talloc3tallochierarchical reference counted memory pool system with destructors#include <talloc/talloc.h>DESCRIPTION
If you are used to talloc from Samba3 then please read this
carefully, as talloc has changed a lot.
The new talloc is a hierarchical, reference counted memory pool
system with destructors. Quite a mouthful really, but not too bad
once you get used to it.
Perhaps the biggest change from Samba3 is that there is no
distinction between a "talloc context" and a "talloc pointer". Any
pointer returned from talloc() is itself a valid talloc context.
This means you can do this:
struct foo *X = talloc(mem_ctx, struct foo);
X->name = talloc_strdup(X, "foo");
and the pointer X->name
would be a "child" of the talloc context X which is itself a child of
mem_ctx. So if you do
talloc_free(mem_ctx) then
it is all destroyed, whereas if you do talloc_free(X) then just X and X->name are destroyed, and if
you do talloc_free(X->name) then just
the name element of X is
destroyed.
If you think about this, then what this effectively gives you is an
n-ary tree, where you can free any part of the tree with
talloc_free().
If you find this confusing, then I suggest you run the testsuite program to watch talloc
in action. You may also like to add your own tests to testsuite.c to clarify how some
particular situation is handled.
TALLOC API
The following is a complete guide to the talloc API. Read it all at
least twice.
(type *)talloc(const void *ctx, type);
The talloc() macro is the core of the talloc library. It takes a
memory ctx and a type, and returns a pointer to a new
area of memory of the given type.
The returned pointer is itself a talloc context, so you can use
it as the ctx argument to more
calls to talloc() if you wish.
The returned pointer is a "child" of the supplied context. This
means that if you talloc_free() the ctx then the new child disappears as
well. Alternatively you can free just the child.
The ctx argument to talloc()
can be NULL, in which case a new top level context is created.
void *talloc_size(const void *ctx, size_t size);
The function talloc_size() should be used when you don't have a
convenient type to pass to talloc(). Unlike talloc(), it is not
type safe (as it returns a void *), so you are on your own for
type checking.
(typeof(ptr)) talloc_ptrtype(const void *ctx, ptr);
The talloc_ptrtype() macro should be used when you have a pointer and
want to allocate memory to point at with this pointer. When compiling
with gcc >= 3 it is typesafe. Note this is a wrapper of talloc_size()
and talloc_get_name() will return the current location in the source file.
and not the type.
int talloc_free(void *ptr);
The talloc_free() function frees a piece of talloc memory, and
all its children. You can call talloc_free() on any pointer
returned by talloc().
The return value of talloc_free() indicates success or failure,
with 0 returned for success and -1 for failure. The only
possible failure condition is if ptr had a destructor attached to it and
the destructor returned -1. See talloc_set_destructor()
for details on destructors.
If this pointer has an additional parent when talloc_free() is
called then the memory is not actually released, but instead the
most recently established parent is destroyed. See talloc_reference()
for details on establishing additional parents.
For more control on which parent is removed, see talloc_unlink().
talloc_free() operates recursively on its children.
void *talloc_reference(const void *ctx, const void *ptr);
The talloc_reference() function makes ctx an additional parent of ptr.
The return value of talloc_reference() is always the original
pointer ptr, unless talloc ran
out of memory in creating the reference in which case it will
return NULL (each additional reference consumes around 48 bytes
of memory on intel x86 platforms).
If ptr is NULL, then the
function is a no-op, and simply returns NULL.
After creating a reference you can free it in one of the
following ways:
you can talloc_free() any parent of the original pointer.
That will reduce the number of parents of this pointer by 1,
and will cause this pointer to be freed if it runs out of
parents.
you can talloc_free() the pointer itself. That will destroy
the most recently established parent to the pointer and leave
the pointer as a child of its current parent.
For more control on which parent to remove, see talloc_unlink().
int talloc_unlink(const void *ctx, const void *ptr);
The talloc_unlink() function removes a specific parent from
ptr. The ctx passed must either be a context used
in talloc_reference() with this pointer, or must be a direct
parent of ptr.
