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include/ruby/internal/memory.h: add doxygen

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Must not be a bad idea to improve documents. [ci skip]
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卜部昌平 2021-01-19 12:55:16 +09:00
parent 00ff6b68e4
commit 4397e737c5
Notes: git 2021-09-10 20:01:50 +09:00
1 changed files with 408 additions and 19 deletions
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427
include/ruby/internal/memory.h
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@ -62,6 +62,8 @@
#include "ruby/backward/2/assume.h"
#include "ruby/defines.h"
/** @cond INTENAL_MACRO */
/* Make alloca work the best possible way. */
#if defined(alloca)
# /* Take that. */
@ -75,18 +77,86 @@ extern "C" void *alloca(size_t);
extern void *alloca();
#endif
#if defined(HAVE_INT128_T) && SIZEOF_SIZE_T <= 8
/** @endcond */
#if defined(__DOXYGEN__)
/**
* @private
*
* Type that is as twice wider as size_t. This is an implementation detail of
* rb_mul_size_overflow(). People should not use it. This is not a good name
* either.
*/
typedef uint128_t DSIZE_T;
#elif defined(HAVE_INT128_T) && SIZEOF_SIZE_T <= 8
# define DSIZE_T uint128_t
#elif SIZEOF_SIZE_T * 2 <= SIZEOF_LONG_LONG
# define DSIZE_T unsigned LONG_LONG
#endif
/**
* @private
*
* Maximum possible number of bytes that #RB_ALLOCV can allocate using
* `alloca`. Anything beyond this is allocated using rb_alloc_tmp_buffer().
* This selection is transparent to users. People don't have to bother.
*/
#ifdef C_ALLOCA
# define RUBY_ALLOCV_LIMIT 0
#else
# define RUBY_ALLOCV_LIMIT 1024
#endif
/**
* Prevents premature destruction of local objects. Ruby's garbage collector
* is conservative; it scans the C level machine stack as well. Possible in-
* use Ruby objects must remain visible on stack, to be properly marked as
* such. However contemporary C compilers do not interface well with this.
* Consider the following example:
*
* ```CXX
* auto s = rb_str_new_cstr(" world");
* auto sptr = RSTRING_PTR(s);
* auto t = rb_str_new_cstr("hello,"); // Possible GC invocation
* auto u = rb_str_cat_cstr(t, sptr);
*
* RB_GC_GUARD(s); // ensure `s` (and thus `sptr`) do not get GC-ed
* ```
*
* Here, without the #RB_GC_GUARD, the last use of `s` is _before_ the last use
* of `sptr`. Compilers could thus think `s` and `t` are allowed to overlap.
* That would eliminate `s` from the stack, while `sptr` is still in use. If
* our GC ran at that very moment, `s` gets swept out, which also destroys
* `sptr`. Boom! You got a SEGV.
*
* In order to prevent this scenario #RB_GC_GUARD must be placed _after_ the
* last use of `sptr`. Placing #RB_GC_GUARD before dereferencing `sptr` would
* be of no use.
*
* #RB_GC_GUARD would not be necessary at all in the above example if non-
* inlined function calls are made on the `s` variable after `sptr` is
* dereferenced. Thus, in the above example, calling any un-inlined function
* on `s` such as `rb_str_modify(s);` will ensure `s` stays on the stack or
* register to prevent a GC invocation from prematurely freeing it.
*
* Using the #RB_GC_GUARD macro is preferable to using the `volatile` keyword
* in C. #RB_GC_GUARD has the following advantages:
*
* - the intent of the macro use is clear.
*
* - #RB_GC_GUARD only affects its call site. OTOH `volatile` generates some
* extra code every time the variable is used, hurting optimisation.
*
* - `volatile` implementations may be buggy/inconsistent in some compilers
* and architectures. #RB_GC_GUARD is customisable for broken
* systems/compilers without negatively affecting other systems.
*
* - C++ since C++20 deprecates `volatile`. If you write your extension
* library in that language there is no escape but to use this macro.
*
* @param v A variable of ::VALUE type.
* @post `v` is still alive.
*/
#ifdef __GNUC__
#define RB_GC_GUARD(v) \
(*__extension__ ({ \
@ -101,65 +171,316 @@ extern void *alloca();
#define RB_GC_GUARD(v) (*rb_gc_guarded_ptr_val(&(v),(v)))
#endif
/* Casts needed because void* is NOT compaible with others in C++. */
/* Casts needed because void* is NOT compatible with others in C++. */
/**
* Convenient macro that allocates an array of n elements.
