diff -r ffa851df0825 -r 2fb8b9db1c86 symbian-qemu-0.9.1-12/python-2.6.1/Modules/gcmodule.c --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/symbian-qemu-0.9.1-12/python-2.6.1/Modules/gcmodule.c Fri Jul 31 15:01:17 2009 +0100 @@ -0,0 +1,1419 @@ +/* + + Reference Cycle Garbage Collection + ================================== + + Neil Schemenauer + + Based on a post on the python-dev list. Ideas from Guido van Rossum, + Eric Tiedemann, and various others. + + http://www.arctrix.com/nas/python/gc/ + 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. + +*/ + +#include "Python.h" +#include "frameobject.h" /* for PyFrame_ClearFreeList */ + +/* Get an object's GC head */ +#define AS_GC(o) ((PyGC_Head *)(o)-1) + +/* Get the object given the GC head */ +#define FROM_GC(g) ((PyObject *)(((PyGC_Head *)g)+1)) + +/*** Global GC state ***/ + +struct gc_generation { + PyGC_Head head; + int threshold; /* collection threshold */ + int count; /* count of allocations or collections of younger + generations */ +}; + +#define NUM_GENERATIONS 3 +#define GEN_HEAD(n) (&generations[n].head) + +/* linked lists of container objects */ +static struct gc_generation generations[NUM_GENERATIONS] = { + /* PyGC_Head, threshold, count */ + {{{GEN_HEAD(0), GEN_HEAD(0), 0}}, 700, 0}, + {{{GEN_HEAD(1), GEN_HEAD(1), 0}}, 10, 0}, + {{{GEN_HEAD(2), GEN_HEAD(2), 0}}, 10, 0}, +}; + +PyGC_Head *_PyGC_generation0 = GEN_HEAD(0); + +static int enabled = 1; /* automatic collection enabled? */ + +/* true if we are currently running the collector */ +static int collecting = 0; + +/* list of uncollectable objects */ +static PyObject *garbage = NULL; + +/* Python string to use if unhandled exception occurs */ +static PyObject *gc_str = NULL; + +/* Python string used to look for __del__ attribute. */ +static PyObject *delstr = NULL; + +/* 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_SAVEALL (1<<5) /* save all garbage in gc.garbage */ +#define DEBUG_LEAK DEBUG_COLLECTABLE | \ + DEBUG_UNCOLLECTABLE | \ + DEBUG_INSTANCES | \ + DEBUG_OBJECTS | \ + DEBUG_SAVEALL +static int debug; +static PyObject *tmod = NULL; + +/*-------------------------------------------------------------------------- +gc_refs values. + +Between collections, every gc'ed object has one of two gc_refs values: + +GC_UNTRACKED + The initial state; objects returned by PyObject_GC_Malloc are in this + state. The object doesn't live in any generation list, and its + tp_traverse slot must not be called. + +GC_REACHABLE + The object lives in some generation list, and its tp_traverse is safe to + call. An object transitions to GC_REACHABLE when PyObject_GC_Track + is called. + +During a collection, gc_refs can temporarily take on other states: + +>= 0 + At the start of a collection, update_refs() copies the true refcount + to gc_refs, for each object in the generation being collected. + subtract_refs() then adjusts gc_refs so that it equals the number of + times an object is referenced directly from outside the generation + being collected. + gc_refs remains >= 0 throughout these steps. + +GC_TENTATIVELY_UNREACHABLE + move_unreachable() then moves objects not reachable (whether directly or + indirectly) from outside the generation into an "unreachable" set. + Objects that are found to be reachable have gc_refs set to GC_REACHABLE + again. Objects that are found to be unreachable have gc_refs set to + GC_TENTATIVELY_UNREACHABLE. It's "tentatively" because the pass doing + this can't be sure until it ends, and GC_TENTATIVELY_UNREACHABLE may + transition back to GC_REACHABLE. + + Only objects with GC_TENTATIVELY_UNREACHABLE still set are candidates + for collection. If it's decided not to collect such an object (e.g., + it has a __del__ method), its gc_refs is restored to GC_REACHABLE again. +---------------------------------------------------------------------------- +*/ +#define GC_UNTRACKED _PyGC_REFS_UNTRACKED +#define GC_REACHABLE _PyGC_REFS_REACHABLE +#define GC_TENTATIVELY_UNREACHABLE _PyGC_REFS_TENTATIVELY_UNREACHABLE + +#define IS_TRACKED(o) ((AS_GC(o))->gc.gc_refs != GC_UNTRACKED) +#define IS_REACHABLE(o) ((AS_GC(o))->gc.gc_refs == GC_REACHABLE) +#define IS_TENTATIVELY_UNREACHABLE(o) ( \ + (AS_GC(o))->gc.gc_refs == GC_TENTATIVELY_UNREACHABLE) + +/*** list functions ***/ + +static void +gc_list_init(PyGC_Head *list) +{ + list->gc.gc_prev = list; + list->gc.gc_next = list; +} + +static int +gc_list_is_empty(PyGC_Head *list) +{ + return (list->gc.gc_next == list); +} + +#if 0 +/* This became unused after gc_list_move() was introduced. */ +/* Append `node` to `list`. */ +static void +gc_list_append(PyGC_Head *node, PyGC_Head *list) +{ + node->gc.gc_next = list; + node->gc.gc_prev = list->gc.gc_prev; + node->gc.gc_prev->gc.gc_next = node; + list->gc.gc_prev = node; +} +#endif + +/* Remove `node` from the gc list it's currently in. */ +static void +gc_list_remove(PyGC_Head *node) +{ + node->gc.gc_prev->gc.gc_next = node->gc.gc_next; + node->gc.gc_next->gc.gc_prev = node->gc.gc_prev; + node->gc.gc_next = NULL; /* object is not currently tracked */ +} + +/* Move `node` from the gc list it's currently in (which is not explicitly + * named here) to the end of `list`. This is semantically the same as + * gc_list_remove(node) followed by gc_list_append(node, list). + */ +static void +gc_list_move(PyGC_Head *node, PyGC_Head *list) +{ + PyGC_Head *new_prev; + PyGC_Head *current_prev = node->gc.gc_prev; + PyGC_Head *current_next = node->gc.gc_next; + /* Unlink from current list. */ + current_prev->gc.gc_next = current_next; + current_next->gc.gc_prev = current_prev; + /* Relink at end of new list. */ + new_prev = node->gc.gc_prev = list->gc.gc_prev; + new_prev->gc.gc_next = list->gc.gc_prev = node; + node->gc.gc_next = list; +} + +/* append list `from` onto list `to`; `from` becomes an empty list */ +static void +gc_list_merge(PyGC_Head *from, PyGC_Head *to) +{ + PyGC_Head *tail; + assert(from != to); + if (!gc_list_is_empty(from)) { + tail = to->gc.gc_prev; + tail->gc.gc_next = from->gc.gc_next; + tail->gc.gc_next->gc.gc_prev = tail; + to->gc.gc_prev = from->gc.gc_prev; + to->gc.gc_prev->gc.gc_next = to; + } + gc_list_init(from); +} + +static Py_ssize_t +gc_list_size(PyGC_Head *list) +{ + PyGC_Head *gc; + Py_ssize_t n = 0; + for (gc = list->gc.gc_next; gc != list; gc = gc->gc.gc_next) { + n++; + } + return n; +} + +/* Append objects in a GC list to a Python list. + * Return 0 if all OK, < 0 if error (out of memory for list). + */ +static int +append_objects(PyObject *py_list, PyGC_Head *gc_list) +{ + PyGC_Head *gc; + for (gc = gc_list->gc.gc_next; gc != gc_list; gc = gc->gc.gc_next) { + PyObject *op = FROM_GC(gc); + if (op != py_list) { + if (PyList_Append(py_list, op)) { + return -1; /* exception */ + } + } + } + return 0; +} + +/*** end of list stuff ***/ + + +/* Set all gc_refs = ob_refcnt. After this, gc_refs is > 0 for all objects + * in containers, and is GC_REACHABLE for all tracked gc objects not in + * containers. + */ +static void +update_refs(PyGC_Head *containers) +{ + PyGC_Head *gc = containers->gc.gc_next; + for (; gc != containers; gc = gc->gc.gc_next) { + assert(gc->gc.gc_refs == GC_REACHABLE); + gc->gc.gc_refs = Py_REFCNT(FROM_GC(gc)); + /* Python's cyclic gc should never see an incoming refcount + * of 0: if something decref'ed to 0, it should have been + * deallocated immediately at that time. + * Possible cause (if the assert triggers): a tp_dealloc + * routine left a gc-aware object tracked during its teardown + * phase, and did something-- or allowed something to happen -- + * that called back into Python. gc can trigger then, and may + * see the still-tracked dying object. Before this assert + * was added, such mistakes went on to allow gc to try to + * delete the object again. In a debug build, that caused + * a mysterious segfault, when _Py_ForgetReference tried + * to remove the object from the doubly-linked list of all + * objects a second time. In a release build, an actual + * double deallocation occurred, which leads to corruption + * of the allocator's internal bookkeeping pointers. That's + * so serious that maybe this should be a release-build + * check instead of an assert? + */ + assert(gc->gc.gc_refs != 0); + } +} + +/* A traversal callback for subtract_refs. */ +static int +visit_decref(PyObject *op, void *data) +{ + assert(op != NULL); + if (PyObject_IS_GC(op)) { + PyGC_Head *gc = AS_GC(op); + /* We're only interested in gc_refs for objects in the + * generation being collected, which can be recognized + * because only they have positive gc_refs. + */ + assert(gc->gc.gc_refs != 0); /* else refcount was too small */ + if (gc->gc.gc_refs > 0) + gc->gc.gc_refs--; + } + return 0; +} + +/* Subtract internal references from gc_refs. After this, gc_refs is >= 0 + * for all objects in containers, and is GC_REACHABLE for all tracked gc + * objects not in containers. The ones with gc_refs > 0 are directly + * reachable from outside containers, and so can't be collected. + */ +static void +subtract_refs(PyGC_Head *containers) +{ + traverseproc traverse; + PyGC_Head *gc = containers->gc.gc_next; + for (; gc != containers; gc=gc->gc.gc_next) { + traverse = Py_TYPE(FROM_GC(gc))->tp_traverse; + (void) traverse(FROM_GC(gc), + (visitproc)visit_decref, + NULL); + } +} + +/* A traversal callback for move_unreachable. */ +static int +visit_reachable(PyObject *op, PyGC_Head *reachable) +{ + if (PyObject_IS_GC(op)) { + PyGC_Head *gc = AS_GC(op); + const Py_ssize_t gc_refs = gc->gc.gc_refs; + + if (gc_refs == 0) { + /* This is in move_unreachable's 'young' list, but + * the traversal hasn't yet gotten to it. All + * we need to do is tell move_unreachable that it's + * reachable. + */ + gc->gc.gc_refs = 1; + } + else if (gc_refs == GC_TENTATIVELY_UNREACHABLE) { + /* This had gc_refs = 0 when move_unreachable got + * to it, but turns out it's reachable after all. + * Move it back to move_unreachable's 'young' list, + * and move_unreachable will eventually get to it + * again. + */ + gc_list_move(gc, reachable); + gc->gc.gc_refs = 1; + } + /* Else there's nothing to do. + * If gc_refs > 0, it must be in move_unreachable's 'young' + * list, and move_unreachable will eventually get to it. + * If gc_refs == GC_REACHABLE, it's either in some other + * generation so we don't care about it, or move_unreachable + * already dealt with it. + * If gc_refs == GC_UNTRACKED, it must be ignored. + */ + else { + assert(gc_refs > 0 + || gc_refs == GC_REACHABLE + || gc_refs == GC_UNTRACKED); + } + } + return 0; +} + +/* Move the unreachable objects from young to unreachable. After this, + * all objects in young have gc_refs = GC_REACHABLE, and all objects in + * unreachable have gc_refs = GC_TENTATIVELY_UNREACHABLE. All tracked + * gc objects not in young or unreachable still have gc_refs = GC_REACHABLE. + * All objects in young after this are directly or indirectly reachable + * from outside the original young; and all objects in unreachable are + * not. + */ +static void +move_unreachable(PyGC_Head *young, PyGC_Head *unreachable) +{ + PyGC_Head *gc = young->gc.gc_next; + + /* Invariants: all objects "to the left" of us in young have gc_refs + * = GC_REACHABLE, and are indeed reachable (directly or indirectly) + * from outside the young list as it was at entry. All other objects + * from the original young "to the left" of us are in unreachable now, + * and have gc_refs = GC_TENTATIVELY_UNREACHABLE. All objects to the + * left of us in 'young' now have been scanned, and no objects here + * or to the right have been scanned yet. + */ + + while (gc != young) { + PyGC_Head *next; + + if (gc->gc.gc_refs) { + /* gc is definitely reachable from outside the + * original 'young'. Mark it as such, and traverse + * its pointers to find any other objects that may + * be directly reachable from it. Note that the + * call to tp_traverse may append objects to young, + * so we have to wait until it returns to determine + * the next object to visit. + */ + PyObject *op = FROM_GC(gc); + traverseproc traverse = Py_TYPE(op)->tp_traverse; + assert(gc->gc.gc_refs > 0); + gc->gc.gc_refs = GC_REACHABLE; + (void) traverse(op, + (visitproc)visit_reachable, + (void *)young); + next = gc->gc.gc_next; + } + else { + /* This *may* be unreachable. To make progress, + * assume it is. gc isn't directly reachable from + * any object we've already traversed, but may be + * reachable from an object we haven't gotten to yet. + * visit_reachable will eventually move gc back into + * young if that's so, and we'll see it again. + */ + next = gc->gc.gc_next; + gc_list_move(gc, unreachable); + gc->gc.gc_refs = GC_TENTATIVELY_UNREACHABLE; + } + gc = next; + } +} + +/* Return true if object has a finalization method. + * CAUTION: An instance of an old-style class has to be checked for a + *__del__ method, and earlier versions of this used to call PyObject_HasAttr, + * which in turn could call the class's __getattr__ hook (if any). That + * could invoke arbitrary Python code, mutating the object graph in arbitrary + * ways, and that was the source of some excruciatingly subtle bugs. + */ +static int +has_finalizer(PyObject *op) +{ + if (PyInstance_Check(op)) { + assert(delstr != NULL); + return _PyInstance_Lookup(op, delstr) != NULL; + } + else if (PyType_HasFeature(op->ob_type, Py_TPFLAGS_HEAPTYPE)) + return op->ob_type->tp_del != NULL; + else if (PyGen_CheckExact(op)) + return PyGen_NeedsFinalizing((PyGenObject *)op); + else + return 0; +} + +/* Move the objects in unreachable with __del__ methods into `finalizers`. + * Objects moved into `finalizers` have gc_refs set to GC_REACHABLE; the + * objects remaining in unreachable are left at GC_TENTATIVELY_UNREACHABLE. + */ +static void +move_finalizers(PyGC_Head *unreachable, PyGC_Head *finalizers) +{ + PyGC_Head *gc; + PyGC_Head *next; + + /* March over unreachable. Move objects with finalizers into + * `finalizers`. + */ + for (gc = unreachable->gc.gc_next; gc != unreachable; gc = next) { + PyObject *op = FROM_GC(gc); + + assert(IS_TENTATIVELY_UNREACHABLE(op)); + next = gc->gc.gc_next; + + if (has_finalizer(op)) { + gc_list_move(gc, finalizers); + gc->gc.gc_refs = GC_REACHABLE; + } + } +} + +/* A traversal callback for move_finalizer_reachable. */ +static int +visit_move(PyObject *op, PyGC_Head *tolist) +{ + if (PyObject_IS_GC(op)) { + if (IS_TENTATIVELY_UNREACHABLE(op)) { + PyGC_Head *gc = AS_GC(op); + gc_list_move(gc, tolist); + gc->gc.gc_refs = GC_REACHABLE; + } + } + return 0; +} + +/* Move objects that are reachable from finalizers, from the unreachable set + * into finalizers set. + */ +static void +move_finalizer_reachable(PyGC_Head *finalizers) +{ + traverseproc traverse; + PyGC_Head *gc = finalizers->gc.gc_next; + for (; gc != finalizers; gc = gc->gc.gc_next) { + /* Note that the finalizers list may grow during this. */ + traverse = Py_TYPE(FROM_GC(gc))->tp_traverse; + (void) traverse(FROM_GC(gc), + (visitproc)visit_move, + (void *)finalizers); + } +} + +/* Clear all weakrefs to unreachable objects, and if such a weakref has a + * callback, invoke