final patches from Neil Schemenauer for garbage collection

1 files changed, 679 insertions, 0 deletions

diff --git a/Modules/gcmodule.c b/Modules/gcmodule.c
new file mode 100644
index 0000000..8c0dc3d
--- /dev/null
+++ b/Modules/gcmodule.c
@@ -0,0 +1,679 @@
+/*
+ 
+  Reference Cycle Garbage Collection
+  ==================================
+
+  Neil Schemenauer <nascheme@enme.ucalgary.ca>
+
+  Based on a post on the python-dev list.  Ideas from Guido van Rossum,
+  Eric Tiedemann, and various others.
+
+  http://www.enme.calgary.ca/~nascheme/python/gc.html
+  http://www.python.org/pipermail/python-dev/2000-March/003869.html
+  http://www.python.org/pipermail/python-dev/2000-March/004010.html
+  http://www.python.org/pipermail/python-dev/2000-March/004022.html
+
+  For a highlevel view of the collection process, read the collect
+  function.
+
+  TODO:
+	use a different interface for set_debug() (keywords)?
+	tune parameters
+
+*/
+
+
+#include "Python.h"
+
+#ifdef WITH_CYCLE_GC
+
+/* magic gc_refs value */
+#define GC_MOVED -1
+
+/*** Global GC state ***/
+
+/* linked lists of container objects */
+static PyGC_Head generation0 = {&generation0, &generation0, 0};
+static PyGC_Head generation1 = {&generation1, &generation1, 0};
+static PyGC_Head generation2 = {&generation2, &generation2, 0};
+static int generation = 0; /* current generation being collected */
+
+/* collection frequencies, XXX tune these */
+static int threshold0 = 100; /* net new containers before collection */
+static int threshold1 = 10;  /* generation0 collections before collecting 1 */
+static int threshold2 = 10;  /* generation1 collections before collecting 2 */
+
+/* net new objects allocated since last collection */
+static int allocated;
+
+/* set for debugging information */
+#define DEBUG_STATS		(1<<0) /* print collection statistics */
+#define DEBUG_COLLECTABLE	(1<<1) /* print collectable objects */
+#define DEBUG_UNCOLLECTABLE	(1<<2) /* print uncollectable objects */
+#define DEBUG_INSTANCES		(1<<3) /* print instances */
+#define DEBUG_OBJECTS		(1<<4) /* print other objects */
+#define DEBUG_LEAK		DEBUG_COLLECTABLE | \
+				DEBUG_UNCOLLECTABLE | \
+				DEBUG_INSTANCES | \
+				DEBUG_OBJECTS
+static int debug;
+
+/* list of uncollectable objects */
+static PyObject *garbage;
+
+
+/*** list functions ***/
+
+static void
+gc_list_init(PyGC_Head *list)
+{
+	list->gc_prev = list;
+	list->gc_next = list;
+}
+
+static void
+gc_list_append(PyGC_Head *node, PyGC_Head *list)
+{
+	node->gc_next = list;
+	node->gc_prev = list->gc_prev;
+	node->gc_prev->gc_next = node;
+	list->gc_prev = node;
+}
+
+static void
+gc_list_remove(PyGC_Head *node)
+{
+	node->gc_prev->gc_next = node->gc_next;
+	node->gc_next->gc_prev = node->gc_prev;
+#ifdef Py_DEBUG
+	node->gc_prev = NULL;
+	node->gc_next = NULL;
+#endif
+}
+
+static void 
+gc_list_move(PyGC_Head *from, PyGC_Head *to)
+{
+	if (from->gc_next == from) {
+		/* empty from list */
+		gc_list_init(to);
+	} else {
+		to->gc_next = from->gc_next;
+		to->gc_next->gc_prev = to;
+		to->gc_prev = from->gc_prev;
+		to->gc_prev->gc_next = to;
+	}
+	gc_list_init(from);
+}
+
+/* append a list onto another list, from becomes an empty list */
+static void
+gc_list_merge(PyGC_Head *from, PyGC_Head *to)
+{
+	PyGC_Head *tail;
+	if (from->gc_next != from) {
+		tail = to->gc_prev;
+		tail->gc_next = from->gc_next;
+		tail->gc_next->gc_prev = tail;
+		to->gc_prev = from->gc_prev;
+		to->gc_prev->gc_next = to;
+	}
+	gc_list_init(from);
+}
+
+static long
+gc_list_size(PyGC_Head *list)
+{
+	PyGC_Head *gc;
+	long n = 0;
+	for (gc = list->gc_next; gc != list; gc = gc->gc_next) {
