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49 lines
1.8 KiB
C
49 lines
1.8 KiB
C
#if defined(__clang__) && !defined(__OBJC_RUNTIME_INTERNAL__)
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#pragma clang system_header
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#endif
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#ifndef __OBJC_SLOT_H_INCLUDED__
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#define __OBJC_SLOT_H_INCLUDED__
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/**
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* The objc_slot structure is used to permit safe IMP caching. It is returned
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* by the new lookup APIs. When you cache an IMP, you should store a copy of
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* the version field and a pointer to the slot.
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*
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* The slot version is guaranteed never to be 0. When updating a cache, you
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* should use code of the following form:
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*
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* 1) version = 0;
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* 2) slot->cachedFor = receiver->isa;
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* 3) slot_cache = slot;
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* 4) version = slot->version;
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*
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* The runtime guarantees that the version in any cachable slot will never be
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* 0. This should ensure that, if the version and cache pointer mismatch, the
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* next access will cause a cache miss.
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*
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* When using a cached slot, you should compare the owner pointer to the isa
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* pointer of the receiver and the message and the version of the slot to your
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* cached version.
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*/
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struct objc_slot
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{
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/** The class to which this slot is attached (used internally). */
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Class owner;
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/** The class for which this slot was cached. Note that this can be
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* modified by different cache owners, in different threads. Doing so may
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* cause some cache misses, but if different methods are sending messages
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* to the same object and sharing a cached slot then it may also improve
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* cache hits. Profiling is probably required here. */
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Class cachedFor;
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/** The (typed) selector for the method identified by this slot. */
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const char *types;
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/** The current version. This changes if the method changes or if a
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* subclass overrides this method, potentially invalidating this cache. */
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int version;
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/** The method pointer for this method. */
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IMP method;
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/** Selector for this method. */
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SEL selector;
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} OBJC_NONPORTABLE;
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#endif // __OBJC_SLOT_H_INCLUDED__
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