织梦图片网站源码,wordpress手机管理软件,wordpress+重复插件,用网站做CAN总线通信好吗编译环境#xff1a;Ubuntu16.04 64位 交叉编译工具#xff1a;arm-hisiv500-linux-gcc 文章目录 1. 项目背景2. 涉及的函数3. 头文件JShm.h4. 类的实现5. sample代码 1. 项目背景
最近项目中需要用到共享内存的交互#xff0c;取走旧数据#xff0c;取数据不及时写入覆盖… 编译环境Ubuntu16.04 64位 交叉编译工具arm-hisiv500-linux-gcc 文章目录 1. 项目背景2. 涉及的函数3. 头文件JShm.h4. 类的实现5. sample代码 1. 项目背景
最近项目中需要用到共享内存的交互取走旧数据取数据不及时写入覆盖旧数据队列长度可配置自己造个轮子吧对照下一篇linux c多线程简单队列实现。
2. 涉及的函数
详细描述可以百度或ubuntu下查询man手册。 共享内存相关 int shmget(key_t key, size_t size, int shmflg); void *shmat(int shmid, const void *shmaddr, int shmflg); int shmctl(int shmid, int cmd, struct shmid_ds *buf);
信号量相关 int semget(key_t key,int nsems,int semflg); int semctl(int semid,int semnum,int cmd, /union semun arg/); semctl是可变参数长度的函数 int semop(int semid, struct sembuf *sops, size_t nsops);
3. 头文件JShm.h
#ifndef __J_SHM__
#define __J_SHM__#ifdef __cplusplus
extern C {
#endiftypedef enum _JShm_ERR{JSHM_NO_DATA -4, // 无数据供读取JSHM_READ_LENGTH_ERR -3, // 读取缓冲区长度不够JSHM_WRITE_LENGTH_ERR -2, // 写入共享内存长度超出JSHM_INIT_FAIL -1, // 初始化异常JSHM_OK 0,JSHM_WRITE_OVERWRITE 1, // 写成功但是覆盖
}JShm_ERR;class JShm {
public:JShm(int key, unsigned int size, unsigned int blockNum 0);~JShm();int Write(unsigned char *buf, unsigned int len);int Read(unsigned char *buf, unsigned int len);private:int Init();int UnInit();int SemP();int SemV();static unsigned int IsPower2(unsigned int size); static unsigned int To2N(unsigned int size);
private:int m_shmKey;unsigned int m_size; // 共享内存大小unsigned int m_blockSize; // 块大小unsigned int m_blockNum; // 块数量unsigned char *m_buffer; // 共享内存地址unsigned int m_offset; // 数据偏移量int m_shmID;int m_semID;
};#ifdef __cplusplus
}
#endif
#endif // __J_SHM__
4. 类的实现
#include errno.h
#include sys/sem.h
#include sys/ipc.h
#include sys/shm.h
#include string.h#include JShm.hunion SemUnion {int val;struct semid_ds *buf;
};struct ShmHead {unsigned int readPos; // 读取位置从0开始blockNum不为0时有效unsigned int dataNum; // 数据数量unsigned int len[0]; // 数据长度根据blockNum分配
};unsigned int JShm::IsPower2(unsigned int size)
{if (size 0)return 0;return ((size (size - 1)) 0);
}unsigned int JShm::To2N(unsigned int size)
{unsigned int i 1;unsigned int tmp size;while (size 1){i 1;}return (i tmp) ? i 1 : i;
}// 构造时请务必保证双方的参数相同
// blockNum默认为0不传时表示只有1块无缓存
JShm::JShm(int key, unsigned int blockSize, unsigned int blockNum)
{m_shmKey key;unsigned int nSize IsPower2(blockSize) ? blockSize : To2N(blockSize);m_blockSize nSize;m_blockNum (blockNum 0) ? 1 : blockNum;m_offset sizeof(ShmHead) sizeof(unsigned int) * m_blockNum;m_size m_blockSize * m_blockNum m_offset;m_buffer NULL;m_shmID -1;m_semID -1;Init();
}JShm::~JShm()
{UnInit();
}int JShm::Init()
