OC判断给定的指针是否是一个有效的NSObject对象

#import <malloc/malloc.h>
#import <objc/runtime.h>
 
static sigjmp_buf sigjmp_env;
 
void PointerReadFailedHandler(int signum)
{
    siglongjmp (sigjmp_env, 1);
}
 
BOOL IsPointerAnObject(const void *testPointer, BOOL *allocatedLargeEnough)
{
    *allocatedLargeEnough = NO;
     
    // Set up SIGSEGV and SIGBUS handlers
    struct sigaction new_segv_action, old_segv_action;
    struct sigaction new_bus_action, old_bus_action;
    new_segv_action.sa_handler = PointerReadFailedHandler;
    new_bus_action.sa_handler = PointerReadFailedHandler;
    sigemptyset(&new_segv_action.sa_mask);
    sigemptyset(&new_bus_action.sa_mask);
    new_segv_action.sa_flags = 0;
    new_bus_action.sa_flags = 0;
    sigaction (SIGSEGV, &new_segv_action, &old_segv_action);
    sigaction (SIGBUS, &new_bus_action, &old_bus_action);
 
    // The signal handler will return us to here if a signal is raised
    if (sigsetjmp(sigjmp_env, 1))
    {
        sigaction (SIGSEGV, &old_segv_action, NULL);
        sigaction (SIGBUS, &old_bus_action, NULL);
        return NO;
    }
     
    Class testPointerClass = *((Class *)testPointer);
 
    // Get the list of classes and look for testPointerClass
    BOOL isClass = NO;
    NSInteger numClasses = objc_getClassList(NULL, 0);
    Class *classesList = malloc(sizeof(Class) * numClasses);
    numClasses = objc_getClassList(classesList, numClasses);
    for (int i = 0; i < numClasses; i++)
    {
        if (classesList[i] == testPointerClass)
        {
            isClass = YES;
            break;
        }
    }
    free(classesList);
 
    // We're done with the signal handlers (install the previous ones)
    sigaction (SIGSEGV, &old_segv_action, NULL);
    sigaction (SIGBUS, &old_bus_action, NULL);
     
    // Pointer does not point to a valid isa pointer
    if (!isClass)
    {
        return NO;
    }
     
    // Check the allocation size
    size_t allocated_size = malloc_size(testPointer);
    size_t instance_size = class_getInstanceSize(testPointerClass);
    if (allocated_size > instance_size)
    {
        *allocatedLargeEnough = YES;
    }
     
    return YES;
}