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Recorded the introduction release for each gimmick, as best I was able to 

reconstruct that info.
Filled out some sketchy explanations of pragmatics.
This commit is contained in:
Tim Peters 2002-07-11 00:23:58 +00:00
parent 20c8a04a08
commit 62fc52e6a1
1 changed files with 18 additions and 10 deletions
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28
Misc/SpecialBuilds.txt
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@ -2,7 +2,8 @@ This file describes some special Python build types enabled via
compile-time preprocessor defines.
---------------------------------------------------------------------------
Py_REF_DEBUG
Py_REF_DEBUG introduced in 1.4
named REF_DEBUG before 1.4
Turn on aggregate reference counting. This arranges that extern
_Py_RefTotal hold a count of all references, the sum of ob_refcnt across
@ -28,7 +29,8 @@ sys.gettotalrefcount()
Available under Py_REF_DEBUG in Python 2.3.
Before 2.3, Py_TRACE_REFS was required to enable this function.
---------------------------------------------------------------------------
Py_TRACE_REFS
Py_TRACE_REFS introduced in 1.4
named TRACE_REFS before 1.4
Turn on heavy reference debugging. This is major surgery. Every PyObject
grows two more pointers, to maintain a doubly-linked list of all live
@ -58,7 +60,7 @@ envar PYTHONDUMPREFS
If this envar exists, Py_Finalize() arranges to print a list of
all still-live heap objects.
---------------------------------------------------------------------------
PYMALLOC_DEBUG
PYMALLOC_DEBUG introduced in 2.3
When pymalloc is enabled (WITH_PYMALLOC is defined), calls to the PyObject_
memory routines are handled by Python's own small-object allocator, while
@ -90,12 +92,12 @@ p[-8:-4]
p[-4:0]
Copies of FORBIDDENBYTE. Used to catch under- writes and reads.
p[0:N]
The requested memory, filled with copies of CLEANBYTE.
Used to catch reference to uninitialized memory.
The requested memory, filled with copies of CLEANBYTE, used to catch
reference to uninitialized memory.
When a realloc-like function is called requesting a larger memory
block, the new excess bytes are also filled with CLEANBYTE.
When a free-like function is called, these are overwritten with
DEADBYTE, to catch reference to free()ed memory. When a realloc-
DEADBYTE, to catch reference to freed memory. When a realloc-
like function is called requesting a smaller memory block, the excess
old bytes are also filled with DEADBYTE.
p[N:N+4]
@ -110,9 +112,14 @@ p[N+4:N+8]
bumpserialno() in obmalloc.c is the only place the serial number
is incremented, and exists so you can set such a breakpoint easily.
A malloc-like or free-like function first checks that the FORBIDDENBYTEs
A realloc-like or free-like function first checks that the FORBIDDENBYTEs
at each end are intact. If they've been altered, diagnostic output is
written to stderr, and the program is aborted by Py_FatalError().
written to stderr, and the program is aborted via Py_FatalError(). The
other main failure mode is provoking a memory error when a program
reads up one of the special bit patterns and tries to use it as an address.
If you get in a debugger then and look at the object, you're likely
to see that it's entirely filled with 0xDB (meaning freed memory is
getting used) or 0xCB (meaning uninitialized memory is getting used).
Note that PYMALLOC_DEBUG requires WITH_PYMALLOC.
@ -123,7 +130,8 @@ envar PYTHONMALLOCSTATS
printed to stderr whenever a new arena is allocated, and also
by Py_Finalize().
---------------------------------------------------------------------------
Py_DEBUG
Py_DEBUG introduced in 1.5
named DEBUG before 1.5
This is what is generally meant by "a debug build" of Python.
@ -132,7 +140,7 @@ WITH_PYMALLOC is enabled). In addition, C assert()s are enabled (via
the C way: by not defining NDEBUG), and some routines do additional
sanity checks inside "#ifdef Py_DEBUG" blocks.
---------------------------------------------------------------------------
COUNT_ALLOCS
COUNT_ALLOCS introduced in 0.9.9
Each type object grows three new members: