb160af637e1347213659f9236adf78f80
branch: master
author: Stefan Krah <skrah at bytereef.org>
committer: GitHub <noreply at github.com>
date: 2020年02月29日T19:43:42+01:00
summary:
bpo-39794: Add --without-decimal-contextvar (#18702)
files:
A Misc/NEWS.d/next/Library/2020-02-29-19-17-39.bpo-39794.7VjatS.rst
M Doc/library/decimal.rst
M Lib/_pydecimal.py
M Lib/test/test_asyncio/test_context.py
M Modules/_decimal/_decimal.c
M Modules/_decimal/tests/runall-memorydebugger.sh
M PC/pyconfig.h
M aclocal.m4
M configure
M configure.ac
M pyconfig.h.in
diff --git a/Doc/library/decimal.rst b/Doc/library/decimal.rst
index 4e640cc695990..9e317816abb50 100644
--- a/Doc/library/decimal.rst
+++ b/Doc/library/decimal.rst
@@ -1475,9 +1475,18 @@ are also included in the pure Python version for compatibility.
 
 .. data:: HAVE_THREADS
 
- The default value is ``True``. If Python is compiled without threads, the
- C version automatically disables the expensive thread local context
- machinery. In this case, the value is ``False``.
+ The value is ``True``. Deprecated, because Python now always has threads.
+
+.. deprecated:: 3.9
+
+.. data:: HAVE_CONTEXTVAR
+
+ The default value is ``True``. If Python is compiled ``--without-decimal-contextvar``,
+ the C version uses a thread-local rather than a coroutine-local context and the value
+ is ``False``. This is slightly faster in some nested context scenarios.
+
+.. versionadded:: 3.9
+
 
 Rounding modes
 --------------
diff --git a/Lib/_pydecimal.py b/Lib/_pydecimal.py
index c14d8ca86a118..ab989e5206a9e 100644
--- a/Lib/_pydecimal.py
+++ b/Lib/_pydecimal.py
@@ -140,8 +140,11 @@
 # Limits for the C version for compatibility
 'MAX_PREC', 'MAX_EMAX', 'MIN_EMIN', 'MIN_ETINY',
 
- # C version: compile time choice that enables the thread local context
- 'HAVE_THREADS'
+ # C version: compile time choice that enables the thread local context (deprecated, now always true)
+ 'HAVE_THREADS',
+
+ # C version: compile time choice that enables the coroutine local context
+ 'HAVE_CONTEXTVAR'
 ]
 
 __xname__ = __name__ # sys.modules lookup (--without-threads)
@@ -172,6 +175,7 @@
 
 # Compatibility with the C version
 HAVE_THREADS = True
+HAVE_CONTEXTVAR = True
 if sys.maxsize == 2**63-1:
 MAX_PREC = 999999999999999999
 MAX_EMAX = 999999999999999999
diff --git a/Lib/test/test_asyncio/test_context.py b/Lib/test/test_asyncio/test_context.py
index c309faa90062e..63b1eb320ce16 100644
--- a/Lib/test/test_asyncio/test_context.py
+++ b/Lib/test/test_asyncio/test_context.py
@@ -7,6 +7,7 @@ def tearDownModule():
 asyncio.set_event_loop_policy(None)
 
 
+ at unittest.skipUnless(decimal.HAVE_CONTEXTVAR, "decimal is built with a thread-local context")
 class DecimalContextTest(unittest.TestCase):
 
 def test_asyncio_task_decimal_context(self):
diff --git a/Misc/NEWS.d/next/Library/2020-02-29-19-17-39.bpo-39794.7VjatS.rst b/Misc/NEWS.d/next/Library/2020-02-29-19-17-39.bpo-39794.7VjatS.rst
new file mode 100644
index 0000000000000..b2a4726068af9
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2020-02-29-19-17-39.bpo-39794.7VjatS.rst
@@ -0,0 +1,2 @@
+Add --without-decimal-contextvar build option. This enables a thread-local
+rather than a coroutine local context.
diff --git a/Modules/_decimal/_decimal.c b/Modules/_decimal/_decimal.c
index e2f6ea17f8927..617941bc5ec88 100644
--- a/Modules/_decimal/_decimal.c
+++ b/Modules/_decimal/_decimal.c
@@ -122,7 +122,14 @@ incr_false(void)
 }
 
 
+#ifndef WITH_DECIMAL_CONTEXTVAR
+/* Key for thread state dictionary */
+static PyObject *tls_context_key = NULL;
+/* Invariant: NULL or the most recently accessed thread local context */
+static PyDecContextObject *cached_context = NULL;
+#else
 static PyObject *current_context_var;
+#endif
 
 /* Template for creating new thread contexts, calling Context() without
 * arguments and initializing the module_context on first access. */
@@ -1217,6 +1224,12 @@ context_new(PyTypeObject *type, PyObject *args UNUSED, PyObject *kwds UNUSED)
 static void
 context_dealloc(PyDecContextObject *self)
 {
+#ifndef WITH_DECIMAL_CONTEXTVAR
+ if (self == cached_context) {
+ cached_context = NULL;
+ }
+#endif
+
 Py_XDECREF(self->traps);
 Py_XDECREF(self->flags);
 Py_TYPE(self)->tp_free(self);
@@ -1491,6 +1504,134 @@ static PyGetSetDef context_getsets [] =
 * operation.
 */
 
+#ifndef WITH_DECIMAL_CONTEXTVAR
+/* Get the context from the thread state dictionary. */
+static PyObject *
+current_context_from_dict(void)
+{
+ PyObject *dict;
+ PyObject *tl_context;
+ PyThreadState *tstate;
+
+ dict = PyThreadState_GetDict();
+ if (dict == NULL) {
+ PyErr_SetString(PyExc_RuntimeError,
+ "cannot get thread state");
+ return NULL;
+ }
+
+ tl_context = PyDict_GetItemWithError(dict, tls_context_key);
+ if (tl_context != NULL) {
+ /* We already have a thread local context. */
+ CONTEXT_CHECK(tl_context);
+ }
+ else {
+ if (PyErr_Occurred()) {
+ return NULL;
+ }
+
+ /* Set up a new thread local context. */
+ tl_context = context_copy(default_context_template, NULL);
+ if (tl_context == NULL) {
+ return NULL;
+ }
+ CTX(tl_context)->status = 0;
+
+ if (PyDict_SetItem(dict, tls_context_key, tl_context) < 0) {
+ Py_DECREF(tl_context);
+ return NULL;
+ }
+ Py_DECREF(tl_context);
+ }
+
+ /* Cache the context of the current thread, assuming that it
+ * will be accessed several times before a thread switch. */
+ tstate = PyThreadState_GET();
+ if (tstate) {
+ cached_context = (PyDecContextObject *)tl_context;
+ cached_context->tstate = tstate;
+ }
+
+ /* Borrowed reference with refcount==1 */
+ return tl_context;
+}
+
+/* Return borrowed reference to thread local context. */
+static PyObject *
+current_context(void)
+{
+ PyThreadState *tstate;
+
+ tstate = PyThreadState_GET();
+ if (cached_context && cached_context->tstate == tstate) {
+ return (PyObject *)cached_context;
+ }
+
+ return current_context_from_dict();
+}
+
+/* ctxobj := borrowed reference to the current context */
+#define CURRENT_CONTEXT(ctxobj) \
+ ctxobj = current_context(); \
+ if (ctxobj == NULL) { \
+ return NULL; \
+ }
+
+/* Return a new reference to the current context */
+static PyObject *
+PyDec_GetCurrentContext(PyObject *self UNUSED, PyObject *args UNUSED)
+{
+ PyObject *context;
+
+ context = current_context();
+ if (context == NULL) {
+ return NULL;
+ }
+
+ Py_INCREF(context);
+ return context;
+}
+
+/* Set the thread local context to a new context, decrement old reference */
+static PyObject *
+PyDec_SetCurrentContext(PyObject *self UNUSED, PyObject *v)
+{
+ PyObject *dict;
+
+ CONTEXT_CHECK(v);
+
+ dict = PyThreadState_GetDict();
+ if (dict == NULL) {
+ PyErr_SetString(PyExc_RuntimeError,
+ "cannot get thread state");
+ return NULL;
+ }
+
+ /* If the new context is one of the templates, make a copy.
+ * This is the current behavior of decimal.py. */
+ if (v == default_context_template ||
+ v == basic_context_template ||
+ v == extended_context_template) {
+ v = context_copy(v, NULL);
+ if (v == NULL) {
+ return NULL;
+ }
+ CTX(v)->status = 0;
+ }
+ else {
+ Py_INCREF(v);
+ }
+
+ cached_context = NULL;
+ if (PyDict_SetItem(dict, tls_context_key, v) < 0) {
+ Py_DECREF(v);
+ return NULL;
+ }
+
+ Py_DECREF(v);
+ Py_RETURN_NONE;
+}
+#else
 static PyObject *
 init_current_context(void)
 {
@@ -1570,6 +1711,7 @@ PyDec_SetCurrentContext(PyObject *self UNUSED, PyObject *v)
 
