嵌套的NSAutoreleasePool

Question

在我的一个ipad应用程序中，我正在使用json字符串远程构建数据库，然后将其转换为NSArray以插入到核心数据中，然后在iPad上加载大约600Mb的图像。所有这些都是在后台线程中创建的，从一开始就会导致一些内存问题。我掌握了在操作中嵌套3个不同的NSAutoreleasePool并在方便的时候释放它们的问题。我没有得到错误，也没有泄漏，也没有警告。我只是想知道这是不是一个好的方法，或者我只是错过了一些东西。

下面是一个示意性的例子(真实的代码很长)：

- (void)main{
@try {


    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; // first pool
    [managedOC lock];
    NSArray *results = [self loadEntitiesWithGroupName:@"Project" andName:@"projects"];
    NSAutoreleasePool *prjPool; // second pool
    for (NSDictionary *thisResult in results) {
        prjPool = [[NSAutoreleasePool alloc] init];

        Project *prj = [[Project alloc] initWithEntity:[NSEntityDescription entityForName:@"Project" inManagedObjectContext:self.managedOC] insertIntoManagedObjectContext:self.managedOC];
        prj.name = [thisResult objectForKey:@"name"];
        [prj saveThumbnail:[thisResult objectForKey:@"thumbnail"]];

        //Slides. Those are the images that take so mutch space.
        NSArray *slides = [thisResult objectForKey:@"slides"];
        NSAutoreleasePool *slidePool; // third pool
        if(slides != kCFNull){
            slidePool = [[NSAutoreleasePool alloc] init];
            for(NSDictionary *slide in slides){
                Slide *thisSlide = [[Slide alloc] initWithEntity:[NSEntityDescription entityForName:@"Slide" inManagedObjectContext:self.managedOC] insertIntoManagedObjectContext: self.managedOC];
                thisSlide.path = prj.path;
                [thisSlide saveFile:[slide objectForKey:@"file"]];
                [prj addSlidesObject:thisSlide];
                [thisSlide release];
                [slidePool drain];
            }
        }

        [prj release];
        [result release];
        [prjPool drain];


    }

    [self.managedOC unlock];
    [totResult release];
    [pool drain];
}
@catch (NSException * e) {

}

Answer 1

我很惊讶你的代码没有崩溃。在引用计数环境中，-drain的行为与-release相同，因此下面的命令会释放池

slidePool = [[NSAutoreleasePool alloc] init];  // this is in the wrong place
for(NSDictionary *slide in slides){
    Slide *thisSlide = [[Slide alloc] initWithEntity:[NSEntityDescription entityForName:@"Slide" inManagedObjectContext:self.managedOC] insertIntoManagedObjectContext: self.managedOC];
    thisSlide.path = prj.path;
    [thisSlide saveFile:[slide objectForKey:@"file"]];
    [prj addSlidesObject:thisSlide];
    [thisSlide release];
    [slidePool drain];
}

除非slides集合中只有一个对象。你需要这样做：

for(NSDictionary *slide in slides){

    slidePool = [[NSAutoreleasePool alloc] init];  // this is in the right place

    Slide *thisSlide = [[Slide alloc] initWithEntity:[NSEntityDescription entityForName:@"Slide" inManagedObjectContext:self.managedOC] insertIntoManagedObjectContext: self.managedOC];
    thisSlide.path = prj.path;
    [thisSlide saveFile:[slide objectForKey:@"file"]];
    [prj addSlidesObject:thisSlide];
    [thisSlide release];
    [slidePool drain];
}

除此之外，你还有一个正确的总体思路。

您应该在异常处理程序的finally块中排空最外层的池，以便在引发异常时不会跳过它，即您应该这样做：

- (void)main{

    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; // first pool

    @try {

        // Do al your stuff
    }
    @catch (NSException * e) {

    }
    @finally
    {
        [pool drain];
    }
}