-This file describes some special Python build types enabled via
-compile-time preprocessor defines.
+This file describes some special Python build types enabled via compile-time
+preprocessor defines.
-It is best to define these options in the EXTRA_CFLAGS make variable;
+IMPORTANT: if you want to build a debug-enabled Python, it is recommended that
+you use ``./configure --with-pydebug``, rather than the options listed here.
+
+However, if you wish to define some of these options individually, it is best
+to define them in the EXTRA_CFLAGS make variable;
``make EXTRA_CFLAGS="-DPy_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
-all objects. In a debug-mode build, this is where the "8288" comes from
-in
+Py_REF_DEBUG
+------------
+
+Turn on aggregate reference counting. This arranges that extern _Py_RefTotal
+hold a count of all references, the sum of ob_refcnt across all objects. In a
+debug-mode build, this is where the "8288" comes from in
>>> 23
23
>>>
Note that if this count increases when you're not storing away new objects,
-there's probably a leak. Remember, though, that in interactive mode the
-special name "_" holds a reference to the last result displayed!
+there's probably a leak. Remember, though, that in interactive mode the special
+name "_" holds a reference to the last result displayed!
-Py_REF_DEBUG also checks after every decref to verify that the refcount
-hasn't gone negative, and causes an immediate fatal error if it has.
+Py_REF_DEBUG also checks after every decref to verify that the refcount hasn't
+gone negative, and causes an immediate fatal error if it has.
Special gimmicks:
sys.gettotalrefcount()
Return current total of all refcounts.
- Available under Py_REF_DEBUG in Python 2.3.
- Before 2.3, Py_TRACE_REFS was required to enable this function.
----------------------------------------------------------------------------
-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
-heap-allocated objects. Most built-in type objects are not in this list,
-as they're statically allocated. Starting in Python 2.3, if COUNT_ALLOCS
-(see below) is also defined, a static type object T does appear in this
-list if at least one object of type T has been created.
+
+
+Py_TRACE_REFS
+-------------
+
+Turn on heavy reference debugging. This is major surgery. Every PyObject grows
+two more pointers, to maintain a doubly-linked list of all live heap-allocated
+objects. Most built-in type objects are not in this list, as they're statically
+allocated. Starting in Python 2.3, if COUNT_ALLOCS (see below) is also defined,
+a static type object T does appear in this list if at least one object of type T
+has been created.
Note that because the fundamental PyObject layout changes, Python modules
-compiled with Py_TRACE_REFS are incompatible with modules compiled without
-it.
+compiled with Py_TRACE_REFS are incompatible with modules compiled without it.
Py_TRACE_REFS implies Py_REF_DEBUG.
Special gimmicks:
sys.getobjects(max[, type])
- Return list of the (no more than) max most-recently allocated objects,
- most recently allocated first in the list, least-recently allocated
- last in the list. max=0 means no limit on list length.
- If an optional type object is passed, the list is also restricted to
- objects of that type.
- The return list itself, and some temp objects created just to call
- sys.getobjects(), are excluded from the return list. Note that the
- list returned is just another object, though, so may appear in the
- return list the next time you call getobjects(); note that every
- object in the list is kept alive too, simply by virtue of being in
- the list.
-
-envar PYTHONDUMPREFS
- If this envar exists, Py_Finalize() arranges to print a list of
- all still-live heap objects. This is printed twice, in different
- formats, before and after Py_Finalize has cleaned up everything it
- can clean up. The first output block produces the repr() of each
- object so is more informative; however, a lot of stuff destined to
- die is still alive then. The second output block is much harder
- to work with (repr() can't be invoked anymore -- the interpreter
- has been torn down too far), but doesn't list any objects that will
- die. The tool script combinerefs.py can be run over this to combine
- the info from both output blocks. The second output block, and
+ Return list of the (no more than) max most-recently allocated objects, most
+ recently allocated first in the list, least-recently allocated last in the
+ list. max=0 means no limit on list length. If an optional type object is
+ passed, the list is also restricted to objects of that type. The return
+ list itself, and some temp objects created just to call sys.getobjects(),
+ are excluded from the return list. Note that the list returned is just
+ another object, though, so may appear in the return list the next time you
+ call getobjects(); note that every object in the list is kept alive too,
+ simply by virtue of being in the list.
+
+envvar PYTHONDUMPREFS
+ If this envvar exists, Py_Finalize() arranges to print a list of all
+ still-live heap objects. This is printed twice, in different formats,
+ before and after Py_Finalize has cleaned up everything it can clean up. The
+ first output block produces the repr() of each object so is more
+ informative; however, a lot of stuff destined to die is still alive then.
+ The second output block is much harder to work with (repr() can't be invoked
+ anymore -- the interpreter has been torn down too far), but doesn't list any
+ objects that will die. The tool script combinerefs.py can be run over this
+ to combine the info from both output blocks. The second output block, and
combinerefs.py, were new in Python 2.3b1.