*
* @param type Type of array elements.
* @param n Length of the array.
* @exception rb_eNoMemError No space left for allocation.
* @exception rb_eArgError Integer overflow trying to calculate the length
* of continuous memory region of `n` elements of
* `type`.
* @return Storage instance that is capable of storing at least `n`
* elements of type `type`.
* @note It doesn't return NULL, even when `n` is zero.
* @warning The return value shall be invalidated exactly once by either
* ruby_xfree(), ruby_xrealloc(), or ruby_xrealloc2(). It is a
* failure to pass it to system free(), because the system and Ruby
* might or might not share the same malloc() implementation.
*/
#define RB_ALLOC_N(type,n) RBIMPL_CAST((type *)ruby_xmalloc2((n), sizeof(type)))
/**
* Shorthand of #RB_ALLOC_N with `n=1`.
*
* @param type Type of allocation.
* @exception rb_eNoMemError No space left for allocation.
* @return Storage instance that can hold an `type` object.
* @note It doesn't return NULL.
* @warning The return value shall be invalidated exactly once by either
* ruby_xfree(), ruby_xrealloc(), or ruby_xrealloc2(). It is a
* failure to pass it to system free(), because the system and Ruby
* might or might not share the same malloc() implementation.
*/
#define RB_ALLOC(type) RBIMPL_CAST((type *)ruby_xmalloc(sizeof(type)))
/**
* Identical to #RB_ALLOC_N() but also nullifies the allocated region before
* returning.
*
* @param type Type of array elements.
* @param n Length of the array.
* @exception rb_eNoMemError No space left for allocation.
* @exception rb_eArgError Integer overflow trying to calculate the length
* of continuous memory region of `n` elements of
* `type`.
* @return Storage instance that is capable of storing at least `n`
* elements of type `type`.
* @post Returned array is filled with zeros.
* @note It doesn't return NULL, even when `n` is zero.
* @warning The return value shall be invalidated exactly once by either
* ruby_xfree(), ruby_xrealloc(), or ruby_xrealloc2(). It is a
* failure to pass it to system free(), because the system and Ruby
* might or might not share the same malloc() implementation.
*/
#define RB_ZALLOC_N(type,n) RBIMPL_CAST((type *)ruby_xcalloc((n), sizeof(type)))
/**
* Shorthand of #RB_ZALLOC_N with `n=1`.
*
* @param type Type of allocation.
* @exception rb_eNoMemError No space left for allocation.
* @return Storage instance that can hold an `type` object.
* @post Returned object is filled with zeros.
* @note It doesn't return NULL.
* @warning The return value shall be invalidated exactly once by either
* ruby_xfree(), ruby_xrealloc(), or ruby_xrealloc2(). It is a
* failure to pass it to system free(), because the system and Ruby
* might or might not share the same malloc() implementation.
*/
#define RB_ZALLOC(type) (RB_ZALLOC_N(type, 1))
/**
* Convenient macro that reallocates an array with a new size.
*
* @param var A variable of `type`, which points to a storage
* instance that was previously returned from
* either
* - ruby_xmalloc(),
* - ruby_xmalloc2(),
* - ruby_xcalloc(),
* - ruby_xrealloc(), or
* - ruby_xrealloc2().
* @param type Type of allocation.
* @param n Requested new size of each element.
* @exception rb_eNoMemError No space left for allocation.
* @exception rb_eArgError Integer overflow trying to calculate the length
* of continuous memory region of `n` elements of
* `type`.
* @return Storage instance that is capable of storing at least `n`
* elements of type `type`.
* @pre The passed variable must point to a valid live storage instance.
* It is a failure to pass a variable that holds an already-freed
* pointer.
* @note It doesn't return NULL, even when `n` is zero.
* @warning Do not assume anything on the alignment of the return value.
* There is no guarantee that it inherits the passed argument's
* one.
* @warning The return value shall be invalidated exactly once by either
* ruby_xfree(), ruby_xrealloc(), or ruby_xrealloc2(). It is a
* failure to pass it to system free(), because the system and Ruby
* might or might not share the same malloc() implementation.
