blocks_runtime.h

/**
 * Block descriptor flags.
 */
enum block_flags
{
	/**
	 * The block descriptor contains copy and dispose helpers.
	 */
	BLOCK_HAS_COPY_DISPOSE = (1 << 25),
	/**
	 * The helpers have C++ code.
	 */
	BLOCK_HAS_CTOR         = (1 << 26),
	/**
	 * Block is stored in global memory and does not need to be copied.
	 */
	BLOCK_IS_GLOBAL        = (1 << 28),
	/**
	 * Block function uses a calling convention that returns a structure via a
	 * pointer passed in by the caller.
	 */
	BLOCK_USE_SRET         = (1 << 29),
	/**
	 * Block has an Objective-C type encoding.
	 */
	BLOCK_HAS_SIGNATURE    = (1 << 30),
	/**
	 * Mask for the reference count in byref structure's flags field.  The low
	 * 3 bytes are reserved for the reference count, the top byte for the
	 * flags.
	 */
	BLOCK_REFCOUNT_MASK    = 0x00ffffff
};

/**
 * Flags used in the final argument to _Block_object_assign() and
 * _Block_object_dispose().  These indicate the type of copy or dispose to
 * perform.
 */
enum
{
	/**
	 * The value is of some id-like type, and should be copied as an
	 * Objective-C object: i.e. by sending -retain or via the GC assign
	 * functions in GC mode (not yet supported).
	 */
	BLOCK_FIELD_IS_OBJECT   =  3,
	/**
	 * The field is a block.  This must be copied by the block copy functions.
	 */
	BLOCK_FIELD_IS_BLOCK	=  7,
	/**
	 * The field is an indirect reference to a variable declared with the
	 * __block storage qualifier.
	 */
	BLOCK_FIELD_IS_BYREF	=  8,  // the on stack structure holding the __block variable

	BLOCK_FIELD_IS_WEAK	 = 16,  // declared __weak

	BLOCK_BYREF_CALLER	  = 128, // called from byref copy/dispose helpers
};
#define IS_SET(x, y) ((x & y) == y)

/*
 * Include the block_descriptor_copydispose and block_literal definitions that
 * are also made public under different names for use in libdispatch.
 */
#include "objc/blocks_private.h"

/**
 * Block descriptor that does not contain copy and dispose helper functions.
 */
struct Block_descriptor_basic
{
	/**
	 * Reserved for future use, currently always 0.
	 */
	unsigned long int reserved;
	/** Size of the block. */
	unsigned long int size;
	/**
	 * Objective-C type encoding of the block.
	 */
	const char *encoding;
};


/**
 * Structure used for on-stack variables that are referenced by blocks.
 */
struct block_byref_obj
{
	/**
	 * Class pointer.  Currently unused and always NULL.  Could be used in the
	 * future to support introspection.
	 */
	void *isa;
	/**
	 * The pointer to the structure that contains the real version of the data.
	 * All accesses go via this pointer.  If an on-stack byref structure is
	 * copied to the heap, then its forwarding pointer should point to the heap
	 * version.  Otherwise it should point to itself.
	 */
	struct block_byref_obj *forwarding;
	/**
	 * Flags and reference count.
	 */
	int flags;   //refcount;
	/**
	 * Size of this structure.
	 */
	int size;
	/**
	 * Copy function.
	 */
	void (*byref_keep)(struct block_byref_obj *dst, const struct block_byref_obj *src);
	/**
	 * Dispose function.
	 */
	void (*byref_dispose)(struct block_byref_obj *);
	/**
	 * __block-qualified variables are copied here.
	 */
};