----------------------------------------------------------------------------
-PYMALLOC_DEBUG introduced in 2.3
+
+
+PYMALLOC_DEBUG
+--------------
When pymalloc is enabled (WITH_PYMALLOC is defined), calls to the PyObject_
-memory routines are handled by Python's own small-object allocator, while
-calls to the PyMem_ memory routines are directed to the system malloc/
-realloc/free. If PYMALLOC_DEBUG is also defined, calls to both PyObject_
-and PyMem_ memory routines are directed to a special debugging mode of
-Python's small-object allocator.
+memory routines are handled by Python's own small-object allocator, while calls
+to the PyMem_ memory routines are directed to the system malloc/ realloc/free.
+If PYMALLOC_DEBUG is also defined, calls to both PyObject_ and PyMem_ memory
+routines are directed to a special debugging mode of Python's small-object
+allocator.
-This mode fills dynamically allocated memory blocks with special,
-recognizable bit patterns, and adds debugging info on each end of
-dynamically allocated memory blocks. The special bit patterns are:
+This mode fills dynamically allocated memory blocks with special, recognizable
+bit patterns, and adds debugging info on each end of dynamically allocated
+memory blocks. The special bit patterns are:
#define CLEANBYTE 0xCB /* clean (newly allocated) memory */
#define DEADBYTE 0xDB /* dead (newly freed) memory */
Strings of these bytes are unlikely to be valid addresses, floats, or 7-bit
ASCII strings.
-Let S = sizeof(size_t). 2*S bytes are added at each end of each block of N
-bytes requested. The memory layout is like so, where p represents the
-address returned by a malloc-like or realloc-like function (p[i:j] means
-the slice of bytes from *(p+i) inclusive up to *(p+j) exclusive; note that
-the treatment of negative indices differs from a Python slice):
+Let S = sizeof(size_t). 2*S bytes are added at each end of each block of N bytes
+requested. The memory layout is like so, where p represents the address
+returned by a malloc-like or realloc-like function (p[i:j] means the slice of
+bytes from *(p+i) inclusive up to *(p+j) exclusive; note that the treatment of
+negative indices differs from a Python slice):
p[-2*S:-S]
- Number of bytes originally asked for. This is a size_t, big-endian
- (easier to read in a memory dump).
+ Number of bytes originally asked for. This is a size_t, big-endian (easier
+ to read in a memory dump).
p[-S: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.
- 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 freed memory. When a realloc-
- like function is called requesting a smaller memory block, the excess
- old bytes are also filled with DEADBYTE.
+ 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 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+S]
Copies of FORBIDDENBYTE. Used to catch over- writes and reads.
p[N+S:N+2*S]
A serial number, incremented by 1 on each call to a malloc-like or
- realloc-like function.
- Big-endian size_t.
- If "bad memory" is detected later, the serial number gives an
- excellent way to set a breakpoint on the next run, to capture the
- instant at which this block was passed out. The static function
- bumpserialno() in obmalloc.c is the only place the serial number
- is incremented, and exists so you can set such a breakpoint easily.
-
-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 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).
+ realloc-like function. Big-endian size_t. If "bad memory" is detected
+ later, the serial number gives an excellent way to set a breakpoint on the
+ next run, to capture the instant at which this block was passed out. The
+ static function bumpserialno() in obmalloc.c is the only place the serial
+ number is incremented, and exists so you can set such a breakpoint easily.
+
+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 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.
Special gimmicks:
-envar PYTHONMALLOCSTATS
- If this envar exists, a report of pymalloc summary statistics is
- printed to stderr whenever a new arena is allocated, and also
- by Py_Finalize().
+envvar PYTHONMALLOCSTATS
+ If this envvar exists, a report of pymalloc summary statistics is printed to
+ stderr whenever a new arena is allocated, and also by Py_Finalize().
Changed in 2.5: The number of extra bytes allocated is 4*sizeof(size_t).
Before it was 16 on all boxes, reflecting that Python couldn't make use of
allocations >= 2**32 bytes even on 64-bit boxes before 2.5.
----------------------------------------------------------------------------
-Py_DEBUG introduced in 1.5
- named DEBUG before 1.5
+
+
+Py_DEBUG
+--------
This is what is generally meant by "a debug build" of Python.
-Py_DEBUG implies LLTRACE, Py_REF_DEBUG, Py_TRACE_REFS, and
-PYMALLOC_DEBUG (if 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 introduced in 0.9.9
- partly broken in 2.2 and 2.2.1
+Py_DEBUG implies LLTRACE, Py_REF_DEBUG, Py_TRACE_REFS, and PYMALLOC_DEBUG (if
+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
+------------
Each type object grows three new members:
*/
int tp_maxalloc;
-Allocation and deallocation code keeps these counts up to date.
-Py_Finalize() displays a summary of the info returned by sys.getcounts()
-(see below), along with assorted other special allocation counts (like
-the number of tuple allocations satisfied by a tuple free-list, the number
-of 1-character strings allocated, etc).
+Allocation and deallocation code keeps these counts up to date. Py_Finalize()
+displays a summary of the info returned by sys.getcounts() (see below), along
+with assorted other special allocation counts (like the number of tuple
+allocations satisfied by a tuple free-list, the number of 1-character strings
+allocated, etc).