+		n++;
+	}
+	return n;
+}
+
+/*** end of list stuff ***/
+
+
+/* Set all gc_refs = ob_refcnt */
+static void
+update_refs(PyGC_Head *containers)
+{
+	PyGC_Head *gc = containers->gc_next;
+	for (; gc != containers; gc=gc->gc_next) {
+		gc->gc_refs = PyObject_FROM_GC(gc)->ob_refcnt;
+	}
+}
+
+static int
+visit_decref(PyObject *op, void *data)
+{
+	if (op && PyObject_IS_GC(op)) {
+		PyObject_AS_GC(op)->gc_refs--;
+	}
+	return 0;
+}
+
+/* Subtract internal references from gc_refs */
+static void
+subtract_refs(PyGC_Head *containers)
+{
+	traverseproc traverse;
+	PyGC_Head *gc = containers->gc_next;
+	for (; gc != containers; gc=gc->gc_next) {
+		traverse = PyObject_FROM_GC(gc)->ob_type->tp_traverse;
+		(void) traverse(PyObject_FROM_GC(gc),
+			       (visitproc)visit_decref,
+			       NULL);
+	}
+}
+
+/* Append objects with gc_refs > 0 to roots list */
+static void
+move_roots(PyGC_Head *containers, PyGC_Head *roots)
+{
+	PyGC_Head *next;
+	PyGC_Head *gc = containers->gc_next;
+	while (gc != containers) {
+		next = gc->gc_next;
+		if (gc->gc_refs > 0) {
+			gc_list_remove(gc);
+			gc_list_append(gc, roots);
+			gc->gc_refs = GC_MOVED;
+		}
+		gc = next;
+	}
+}
+
+static int
+visit_reachable(PyObject *op, PyGC_Head *roots)
+{
+	if (PyObject_IS_GC(op)) {
+		PyGC_Head *gc = PyObject_AS_GC(op);
+		if (gc && gc->gc_refs != GC_MOVED) {
+			gc_list_remove(gc);
+			gc_list_append(gc, roots);
+			gc->gc_refs = GC_MOVED;
+		}
+	}
+	return 0;
+}
+
+/* Move objects referenced from reachable to reachable set. */
+static void
+move_root_reachable(PyGC_Head *reachable)
+{
+	traverseproc traverse;
+	PyGC_Head *gc = reachable->gc_next;
+	for (; gc != reachable; gc=gc->gc_next) {
+		/* careful, reachable list is growing here */
+		PyObject *op = PyObject_FROM_GC(gc);
+		traverse = op->ob_type->tp_traverse;
+		(void) traverse(op,
+			       (visitproc)visit_reachable,
+			       (void *)reachable);
+	}
+}
+
+/* move all objects with finalizers (instances with __del__) */
+static void
+move_finalizers(PyGC_Head *unreachable, PyGC_Head *finalizers)
+{
+	PyGC_Head *next;
+	PyGC_Head *gc = unreachable->gc_next;
+	static PyObject *delstr;
+	if (delstr == NULL) {
+		delstr = PyString_InternFromString("__del__");
+	}
+	for (; gc != unreachable; gc=next) {
+		PyObject *op = PyObject_FROM_GC(gc);
+		next = gc->gc_next;
+		if (PyInstance_Check(op) && PyObject_HasAttr(op, delstr)) {
+			gc_list_remove(gc);
+			gc_list_append(gc, finalizers);
+		}
+	}
+}
+
+
+/* called by tp_traverse */
+static int
+visit_finalizer_reachable(PyObject *op, PyGC_Head *finalizers)
+{
+	if (PyObject_IS_GC(op)) {
+		PyGC_Head *gc = PyObject_AS_GC(op);
+		if (gc && gc->gc_refs != GC_MOVED) {
+			gc_list_remove(gc);
+			gc_list_append(gc, finalizers);
+			gc->gc_refs = GC_MOVED;
+		}
+	}
+	return 0;
+}
+
+/* Move objects referenced from roots to roots */
+static void
+move_finalizer_reachable(PyGC_Head *finalizers)
+{
+	traverseproc traverse;
+	PyGC_Head *gc = finalizers->gc_next;
+	for (; gc != finalizers; gc=gc->gc_next) {
+		/* careful, finalizers list is growing here */
+		traverse = PyObject_FROM_GC(gc)->ob_type->tp_traverse;
+		(void) traverse(PyObject_FROM_GC(gc), 
+			       (visitproc)visit_finalizer_reachable,
+			       (void *)finalizers);
+	}
+}
+
+static void
+debug_instance(PyObject *output, char *msg, PyInstanceObject *inst)
+{
+	char buf[200];
+	char *cname;
+	/* be careful not to create new dictionaries */
+	PyObject *classname = inst->in_class->cl_name;
+	if (classname != NULL && PyString_Check(classname))
+		cname = PyString_AsString(classname);
