雪花算法

#include <stdio.h>#include <fcntl.h>
int main(){        int randNum = 0;        int fd = 0;
    for(int i=0;i<5;i++)    {            fd = open("/dev/urandom", O_RDONLY);        read(fd, (char *)&randNum, sizeof(int));      close(fd);       printf("randNum is %d\n", randNum);    }
        return 0;}

mapan@mapan-virtual-machine:~/c++$ ./a.out randNum is 94961710randNum is -523780773randNum is 1542169420randNum is -1632410867

/*     snowflake 
    ID 生成策略     毫秒级时间41位+机器ID 10位+毫秒内序列12位。    0 41 51 64 +-----------+------+------+ |time |pc |inc | +-----------+------+------+     前41bits是以微秒为单位的timestamp。    接着10bits是事先配置好的机器ID。    最后12bits是累加计数器。    macheine id(10bits)标明最多只能有1024台机器同时产生ID，sequence number(12bits)也标明1台机器1ms中最多产生4096个ID， *       注意点，因为使用到位移运算，所以需要64位操作系统，不然生成的ID会有可能不正确 */  
#include <stdio.h>  #include <pthread.h>  #include <unistd.h>  #include <stdlib.h>  #include <sched.h>  #include <linux/unistd.h>  #include <sys/syscall.h>  #include <errno.h>  #include<linux/types.h>  #include<time.h>  #include <stdint.h>  #include <sys/time.h>  
struct  globle  {      int global_int:12;      uint64_t last_stamp;      int workid;      int seqid;  };  
void set_workid(int workid);  pid_t gettid( void );  uint64_t get_curr_ms();  uint64_t wait_next_ms(uint64_t lastStamp);  int atomic_incr(int id);  uint64_t get_unique_id();

#include "snowflake.h"
struct globle g_info;
#define   sequenceMask  (-1L ^ (-1L << 12L))  //L表示long型     4095
void set_workid(int workid){ g_info.workid = workid;}
pid_t gettid( void )//获取线程ID{  return syscall( __NR_gettid );}
uint64_t get_curr_ms()  //获取毫秒{  struct timeval time_now;  gettimeofday(&time_now,NULL);  uint64_t ms_time =time_now.tv_sec*1000+time_now.tv_usec/1000;  return ms_time;}
uint64_t wait_next_ms(uint64_t lastStamp){  uint64_t cur = 0;  do {    cur = get_curr_ms();  } while (cur <= lastStamp);  return cur;}
int atomic_incr(int id)//累加{  __sync_add_and_fetch(&id, 1);  return id;}
uint64_t get_unique_id(){  uint64_t  uniqueId=0;  uint64_t nowtime = get_curr_ms();//获取当前毫秒数
  uniqueId = nowtime << 22;   //填补时间戳部分
  //0x3ff 1023,二进制对应11 1111 1111   //100的二进制0000 0000 0000 0000 0000 0000 0110 0100  //先执行移位  uniqueId |= (g_info.workid & 0x3ff) << 12;   //填补节点部分
  if (nowtime < g_info.last_stamp)  {    perror("error");    exit(-1);  }
  if (nowtime == g_info.last_stamp)  {    //4095的二进制0000 1111 1111 1111      [long型]    g_info.seqid = atomic_incr(g_info.seqid) & sequenceMask;    if (g_info.seqid == 0)  //seqid=0防止冲突，修改时间    {      nowtime = wait_next_ms(g_info.last_stamp);//获取大于当前时间的time    }  }  else  {    g_info.seqid  = 0;  }  g_info.last_stamp = nowtime;
  uniqueId |= g_info.seqid;//填补序列号部分  return uniqueId;}
int main(){  set_workid(100);  int i;  for(i=0;i<10;i++)  {    uint64_t unquie = get_unique_id();    printf("pthread_id:%u, id [%llu]\n",gettid(),unquie);  }
  return;  }

mapan@mapan-virtual-machine:~/c++$ ./a.out pthread_id:4970, id [6595660141600063488]pthread_id:4970, id [6595660141600063489]pthread_id:4970, id [6595660141600063490]pthread_id:4970, id [6595660141600063491]pthread_id:4970, id [6595660141600063492]