 Py_RETURN_NONE;
 }
+#endif
 
 /* Context manager object for the 'with' statement. The manager
 * owns one reference to the global (outer) context and one
@@ -4388,15 +4530,8 @@ _dec_hash(PyDecObject *v)
 mpd_ssize_t exp;
 uint32_t status = 0;
 mpd_context_t maxctx;
- PyObject *context;
 
 
- context = current_context();
- if (context == NULL) {
- return -1;
- }
- Py_DECREF(context);
-
 if (mpd_isspecial(MPD(v))) {
 if (mpd_issnan(MPD(v))) {
 PyErr_SetString(PyExc_TypeError,
@@ -5538,11 +5673,6 @@ PyInit__decimal(void)
 mpd_free = PyMem_Free;
 mpd_setminalloc(_Py_DEC_MINALLOC);
 
- /* Init context variable */
- current_context_var = PyContextVar_New("decimal_context", NULL);
- if (current_context_var == NULL) {
- goto error;
- }
 
 /* Init external C-API functions */
 _py_long_multiply = PyLong_Type.tp_as_number->nb_multiply;
@@ -5714,6 +5844,15 @@ PyInit__decimal(void)
 CHECK_INT(PyModule_AddObject(m, "DefaultContext",
 default_context_template));
 
+#ifndef WITH_DECIMAL_CONTEXTVAR
+ ASSIGN_PTR(tls_context_key, PyUnicode_FromString("___DECIMAL_CTX__"));
+ Py_INCREF(Py_False);
+ CHECK_INT(PyModule_AddObject(m, "HAVE_CONTEXTVAR", Py_False));
+#else
+ ASSIGN_PTR(current_context_var, PyContextVar_New("decimal_context", NULL));
+ Py_INCREF(Py_True);
+ CHECK_INT(PyModule_AddObject(m, "HAVE_CONTEXTVAR", Py_True));
+#endif
 Py_INCREF(Py_True);
 CHECK_INT(PyModule_AddObject(m, "HAVE_THREADS", Py_True));
 