Before Python 2.2, type objects were immortal, and the COUNT_ALLOCS
-implementation relies on that. As of Python 2.2, heap-allocated type/
-class objects can go away. COUNT_ALLOCS can blow up in 2.2 and 2.2.1
-because of this; this was fixed in 2.2.2. Use of COUNT_ALLOCS makes
-all heap-allocated type objects immortal, except for those for which no
-object of that type is ever allocated.
+implementation relies on that. As of Python 2.2, heap-allocated type/ class
+objects can go away. COUNT_ALLOCS can blow up in 2.2 and 2.2.1 because of this;
+this was fixed in 2.2.2. Use of COUNT_ALLOCS makes all heap-allocated type
+objects immortal, except for those for which no object of that type is ever
+allocated.
Starting with Python 2.3, If Py_TRACE_REFS is also defined, COUNT_ALLOCS
-arranges to ensure that the type object for each allocated object
-appears in the doubly-linked list of all objects maintained by
-Py_TRACE_REFS.
+arranges to ensure that the type object for each allocated object appears in the
+doubly-linked list of all objects maintained by Py_TRACE_REFS.
Special gimmicks:
sys.getcounts()
- Return a list of 4-tuples, one entry for each type object for which
- at least one object of that type was allocated. Each tuple is of
- the form:
+ Return a list of 4-tuples, one entry for each type object for which at least
+ one object of that type was allocated. Each tuple is of the form:
(tp_name, tp_allocs, tp_frees, tp_maxalloc)
- Each distinct type object gets a distinct entry in this list, even
- if two or more type objects have the same tp_name (in which case
- there's no way to distinguish them by looking at this list). The
- list is ordered by time of first object allocation: the type object
- for which the first allocation of an object of that type occurred
- most recently is at the front of the list.
----------------------------------------------------------------------------
-LLTRACE introduced well before 1.0
+ Each distinct type object gets a distinct entry in this list, even if two or
+ more type objects have the same tp_name (in which case there's no way to
+ distinguish them by looking at this list). The list is ordered by time of
+ first object allocation: the type object for which the first allocation of
+ an object of that type occurred most recently is at the front of the list.
+
+
+LLTRACE
+-------
Compile in support for Low Level TRACE-ing of the main interpreter loop.
-When this preprocessor symbol is defined, before PyEval_EvalFrame
-(eval_frame in 2.3 and 2.2, eval_code2 before that) executes a frame's code
-it checks the frame's global namespace for a variable "__lltrace__". If
-such a variable is found, mounds of information about what the interpreter
-is doing are sprayed to stdout, such as every opcode and opcode argument
-and values pushed onto and popped off the value stack.
+When this preprocessor symbol is defined, before PyEval_EvalFrame (eval_frame in
+2.3 and 2.2, eval_code2 before that) executes a frame's code it checks the
+frame's global namespace for a variable "__lltrace__". If such a variable is
+found, mounds of information about what the interpreter is doing are sprayed to
+stdout, such as every opcode and opcode argument and values pushed onto and
+popped off the value stack.
Not useful very often, but very useful when needed.
----------------------------------------------------------------------------
-CALL_PROFILE introduced for Python 2.3
+
+CALL_PROFILE
+------------
Count the number of function calls executed.
-When this symbol is defined, the ceval mainloop and helper functions
-count the number of function calls made. It keeps detailed statistics
-about what kind of object was called and whether the call hit any of
-the special fast paths in the code.
+When this symbol is defined, the ceval mainloop and helper functions count the
+number of function calls made. It keeps detailed statistics about what kind of
+object was called and whether the call hit any of the special fast paths in the
+code.
+
----------------------------------------------------------------------------
-WITH_TSC introduced for Python 2.4
+WITH_TSC
+--------
-Super-lowlevel profiling of the interpreter. When enabled, the sys
-module grows a new function:
+Super-lowlevel profiling of the interpreter. When enabled, the sys module grows
+a new function:
settscdump(bool)
- If true, tell the Python interpreter to dump VM measurements to
- stderr. If false, turn off dump. The measurements are based on the
- processor's time-stamp counter.
+ If true, tell the Python interpreter to dump VM measurements to stderr. If
+ false, turn off dump. The measurements are based on the processor's
+ time-stamp counter.
-This build option requires a small amount of platform specific code.
-Currently this code is present for linux/x86 and any PowerPC platform
-that uses GCC (i.e. OS X and linux/ppc).
+This build option requires a small amount of platform specific code. Currently
+this code is present for linux/x86 and any PowerPC platform that uses GCC
+(i.e. OS X and linux/ppc).
-On the PowerPC the rate at which the time base register is incremented
-is not defined by the architecture specification, so you'll need to
-find the manual for your specific processor. For the 750CX, 750CXe
-and 750FX (all sold as the G3) we find:
+On the PowerPC the rate at which the time base register is incremented is not
+defined by the architecture specification, so you'll need to find the manual for
+your specific processor. For the 750CX, 750CXe and 750FX (all sold as the G3)
+we find:
- The time base counter is clocked at a frequency that is
- one-fourth that of the bus clock.
+ The time base counter is clocked at a frequency that is one-fourth that of
+ the bus clock.
This build is enabled by the --with-tsc flag to configure.
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