it if necessary. Note that it's possible for such + * weakrefs to be outside the unreachable set -- indeed, those are precisely + * the weakrefs whose callbacks must be invoked. See gc_weakref.txt for + * overview & some details. Some weakrefs with callbacks may be reclaimed + * directly by this routine; the number reclaimed is the return value. Other + * weakrefs with callbacks may be moved into the `old` generation. Objects + * moved into `old` have gc_refs set to GC_REACHABLE; the objects remaining in + * unreachable are left at GC_TENTATIVELY_UNREACHABLE. When this returns, + * no object in `unreachable` is weakly referenced anymore. + */ +static int +handle_weakrefs(PyGC_Head *unreachable, PyGC_Head *old) +{ + PyGC_Head *gc; + PyObject *op; /* generally FROM_GC(gc) */ + PyWeakReference *wr; /* generally a cast of op */ + PyGC_Head wrcb_to_call; /* weakrefs with callbacks to call */ + PyGC_Head *next; + int num_freed = 0; + + gc_list_init(&wrcb_to_call); + + /* Clear all weakrefs to the objects in unreachable. If such a weakref + * also has a callback, move it into `wrcb_to_call` if the callback + * needs to be invoked. Note that we cannot invoke any callbacks until + * all weakrefs to unreachable objects are cleared, lest the callback + * resurrect an unreachable object via a still-active weakref. We + * make another pass over wrcb_to_call, invoking callbacks, after this + * pass completes. + */ + for (gc = unreachable->gc.gc_next; gc != unreachable; gc = next) { + PyWeakReference **wrlist; + + op = FROM_GC(gc); + assert(IS_TENTATIVELY_UNREACHABLE(op)); + next = gc->gc.gc_next; + + if (! PyType_SUPPORTS_WEAKREFS(Py_TYPE(op))) + continue; + + /* It supports weakrefs. Does it have any? */ + wrlist = (PyWeakReference **) + PyObject_GET_WEAKREFS_LISTPTR(op); + + /* `op` may have some weakrefs. March over the list, clear + * all the weakrefs, and move the weakrefs with callbacks + * that must be called into wrcb_to_call. + */ + for (wr = *wrlist; wr != NULL; wr = *wrlist) { + PyGC_Head *wrasgc; /* AS_GC(wr) */ + + /* _PyWeakref_ClearRef clears the weakref but leaves + * the callback pointer intact. Obscure: it also + * changes *wrlist. + */ + assert(wr->wr_object == op); + _PyWeakref_ClearRef(wr); + assert(wr->wr_object == Py_None); + if (wr->wr_callback == NULL) + continue; /* no callback */ + + /* Headache time. `op` is going away, and is weakly referenced by + * `wr`, which has a callback. Should the callback be invoked? If wr + * is also trash, no: + * + * 1. There's no need to call it. The object and the weakref are + * both going away, so it's legitimate to pretend the weakref is + * going away first. The user has to ensure a weakref outlives its + * referent if they want a guarantee that the wr callback will get + * invoked. + * + * 2. It may be catastrophic to call it. If the callback is also in + * cyclic trash (CT), then although the CT is unreachable from + * outside the current generation, CT may be reachable from the + * callback. Then the callback could resurrect insane objects. + * + * Since the callback is never needed and may be unsafe in this case, + * wr is simply left in the unreachable set. Note that because we + * already called _PyWeakref_ClearRef(wr), its callback will never + * trigger. + * + * OTOH, if wr isn't part of CT, we should invoke the callback: the + * weakref outlived the trash. Note that since wr isn't CT in this + * case, its callback can't be CT either -- wr acted as an external + * root to this generation, and therefore its callback did too. So + * nothing in CT is reachable from the callback either, so it's hard + * to imagine how calling it later could create a problem for us. wr + * is moved to wrcb_to_call in this case. + */ + if (IS_TENTATIVELY_UNREACHABLE(wr)) + continue; + assert(IS_REACHABLE(wr)); + + /* Create a new reference so that wr can't go away + * before we can process it again. + */ + Py_INCREF(wr); + + /* Move wr to wrcb_to_call, for the next pass. */ + wrasgc = AS_GC(wr); + assert(wrasgc != next); /* wrasgc is reachable, but + next isn't, so they can't + be the same */ + gc_list_move(wrasgc, &wrcb_to_call); + } + } + + /* Invoke the callbacks we decided to honor. It's safe to invoke them + * because they can't reference unreachable objects. + */ + while (! gc_list_is_empty(&wrcb_to_call)) { + PyObject *temp; + PyObject *callback; + + gc = wrcb_to_call.gc.gc_next; + op = FROM_GC(gc); + assert(IS_REACHABLE(op)); + assert(PyWeakref_Check(op)); + wr = (PyWeakReference *)op; + callback = wr->wr_callback; + assert(callback != NULL); + + /* copy-paste of weakrefobject.c's handle_callback() */ + temp = PyObject_CallFunctionObjArgs(callback, wr, NULL); + if (temp == NULL) + PyErr_WriteUnraisable(callback); + else + Py_DECREF(temp); + + /* Give up the reference we created in the first pass. When + * op's refcount hits 0 (which it may or may not do right now), + * op's tp_dealloc will decref op->wr_callback too. Note + * that the refcount probably will hit 0 now, and because this + * weakref was reachable to begin with, gc didn't already + * add it to its count of freed objects. Example: a reachable + * weak value dict maps some key to this reachable weakref. + * The callback removes this key->weakref mapping from the + * dict, leaving no other references to the weakref (excepting + * ours). + */ + Py_DECREF(op); + if (wrcb_to_call.gc.gc_next == gc) { + /* object is still alive -- move it */ + gc_list_move(gc, old); + } + else + ++num_freed; + } + + return num_freed; +} + +static void +debug_instance(char *msg, PyInstanceObject *inst) +{ + char *cname; + /* simple version of instance_repr */ + PyObject *classname = inst->in_class->cl_name; + if (classname != NULL && PyString_Check(classname)) + cname = PyString_AsString(classname); + else + cname = "?"; + PySys_WriteStderr("gc: %.100s <%.100s instance at %p>\n", + msg, cname, inst); +} + +static void +debug_cycle(char *msg, PyObject *op) +{ + if ((debug & DEBUG_INSTANCES) && PyInstance_Check(op)) { + debug_instance(msg, (PyInstanceObject *)op); + } + else if (debug & DEBUG_OBJECTS) { + PySys_WriteStderr("gc: %.100s <%.100s %p>\n", + msg, Py_TYPE(op)->tp_name, op); + } +} + +/* Handle uncollectable garbage (cycles with finalizers, and stuff reachable + * only from such cycles). + * If DEBUG_SAVEALL, all objects in finalizers are appended to the module + * garbage list (a Python list), else only the objects in finalizers with + * __del__ methods are appended to garbage. All objects in finalizers are + * merged into the old list regardless. + * Returns 0 if all OK, <0 on error (out of memory to grow the garbage list). + * The finalizers list is made empty on a successful return. + */ +static int +handle_finalizers(PyGC_Head *finalizers, PyGC_Head *old) +{ + PyGC_Head *gc = finalizers->gc.gc_next; + + if (garbage == NULL) { + garbage = PyList_New(0); + if (garbage == NULL) + Py_FatalError("gc couldn't create gc.garbage list"); + } + for (; gc != finalizers; gc = gc->gc.gc_next) { + PyObject *op = FROM_GC(gc); + + if ((debug & DEBUG_SAVEALL) || has_finalizer(op)) { + if (PyList_Append(garbage, op) < 0) + return -1; + } + } + + gc_list_merge(finalizers, old); + return 0; +} + +/* 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 *collectable, PyGC_Head *old) +{ + inquiry clear; + + while (!gc_list_is_empty(collectable)) { + PyGC_Head *gc = collectable->gc.gc_next; + PyObject *op = FROM_GC(gc); + + assert(IS_TENTATIVELY_UNREACHABLE(op)); + if (debug & DEBUG_SAVEALL) { + PyList_Append(garbage, op); + } + else { + if ((clear = Py_TYPE(op)->tp_clear) != NULL) { + Py_INCREF(op); + clear(op); + Py_DECREF(op); + } + } + if (collectable->gc.gc_next == gc) { + /* object is still alive, move it, it may die later */ + gc_list_move(gc, old); + gc->gc.gc_refs = GC_REACHABLE; + } + } +} + +/* Clear all free lists + * All free lists are cleared during the collection of the highest generation. + * Allocated items in the free list may keep a pymalloc arena occupied. + * Clearing the free lists may give back memory to the OS earlier. + */ +static void +clear_freelists(void) +{ + (void)PyMethod_ClearFreeList(); + (void)PyFrame_ClearFreeList(); + (void)PyCFunction_ClearFreeList(); + (void)PyTuple_ClearFreeList(); + (void)PyUnicode_ClearFreeList(); + (void)PyInt_ClearFreeList(); + (void)PyFloat_ClearFreeList(); +} + +/* This is the main function. Read this to understand how the + * collection process works. */ +static Py_ssize_t +collect(int generation) +{ + int i; + Py_ssize_t m = 0; /* # objects collected */ + Py_ssize_t n = 0; /* # unreachable objects that couldn't be collected */ + PyGC_Head *young; /* the generation we are examining */ + PyGC_Head *old; /* next older generation */ + PyGC_Head unreachable; /* non-problematic unreachable trash */ + PyGC_Head finalizers; /* objects with, & reachable from, __del__ */ + PyGC_Head *gc; + double t1 = 0.0; + + if (delstr == NULL) { + delstr = PyString_InternFromString("__del__"); + if (delstr == NULL) + Py_FatalError("gc couldn't allocate \"__del__\""); + } + + if (debug & DEBUG_STATS) { + if (tmod != NULL) { + PyObject *f = PyObject_CallMethod(tmod, "time", NULL); + if (f == NULL) { + PyErr_Clear(); + } + else { + t1 = PyFloat_AsDouble(f); + Py_DECREF(f); + } + } + PySys_WriteStderr("gc: collecting generation %d...