@@ -5773,9 +5912,13 @@ PyInit__decimal(void)
 Py_CLEAR(SignalTuple); /* GCOV_NOT_REACHED */
 Py_CLEAR(DecimalTuple); /* GCOV_NOT_REACHED */
 Py_CLEAR(default_context_template); /* GCOV_NOT_REACHED */
+#ifndef WITH_DECIMAL_CONTEXTVAR
+ Py_CLEAR(tls_context_key); /* GCOV_NOT_REACHED */
+#else
+ Py_CLEAR(current_context_var); /* GCOV_NOT_REACHED */
+#endif
 Py_CLEAR(basic_context_template); /* GCOV_NOT_REACHED */
 Py_CLEAR(extended_context_template); /* GCOV_NOT_REACHED */
- Py_CLEAR(current_context_var); /* GCOV_NOT_REACHED */
 Py_CLEAR(m); /* GCOV_NOT_REACHED */
 
 return NULL; /* GCOV_NOT_REACHED */
diff --git a/Modules/_decimal/tests/runall-memorydebugger.sh b/Modules/_decimal/tests/runall-memorydebugger.sh
index 29b7723dd50c0..7f3e527461871 100755
--- a/Modules/_decimal/tests/runall-memorydebugger.sh
+++ b/Modules/_decimal/tests/runall-memorydebugger.sh
@@ -1,8 +1,8 @@
 #!/bin/sh
 
 #
-# Purpose: test all machine configurations, pydebug, refleaks, release build
-# and release build with valgrind.
+# Purpose: test with and without contextvar, all machine configurations, pydebug,
+# refleaks, release build and release build with valgrind.
 #
 # Synopsis: ./runall-memorydebugger.sh [--all-configs64 | --all-configs32]
 #
@@ -57,7 +57,8 @@ print_config ()
 cd ..
 
 # test_decimal: refleak, regular and Valgrind tests
-for config in $CONFIGS; do
+for args in "--without-decimal-contextvar" ""; do
+ for config in $CONFIGS; do
 
 unset PYTHON_DECIMAL_WITH_MACHINE
 libmpdec_config=$config
@@ -69,12 +70,12 @@ for config in $CONFIGS; do
 fi
 
 ############ refleak tests ###########
- print_config "refleak tests: config=$config"
+ print_config "refleak tests: config=$config" $args
 printf "\nbuilding python ...\n\n"
 
 cd ../../
 $GMAKE distclean > /dev/null 2>&1
- ./configure CFLAGS="$ADD_CFLAGS" LDFLAGS="$ADD_LDFLAGS" --with-pydebug > /dev/null 2>&1
+ ./configure CFLAGS="$ADD_CFLAGS" LDFLAGS="$ADD_LDFLAGS" --with-pydebug $args > /dev/null 2>&1
 $GMAKE | grep _decimal
 
 printf "\n\n# ======================== refleak tests ===========================\n\n"
@@ -82,11 +83,11 @@ for config in $CONFIGS; do
 
 
 ############ regular tests ###########
- print_config "regular tests: config=$config"
+ print_config "regular tests: config=$config" $args
 printf "\nbuilding python ...\n\n"
 
 $GMAKE distclean > /dev/null 2>&1
- ./configure CFLAGS="$ADD_CFLAGS" LDFLAGS="$ADD_LDFLAGS" > /dev/null 2>&1
+ ./configure CFLAGS="$ADD_CFLAGS" LDFLAGS="$ADD_LDFLAGS" $args > /dev/null 2>&1
 $GMAKE | grep _decimal
 
 printf "\n\n# ======================== regular tests ===========================\n\n"
@@ -103,21 +104,23 @@ for config in $CONFIGS; do
 esac
 esac
 
- print_config "valgrind tests: config=$config"
+ print_config "valgrind tests: config=$config" $args
 printf "\nbuilding python ...\n\n"
 $GMAKE distclean > /dev/null 2>&1
- ./configure CFLAGS="$ADD_CFLAGS" LDFLAGS="$ADD_LDFLAGS" --without-pymalloc > /dev/null 2>&1
+ ./configure CFLAGS="$ADD_CFLAGS" LDFLAGS="$ADD_LDFLAGS" --without-pymalloc $args > /dev/null 2>&1
 $GMAKE | grep _decimal
 
 printf "\n\n# ======================== valgrind tests ===========================\n\n"
 $valgrind ./python -m test -uall test_decimal
 
 cd Modules/_decimal
+ done
 done
 
 # deccheck
 cd ../../
-for config in $CONFIGS; do
+for args in "--without-decimal-contextvar" ""; do
+ for config in $CONFIGS; do
 
 unset PYTHON_DECIMAL_WITH_MACHINE
 if [ X"$config" != X"auto" ]; then
@@ -126,22 +129,22 @@ for config in $CONFIGS; do
 fi
 