+	else
+		cname = "?";
+	sprintf(buf, "gc: %s<%.100s instance at %lx>\n", 
+			msg, cname, (long)inst);
+	PyFile_WriteString(buf, output);
+}
+
+static void
+debug_cycle(PyObject *output, char *msg, PyObject *op)
+{
+	if ((debug & DEBUG_INSTANCES) && PyInstance_Check(op)) {
+		debug_instance(output, msg, (PyInstanceObject *)op);
+	} else if (debug & DEBUG_OBJECTS) {
+		char buf[200];
+		sprintf(buf, "gc: %s<%s 0x%x>\n",
+				msg,
+				op->ob_type->tp_name,
+				(long)op);
+		PyFile_WriteString(buf, output);
+	}
+}
+
+/* Handle uncollectable garbage (cycles with finalizers). */
+static void
+handle_finalizers(PyGC_Head *finalizers, PyGC_Head *old)
+{
+	PyGC_Head *gc;
+	if (garbage == NULL) {
+		garbage = PyList_New(0);
+	}
+	for (gc = finalizers->gc_next; gc != finalizers;
+			gc = finalizers->gc_next) {
+		PyObject *op = PyObject_FROM_GC(gc);
+		/* Add all instances to a Python accessible list of garbage */
+		if (PyInstance_Check(op)) {
+			PyList_Append(garbage, op);
+		}
+		/* We assume that all objects in finalizers are reachable from
+		 * instances.  Once we add the instances to the garbage list
+		 * everything is reachable from Python again. */
+		gc_list_remove(gc);
+		gc_list_append(gc, old);
+	}
+}
+
+/* Break reference cycles by clearing the containers involved.  This is
+ * tricky business as the lists can be changing and we don't know which
+ * objects may be freed.  It is possible I screwed something up here. */
+static void
+delete_garbage(PyGC_Head *unreachable, PyGC_Head *old)
+{
+	inquiry clear;
+
+	while (unreachable->gc_next != unreachable) {
+		PyGC_Head *gc = unreachable->gc_next;
+		PyObject *op = PyObject_FROM_GC(gc);
+		/*
+		PyList_Append(garbage, op);
+		*/
+		if ((clear = op->ob_type->tp_clear) != NULL) {
+			Py_INCREF(op);
+			clear((PyObject *)op);
+			Py_DECREF(op);
+		}
+		/* only try to call tp_clear once for each object */
+		if (unreachable->gc_next == gc) {
+			/* still alive, move it, it may die later */
+			gc_list_remove(gc);
+			gc_list_append(gc, old);
+		}
+	}
+}
+
+/* This is the main function.  Read this to understand how the
+ * collection process works. */
+static long
+collect(PyGC_Head *young, PyGC_Head *old)
+{
+	long n = 0;
+	long m = 0;
+	PyGC_Head reachable;
+	PyGC_Head unreachable;
+	PyGC_Head finalizers;
+	PyGC_Head *gc;
+	PyObject *output = NULL;
+
+	if (debug) {
+		output = PySys_GetObject("stderr");
+	}
+	if (debug & DEBUG_STATS) {
+		char buf[100];
+		sprintf(buf, "gc: collecting generation %d...\n", generation);
+		PyFile_WriteString(buf,output);
+		sprintf(buf, "gc: objects in each generation: %d %d %d\n",
+			gc_list_size(&generation0),
+			gc_list_size(&generation1),
+			gc_list_size(&generation2));
+		PyFile_WriteString(buf,output);
+	}
+
+	/* Using ob_refcnt and gc_refs, calculate which objects in the
+	 * container set are reachable from outside the set (ie. have a
+	 * refcount greater than 0 when all the references within the
+	 * set are taken into account */
+	update_refs(young);
+	subtract_refs(young);
+
+	/* Move everything reachable from outside the set into the
+	 * reachable set (ie. gc_refs > 0).  Next, move everything
+	 * reachable from objects in the reachable set. */
+	gc_list_init(&reachable);
+	move_roots(young, &reachable);
+	move_root_reachable(&reachable);
+
+	/* move unreachable objects to a temporary list, new objects can be
+	 * allocated after this point */
+	gc_list_init(&unreachable);
+	gc_list_move(young, &unreachable);
+
+	/* move reachable objects to next generation */
+	gc_list_merge(&reachable, old);
+
+	/* Move objects reachable from finalizers, we can't safely delete