Note that if the parent has already been removed using
talloc_free() then this function will fail and will return -1.
Likewise, if ptr is NULL, then
the function will make no modifications and return -1.
Usually you can just use talloc_free() instead of
talloc_unlink(), but sometimes it is useful to have the
additional control on which parent is removed.
void talloc_set_destructor(const void *ptr, int (*destructor)(void *));
The function talloc_set_destructor() sets the destructor for the pointer ptr. A destructor is a function that is called
when the memory used by a pointer is about to be released. The
destructor receives ptr as an
argument, and should return 0 for success and -1 for failure.
The destructor can do anything
it wants to, including freeing other pieces of memory. A common
use for destructors is to clean up operating system resources
(such as open file descriptors) contained in the structure the
destructor is placed on.
You can only place one destructor on a pointer. If you need more
than one destructor then you can create a zero-length child of
the pointer and place an additional destructor on that.
To remove a destructor call talloc_set_destructor() with NULL for
the destructor.
If your destructor attempts to talloc_free() the pointer that it
is the destructor for then talloc_free() will return -1 and the
free will be ignored. This would be a pointless operation
anyway, as the destructor is only called when the memory is just
about to go away.
int talloc_increase_ref_count(const void *<emphasis role="italic">ptr</emphasis>);
The talloc_increase_ref_count(ptr) function is exactly equivalent to:
talloc_reference(NULL, ptr);
You can use either syntax, depending on which you think is
clearer in your code.
It returns 0 on success and -1 on failure.
size_t talloc_reference_count(const void *<emphasis role="italic">ptr</emphasis>);
Return the number of references to the pointer.
void talloc_set_name(const void *ptr, const char *fmt, ...);
Each talloc pointer has a "name". The name is used principally
for debugging purposes, although it is also possible to set and
get the name on a pointer in as a way of "marking" pointers in
your code.
The main use for names on pointer is for "talloc reports". See
talloc_report_depth_cb(),
talloc_report_depth_file(),
talloc_report()talloc_report()
and talloc_report_full()
for details. Also see talloc_enable_leak_report()
and talloc_enable_leak_report_full().
The talloc_set_name() function allocates memory as a child of the
pointer. It is logically equivalent to:
talloc_set_name_const(ptr, talloc_asprintf(ptr, fmt, ...));
Note that multiple calls to talloc_set_name() will allocate more
memory without releasing the name. All of the memory is released
when the ptr is freed using talloc_free().
void talloc_set_name_const(const void *<emphasis role="italic">ptr</emphasis>, const char *<emphasis role="italic">name</emphasis>);
The function talloc_set_name_const() is just like
talloc_set_name(), but it takes a string constant, and is much
faster. It is extensively used by the "auto naming" macros, such
as talloc_p().
This function does not allocate any memory. It just copies the
supplied pointer into the internal representation of the talloc
ptr. This means you must not pass a name pointer to memory that will
disappear before ptr is freed
with talloc_free().
void *talloc_named(const void *<emphasis role="italic">ctx</emphasis>, size_t <emphasis role="italic">size</emphasis>, const char *<emphasis role="italic">fmt</emphasis>, ...);
The talloc_named() function creates a named talloc pointer. It
is equivalent to:
ptr = talloc_size(ctx, size);
talloc_set_name(ptr, fmt, ....);void *talloc_named_const(const void *<emphasis role="italic">ctx</emphasis>, size_t <emphasis role="italic">size</emphasis>, const char *<emphasis role="italic">name</emphasis>);
This is equivalent to:
ptr = talloc_size(ctx, size);
talloc_set_name_const(ptr, name);const char *talloc_get_name(const void *<emphasis role="italic">ptr</emphasis>);
This returns the current name for the given talloc pointer,
ptr. See talloc_set_name()
for details.
void *talloc_init(const char *<emphasis role="italic">fmt</emphasis>, ...);
This function creates a zero length named talloc context as a top
level context. It is equivalent to:
talloc_named(NULL, 0, fmt, ...);void *talloc_new(void *<emphasis role="italic">ctx</emphasis>);
This is a utility macro that creates a new memory context hanging
off an exiting context, automatically naming it "talloc_new:
__location__" where __location__ is the source line it is called
from. It is particularly useful for creating a new temporary
working context.
