linux C编程之死锁

死锁：

死锁就是你和小明打架,互相掐住对方脖子,你们都说“你先放!”,结果谁都不放,死锁了.
在程序里面,有两个锁,A线程锁住第一个,B线程锁住了第二个,这时如果A再试图锁第二个,失败,因为B已经锁住了,A只能等待.就在这时B试图锁第一个,结果失败,因为A已经锁住了,B只好等待.就这样大家一直等下去,谁都不放,天荒地老...

举例：

#include <unistd.h> 
#include <pthread.h> 
#include <string.h> 

pthread_mutex_t mutex1 = PTHREAD_MUTEX_INITIALIZER; 
pthread_mutex_t mutex2 = PTHREAD_MUTEX_INITIALIZER; 
pthread_mutex_t mutex3 = PTHREAD_MUTEX_INITIALIZER; 
pthread_mutex_t mutex4 = PTHREAD_MUTEX_INITIALIZER; 

static int sequence1 = 0; 
static int sequence2 = 0; 

 int func1() 
 { 
    pthread_mutex_lock(&mutex1); 
    ++sequence1; 
    sleep(1); 
    pthread_mutex_lock(&mutex2); 
    ++sequence2; 
    pthread_mutex_unlock(&mutex2); 
    pthread_mutex_unlock(&mutex1); 

    return sequence1; 
 } 

 int func2() 
 { 
    pthread_mutex_lock(&mutex2); 
    +