三个线程无限循环打印出ABC，小弟这段代码错在何处，为何会死锁，请各位指教
C/C++ code:
#include <stdio.h>
#include <assert.h>
#include <stdlib.h>
#include <string.h>
#include <stdarg.h>
#include <errno.h>
#include <string.h>
#include <pthread.h>
#include <sys/types.h>
#include <limits.h>
#include <time.h>
#include <sys/time.h>
#define MAX 1024
#define BUFFSIZE 1024
static void err_sys(char *fmt,...);
pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
int flag = 0;
void *thread1(void *arg){
while(1){
pthread_mutex_trylock(&lock);
while(flag!=0)
pthread_cond_wait(&cond,&lock);
if(flag==0){
putchar('A');
flag = 1;
}
pthread_mutex_unlock(&lock);
pthread_cond_signal(&cond);
}
return ((void*)1);
}
void *thread2(void *arg){
while(1){
pthread_mutex_trylock(&lock);
while(flag!=1)
pthread_cond_wait(&cond,&lock);
if(flag==1){
putchar('B');
fla