(<emphasis role="italic">type</emphasis> *)talloc_realloc(const void *<emphasis role="italic">ctx</emphasis>, void *<emphasis role="italic">ptr</emphasis>, <emphasis role="italic">type</emphasis>, <emphasis role="italic">count</emphasis>);
The talloc_realloc() macro changes the size of a talloc pointer.
It has the following equivalences:
talloc_realloc(ctx, NULL, type, 1) ==> talloc(ctx, type);
talloc_realloc(ctx, ptr, type, 0) ==> talloc_free(ptr);
The ctx argument is only used
if ptr is not NULL, otherwise
it is ignored.
talloc_realloc() returns the new pointer, or NULL on failure.
The call will fail either due to a lack of memory, or because the
pointer has more than one parent (see talloc_reference()).
void *talloc_realloc_size(const void *ctx, void *ptr, size_t size);
the talloc_realloc_size() function is useful when the type is not
known so the type-safe talloc_realloc() cannot be used.
TYPE *talloc_steal(const void *<emphasis role="italic">new_ctx</emphasis>, const TYPE *<emphasis role="italic">ptr</emphasis>);
The talloc_steal() function changes the parent context of a
talloc pointer. It is typically used when the context that the
pointer is currently a child of is going to be freed and you wish
to keep the memory for a longer time.
The talloc_steal() function returns the pointer that you pass it.
It does not have any failure modes.
NOTE: It is possible to produce loops in the parent/child
relationship if you are not careful with talloc_steal(). No
guarantees are provided as to your sanity or the safety of your
data if you do this.
TYPE *talloc_move(const void *<emphasis role="italic">new_ctx</emphasis>, TYPE **<emphasis role="italic">ptr</emphasis>);
The talloc_move() function is a wrapper around
talloc_steal() which zeros the source pointer after the
move. This avoids a potential source of bugs where a
programmer leaves a pointer in two structures, and uses the
pointer from the old structure after it has been moved to a
new one.
size_t talloc_total_size(const void *<emphasis role="italic">ptr</emphasis>);
The talloc_total_size() function returns the total size in bytes
used by this pointer and all child pointers. Mostly useful for
debugging.
Passing NULL is allowed, but it will only give a meaningful
result if talloc_enable_leak_report() or
talloc_enable_leak_report_full() has been called.
size_t talloc_total_blocks(const void *<emphasis role="italic">ptr</emphasis>);
The talloc_total_blocks() function returns the total memory block
count used by this pointer and all child pointers. Mostly useful
for debugging.
Passing NULL is allowed, but it will only give a meaningful
result if talloc_enable_leak_report() or
talloc_enable_leak_report_full() has been called.
void talloc_report(const void *ptr, FILE *f);
The talloc_report() function prints a summary report of all
memory used by ptr. One line
of report is printed for each immediate child of ptr, showing the
total memory and number of blocks used by that child.
You can pass NULL for the pointer, in which case a report is
printed for the top level memory context, but only if
talloc_enable_leak_report() or talloc_enable_leak_report_full()
has been called.
void talloc_report_full(const void *<emphasis role="italic">ptr</emphasis>, FILE *<emphasis role="italic">f</emphasis>);
This provides a more detailed report than talloc_report(). It
will recursively print the entire tree of memory referenced by
the pointer. References in the tree are shown by giving the name
of the pointer that is referenced.
You can pass NULL for the pointer, in which case a report is
printed for the top level memory context, but only if
talloc_enable_leak_report() or talloc_enable_leak_report_full()
has been called.
void talloc_report_depth_cbconst void *ptrint depthint max_depthvoid (*callback)(const void *ptr, int depth, int max_depth, int is_ref, void *priv)void *priv
This provides a more flexible reports than talloc_report(). It
will recursively call the callback for the entire tree of memory
referenced by the pointer. References in the tree are passed with
is_ref = 1 and the pointer that is referenced.