*/
#define RB_REALLOC_N(var,type,n) \
((var) = RBIMPL_CAST((type *)ruby_xrealloc2((void *)(var), (n), sizeof(type))))
/**
* @deprecated This macro is dangerous (does not bother stack overflow at
* all). #RB_ALLOCV is the modern way to do the same thing.
* @param type Type of array elements.
* @param n Length of the array.
* @return A pointer on stack.
*/
#define ALLOCA_N(type,n) \
RBIMPL_CAST((type *)alloca(rbimpl_size_mul_or_raise(sizeof(type), (n))))
/* allocates _n_ bytes temporary buffer and stores VALUE including it
* in _v_. _n_ may be evaluated twice. */
/**
* Identical to #RB_ALLOCV_N(), except it implicitly assumes the type of array
* is ::VALUE.
*
* @param v A variable to hold the just-in-case opaque Ruby object.
* @param n Size of allocation, in bytes.
* @return An array of `n` bytes of ::VALUE.
* @note `n` may be evaluated twice.
*/
#define RB_ALLOCV(v, n) \
((n) < RUBY_ALLOCV_LIMIT ? \
((v) = 0, alloca(n)) : \
rb_alloc_tmp_buffer(&(v), (n)))
/**
* Allocates a memory region, possibly on stack. If the given size exceeds
* #RUBY_ALLOCV_LIMIT, it allocates a dedicated opaque ruby object instead and
* let our GC sweep that region after use. Either way you can fire-and-forget.
*
* ```CXX
* #include <sys/types.h>
*
* VALUE
* foo(int n)
* {
* VALUE v;
* auto ptr = RB_ALLOCV(struct tms, v, n);
* ...
* // no need to free `ptr`.
* }
* ```
*
* If you want to be super-duper polite you can also explicitly state the end
* of use of such memory region by calling #RB_ALLOCV_END().
*
* @param type The type of array elements.
* @param v A variable to hold the just-in-case opaque Ruby object.
* @param n Number of elements requested to allocate.
* @return An array of `n` elements of `type`.
* @note `n` may be evaluated twice.
*/
#define RB_ALLOCV_N(type, v, n) \
RBIMPL_CAST((type *) \
(((size_t)(n) < RUBY_ALLOCV_LIMIT / sizeof(type)) ? \
((v) = 0, alloca((n) * sizeof(type))) : \
rb_alloc_tmp_buffer2(&(v), (n), sizeof(type))))
/**
* Polite way to declare that the given array is not used any longer. Calling
* this not mandatory. Our GC can baby-sit you. However it is not a very bad
* idea to use it when possible. Doing so could reduce memory footprint.
*
* @param v A variable previously passed to either #RB_ALLOCV/#RB_ALLOCV_N.
*/
#define RB_ALLOCV_END(v) rb_free_tmp_buffer(&(v))
/**
* Handy macro to erase a region of memory.
*
* @param p Target pointer.
* @param type Type of `p[0]`
* @param n Length of `p`.
* @return `p`.
* @post First `n` elements of `p` are squashed.
*/
#define MEMZERO(p,type,n) memset((p), 0, rbimpl_size_mul_or_raise(sizeof(type), (n)))
/**
* Handy macro to call memcpy.
*
* @param p1 Destination pointer.
* @param p2 Source pointer.
* @param type Type of `p2[0]`
* @param n Length of `p2`.
* @return `p1`.
* @post First `n` elements of `p2` are copied into `p1`.
*/
#define MEMCPY(p1,p2,type,n) memcpy((p1), (p2), rbimpl_size_mul_or_raise(sizeof(type), (n)))
/**
* Handy macro to call memmove.
*
* @param p1 Destination pointer.
* @param p2 Source pointer.
* @param type Type of `p2[0]`
* @param n Length of `p2`.
* @return `p1`.
* @post First `n` elements of `p2` are copied into `p1`.
*/
#define MEMMOVE(p1,p2,type,n) memmove((p1), (p2), rbimpl_size_mul_or_raise(sizeof(type), (n)))
/**
* Handy macro to call memcmp
*
* @param p1 Target LHS.
* @param p2 Target RHS.
* @param type Type of `p1[0]`
* @param n Length of `p1`.
* @retval <0 `p1` is "less" than `p2`.
* @retval 0 `p1` is equal to `p2`.
* @retval >0 `p1` is "greater" than `p2`.
