objectivec/GPBMessage_PackagePrivate.h

// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc.  All rights reserved.
// https://developers.google.com/protocol-buffers/
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//
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//
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// This header is private to the ProtobolBuffers library and must NOT be
// included by any sources outside this library. The contents of this file are
// subject to change at any time without notice.

#import "GPBMessage.h"

#import <libkern/OSAtomic.h>

#import "GPBBootstrap.h"

typedef struct GPBMessage_Storage {
  uint32_t _has_storage_[0];
} GPBMessage_Storage;

typedef struct GPBMessage_Storage *GPBMessage_StoragePtr;

@interface GPBMessage () {
 @package
  // NOTE: Because of the +allocWithZone code using NSAllocateObject(),
  // this structure should ideally always be kept pointer aligned where the
  // real storage starts is also pointer aligned. The compiler/runtime already
  // do this, but it may not be documented.

  // A pointer to the actual fields of the subclasses. The actual structure
  // pointed to by this pointer will depend on the subclass.
  // All of the actual structures will start the same as
  // GPBMessage_Storage with _has_storage__ as the first field.
  // Kept public because static functions need to access it.
  GPBMessage_StoragePtr messageStorage_;

  // A lock to provide mutual exclusion from internal data that can be modified
  // by *read* operations such as getters (autocreation of message fields and
  // message extensions, not setting of values). Used to guarantee thread safety
  // for concurrent reads on the message.
  // NOTE: OSSpinLock may seem like a good fit here but Apple engineers have
  // pointed out that they are vulnerable to live locking on iOS in cases of
  // priority inversion:
  //   http://mjtsai.com/blog/2015/12/16/osspinlock-is-unsafe/
  //   https://lists.swift.org/pipermail/swift-dev/Week-of-Mon-20151214/000372.html
  // Use of readOnlySemaphore_ must be prefaced by a call to
  // GPBPrepareReadOnlySemaphore to ensure it has been created. This allows
  // readOnlySemaphore_ to be only created when actually needed.
  dispatch_once_t readOnlySemaphoreCreationOnce_;
  dispatch_semaphore_t readOnlySemaphore_;
}

// Gets an extension value without autocreating the result if not found. (i.e.
// returns nil if the extension is not set)
- (id)getExistingExtension:(GPBExtensionDescriptor *)extension;

// Parses a message of this type from the input and merges it with this
// message.
//
// Warning:  This does not verify that all required fields are present in
// the input message.
// Note:  The caller should call
// -[CodedInputStream checkLastTagWas:] after calling this to
// verify that the last tag seen was the appropriate end-group tag,
// or zero for EOF.
// NOTE: This will throw if there is an error while parsing.
- (void)mergeFromCodedInputStream:(GPBCodedInputStream *)input
                extensionRegistry:(GPBExtensionRegistry *)extensionRegistry;

// Parses the next delimited message of this type from the input and merges it
// with this message.
- (void)mergeDelimitedFromCodedInputStream:(GPBCodedInputStream *)input
                         extensionRegistry:
                             (GPBExtensionRegistry *)extensionRegistry;

- (void)addUnknownMapEntry:(int32_t)fieldNum value:(NSData *)data;

@end

CF_EXTERN_C_BEGIN


// Call this before using the readOnlySemaphore_. This ensures it is created only once.
NS_INLINE void GPBPrepareReadOnlySemaphore(GPBMessage *self) {
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wdirect-ivar-access"
  dispatch_once(&self->readOnlySemaphoreCreationOnce_, ^{
    self->readOnlySemaphore_ = dispatch_semaphore_create(1);
  });
#pragma clang diagnostic pop
}

// Returns a new instance that was automatically created by |autocreator| for
// its field |field|.
GPBMessage *GPBCreateMessageWithAutocreator(Class msgClass,
                                            GPBMessage *autocreator,
                                            GPBFieldDescriptor *field)
    __attribute__((ns_returns_retained));

// Returns whether |message| autocreated this message. This is NO if the message
// was not autocreated by |message| or if it has been mutated since
// autocreation.
BOOL GPBWasMessageAutocreatedBy(GPBMessage *message, GPBMessage *parent);

// Call this when you mutate a message. It will cause the message to become
// visible to its autocreator.
void GPBBecomeVisibleToAutocreator(GPBMessage *self);

// Call this when an array/dictionary is mutated so the parent message that
// autocreated it can react.
void GPBAutocreatedArrayModified(GPBMessage *self, id array);
void GPBAutocreatedDictionaryModified(GPBMessage *self, id dictionary);

// Clear the autocreator, if any. Asserts if the autocreator still has an
// autocreated reference to this message.
void GPBClearMessageAutocreator(GPBMessage *self);

CF_EXTERN_C_END