You can pass NULL for the pointer, in which case a report is
printed for the top level memory context, but only if
talloc_enable_leak_report() or talloc_enable_leak_report_full()
has been called.
The recursion is stopped when depth >= max_depth.
max_depth = -1 means only stop at leaf nodes.
void talloc_report_depth_fileconst void *ptrint depthint max_depthFILE *f
This provides a more flexible reports than talloc_report(). It
will let you specify the depth and max_depth.
void talloc_enable_leak_report(void);
This enables calling of talloc_report(NULL, stderr) when the
program exits. In Samba4 this is enabled by using the
--leak-report command line option.
For it to be useful, this function must be called before any
other talloc function as it establishes a "null context" that
acts as the top of the tree. If you don't call this function
first then passing NULL to talloc_report() or
talloc_report_full() won't give you the full tree printout.
Here is a typical talloc report:
talloc report on 'null_context' (total 267 bytes in 15 blocks)
libcli/auth/spnego_parse.c:55 contains 31 bytes in 2 blocks
libcli/auth/spnego_parse.c:55 contains 31 bytes in 2 blocks
iconv(UTF8,CP850) contains 42 bytes in 2 blocks
libcli/auth/spnego_parse.c:55 contains 31 bytes in 2 blocks
iconv(CP850,UTF8) contains 42 bytes in 2 blocks
iconv(UTF8,UTF-16LE) contains 45 bytes in 2 blocks
iconv(UTF-16LE,UTF8) contains 45 bytes in 2 blocks
void talloc_enable_leak_report_full(void);
This enables calling of talloc_report_full(NULL, stderr) when the
program exits. In Samba4 this is enabled by using the
--leak-report-full command line option.
For it to be useful, this function must be called before any
other talloc function as it establishes a "null context" that
acts as the top of the tree. If you don't call this function
first then passing NULL to talloc_report() or
talloc_report_full() won't give you the full tree printout.
Here is a typical full report:
full talloc report on 'root' (total 18 bytes in 8 blocks)
p1 contains 18 bytes in 7 blocks (ref 0)
r1 contains 13 bytes in 2 blocks (ref 0)
reference to: p2
p2 contains 1 bytes in 1 blocks (ref 1)
x3 contains 1 bytes in 1 blocks (ref 0)
x2 contains 1 bytes in 1 blocks (ref 0)
x1 contains 1 bytes in 1 blocks (ref 0)
(<emphasis role="italic">type</emphasis> *)talloc_zero(const void *<emphasis role="italic">ctx</emphasis>, <emphasis role="italic">type</emphasis>);
The talloc_zero() macro is equivalent to:
ptr = talloc(ctx, type);
if (ptr) memset(ptr, 0, sizeof(type));void *talloc_zero_size(const void *<emphasis role="italic">ctx</emphasis>, size_t <emphasis role="italic">size</emphasis>)
The talloc_zero_size() function is useful when you don't have a
known type.
void *talloc_memdup(const void *<emphasis role="italic">ctx</emphasis>, const void *<emphasis role="italic">p</emphasis>, size_t size);
The talloc_memdup() function is equivalent to:
ptr = talloc_size(ctx, size);
if (ptr) memcpy(ptr, p, size);char *talloc_strdup(const void *<emphasis role="italic">ctx</emphasis>, const char *<emphasis role="italic">p</emphasis>);
The talloc_strdup() function is equivalent to:
ptr = talloc_size(ctx, strlen(p)+1);
if (ptr) memcpy(ptr, p, strlen(p)+1);
This function sets the name of the new pointer to the passed
string. This is equivalent to:
talloc_set_name_const(ptr, ptr)char *talloc_strndup(const void *<emphasis role="italic">t</emphasis>, const char *<emphasis role="italic">p</emphasis>, size_t <emphasis role="italic">n</emphasis>);
The talloc_strndup() function is the talloc equivalent of the C
library function strndup(3).