*/
#define MEMCMP(p1,p2,type,n) memcmp((p1), (p2), rbimpl_size_mul_or_raise(sizeof(type), (n)))
#define ALLOC_N RB_ALLOC_N
#define ALLOC RB_ALLOC
#define ZALLOC_N RB_ZALLOC_N
#define ZALLOC RB_ZALLOC
#define REALLOC_N RB_REALLOC_N
#define ALLOCV RB_ALLOCV
#define ALLOCV_N RB_ALLOCV_N
#define ALLOCV_END RB_ALLOCV_END
#define ALLOC_N RB_ALLOC_N /**< @old{RB_ALLOC_N} */
#define ALLOC RB_ALLOC /**< @old{RB_ALLOC} */
#define ZALLOC_N RB_ZALLOC_N /**< @old{RB_ZALLOC_N} */
#define ZALLOC RB_ZALLOC /**< @old{RB_ZALLOC} */
#define REALLOC_N RB_REALLOC_N /**< @old{RB_REALLOC_N} */
#define ALLOCV RB_ALLOCV /**< @old{RB_ALLOCV} */
#define ALLOCV_N RB_ALLOCV_N /**< @old{RB_ALLOCV_N} */
#define ALLOCV_END RB_ALLOCV_END /**< @old{RB_ALLOCV_END} */
/* Expecting this struct to be eliminated by function inlinings */
/**
* @private
*
* This is an implementation detail of rbimpl_size_mul_overflow().
*
* @internal
*
* Expecting this struct to be eliminated by function inlinings. This is
* nothing more than std::variant<std::size_t> if we could use recent C++, but
* reality is we cannot.
*/
struct rbimpl_size_mul_overflow_tag {
bool left;
size_t right;
bool left; /**< Whether overflow happened or not. */
size_t right; /**< Multiplication result. */
};
RBIMPL_SYMBOL_EXPORT_BEGIN()
RBIMPL_ATTR_RESTRICT()
RBIMPL_ATTR_RETURNS_NONNULL()
RBIMPL_ATTR_ALLOC_SIZE((2))
RBIMPL_ATTR_NONNULL(())
/**
* @private
*
* This is an implementation detail of #RB_ALLOCV(). People don't use this
* directly.
*
* @param[out] store Pointer to a variable.
* @param[in] len Requested number of bytes to allocate.
* @return Allocated `len` bytes array.
* @post `store` holds the corresponding tmp buffer object.
*/
void *rb_alloc_tmp_buffer(volatile VALUE *store, long len);
RBIMPL_ATTR_RESTRICT()
RBIMPL_ATTR_RETURNS_NONNULL()
RBIMPL_ATTR_ALLOC_SIZE((2,3))
RBIMPL_ATTR_NONNULL(())
/**
* @private
*
* This is an implementation detail of #RB_ALLOCV_N(). People don't use this
* directly.
*
* @param[out] store Pointer to a variable.
* @param[in] len Requested number of bytes to allocate.
* @param[in] count Number of elements in an array.
* @return Allocated `len` bytes array.
* @post `store` holds the corresponding tmp buffer object.
*
* @internal
*
* Although the meaning of `count` variable is clear, @shyouhei doesn't
* understand its needs.
*/
void *rb_alloc_tmp_buffer_with_count(volatile VALUE *store, size_t len,size_t count);
/**
* @private
*
* This is an implementation detail of #RB_ALLOCV_END(). People don't use this
* directly.
*
* @param[out] store Pointer to a variable.
* @pre `store` is a NULL, or a pointer to a tmp buffer object.
* @post `*store` is ::RUBY_Qfalse.
* @post The object formerly stored in `store` is destroyed.
*/
void rb_free_tmp_buffer(volatile VALUE *store);
RBIMPL_ATTR_NORETURN()
void ruby_malloc_size_overflow(size_t, size_t);
/**
* @private
*
* This is an implementation detail of #RB_ALLOCV_N(). People don't use this
* directly.
*
* @param[in] x Arbitrary value.
* @param[in] y Arbitrary value.
* @exception rb_eArgError `x` * `y` would integer overflow.
*/
void ruby_malloc_size_overflow(size_t x, size_t y);
#ifdef HAVE_RB_GC_GUARDED_PTR_VAL
volatile VALUE *rb_gc_guarded_ptr_val(volatile VALUE *ptr, VALUE val);
@ -169,6 +490,15 @@ RBIMPL_SYMBOL_EXPORT_END()
#ifdef _MSC_VER
# pragma optimize("", off)
/**
* @private
*
* This is an implementation detail of #RB_GC_GUARD(). People don't use this
* directly.
