diff options
Diffstat (limited to 'Include/object.h')
| -rw-r--r-- | Include/object.h | 103 |
1 files changed, 53 insertions, 50 deletions
diff --git a/Include/object.h b/Include/object.h index 7bb1eac..a0997f2 100644 --- a/Include/object.h +++ b/Include/object.h @@ -76,7 +76,7 @@ whose size is determined when the object is allocated. #define PyObject_VAR_HEAD \ PyObject_HEAD \ int ob_size; /* Number of items in variable part */ - + typedef struct _object { PyObject_HEAD } PyObject; @@ -197,7 +197,7 @@ typedef struct { getsegcountproc bf_getsegcount; getcharbufferproc bf_getcharbuffer; } PyBufferProcs; - + typedef void (*freefunc)(void *); typedef void (*destructor)(PyObject *); @@ -222,18 +222,18 @@ typedef struct _typeobject { PyObject_VAR_HEAD char *tp_name; /* For printing, in format "<module>.<name>" */ int tp_basicsize, tp_itemsize; /* For allocation */ - + /* Methods to implement standard operations */ - + destructor tp_dealloc; printfunc tp_print; getattrfunc tp_getattr; setattrfunc tp_setattr; cmpfunc tp_compare; reprfunc tp_repr; - + /* Method suites for standard classes */ - + PyNumberMethods *tp_as_number; PySequenceMethods *tp_as_sequence; PyMappingMethods *tp_as_mapping; @@ -248,7 +248,7 @@ typedef struct _typeobject { /* Functions to access object as input/output buffer */ PyBufferProcs *tp_as_buffer; - + /* Flags to define presence of optional/expanded features */ long tp_flags; @@ -257,7 +257,7 @@ typedef struct _typeobject { /* Assigned meaning in release 2.0 */ /* call function for all accessible objects */ traverseproc tp_traverse; - + /* delete references to contained objects */ inquiry tp_clear; @@ -654,58 +654,61 @@ it carefully, it may save lots of calls to Py_INCREF() and Py_DECREF() at times. */ -/* - trashcan - CT 2k0130 - non-recursively destroy nested objects - - CT 2k0223 - redefinition for better locality and less overhead. - - Objects that want to be recursion safe need to use - the macro's - Py_TRASHCAN_SAFE_BEGIN(name) - and - Py_TRASHCAN_SAFE_END(name) - surrounding their actual deallocation code. - - It would be nice to do this using the thread state. - Also, we could do an exact stack measure then. - Unfortunately, deallocations also take place when - the thread state is undefined. - - CT 2k0422 complete rewrite. - There is no need to allocate new objects. - Everything is done vialob_refcnt and ob_type now. - Adding support for free-threading should be easy, too. -*/ -#define PyTrash_UNWIND_LEVEL 50 +/* Trashcan mechanism, thanks to Christian Tismer. -#define Py_TRASHCAN_SAFE_BEGIN(op) \ - { \ - ++_PyTrash_delete_nesting; \ - if (_PyTrash_delete_nesting < PyTrash_UNWIND_LEVEL) { \ +When deallocating a container object, it's possible to trigger an unbounded +chain of deallocations, as each Py_DECREF in turn drops the refcount on "the +next" object in the chain to 0. This can easily lead to stack faults, and +especially in threads (which typically have less stack space to work with). -#define Py_TRASHCAN_SAFE_END(op) \ - ;} \ - else \ - _PyTrash_deposit_object((PyObject*)op);\ - --_PyTrash_delete_nesting; \ - if (_PyTrash_delete_later && _PyTrash_delete_nesting <= 0) \ - _PyTrash_destroy_chain(); \ - } \ +A container object that participates in cyclic gc can avoid this by +bracketing the body of its tp_dealloc function with a pair of macros: + +static void +mytype_dealloc(mytype *p) +{ + ... declarations go here ... + + PyObject_GC_UnTrack(p); // must untrack first + Py_TRASHCAN_SAFE_BEGIN(p) + ... The body of the deallocator goes here, including all calls ... + ... to Py_DECREF on contained objects. ... + Py_TRASHCAN_SAFE_END(p) +} + +How it works: The BEGIN macro increments a call-depth counter. So long +as this counter is small, the body of the deallocator is run directly without +further ado. But if the counter gets large, it instead adds p to a list of +objects to be deallocated later, skips the body of the deallocator, and +resumes execution after the END macro. The tp_dealloc routine then returns +without deallocating anything (and so unbounded call-stack depth is avoided). + +When the call stack finishes unwinding again, code generated by the END macro +notices this, and calls another routine to deallocate all the objects that +may have been added to the list of deferred deallocations. In effect, a +chain of N deallocations is broken into N / PyTrash_UNWIND_LEVEL pieces, +with the call stack never exceeding a depth of PyTrash_UNWIND_LEVEL. +*/ extern DL_IMPORT(void) _PyTrash_deposit_object(PyObject*); extern DL_IMPORT(void) _PyTrash_destroy_chain(void); - extern DL_IMPORT(int) _PyTrash_delete_nesting; extern DL_IMPORT(PyObject *) _PyTrash_delete_later; -/* swap the "xx" to check the speed loss */ +#define PyTrash_UNWIND_LEVEL 50 -#define xxPy_TRASHCAN_SAFE_BEGIN(op) -#define xxPy_TRASHCAN_SAFE_END(op) ; +#define Py_TRASHCAN_SAFE_BEGIN(op) \ + if (_PyTrash_delete_nesting < PyTrash_UNWIND_LEVEL) { \ + ++_PyTrash_delete_nesting; + /* The body of the deallocator is here. */ +#define Py_TRASHCAN_SAFE_END(op) \ + --_PyTrash_delete_nesting; \ + if (_PyTrash_delete_later && _PyTrash_delete_nesting <= 0) \ + _PyTrash_destroy_chain(); \ + } \ + else \ + _PyTrash_deposit_object((PyObject*)op); #ifdef __cplusplus } |