 ############ debug ############
- print_config "deccheck: config=$config --with-pydebug"
+ print_config "deccheck: config=$config --with-pydebug" $args
 printf "\nbuilding python ...\n\n"
 
 $GMAKE distclean > /dev/null 2>&1
- ./configure CFLAGS="$ADD_CFLAGS" LDFLAGS="$ADD_LDFLAGS" --with-pydebug > /dev/null 2>&1
+ ./configure CFLAGS="$ADD_CFLAGS" LDFLAGS="$ADD_LDFLAGS" --with-pydebug $args > /dev/null 2>&1
 $GMAKE | grep _decimal
 
 printf "\n\n# ========================== debug ===========================\n\n"
 ./python Modules/_decimal/tests/deccheck.py
 
 ########### regular ###########
- print_config "deccheck: config=$config "
+ print_config "deccheck: config=$config" $args
 printf "\nbuilding python ...\n\n"
 
 $GMAKE distclean > /dev/null 2>&1
- ./configure CFLAGS="$ADD_CFLAGS" LDFLAGS="$ADD_LDFLAGS" > /dev/null 2>&1
+ ./configure CFLAGS="$ADD_CFLAGS" LDFLAGS="$ADD_LDFLAGS" $args > /dev/null 2>&1
 $GMAKE | grep _decimal
 
 printf "\n\n# ======================== regular ===========================\n\n"
@@ -157,15 +160,16 @@ for config in $CONFIGS; do
 esac
 esac
 
- print_config "valgrind deccheck: config=$config "
+ print_config "valgrind deccheck: config=$config" $args
 printf "\nbuilding python ...\n\n"
 
 $GMAKE distclean > /dev/null 2>&1
- ./configure CFLAGS="$ADD_CFLAGS" LDFLAGS="$ADD_LDFLAGS" --without-pymalloc > /dev/null 2>&1
+ ./configure CFLAGS="$ADD_CFLAGS" LDFLAGS="$ADD_LDFLAGS" --without-pymalloc $args > /dev/null 2>&1
 $GMAKE | grep _decimal
 
 printf "\n\n# ======================== valgrind ==========================\n\n"
 $valgrind ./python Modules/_decimal/tests/deccheck.py
+ done
 done
 
 
diff --git a/PC/pyconfig.h b/PC/pyconfig.h
index 424c5be370927..0aa4f95bf8d2f 100644
--- a/PC/pyconfig.h
+++ b/PC/pyconfig.h
@@ -465,6 +465,10 @@ Py_NO_ENABLE_SHARED to find out. Also support MS_NO_COREDLL for b/w compat */
 (which you can't on SCO ODT 3.0). */
 /* #undef SYS_SELECT_WITH_SYS_TIME */
 
+/* Define if you want build the _decimal module using a coroutine-local rather
+ than a thread-local context */
+#define WITH_DECIMAL_CONTEXTVAR 1
+
 /* Define if you want documentation strings in extension modules */
 #define WITH_DOC_STRINGS 1
 
diff --git a/aclocal.m4 b/aclocal.m4
index 85f00dd5fac7f..f98db73656d30 100644
--- a/aclocal.m4
+++ b/aclocal.m4
@@ -1,6 +1,6 @@
-# generated automatically by aclocal 1.16.1 -*- Autoconf -*-
+# generated automatically by aclocal 1.15 -*- Autoconf -*-
 
-# Copyright (C) 1996-2018 Free Software Foundation, Inc.
+# Copyright (C) 1996-2014 Free Software Foundation, Inc.
 