*
* @param[in] ptr A pointer to an on-stack C variable.
* @return `ptr` as-is.
*/
static inline volatile VALUE *
rb_gc_guarded_ptr(volatile VALUE *ptr)
{
@ -178,7 +508,19 @@ rb_gc_guarded_ptr(volatile VALUE *ptr)
# pragma optimize("", on)
#endif
/* Does anyone use it? Just here for backwards compatibility. */
/**
* @deprecated This function was an implementation detail of old
* #RB_ALLOCV_N(). We no longer use it. @shyouhei suspects that
* there are no actual usage now. However it was not marked as
* private before. We cannot delete it any longer.
* @param[in] a Arbitrary value.
* @param[in] b Arbitrary value.
* @param[in] max Possible maximum value.
* @param[out] c A pointer to return the computation result.
* @retval 1 `c` is insane.
* @retval 0 `c` is sane.
* @post `c` holds `a` * `b`, but could be overflowed.
*/
static inline int
rb_mul_size_overflow(size_t a, size_t b, size_t max, size_t *c)
{
@ -196,12 +538,30 @@ rb_mul_size_overflow(size_t a, size_t b, size_t max, size_t *c)
return 0;
}
#if RBIMPL_COMPILER_SINCE(GCC, 7, 0, 0)
#if defined(__DOXYGEN__)
RBIMPL_ATTR_CONSTEXPR(CXX14)
#elif RBIMPL_COMPILER_SINCE(GCC, 7, 0, 0)
RBIMPL_ATTR_CONSTEXPR(CXX14) /* https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70507 */
#elif RBIMPL_COMPILER_SINCE(Clang, 7, 0, 0)
RBIMPL_ATTR_CONSTEXPR(CXX14) /* https://bugs.llvm.org/show_bug.cgi?id=37633 */
#endif
RBIMPL_ATTR_CONST()
/**
* @private
*
* This is an implementation detail of #RB_ALLOCV_N(). People don't use this
* directly.
*
* @param[in] x Arbitrary value.
* @param[in] y Arbitrary value.
* @return `{ left, right }`, where `left` is whether there is an integer
* overflow or not, and `right` is a (possibly overflowed) result
* of `x` * `y`.
*
* @internal
*
* This is in fact also an implementation detail of ruby_xmalloc2() etc.
*/
static inline struct rbimpl_size_mul_overflow_tag
rbimpl_size_mul_overflow(size_t x, size_t y)
{
@ -232,6 +592,21 @@ rbimpl_size_mul_overflow(size_t x, size_t y)
return ret;
}
/**
* @private
*
* This is an implementation detail of #RB_ALLOCV_N(). People don't use this
* directly.
*
* @param[in] x Arbitrary value.
* @param[in] y Arbitrary value.
* @exception rb_eArgError Multiplication could integer overflow.
* @return `x` * `y`.
*
* @internal
*
* This is in fact also an implementation detail of ruby_xmalloc2() etc.
*/
static inline size_t
rbimpl_size_mul_or_raise(size_t x, size_t y)
{
@ -247,6 +622,20 @@ rbimpl_size_mul_or_raise(size_t x, size_t y)
}
}
/**
* This is an implementation detail of #RB_ALLOCV_N(). People don't use this
* directly.
*
* @param[out] store Pointer to a variable.
* @param[in] count Number of elements in an array.
* @param[in] elsize Size of each elements.
* @return Region of `count` * `elsize` bytes.
* @post `store` holds the corresponding tmp buffer object.
*
* @internal
*
* We might want to deprecate this function and make a `rbimpl_` counterpart.
*/
static inline void *
rb_alloc_tmp_buffer2(volatile VALUE *store, long count, size_t elsize)
{
@ -255,7 +644,7 @@ rb_alloc_tmp_buffer2(volatile VALUE *store, long count, size_t elsize)
return rb_alloc_tmp_buffer_with_count(store, total_size, cnt);
}
#ifndef __MINGW32__
#if ! defined(__MINGW32__) && ! defined(__DOXYGEN__)
RBIMPL_SYMBOL_EXPORT_BEGIN()
RBIMPL_ATTR_NOALIAS()
RBIMPL_ATTR_NONNULL((1))