在init中调用dealloc？

发布于 2024-09-30 06:36:42 字数 675 浏览 5 评论 0原文

我正在编写一个框架，并且有一个带有自定义 init 方法的对象：

@implementation OSDatabase
@synthesize database;

// MEM
- (void)dealloc {
  sqlite3_close(database);

  [super dealloc];
}

// INIT
- (id)initWithDatabasePath:(NSString *)path error:(NSError **)error {
  if (self = [super init]) {
    if (!sqlite3_open_v2([path UTF8String], &database, SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE, NULL)) {
      error = [NSError errorWithDomain:@"OSDatabaseErrorDomain" code:1 userInfo:nil];
      [self dealloc];
      return nil;
    }
  }

  return self;
}

@end

如果发生错误，在 init 方法内部调用 dealloc 是否安全？我对此不确定，内存管理是我一生中最重要的事情之一。

谢谢。

原文

I am writing a framework and I have an object with a custom init method:

@implementation OSDatabase
@synthesize database;

// MEM
- (void)dealloc {
  sqlite3_close(database);

  [super dealloc];
}

// INIT
- (id)initWithDatabasePath:(NSString *)path error:(NSError **)error {
  if (self = [super init]) {
    if (!sqlite3_open_v2([path UTF8String], &database, SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE, NULL)) {
      error = [NSError errorWithDomain:@"OSDatabaseErrorDomain" code:1 userInfo:nil];
      [self dealloc];
      return nil;
    }
  }

  return self;
}

@end

Is it safe to call dealloc inside of an init method if an error occoured? I'm not sure about this and memory management is one of the most important things in my life.

Thanks.

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情何以堪。 2024-10-07 06:36:42

如果发生错误，在 init 方法内部调用 dealloc 是否安全？

不，像在其他地方一样发送 -release 。即使在 -init 中，您也不能保证当前保留计数为 1。

为什么除了 [super dealloc]-dealloc > 在 -dealloc 中？原因是，即使在对象的 -init 中，您也无法保证其他对象也引用您的对象，因为 [super init] 可能会选择保留目的。

如果[super init]返回的对象的保留计数为1，发送-release将与发送-dealloc具有相同的效果。如果它的保留计数超过 1，则其他东西会认为它拥有该对象，并且释放它会留下无效的指针，因此 -release 仍然是正确的做法。

另外，这

while([self retainCount] != 0){[self release];}

会导致无限循环，并且出于多种原因是一个糟糕的主意。对象的保留计数永远不会降至 0。-release 看起来像这样：

- (id)release
{
    if (retainCount == 1)
    {
        [self dealloc];
    }
    else
    {
        retainCount--;
    }
}

因此循环会将保留计数减少到 1，然后永远不断地调用 dealloc，或者直到它导致堆损坏为止段错误。

除了永远不会达到零之外，保留可能是UINT_MAX（例如在字符串或数字文字中），通俗地说就是“这个对象永远不能被释放”。如果保留计数为 UINT_MAX，-release 不会减少它。

Is it safe to call dealloc inside of an init method if an error occoured?

No. send -release like you would everywhere else. Even in -init you can't guarantee that the current retain count is 1.

Why must you never ever send -dealloc except [super dealloc] in -dealloc? The reason is that you cannot ever guarantee that something else also has a reference to your object, even in your object's -init because the [super init] might choose to retain the object.

If the object returned by [super init] has a retain count of 1, sending -release will have the same effect as sending -dealloc. If it has a retain count of more than 1, something else thinks it owns the object and deallocing it would leave it with an invalid pointer, so -release is still the right thing to do.

Also, this:

while([self retainCount] != 0){[self release];}

would result in an infinite loop and is a terrible idea for a number of reasons. The retain counts of objects never go down to 0. -release looks something like this:

- (id)release
{
    if (retainCount == 1)
    {
        [self dealloc];
    }
    else
    {
        retainCount--;
    }
}

so the loop will decrement the retain count to 1 and then continually call dealloc forever or until the heap corruption it has caused leads to a seg fault.

Apart from never reaching zero, the retain may be UINT_MAX (for example in string or numeric literals) which colloquially means "this object must never be deallocated". If the retain count is UINT_MAX, -release won't decrement it.

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