Edit: mem.h
#ifndef Py_INTERNAL_MEM_H #define Py_INTERNAL_MEM_H #ifdef __cplusplus extern "C" { #endif #include "objimpl.h" #include "pymem.h" /* GC runtime state */ /* If we change this, we need to change the default value in the signature of gc.collect. */ #define NUM_GENERATIONS 3 /* NOTE: about the counting of long-lived objects. To limit the cost of garbage collection, there are two strategies; - make each collection faster, e.g. by scanning fewer objects - do less collections This heuristic is about the latter strategy. In addition to the various configurable thresholds, we only trigger a full collection if the ratio long_lived_pending / long_lived_total is above a given value (hardwired to 25%). The reason is that, while "non-full" collections (i.e., collections of the young and middle generations) will always examine roughly the same number of objects -- determined by the aforementioned thresholds --, the cost of a full collection is proportional to the total number of long-lived objects, which is virtually unbounded. Indeed, it has been remarked that doing a full collection every <constant number> of object creations entails a dramatic performance degradation in workloads which consist in creating and storing lots of long-lived objects (e.g. building a large list of GC-tracked objects would show quadratic performance, instead of linear as expected: see issue #4074). Using the above ratio, instead, yields amortized linear performance in the total number of objects (the effect of which can be summarized thusly: "each full garbage collection is more and more costly as the number of objects grows, but we do fewer and fewer of them"). This heuristic was suggested by Martin von Löwis on python-dev in June 2008. His original analysis and proposal can be found at: http://mail.python.org/pipermail/python-dev/2008-June/080579.html */ /* NOTE: about untracking of mutable objects. Certain types of container cannot participate in a reference cycle, and so do not need to be tracked by the garbage collector. Untracking these objects reduces the cost of garbage collections. However, determining which objects may be untracked is not free, and the costs must be weighed against the benefits for garbage collection. There are two possible strategies for when to untrack a container: i) When the container is created. ii) When the container is examined by the garbage collector. Tuples containing only immutable objects (integers, strings etc, and recursively, tuples of immutable objects) do not need to be tracked. The interpreter creates a large number of tuples, many of which will not survive until garbage collection. It is therefore not worthwhile to untrack eligible tuples at creation time. Instead, all tuples except the empty tuple are tracked when created. During garbage collection it is determined whether any surviving tuples can be untracked. A tuple can be untracked if all of its contents are already not tracked. Tuples are examined for untracking in all garbage collection cycles. It may take more than one cycle to untrack a tuple. Dictionaries containing only immutable objects also do not need to be tracked. Dictionaries are untracked when created. If a tracked item is inserted into a dictionary (either as a key or value), the dictionary becomes tracked. During a full garbage collection (all generations), the collector will untrack any dictionaries whose contents are not tracked. The module provides the python function is_tracked(obj), which returns the CURRENT tracking status of the object. Subsequent garbage collections may change the tracking status of the object. Untracking of certain containers was introduced in issue #4688, and the algorithm was refined in response to issue #14775. */ struct gc_generation { PyGC_Head head; int threshold; /* collection threshold */ int count; /* count of allocations or collections of younger generations */ }; /* Running stats per generation */ struct gc_generation_stats { /* total number of collections */ Py_ssize_t collections; /* total number of collected objects */ Py_ssize_t collected; /* total number of uncollectable objects (put into gc.garbage) */ Py_ssize_t uncollectable; }; struct _gc_runtime_state { /* List of objects that still need to be cleaned up, singly linked * via their gc headers' gc_prev pointers. */ PyObject *trash_delete_later; /* Current call-stack depth of tp_dealloc calls. */ int trash_delete_nesting; int enabled; int debug; /* linked lists of container objects */ struct gc_generation generations[NUM_GENERATIONS]; PyGC_Head *generation0; /* a permanent generation which won't be collected */ struct gc_generation permanent_generation; struct gc_generation_stats generation_stats[NUM_GENERATIONS]; /* true if we are currently running the collector */ int collecting; /* list of uncollectable objects */ PyObject *garbage; /* a list of callbacks to be invoked when collection is performed */ PyObject *callbacks; /* This is the number of objects that survived the last full collection. It approximates the number of long lived objects tracked by the GC. (by "full collection", we mean a collection of the oldest generation). */ Py_ssize_t long_lived_total; /* This is the number of objects that survived all "non-full" collections, and are awaiting to undergo a full collection for the first time. */ Py_ssize_t long_lived_pending; }; PyAPI_FUNC(void) _PyGC_Initialize(struct _gc_runtime_state *); #define _PyGC_generation0 _PyRuntime.gc.generation0 /* Heuristic checking if a pointer value is newly allocated (uninitialized) or newly freed. The pointer is not dereferenced, only the pointer value is checked. The heuristic relies on the debug hooks on Python memory allocators which fills newly allocated memory with CLEANBYTE (0xCD) and newly freed memory with DEADBYTE (0xDD). Detect also "untouchable bytes" marked with FORBIDDENBYTE (0xFD). */ static inline int _PyMem_IsPtrFreed(void *ptr) { uintptr_t value = (uintptr_t)ptr; #if SIZEOF_VOID_P == 8 return (value == (uintptr_t)0xCDCDCDCDCDCDCDCD || value == (uintptr_t)0xDDDDDDDDDDDDDDDD || value == (uintptr_t)0xFDFDFDFDFDFDFDFD); #elif SIZEOF_VOID_P == 4 return (value == (uintptr_t)0xCDCDCDCD || value == (uintptr_t)0xDDDDDDDD || value == (uintptr_t)0xFDFDFDFD); #else # error "unknown pointer size" #endif } #ifdef __cplusplus } #endif #endif /* !Py_INTERNAL_MEM_H */
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