\n", + generation); + PySys_WriteStderr("gc: objects in each generation:"); + for (i = 0; i < NUM_GENERATIONS; i++) + PySys_WriteStderr(" %" PY_FORMAT_SIZE_T "d", + gc_list_size(GEN_HEAD(i))); + PySys_WriteStderr("\n"); + } + + /* update collection and allocation counters */ + if (generation+1 < NUM_GENERATIONS) + generations[generation+1].count += 1; + for (i = 0; i <= generation; i++) + generations[i].count = 0; + + /* merge younger generations with one we are currently collecting */ + for (i = 0; i < generation; i++) { + gc_list_merge(GEN_HEAD(i), GEN_HEAD(generation)); + } + + /* handy references */ + young = GEN_HEAD(generation); + if (generation < NUM_GENERATIONS-1) + old = GEN_HEAD(generation+1); + else + old = young; + + /* Using ob_refcnt and gc_refs, calculate which objects in the + * container set are reachable from outside the set (i.e., have a + * refcount greater than 0 when all the references within the + * set are taken into account). + */ + update_refs(young); + subtract_refs(young); + + /* Leave everything reachable from outside young in young, and move + * everything else (in young) to unreachable. + * NOTE: This used to move the reachable objects into a reachable + * set instead. But most things usually turn out to be reachable, + * so it's more efficient to move the unreachable things. + */ + gc_list_init(&unreachable); + move_unreachable(young, &unreachable); + + /* Move reachable objects to next generation. */ + if (young != old) + gc_list_merge(young, old); + + /* All objects in unreachable are trash, but objects reachable from + * finalizers can't safely be deleted. Python programmers should take + * care not to create such things. For Python, finalizers means + * instance objects with __del__ methods. Weakrefs with callbacks + * can also call arbitrary Python code but they will be dealt with by + * handle_weakrefs(). + */ + gc_list_init(&finalizers); + move_finalizers(&unreachable, &finalizers); + /* finalizers contains the unreachable objects with a finalizer; + * unreachable objects reachable *from* those are also uncollectable, + * and we move those into the finalizers list too. + */ + move_finalizer_reachable(&finalizers); + + /* Collect statistics on collectable objects found and print + * debugging information. + */ + for (gc = unreachable.gc.gc_next; gc != &unreachable; + gc = gc->gc.gc_next) { + m++; + if (debug & DEBUG_COLLECTABLE) { + debug_cycle("collectable", FROM_GC(gc)); + } + if (tmod != NULL && (debug & DEBUG_STATS)) { + PyObject *f = PyObject_CallMethod(tmod, "time", NULL); + if (f == NULL) { + PyErr_Clear(); + } + else { + t1 = PyFloat_AsDouble(f)-t1; + Py_DECREF(f); + PySys_WriteStderr("gc: %.4fs elapsed.\n", t1); + } + } + } + + /* Clear weakrefs and invoke callbacks as necessary. */ + m += handle_weakrefs(&unreachable, old); + + /* Call tp_clear on objects in the unreachable 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.gc_next; + gc != &finalizers; + gc = gc->gc.gc_next) { + n++; + if (debug & DEBUG_UNCOLLECTABLE) + debug_cycle("uncollectable", FROM_GC(gc)); + } + if (debug & DEBUG_STATS) { + if (m == 0 && n == 0) + PySys_WriteStderr("gc: done.\n"); + else + PySys_WriteStderr( + "gc: done, " + "%" PY_FORMAT_SIZE_T "d unreachable, " + "%" PY_FORMAT_SIZE_T "d uncollectable.\n", + n+m, n); + } + + /* 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. + */ + (void)handle_finalizers(&finalizers, old); + + /* Clear free list only during the collection of the higest + * generation */ + if (generation == NUM_GENERATIONS-1) { + clear_freelists(); + } + + if (PyErr_Occurred()) { + if (gc_str == NULL) + gc_str = PyString_FromString("garbage collection"); + PyErr_WriteUnraisable(gc_str); + Py_FatalError("unexpected exception during garbage collection"); + } + return n+m; +} + +static Py_ssize_t +collect_generations(void) +{ + int i; + Py_ssize_t n = 0; + + /* Find the oldest generation (higest numbered) where the count + * exceeds the threshold. Objects in the that generation and + * generations younger than it will be collected. */ + for (i = NUM_GENERATIONS-1; i >= 0; i--) { + if (generations[i].count > generations[i].threshold) { + n = collect(i); + break; + } + } + return n; +} + +PyDoc_STRVAR(gc_enable__doc__, +"enable() -> None\n" +"\n" +"Enable automatic garbage collection.\n"); + +static PyObject * +gc_enable(PyObject *self, PyObject *noargs) +{ + enabled = 1; + Py_INCREF(Py_None); + return Py_None; +} + +PyDoc_STRVAR(gc_disable__doc__, +"disable() -> None\n" +"\n" +"Disable automatic garbage collection.\n"); + +static PyObject * +gc_disable(PyObject *self, PyObject *noargs) +{ + enabled = 0; + Py_INCREF(Py_None); + return Py_None; +} + +PyDoc_STRVAR(gc_isenabled__doc__, +"isenabled() -> status\n" +"\n" +"Returns true if automatic garbage collection is enabled.\n"); + +static PyObject * +gc_isenabled(PyObject *self, PyObject *noargs) +{ + return PyBool_FromLong((long)enabled); +} + +PyDoc_STRVAR(gc_collect__doc__, +"collect([generation]) -> n\n" +"\n" +"With no arguments, run a full collection. The optional argument\n" +"may be an integer specifying which generation to collect. A ValueError\n" +"is raised if the generation number is invalid.\n\n" +"The number of unreachable objects is returned.\n"); + +static PyObject * +gc_collect(PyObject *self, PyObject *args, PyObject *kws) +{ + static char *keywords[] = {"generation", NULL}; + int genarg = NUM_GENERATIONS - 1; + Py_ssize_t n; + + if (!PyArg_ParseTupleAndKeywords(args, kws, "|i", keywords, &genarg)) + return NULL; + + else if (genarg < 0 || genarg >= NUM_GENERATIONS) { + PyErr_SetString(PyExc_ValueError, "invalid generation"); + return NULL; + } + + if (collecting) + n = 0; /* already collecting, don't do anything */ + else { + collecting = 1; + n = collect(genarg); + collecting = 0; + } + + return PyInt_FromSsize_t(n); +} + +PyDoc_STRVAR(gc_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_SAVEALL - Save objects to gc.garbage rather than freeing them.