This function sets the name of the new pointer to the passed
string. This is equivalent to:
talloc_set_name_const(ptr, ptr)char *talloc_append_string(const void *<emphasis role="italic">t</emphasis>, char *<emphasis role="italic">orig</emphasis>, const char *<emphasis role="italic">append</emphasis>);
The talloc_append_string() function appends the given formatted
string to the given string.
This function sets the name of the new pointer to the new
string. This is equivalent to:
talloc_set_name_const(ptr, ptr)char *talloc_vasprintf(const void *<emphasis role="italic">t</emphasis>, const char *<emphasis role="italic">fmt</emphasis>, va_list <emphasis role="italic">ap</emphasis>);
The talloc_vasprintf() function is the talloc equivalent of the C
library function vasprintf(3).
This function sets the name of the new pointer to the new
string. This is equivalent to:
talloc_set_name_const(ptr, ptr)char *talloc_asprintf(const void *<emphasis role="italic">t</emphasis>, const char *<emphasis role="italic">fmt</emphasis>, ...);
The talloc_asprintf() function is the talloc equivalent of the C
library function asprintf(3).
This function sets the name of the new pointer to the passed
string. This is equivalent to:
talloc_set_name_const(ptr, ptr)char *talloc_asprintf_append(char *s, const char *fmt, ...);
The talloc_asprintf_append() function appends the given formatted
string to the given string.
This function sets the name of the new pointer to the new
string. This is equivalent to:
talloc_set_name_const(ptr, ptr)(type *)talloc_array(const void *ctx, type, uint_t count);
The talloc_array() macro is equivalent to:
(type *)talloc_size(ctx, sizeof(type) * count);
except that it provides integer overflow protection for the
multiply, returning NULL if the multiply overflows.
void *talloc_array_size(const void *ctx, size_t size, uint_t count);
The talloc_array_size() function is useful when the type is not
known. It operates in the same way as talloc_array(), but takes a
size instead of a type.
(typeof(ptr)) talloc_array_ptrtype(const void *ctx, ptr, uint_t count);
The talloc_ptrtype() macro should be used when you have a pointer to an array
and want to allocate memory of an array to point at with this pointer. When compiling
with gcc >= 3 it is typesafe. Note this is a wrapper of talloc_array_size()
and talloc_get_name() will return the current location in the source file.
and not the type.
void *talloc_realloc_fn(const void *ctx, void *ptr, size_t size)
This is a non-macro version of talloc_realloc(), which is useful
as libraries sometimes want a realloc function pointer. A
realloc(3) implementation encapsulates the functionality of
malloc(3), free(3) and realloc(3) in one call, which is why it is
useful to be able to pass around a single function pointer.
void *talloc_autofree_context(void);
This is a handy utility function that returns a talloc context
which will be automatically freed on program exit. This can be
used to reduce the noise in memory leak reports.
void *talloc_check_name(const void *ptr, const char *name);
This function checks if a pointer has the specified name. If it does then the pointer is
returned. It it doesn't then NULL is returned.
(type *)talloc_get_type(const void *ptr, type);
This macro allows you to do type checking on talloc pointers. It
is particularly useful for void* private pointers. It is
equivalent to this:
(type *)talloc_check_name(ptr, #type)talloc_set_type(const void *ptr, type);
This macro allows you to force the name of a pointer to be a
particular type. This can be
used in conjunction with talloc_get_type() to do type checking on
void* pointers.
It is equivalent to this:
talloc_set_name_const(ptr, #type)PERFORMANCE
All the additional features of talloc(3) over malloc(3) do come at a
price. We have a simple performance test in Samba4 that measures
talloc() versus malloc() performance, and it seems that talloc() is
about 10% slower than malloc() on my x86 Debian Linux box. For
Samba, the great reduction in code complexity that we get by using
talloc makes this worthwhile, especially as the total overhead of
talloc/malloc in Samba is already quite small.
SEE ALSO
malloc(3), strndup(3), vasprintf(3), asprintf(3),
COPYRIGHT/LICENSE
Copyright (C) Andrew Tridgell 2004
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or (at
your option) any later version.
This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.