+	 * them.  Python programmers should take care not to create such
+	 * things.  For Python finalizers means instance objects with
+	 * __del__ methods. */
+	gc_list_init(&finalizers);
+	move_finalizers(&unreachable, &finalizers);
+	move_finalizer_reachable(&finalizers);
+
+	/* Collect statistics on collectable objects found and print
+	 * debugging information. */
+	for (gc = unreachable.gc_next; gc != &unreachable;
+			gc = gc->gc_next) {
+		m++;
+		if (output != NULL && (debug & DEBUG_COLLECTABLE)) {
+			debug_cycle(output, "collectable ", PyObject_FROM_GC(gc));
+		}
+	}
+	/* call tp_clear on objects in the collectable set.  This will cause
+	 * the reference cycles to be broken. It may also cause some objects in
+	 * finalizers to be freed */
+	delete_garbage(&unreachable, old);
+
+	/* Collect statistics on uncollectable objects found and print
+	 * debugging information. */
+	for (gc = finalizers.gc_next; gc != &finalizers;
+			gc = gc->gc_next) {
+		n++;
+		if (output != NULL && (debug & DEBUG_UNCOLLECTABLE)) {
+			debug_cycle(output, "uncollectable ", PyObject_FROM_GC(gc));
+		}
+	}
+	if (output != NULL && (debug & DEBUG_STATS)) {
+		if (m == 0 && n == 0) {
+			PyFile_WriteString("gc: done.\n", output);
+		} else {
+			char buf[200];
+			sprintf(buf,
+				"gc: done, %d unreachable, %d uncollectable.\n",
+				n+m, n);
+			PyFile_WriteString(buf, output);
+		}
+	}
+
+	/* Append instances in the uncollectable set to a Python
+	 * reachable list of garbage.  The programmer has to deal with
+	 * this if they insist on creating this type of structure. */
+	handle_finalizers(&finalizers, old);
+
+	allocated = 0;
+	PyErr_Clear(); /* in case writing to sys.stderr failed */
+	return n+m;
+}
+
+static long
+collect_generations(void)
+{
+	static long collections0 = 0;
+	static long collections1 = 0;
+	long n;
+
+
+	if (collections1 > threshold2) {
+		generation = 2;
+		gc_list_merge(&generation0, &generation2);
+		gc_list_merge(&generation1, &generation2);
+		if (generation2.gc_next != &generation2) {
+			n = collect(&generation2, &generation2);
+		}
+		collections1 = 0;
+	} else if (collections0 > threshold1) {
+		generation = 1;
+		collections1++;
+		gc_list_merge(&generation0, &generation1);
+		if (generation1.gc_next != &generation1) {
+			n = collect(&generation1, &generation2);
+		}
+		collections0 = 0;
+	} else {
+		generation = 0;
+		collections0++;
+		if (generation0.gc_next != &generation0) {
+			n = collect(&generation0, &generation1);
+		}
+	}
+	return n;
+}
+
+void
+_PyGC_Insert(PyObject *op)
+{
+	/* collection lock since collecting may cause allocations */
+	static int collecting = 0;
+
+#ifdef Py_DEBUG
+	if (!PyObject_IS_GC(op)) {
+		abort();
+	}
+#endif
+	if (threshold0 && allocated > threshold0 && !collecting) {
+		collecting++;
+		collect_generations();
+		collecting--;
+	}
+	allocated++;
+	gc_list_append(PyObject_AS_GC(op), &generation0);
+}
+
+void
+_PyGC_Remove(PyObject *op)
+{
+	PyGC_Head *g = PyObject_AS_GC(op);
+#ifdef Py_DEBUG
+	if (!PyObject_IS_GC(op)) {
+		abort();
+	}
+#endif
+	gc_list_remove(g);
+	if (allocated > 0) {
+		allocated--;
+	}
+}
+
+
+static char collect__doc__[] =
+"collect() -> n\n"
+"\n"
+"Run a full collection.  The number of unreachable objects is returned.\n"
+;
+
+static PyObject *
+Py_collect(self, args)
+	PyObject *self;
+	PyObject *args;
+{
+	long n;
+
+	if(!PyArg_ParseTuple(args, ""))	/* check no args */
+		return NULL;
+
+	generation = 2;
+	gc_list_merge(&generation0, &generation2);
+	gc_list_merge(&generation1, &generation2);
+	n = collect(&generation2, &generation2);