\n" +" DEBUG_LEAK - Debug leaking programs (everything but STATS).\n"); + +static PyObject * +gc_set_debug(PyObject *self, PyObject *args) +{ + if (!PyArg_ParseTuple(args, "i:set_debug", &debug)) + return NULL; + + Py_INCREF(Py_None); + return Py_None; +} + +PyDoc_STRVAR(gc_get_debug__doc__, +"get_debug() -> flags\n" +"\n" +"Get the garbage collection debugging flags.\n"); + +static PyObject * +gc_get_debug(PyObject *self, PyObject *noargs) +{ + return Py_BuildValue("i", debug); +} + +PyDoc_STRVAR(gc_set_thresh__doc__, +"set_threshold(threshold0, [threshold1, threshold2]) -> None\n" +"\n" +"Sets the collection thresholds. Setting threshold0 to zero disables\n" +"collection.\n"); + +static PyObject * +gc_set_thresh(PyObject *self, PyObject *args) +{ + int i; + if (!PyArg_ParseTuple(args, "i|ii:set_threshold", + &generations[0].threshold, + &generations[1].threshold, + &generations[2].threshold)) + return NULL; + for (i = 2; i < NUM_GENERATIONS; i++) { + /* generations higher than 2 get the same threshold */ + generations[i].threshold = generations[2].threshold; + } + + Py_INCREF(Py_None); + return Py_None; +} + +PyDoc_STRVAR(gc_get_thresh__doc__, +"get_threshold() -> (threshold0, threshold1, threshold2)\n" +"\n" +"Return the current collection thresholds\n"); + +static PyObject * +gc_get_thresh(PyObject *self, PyObject *noargs) +{ + return Py_BuildValue("(iii)", + generations[0].threshold, + generations[1].threshold, + generations[2].threshold); +} + +PyDoc_STRVAR(gc_get_count__doc__, +"get_count() -> (count0, count1, count2)\n" +"\n" +"Return the current collection counts\n"); + +static PyObject * +gc_get_count(PyObject *self, PyObject *noargs) +{ + return Py_BuildValue("(iii)", + generations[0].count, + generations[1].count, + generations[2].count); +} + +static int +referrersvisit(PyObject* obj, PyObject *objs) +{ + Py_ssize_t i; + for (i = 0; i < PyTuple_GET_SIZE(objs); i++) + if (PyTuple_GET_ITEM(objs, i) == obj) + return 1; + return 0; +} + +static int +gc_referrers_for(PyObject *objs, PyGC_Head *list, PyObject *resultlist) +{ + PyGC_Head *gc; + PyObject *obj; + traverseproc traverse; + for (gc = list->gc.gc_next; gc != list; gc = gc->gc.gc_next) { + obj = FROM_GC(gc); + traverse = Py_TYPE(obj)->tp_traverse; + if (obj == objs || obj == resultlist) + continue; + if (traverse(obj, (visitproc)referrersvisit, objs)) { + if (PyList_Append(resultlist, obj) < 0) + return 0; /* error */ + } + } + return 1; /* no error */ +} + +PyDoc_STRVAR(gc_get_referrers__doc__, +"get_referrers(*objs) -> list\n\ +Return the list of objects that directly refer to any of objs."); + +static PyObject * +gc_get_referrers(PyObject *self, PyObject *args) +{ + int i; + PyObject *result = PyList_New(0); + if (!result) return NULL; + + for (i = 0; i < NUM_GENERATIONS; i++) { + if (!(gc_referrers_for(args, GEN_HEAD(i), result))) { + Py_DECREF(result); + return NULL; + } + } + return result; +} + +/* Append obj to list; return true if error (out of memory), false if OK. */ +static int +referentsvisit(PyObject *obj, PyObject *list) +{ + return PyList_Append(list, obj) < 0; +} + +PyDoc_STRVAR(gc_get_referents__doc__, +"get_referents(*objs) -> list\n\ +Return the list of objects that are directly referred to by objs."); + +static PyObject * +gc_get_referents(PyObject *self, PyObject *args) +{ + Py_ssize_t i; + PyObject *result = PyList_New(0); + + if (result == NULL) + return NULL; + + for (i = 0; i < PyTuple_GET_SIZE(args); i++) { + traverseproc traverse; + PyObject *obj = PyTuple_GET_ITEM(args, i); + + if (! PyObject_IS_GC(obj)) + continue; + traverse = Py_TYPE(obj)->tp_traverse; + if (! traverse) + continue; + if (traverse(obj, (visitproc)referentsvisit, result)) { + Py_DECREF(result); + return NULL; + } + } + return result; +} + +PyDoc_STRVAR(gc_get_objects__doc__, +"get_objects() -> [...]\n" +"\n" +"Return a list of objects tracked by the collector (excluding the list\n" +"returned).\n"); + +static PyObject * +gc_get_objects(PyObject *self, PyObject *noargs) +{ + int i; + PyObject* result; + + result = PyList_New(0); + if (result == NULL) + return NULL; + for (i = 0; i < NUM_GENERATIONS; i++) { + if (append_objects(result, GEN_HEAD(i))) { + Py_DECREF(result); + return NULL; + } + } + return result; +} + + +PyDoc_STRVAR(gc__doc__, +"This module provides access to the garbage collector for reference cycles.\n" +"\n" +"enable() -- Enable automatic garbage collection.\n" +"disable() -- Disable automatic garbage collection.\n" +"isenabled() -- Returns true if automatic collection is enabled.\n" +"collect() -- Do a full collection right now.\n" +"get_count() -- Return the current collection counts.\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" +"get_objects() -- Return a list of all objects tracked by the collector.