{m_shmID shmget(m_shmKey, m_size, IPC_CREAT | IPC_EXCL | 0666);if (m_shmID 0){if (errno ! EEXIST){return JSHM_INIT_FAIL;}m_shmID shmget(m_shmKey, m_size, IPC_CREAT | 0666);if (m_shmID 0){m_shmID shmget(m_shmKey, 0, 0666);if (m_shmID 0){return JSHM_INIT_FAIL;}if (shmctl(m_shmID, IPC_RMID, NULL)! 0){return JSHM_INIT_FAIL;}m_shmID shmget(m_shmKey, m_size, IPC_CREAT | IPC_EXCL | 0666);if (m_shmID 0){return JSHM_INIT_FAIL;}}}m_buffer (unsigned char *)shmat(m_shmID, NULL, 0);if (m_buffer (unsigned char *)-1){return JSHM_INIT_FAIL;}memset(m_buffer, 0, m_size);m_semID semget(m_shmKey, 1, 0666 | IPC_CREAT);if (m_semID 0){return JSHM_INIT_FAIL;}union SemUnion semUnion;semUnion.val 1;semctl(m_semID, 0, SETVAL, semUnion);return JSHM_OK;
}int JShm::UnInit()
{shmdt(m_buffer);m_buffer NULL;shmctl(m_shmID, IPC_RMID, NULL);m_shmID -1;semctl(m_semID, 0, IPC_RMID);m_semID -1;return JSHM_OK;
}int JShm::SemP()
{// 申请信号信号量-1sembuf semP;semP.sem_num 0;semP.sem_op -1;semP.sem_flg SEM_UNDO;semop(m_semID, semP, 1);return JSHM_OK;
}int JShm::SemV()
{// 释放信号信号量1sembuf semV;semV.sem_num 0;semV.sem_op 1;semV.sem_flg SEM_UNDO;semop(m_semID, semV, 1);return JSHM_OK;
}// !!!note写入共享内存写入长度需要小于等于块长度
// buf要写入的数据
// len要写入的数据的长度
// 返回值0表示成功0成功1覆盖旧数据-1表示失败
int JShm::Write(unsigned char *buf, unsigned int len)
{if (m_buffer NULL)return JSHM_INIT_FAIL;if (len m_blockSize)return JSHM_WRITE_LENGTH_ERR; int ret JSHM_OK;SemP();ShmHead *head (ShmHead *)m_buffer; unsigned int writePos head-readPos head-dataNum;if (writePos m_blockNum)writePos writePos - m_blockNum;memcpy(m_buffer m_offset m_blockSize * writePos, buf, len);head-len[writePos] len;if (head-dataNum m_blockNum) // 满的{head-readPos (writePos 1 m_blockNum) ? 0 : writePos 1;ret JSHM_WRITE_OVERWRITE;}else{head-dataNum head-dataNum 1;}SemV();return ret;
}// !!!note读取共享内存读取长度需要大于等于数据长度
// buf读数据的缓冲区
// len缓冲区的长度
// 返回值实际读取到的长度0表示失败
int JShm::Read(unsigned char *buf, unsigned int len)
{if (m_buffer NULL)return JSHM_INIT_FAIL;int ret JSHM_OK;SemP();ShmHead *head (ShmHead *)m_buffer;if (head-dataNum 0){SemV();return JSHM_NO_DATA;}unsigned int readPos head-readPos;if (len head-len[readPos]){SemV(); return JSHM_READ_LENGTH_ERR;}memcpy(buf, m_buffer m_offset m_blockSize * readPos, head-len[readPos]);ret head-len[readPos];head-readPos (readPos 1 m_blockNum) ? 0 : readPos 1;head-dataNum head-dataNum - 1;SemV();return ret;
}
5. sample代码
#include stdio.h#define SHM_KEY 101
#define SHM_BLOCKSIZE 1024
#define SHM_BLOCKNUM 2
int main(int argc, char* argv[])
{if (argc 2){return -1;}if (argv[1][0] w){JShm *ShmWrite new JShm(SHM_KEY, SHM_BLOCKSIZE, SHM_BLOCKNUM);while (true){char writeBuf[128] {0};fgets(writeBuf, sizeof(writeBuf), stdin);if (writeBuf[0] q){delete ShmWrite;return 0;}printf(write data:%s\n, writeBuf);ShmWrite-Write((unsigned char *)writeBuf, strlen(writeBuf));}} else if (argv[1][0] r) {JShm *ShmRead new JShm(SHM_KEY ,SHM_BLOCKSIZE, SHM_BLOCKNUM);while (true) {char writeBuf[128] {0};fgets(writeBuf, sizeof(writeBuf), stdin);if (writeBuf[0] q){delete ShmRead;return 0;}unsigned char readBuf[128] { 0 };int ret ShmRead-Read(readBuf, 127);printf(read %d data:%s\n, ret, readBuf);}}return 0;
}
编译完成之后ubuntu下分别执行./a.out w和./a.out r测试。
以上。 转载请注明出处如有错漏之处敬请指正。
