Retrospective function pointer

C function syntax: return value type function name (argument list){function body; } * /
        void test(){
            NSLog(@ "...");
        }
 /* Function pointer syntax: return value type (* function name)(argument list) */
    	void (*p)();  // This is a pointer variable named p that points to a function with no parameters and no return value
    	int (*p2)();   // this is a pointer variable named p2 that points to a function that has no argument and returns a value of type int
    	int (*p3)(int num); // this is a pointer variable named p3, which points to a function that takes an int argument and returns an int value
 /* How to assign a pointer to a function? P = function name; Because the function name is the function address */
        p = test;
 
 //void* is a universal pointer to OC
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The use of pthread

  • Pthread opens child threads
    • Before using pthreads, you must import the header file#import <pthread.h>
- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{
    //NSLog(@" click in, create before %@",[NSThread currentThread])
    //[self demo];
    
    //C types that end in _t or _ref are C types
    pthread_t p;
  
    NSString *str = @"abc";
    
    If &p is passed, the thread is pointed to by p. In other words, the child thread can be found by p
    // Parameter 2: thread attribute (can set the size of memory used by the thread, usually NULL)
    // Parameter 3: function name (the function that needs this thread to execute)
    // Argument 4: function argument, NULL if no argument
    // Arguments 3 and 4 mean: which function code is executed by the child thread and what arguments are passed to this function
    int res = pthread_create(&p, NULL,test, (__bridge void *)(str));
    // Bridge: a bridge that connects two types
    // Why? Because OC objects are currently collected by the system management under ARC
    // However, C objects are not managed by the system, so we need to bridge OC to C objects
    // This means that the system will manage the object after it is converted to C
    
    // The return value is int, indicating whether the thread was created successfully
    // Return 0 for success, return other for failure
    // The return value is actually an error identifier. Only 0 indicates that there is no error. Other numbers indicate different errors
    For example, 1 indicates an XXX error, and 2 indicates an YYy error
    if(res == 0) {NSLog(@" Created successfully");
    }else{
        NSLog(@" create failed");
    }
    //NSLog(@" create %@",[NSThread currentThread]);
}

void *test(void *num){
    NSString *str = (__bridge NSString *)(num);
    
    //NSLog(@"%p",num);
// NSLog(@"test %@",[NSThread currentThread]);
    
    NSLog(@ "% @",str);
    
    return NULL; } - (void)demo{
    [NSThread currentThread] prints information about the currentThread object
    // See which thread is executing the current code
    Number ==1; =1 is the child thread */
    NSLog(% @ "@" demo method[NSThread currentThread]);
}
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The use of the NSThread

There are three creation methods

  1. Method of construction

    //NSThread is a thread object
Arguments 1 and 2: Which method of which object is to be called by the opened child thread
// Argument 3: Arguments to this method are passed nil if they exist
NSThread *th1 = [[NSThread alloc] initWithTarget:self selector:@selector(demo:) object:@"hello"];

// To create it this way, be sure to start
[th1 start];
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    PS: Need to start!!

    This thread object can also be accessed outside of methods executed by the thread

  2. Class method mode

    // Parameter 1: which method
// Parameter 2: which object
// Parameter 3: method parameter
// This method creates a new thread to execute a method on an object
[NSThread detachNewThreadSelector:@selector(demo:) toTarget:self withObject:@"hello"];
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    Don’t need to start

    The thread object is not accessible outside the invoked method

  3. Classification (classification of NSObject)

    // Parameter 1: which method to call
// Parameter 2: method parameter
[self performSelectorInBackground:@selector(demo:) withObject:@"abc"];
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    You don’t need to start

    The thread object is not accessible outside the called method

Commonly used attributes

  • Name (thread name)
  • StackSize (stackSize)
    • By default, the stack size is 512K for both main and child threads (values smaller than 512 do not work).
    • The stack size can be set[NSThread currentThread].stackSize = 1024 * 1024;
    • It must be a multiple of 4KB
  • isMainTread
  • ThreadPriority (threadPriority)
    • Priority. It is a floating point number ranging from 0 to 1.0
    • 1.0 is the highest,0.0 is the lowest
    • The default priority is 0.5
    • A high priority only ensures that the CPU scheduling possibility is high, not that the process with a high priority is called first
  • QualityOfService (available with iOS8.0)
    • NSQualityOfServiceUserInteractive – user interaction, such as drawing or handling user events
    • NSQualityOfServiceUserInitiated – user needs
    • NSQualityOfServiceUtility – utilities, users do not need to get results immediately
    • NSQualityOfServiceBackground – the background
    • NSQualityOfServiceDefault – by default, between user needs and utility