\n" +"get_referrers() -- Return the list of objects that refer to an object.\n" +"get_referents() -- Return the list of objects that an object refers to.\n"); + +static PyMethodDef GcMethods[] = { + {"enable", gc_enable, METH_NOARGS, gc_enable__doc__}, + {"disable", gc_disable, METH_NOARGS, gc_disable__doc__}, + {"isenabled", gc_isenabled, METH_NOARGS, gc_isenabled__doc__}, + {"set_debug", gc_set_debug, METH_VARARGS, gc_set_debug__doc__}, + {"get_debug", gc_get_debug, METH_NOARGS, gc_get_debug__doc__}, + {"get_count", gc_get_count, METH_NOARGS, gc_get_count__doc__}, + {"set_threshold", gc_set_thresh, METH_VARARGS, gc_set_thresh__doc__}, + {"get_threshold", gc_get_thresh, METH_NOARGS, gc_get_thresh__doc__}, + {"collect", (PyCFunction)gc_collect, + METH_VARARGS | METH_KEYWORDS, gc_collect__doc__}, + {"get_objects", gc_get_objects,METH_NOARGS, gc_get_objects__doc__}, + {"get_referrers", gc_get_referrers, METH_VARARGS, + gc_get_referrers__doc__}, + {"get_referents", gc_get_referents, METH_VARARGS, + gc_get_referents__doc__}, + {NULL, NULL} /* Sentinel */ +}; + +PyMODINIT_FUNC +initgc(void) +{ + PyObject *m; + + m = Py_InitModule4("gc", + GcMethods, + gc__doc__, + NULL, + PYTHON_API_VERSION); + if (m == NULL) + return; + + if (garbage == NULL) { + garbage = PyList_New(0); + if (garbage == NULL) + return; + } + Py_INCREF(garbage); + if (PyModule_AddObject(m, "garbage", garbage) < 0) + return; + + /* Importing can't be done in collect() because collect() + * can be called via PyGC_Collect() in Py_Finalize(). + * This wouldn't be a problem, except that is + * reset to 0 before calling collect which trips up + * the import and triggers an assertion. + */ + if (tmod == NULL) { + tmod = PyImport_ImportModuleNoBlock("time"); + if (tmod == NULL) + PyErr_Clear(); + } + +#define ADD_INT(NAME) if (PyModule_AddIntConstant(m, #NAME, NAME) < 0) return + ADD_INT(DEBUG_STATS); + ADD_INT(DEBUG_COLLECTABLE); + ADD_INT(DEBUG_UNCOLLECTABLE); + ADD_INT(DEBUG_INSTANCES); + ADD_INT(DEBUG_OBJECTS); + ADD_INT(DEBUG_SAVEALL); + ADD_INT(DEBUG_LEAK); +#undef ADD_INT +} + +/* API to invoke gc.collect() from C */ +Py_ssize_t +PyGC_Collect(void) +{ + Py_ssize_t n; + + if (collecting) + n = 0; /* already collecting, don't do anything */ + else { + collecting = 1; + n = collect(NUM_GENERATIONS - 1); + collecting = 0; + } + + return n; +} + +/* for debugging */ +void +_PyGC_Dump(PyGC_Head *g) +{ + _PyObject_Dump(FROM_GC(g)); +} + +/* extension modules might be compiled with GC support so these + functions must always be available */ + +#undef PyObject_GC_Track +#undef PyObject_GC_UnTrack +#undef PyObject_GC_Del +#undef _PyObject_GC_Malloc + +void +PyObject_GC_Track(void *op) +{ + _PyObject_GC_TRACK(op); +} + +/* for binary compatibility with 2.2 */ +void +_PyObject_GC_Track(PyObject *op) +{ + PyObject_GC_Track(op); +} + +void +PyObject_GC_UnTrack(void *op) +{ + /* Obscure: the Py_TRASHCAN mechanism requires that we be able to + * call PyObject_GC_UnTrack twice on an object. + */ + if (IS_TRACKED(op)) + _PyObject_GC_UNTRACK(op); +} + +/* for binary compatibility with 2.2 */ +void +_PyObject_GC_UnTrack(PyObject *op) +{ + PyObject_GC_UnTrack(op); +} + +PyObject * +_PyObject_GC_Malloc(size_t basicsize) +{ + PyObject *op; + PyGC_Head *g; + if (basicsize > PY_SSIZE_T_MAX - sizeof(PyGC_Head)) + return PyErr_NoMemory(); + g = (PyGC_Head *)PyObject_MALLOC( + sizeof(PyGC_Head) + basicsize); + if (g == NULL) + return PyErr_NoMemory(); + g->gc.gc_refs = GC_UNTRACKED; + generations[0].count++; /* number of allocated GC objects */ + if (generations[0].count > generations[0].threshold && + enabled && + generations[0].threshold && + !collecting && + !PyErr_Occurred()) { + collecting = 1; + collect_generations(); + collecting = 0; + } + op = FROM_GC(g); + return op; +} + +PyObject * +_PyObject_GC_New(PyTypeObject *tp) +{ + PyObject *op = _PyObject_GC_Malloc(_PyObject_SIZE(tp)); + if (op != NULL) + op = PyObject_INIT(op, tp); + return op; +} + +PyVarObject * +_PyObject_GC_NewVar(PyTypeObject *tp, Py_ssize_t nitems) +{ + const size_t size = _PyObject_VAR_SIZE(tp, nitems); + PyVarObject *op = (PyVarObject *) _PyObject_GC_Malloc(size); + if (op != NULL) + op = PyObject_INIT_VAR(op, tp, nitems); + return op; +} + +PyVarObject * +_PyObject_GC_Resize(PyVarObject *op, Py_ssize_t nitems) +{ + const size_t basicsize = _PyObject_VAR_SIZE(Py_TYPE(op), nitems); + PyGC_Head *g = AS_GC(op); + if (basicsize > PY_SSIZE_T_MAX - sizeof(PyGC_Head)) + return (PyVarObject *)PyErr_NoMemory(); + g = (PyGC_Head *)PyObject_REALLOC(g, sizeof(PyGC_Head) + basicsize); + if (g == NULL) + return (PyVarObject *)PyErr_NoMemory(); + op = (PyVarObject *) FROM_GC(g); + Py_SIZE(op) = nitems; + return op; +} + +void +PyObject_GC_Del(void *op) +{ + PyGC_Head *g = AS_GC(op); + if (IS_TRACKED(op)) + gc_list_remove(g); + if (generations[0].count > 0) { + generations[0].count--; + } + PyObject_FREE(g); +} + +/* for binary compatibility with 2.2 */ +#undef _PyObject_GC_Del +void +_PyObject_GC_Del(PyObject *op) +{ + PyObject_GC_Del(op); +}