不捕获任何变量，用weak引用则是栈block
捕获全局static变量
则一般情况下是全局block
捕获如果不带__block的变量
1、创建block对象：将局部变量拷贝到block对象的成员变量中
- 基本类型，则是值拷贝
- 对象类型，则是拷贝对象地址
2、栈block拷贝到堆上，新增一个堆block
捕获__block修饰的局部变量，三次拷贝
1、创建block_ref对象：将__block变量地址拷贝到block_ref对象中
__attribute__((__blocks__(byref))) __Block_byref_cjl_name_0 cjl_name = {
(void*)0,
(__Block_byref_cjl_name_0 *)&cjl_name,
33554432,
sizeof(__Block_byref_cjl_name_0),
__Block_byref_id_object_copy_131,
__Block_byref_id_object_dispose_131,
((NSString * _Nonnull (*)(id, SEL, NSString * _Nonnull, ...))(void *)objc_msgSend)((id)objc_getClass("NSString"), sel_registerName("stringWithFormat:"), (NSString *)&__NSConstantStringImpl__var_folders_tc_8chhyp952y3f__yg27cncgc00000gn_T_main_8da471_mi_1)
};
2、创建block对象：将block_ref对象拷贝到block对象中
void (*block1)(void) = ((void (*)())&__main_block_impl_0(
(void *)__main_block_func_0,
&__main_block_desc_0_DATA,
(__Block_byref_cjl_name_0 *)&cjl_name,
570425344));
底层调用_Block_object_assign -> _Block_byref_copy
static struct Block_byref *_Block_byref_copy(const void *arg) {
// Block_byref 结构体
struct Block_byref *src = (struct Block_byref *)arg;
if ((src->forwarding->flags & BLOCK_REFCOUNT_MASK) == 0) {
// src points to stack
struct Block_byref *copy = (struct Block_byref *)malloc(src->size);
copy->isa = NULL;
// byref value 4 is logical refcount of 2: one for caller, one for stack
copy->flags = src->flags | BLOCK_BYREF_NEEDS_FREE | 4;
// 问题 - block 内部 持有的 Block_byref 锁持有的对象 是不是同一个
copy->forwarding = copy; // patch heap copy to point to itself
src->forwarding = copy; // patch stack to point to heap copy
copy->size = src->size;
if (src->flags & BLOCK_BYREF_HAS_COPY_DISPOSE) {
// Trust copy helper to copy everything of interest
// If more than one field shows up in a byref block this is wrong XXX
struct Block_byref_2 *src2 = (struct Block_byref_2 *)(src+1);
struct Block_byref_2 *copy2 = (struct Block_byref_2 *)(copy+1);
copy2->byref_keep = src2->byref_keep;
copy2->byref_destroy = src2->byref_destroy;
if (src->flags & BLOCK_BYREF_LAYOUT_EXTENDED) {
struct Block_byref_3 *src3 = (struct Block_byref_3 *)(src2+1);
struct Block_byref_3 *copy3 = (struct Block_byref_3*)(copy2+1);
copy3->layout = src3->layout;
}
(*src2->byref_keep)(copy, src);
}
else {
// Bitwise copy.
// This copy includes Block_byref_3, if any.
memmove(copy+1, src+1, src->size - sizeof(*src));
}
}
// already copied to heap
else if ((src->forwarding->flags & BLOCK_BYREF_NEEDS_FREE) == BLOCK_BYREF_NEEDS_FREE) {
latching_incr_int(&src->forwarding->flags);
}
return src->forwarding;
}
3、栈block拷贝到堆上，新增一个堆block
// Copy, or bump refcount, of a block. If really copying, call the copy helper if present.
// CJL重点提示: 这里是核心重点 block的拷贝操作: 栈Block -> 堆Block
void *_Block_copy(const void *arg) {
struct Block_layout *aBlock;
if (!arg) return NULL;
// The following would be better done as a switch statement
aBlock = (struct Block_layout *)arg;//强转为Block_layout类型对象，防止对外界造成影响
if (aBlock->flags & BLOCK_NEEDS_FREE) {//是否需要释放
// latches on high
latching_incr_int(&aBlock->flags);
return aBlock;
}
else if (aBlock->flags & BLOCK_IS_GLOBAL) {//如果是全局block，直接返回
return aBlock;
}
else {//为栈block 或者 堆block，由于堆区需要申请内存，所以只可能是栈区
// Its a stack block. Make a copy. 它是一个堆栈块block，拷贝。
struct Block_layout *result =
(struct Block_layout *)malloc(aBlock->descriptor->size);//申请空间并接收
if (!result) return NULL;
//通过memmove内存拷贝，将 aBlock 拷贝至result
memmove(result, aBlock, aBlock->descriptor->size); // bitcopy first
#if __has_feature(ptrauth_calls)
// Resign the invoke pointer as it uses address authentication.
result->invoke = aBlock->invoke;//可以直接调起invoke
#endif
// reset refcount
result->flags &= ~(BLOCK_REFCOUNT_MASK|BLOCK_DEALLOCATING); // XXX not needed 告知可释放
result->flags |= BLOCK_NEEDS_FREE | 2; // logical refcount 1
_Block_call_copy_helper(result, aBlock);
// Set isa last so memory analysis tools see a fully-initialized object.
result->isa = _NSConcreteMallocBlock;//设置block对象类型为堆区block
return result;
}
}
附上_Block_object_assign的源码
void _Block_object_assign(void *destArg, const void *object, const int flags) {
const void **dest = (const void **)destArg;
switch (os_assumes(flags & BLOCK_ALL_COPY_DISPOSE_FLAGS)) {
case BLOCK_FIELD_IS_OBJECT:
/*******
id object = ...;
[^{ object; } copy];
********/
// objc 指针地址 weakSelf (self)
// arc
_Block_retain_object(object);
// 持有
*dest = object;
break;
case BLOCK_FIELD_IS_BLOCK:
/*******
void (^object)(void) = ...;
[^{ object; } copy];
********/
// block 被一个 block 捕获
*dest = _Block_copy(object);
break;
case BLOCK_FIELD_IS_BYREF | BLOCK_FIELD_IS_WEAK:
case BLOCK_FIELD_IS_BYREF:
/*******
// copy the onstack __block container to the heap
// Note this __weak is old GC-weak/MRC-unretained.
