加锁 synchronize

(gdb) p *((UIButton*)0x6d98ce0)

$1 = {

  <UIControl> = {

    <UIView> = {

      <UIResponder> = {

        <NSO

  _backgroundView = 0x6dc0210, 

  _imageView = 0x0, 

  _titleView = 0x6dc00c0, 

  _initialized = 1 '\001', 

(gdb) po 0x6dc00c0

<UIButtonLabel: 0x6dc00c0; frame = (15 6; 58 22); text = '记录(2)'; clipsToBounds = YES; opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x6dc02d0>>

(gdb) 

//make a call 

NSString * teluri = [NSStringstringWithFormat:@"tel:%@", phoneNumber];

    NSURL * url = [NSURL URLWithString:teluri];

    [[UIApplicationsharedApplication] openURL:url];

@synchronized (A) {}  的本质就是根据一个标志A对一段代码进行加锁，开始处lock(sign), 结束时 unlock(sign)

而不是对A进行加锁

//thread 1

m_strTest =@"0";//this is needed, form_strTest should not be nil, if it is nil, it won't work

@synchronized(m_strTest)

{

NSLog(@"@synchronized(m_strTest)");

sleep(200);

}

//thread 2

sleep(1);

NSLog(@"========= begin");

@synchronized(m_strTest)

{

m_strTest = [NSStringstringWithFormat:@"%d", i];

NSLog(@"========= m_strTest is %@",m_strTest);

}

NSLog(@"========= end");

in this case,//thread 2 stopped at @synchronized(m_strTest)

sleep(1);

NSLog(@"========= begin");

//@synchronized(m_strTest)

{

m_strTest = [NSStringstringWithFormat:@"%d", i];

NSLog(@"========= m_strTest is %@",m_strTest);

}

NSLog(@"========= end");

in this case, the code will run

===

m_strTest =@"0";

@synchronized(m_strTest)

{

NSLog(@"@synchronized(m_strTest)");

m_strTest =@"100";

sleep(200);

}

－－

sleep(1);

NSLog(@"========= begin");

@synchronized(m_strTest)

{

m_strTest = [NSStringstringWithFormat:@"%d", i];

NSLog(@"========= m_strTest is %@",m_strTest);

}

NSLog(@"========= end");

synchronized do not work at here,代码都会执行到，因为 m_strTest改变了，2个锁变量标识不一样