X-Git-Url: https://git.ozlabs.org/?a=blobdiff_plain;f=talloc%2Ftalloc.3.xml;fp=talloc%2Ftalloc.3.xml;h=83ca67a495114308a719f84fef5010540230f15c;hb=29149d39d59c6b46535f237563732092397331f0;hp=0000000000000000000000000000000000000000;hpb=f7315b84a70f81579971d3450a2865fde3b71a7a;p=ccan diff --git a/talloc/talloc.3.xml b/talloc/talloc.3.xml new file mode 100644 index 00000000..83ca67a4 --- /dev/null +++ b/talloc/talloc.3.xml @@ -0,0 +1,739 @@ + + + + + talloc + 3 + + + talloc +hierarchical 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_cb + const void *ptr + int depth + int max_depth + void (*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_file + const void *ptr + int depth + int max_depth + FILE *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. + + +