// ARC-style __weak is handled by the copy helper directly.
__block ... x;
__weak __block ... x;
[^{ x; } copy];
********/
*dest = _Block_byref_copy(object);
break;
case BLOCK_BYREF_CALLER | BLOCK_FIELD_IS_OBJECT:
case BLOCK_BYREF_CALLER | BLOCK_FIELD_IS_BLOCK:
/*******
// copy the actual field held in the __block container
// Note this is MRC unretained __block only.
// ARC retained __block is handled by the copy helper directly.
__block id object;
__block void (^object)(void);
[^{ object; } copy];
********/
*dest = object;
break;
case BLOCK_BYREF_CALLER | BLOCK_FIELD_IS_OBJECT | BLOCK_FIELD_IS_WEAK:
case BLOCK_BYREF_CALLER | BLOCK_FIELD_IS_BLOCK | BLOCK_FIELD_IS_WEAK:
/*******
// copy the actual field held in the __block container
// Note this __weak is old GC-weak/MRC-unretained.
// ARC-style __weak is handled by the copy helper directly.
__weak __block id object;
__weak __block void (^object)(void);
[^{ object; } copy];
********/
*dest = object;
break;
default:
break;
}
}
附初始函数
int main(int argc, const char * argv[]) {
@autoreleasepool {
// insert code here...
NSLog(@"Hello, World!");
__block NSString *cjl_name = [NSString stringWithFormat:@"CJL"];
void (^block1)(void) = ^{ // block_copy
cjl_name = @"CJL";
NSLog(@"CJL - %@",cjl_name);
// block 内存
};
block1();
}
return 0;
}
附上转码后的函数
struct __Block_byref_cjl_name_0 {
void *__isa;
__Block_byref_cjl_name_0 *__forwarding;
int __flags;
int __size;
void (*__Block_byref_id_object_copy)(void*, void*);
void (*__Block_byref_id_object_dispose)(void*);
NSString *cjl_name;
};
struct __main_block_impl_0 {
struct __block_impl impl;
struct __main_block_desc_0* Desc;
__Block_byref_cjl_name_0 *cjl_name; // by ref
__main_block_impl_0(void *fp, struct __main_block_desc_0 *desc, __Block_byref_cjl_name_0 *_cjl_name, int flags=0) : cjl_name(_cjl_name->__forwarding) {
impl.isa = &_NSConcreteStackBlock;
impl.Flags = flags;
impl.FuncPtr = fp;
Desc = desc;
}
};
static void __main_block_func_0(struct __main_block_impl_0 *__cself) {
__Block_byref_cjl_name_0 *cjl_name = __cself->cjl_name; // bound by ref
(cjl_name->__forwarding->cjl_name) = (NSString *)&__NSConstantStringImpl__var_folders_tc_8chhyp952y3f__yg27cncgc00000gn_T_main_8da471_mi_2;
NSLog((NSString *)&__NSConstantStringImpl__var_folders_tc_8chhyp952y3f__yg27cncgc00000gn_T_main_8da471_mi_3,(cjl_name->__forwarding->cjl_name));
}
static void __main_block_copy_0(struct __main_block_impl_0*dst, struct __main_block_impl_0*src) {_Block_object_assign((void*)&dst->cjl_name, (void*)src->cjl_name, 8/*BLOCK_FIELD_IS_BYREF*/);}
static void __main_block_dispose_0(struct __main_block_impl_0*src) {_Block_object_dispose((void*)src->cjl_name, 8/*BLOCK_FIELD_IS_BYREF*/);}
static struct __main_block_desc_0 {
size_t reserved;
size_t Block_size;
void (*copy)(struct __main_block_impl_0*, struct __main_block_impl_0*);
void (*dispose)(struct __main_block_impl_0*);
} __main_block_desc_0_DATA = { 0, sizeof(struct __main_block_impl_0), __main_block_copy_0, __main_block_dispose_0};
int main(int argc, const char * argv[]) {
/* @autoreleasepool */ { __AtAutoreleasePool __autoreleasepool;
NSLog((NSString *)&__NSConstantStringImpl__var_folders_tc_8chhyp952y3f__yg27cncgc00000gn_T_main_8da471_mi_0);
__attribute__((__blocks__(byref))) __Block_byref_cjl_name_0 cjl_name = {
(void*)0,
(__Block_byref_cjl_name_0 *)&cjl_name,
33554432,
sizeof(__Block_byref_cjl_name_0),
__Block_byref_id_object_copy_131,
__Block_byref_id_object_dispose_131,
((NSString * _Nonnull (*)(id, SEL, NSString * _Nonnull, ...))(void *)objc_msgSend)((id)objc_getClass("NSString"), sel_registerName("stringWithFormat:"), (NSString *)&__NSConstantStringImpl__var_folders_tc_8chhyp952y3f__yg27cncgc00000gn_T_main_8da471_mi_1)
};
void (*block1)(void) = ((void (*)())&__main_block_impl_0((void *)__main_block_func_0, &__main_block_desc_0_DATA, (__Block_byref_cjl_name_0 *)&cjl_name, 570425344));
((void (*)(__block_impl *))((__block_impl *)block1)->FuncPtr)((__block_impl *)block1);
}
return 0;
}
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