 # This file is free software; the Free Software Foundation
 # gives unlimited permission to copy and/or distribute it,
diff --git a/configure b/configure
index 846116e1128ee..0bffe8b035686 100755
--- a/configure
+++ b/configure
@@ -826,6 +826,7 @@ with_libs
 with_system_expat
 with_system_ffi
 with_system_libmpdec
+with_decimal_contextvar
 enable_loadable_sqlite_extensions
 with_tcltk_includes
 with_tcltk_libs
@@ -1548,6 +1549,9 @@ Optional Packages:
 system-dependent)
 --with-system-libmpdec build _decimal module using an installed libmpdec
 library, see Doc/library/decimal.rst (default is no)
+ --with-decimal-contextvar
+ build _decimal module using a coroutine-local rather
+ than a thread-local context (default is yes)
 --with-tcltk-includes='-I...'
 override search for Tcl and Tk include files
 --with-tcltk-libs='-L...'
@@ -10496,6 +10500,28 @@ fi
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $with_system_libmpdec" >&5
 $as_echo "$with_system_libmpdec" >&6; }
 
+# Check whether _decimal should use a coroutine-local or thread-local context
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for --with-decimal-contextvar" >&5
+$as_echo_n "checking for --with-decimal-contextvar... " >&6; }
+
+# Check whether --with-decimal_contextvar was given.
+if test "${with_decimal_contextvar+set}" = set; then :
+ withval=$with_decimal_contextvar;
+else
+ with_decimal_contextvar="yes"
+fi
+
+
+if test "$with_decimal_contextvar" != "no"
+then
+
+$as_echo "#define WITH_DECIMAL_CONTEXTVAR 1" >>confdefs.h
+
+fi
+
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $with_decimal_contextvar" >&5
+$as_echo "$with_decimal_contextvar" >&6; }
+
 # Check for support for loadable sqlite extensions
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for --enable-loadable-sqlite-extensions" >&5
 $as_echo_n "checking for --enable-loadable-sqlite-extensions... " >&6; }
diff --git a/configure.ac b/configure.ac
index 840caf352d1dd..bdd607390da90 100644
--- a/configure.ac
+++ b/configure.ac
@@ -3050,6 +3050,21 @@ AC_ARG_WITH(system_libmpdec,
 
 AC_MSG_RESULT($with_system_libmpdec)
 
+# Check whether _decimal should use a coroutine-local or thread-local context
+AC_MSG_CHECKING(for --with-decimal-contextvar)
+AC_ARG_WITH(decimal_contextvar,
+ AS_HELP_STRING([--with-decimal-contextvar], [build _decimal module using a coroutine-local rather than a thread-local context (default is yes)]),
+ [],
+ [with_decimal_contextvar="yes"])
+
+if test "$with_decimal_contextvar" != "no"
+then
+ AC_DEFINE(WITH_DECIMAL_CONTEXTVAR, 1,
+ [Define if you want build the _decimal module using a coroutine-local rather than a thread-local context])
+fi
+
+AC_MSG_RESULT($with_decimal_contextvar)
+
 # Check for support for loadable sqlite extensions
 AC_MSG_CHECKING(for --enable-loadable-sqlite-extensions)
 AC_ARG_ENABLE(loadable-sqlite-extensions,
diff --git a/pyconfig.h.in b/pyconfig.h.in
index b5602134d703a..2a72e9ed7fe9c 100644
--- a/pyconfig.h.in
+++ b/pyconfig.h.in
@@ -1512,6 +1512,10 @@
 /* Define if WINDOW in curses.h offers a field _flags. */
 #undef WINDOW_HAS_FLAGS
 
+/* Define if you want build the _decimal module using a coroutine-local rather
+ than a thread-local context */
+#undef WITH_DECIMAL_CONTEXTVAR
+
 /* Define if you want documentation strings in extension modules */
 #undef WITH_DOC_STRINGS
 

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