+
+	return Py_BuildValue("i", n);
+}
+
+static char set_debug__doc__[] = 
+"set_debug(flags) -> None\n"
+"\n"
+"Set the garbage collection debugging flags. Debugging information is\n"
+"written to sys.stderr.\n"
+"\n"
+"flags is an integer and can have the following bits turned on:\n"
+"\n"
+"  DEBUG_STATS - Print statistics during collection.\n"
+"  DEBUG_COLLECTABLE - Print collectable objects found.\n"
+"  DEBUG_UNCOLLECTABLE - Print unreachable but uncollectable objects found.\n"
+"  DEBUG_INSTANCES - Print instance objects.\n"
+"  DEBUG_OBJECTS - Print objects other than instances.\n"
+"  DEBUG_LEAK - Debug leaking programs (everything but STATS).\n"
+;
+
+static PyObject *
+Py_set_debug(self, args)
+	PyObject *self;
+	PyObject *args;
+{
+	if (!PyArg_ParseTuple(args, "l", &debug))
+		return NULL;
+
+	Py_INCREF(Py_None);
+	return Py_None;
+}
+
+static char get_debug__doc__[] = 
+"get_debug() -> flags\n"
+"\n"
+"Get the garbage collection debugging flags.\n"
+;
+
+static PyObject *
+Py_get_debug(self, args)
+	PyObject *self;
+	PyObject *args;
+{
+	if(!PyArg_ParseTuple(args, ""))	/* no args */
+		return NULL;
+
+	return Py_BuildValue("i", debug);
+}
+
+static char set_thresh__doc__[] =
+"set_threshold(threshold0, [threhold1, threshold2]) -> None\n"
+"\n"
+"Sets the collection thresholds.  Setting threshold0 to zero disables\n"
+"collection.\n"
+;
+
+static PyObject *
+Py_set_thresh(self, args)
+	PyObject *self;
+	PyObject *args;
+{
+	if (!PyArg_ParseTuple(args, "i|ii", &threshold0, 
+				&threshold1, &threshold2))
+		return NULL;
+
+	Py_INCREF(Py_None);
+	return Py_None;
+}
+
+static char get_thresh__doc__[] =
+"get_threshold() -> (threshold0, threshold1, threshold2)\n"
+"\n"
+"Return the current collection thresholds\n"
+;
+
+static PyObject *
+Py_get_thresh(self, args)
+	PyObject *self;
+	PyObject *args;
+{
+	if(!PyArg_ParseTuple(args, ""))	/* no args */
+		return NULL;
+
+	return Py_BuildValue("(iii)", threshold0, threshold1, threshold2);
+}
+
+
+static char gc__doc__ [] =
+"This module provides access to the garbage collector for reference cycles.\n"
+"\n"
+"collect() -- Do a full collection right now.\n"
+"set_debug() -- Set debugging flags.\n"
+"get_debug() -- Get debugging flags.\n"
+"set_threshold() -- Set the collection thresholds.\n"
+"get_threshold() -- Return the current the collection thresholds.\n"
+;
+
+static PyMethodDef GcMethods[] = {
+	{"set_debug",		Py_set_debug,  METH_VARARGS, set_debug__doc__},
+	{"get_debug",		Py_get_debug,  METH_VARARGS, get_debug__doc__},
+	{"set_threshold",	Py_set_thresh, METH_VARARGS, set_thresh__doc__},
+	{"get_threshold",	Py_get_thresh, METH_VARARGS, get_thresh__doc__},
+	{"collect",		Py_collect,    METH_VARARGS, collect__doc__},
+	{NULL,	NULL}		/* Sentinel */
+};
+
+void
+initgc(void)
+{
+	PyObject *m;
+	PyObject *d;
+
+	m = Py_InitModule4("gc",
+			      GcMethods,
+			      gc__doc__,
+			      NULL,
+			      PYTHON_API_VERSION);
+	d = PyModule_GetDict(m);
+	if (garbage == NULL) {
+		garbage = PyList_New(0);
+	}
+	PyDict_SetItemString(d, "garbage", garbage);
+	PyDict_SetItemString(d, "DEBUG_STATS",
+			PyInt_FromLong(DEBUG_STATS));
+	PyDict_SetItemString(d, "DEBUG_COLLECTABLE",
+			PyInt_FromLong(DEBUG_COLLECTABLE));
+	PyDict_SetItemString(d, "DEBUG_UNCOLLECTABLE",
+			PyInt_FromLong(DEBUG_UNCOLLECTABLE));
+	PyDict_SetItemString(d, "DEBUG_INSTANCES",
+			PyInt_FromLong(DEBUG_INSTANCES));
+	PyDict_SetItemString(d, "DEBUG_OBJECTS",
+			PyInt_FromLong(DEBUG_OBJECTS));
+	PyDict_SetItemString(d, "DEBUG_LEAK",
+			PyInt_FromLong(DEBUG_LEAK));
+}
+
+#endif /* WITH_CYCLE_GC */