data-stack.h revision 17654607d6adbe64923f023a7120627544c540c8
#ifndef DATA_STACK_H
#define DATA_STACK_H
/* Data stack makes it very easy to implement functions returning dynamic data
without having to worry much about memory management like freeing the
result or having large enough buffers for the result.
t_ prefix was chosen to describe functions allocating memory from data
stack. "t" meaning temporary.
Advantages over control stack and alloca():
- Functions can return a value allocated from data stack
- We can portably specify how much data we want to allocate at runtime
Advantages over malloc():
- FAST, most of the time allocating memory means only updating a couple of
pointers and integers. Freeing the memory all at once also is a fast
operation.
- No need to free() each allocation resulting in prettier code
- No memory leaks
- No memory fragmentation
Disadvantages:
- Allocating memory inside loops can accidentally allocate a lot of memory
if the loops are long and you forgot to place t_push() and t_pop() there.
- t_malloc()ed data could be accidentally stored into permanent location
and accessed after it's already been freed. const'ing the return values
helps for most uses though (see the t_malloc() description).
- Debugging invalid memory usage may be difficult using existing tools,
although compiling with DEBUG enabled helps finding simple buffer
overflows.
*/
extern unsigned int data_stack_frame;
/* All t_..() allocations between t_push() and t_pop() are freed after t_pop()
is called. Returns the current stack frame number, which can be used
to detect missing t_pop() calls:
x = t_push(); .. if (t_pop() != x) abort();
*/
unsigned int t_push(void) ATTR_HOT;
unsigned int t_pop(void) ATTR_HOT;
/* Simplifies the if (t_pop() != x) check by comparing it internally and
panicking if it doesn't match. */
void t_pop_check(unsigned int *id) ATTR_HOT;
/* Usage: T_BEGIN { code } T_END */
#define T_BEGIN \
STMT_START { unsigned int _data_stack_cur_id = t_push();
#define T_END \
t_pop_check(&_data_stack_cur_id); } STMT_END
/* WARNING: Be careful when using these functions, it's too easy to
accidentally save the returned value somewhere permanently.
You probably should never use these functions directly, rather
create functions that return 'const xxx*' types and use t_malloc()
internally in them. This is a lot safer, since usually compiler
warns if you try to place them in xxx*. See strfuncs.c for examples.
t_malloc() calls never fail. If there's not enough memory left,
i_panic() will be called. */
void *t_malloc(size_t size) ATTR_MALLOC ATTR_RETURNS_NONNULL;
void *t_malloc0(size_t size) ATTR_MALLOC ATTR_RETURNS_NONNULL;
/* Try growing allocated memory. Returns TRUE if successful. Works only
for last allocated memory in current stack frame. */
bool t_try_realloc(void *mem, size_t size);
/* Returns the number of bytes available in data stack without allocating
more memory. */
size_t t_get_bytes_available(void) ATTR_PURE;
#define t_new(type, count) \
((type *) t_malloc0(sizeof(type) * (count)))
/* Returns pointer to a temporary buffer you can use. The buffer will be
invalid as soon as next t_malloc() is called!
If you wish to grow the buffer, you must give the full wanted size
in the size parameter. If return value doesn't point to the same value
as last time, you need to memcpy() data from the old buffer to the
new one (or do some other trickery). See t_buffer_reget(). */
#define t_buffer_get_type(type, size) \
t_buffer_get(sizeof(type) * (size))
void *t_buffer_get(size_t size) ATTR_RETURNS_NONNULL;
/* Grow the buffer, memcpy()ing the memory to new location if needed. */
#define t_buffer_reget_type(buffer, type, size) \
t_buffer_reget(buffer, sizeof(type) * (size))
void *t_buffer_reget(void *buffer, size_t size) ATTR_RETURNS_NONNULL;
/* Make the last t_buffer_get()ed buffer permanent. Note that size MUST be
less or equal than the size you gave with last t_buffer_get() or the
result will be undefined. */
#define t_buffer_alloc_type(type, size) \
t_buffer_alloc(sizeof(type) * (size))
void t_buffer_alloc(size_t size);
/* Allocate the last t_buffer_get()ed data entirely. */
void t_buffer_alloc_last_full(void);
/* If enabled, all the used memory is cleared after t_pop(). */
void data_stack_set_clean_after_pop(bool enable);
void data_stack_init(void);
void data_stack_deinit(void);
#endif