Linux File lock implementation

Linux File locks are the default recommended locks.

Two points are confirmed as follows:

1) exclusive read/write locks.

2) Lock contention when the file lock areas cross.

Filemutex. h:

class FileMutex {public:FileMutex(const string& filename);virtual ~FileMutex();int lockR(int offset,int len);int lockW(int offset,int len);int lockRWait(int offset,int len,int millseconds);int lockWWait(int offset,int len,int millseconds);int unlock(int offset,int len);private:int fd;};

Filemutex. cpp

#include "FileMutex.h"FileMutex::FileMutex(const string& filename) {fd = open(filename.c_str(),O_RDWR| O_CREAT, 0600);if(fd<0){perror("FileMutex init:");}cout << "fd:" << fd << endl;assert(fd);}FileMutex::~FileMutex() {if (fd > 0) {close(fd);}}int FileMutex::lockR(int offset, int len) {struct flock lock;lock.l_start = offset;lock.l_len = len;lock.l_type = F_RDLCK;lock.l_whence = SEEK_SET;int result=fcntl(fd, F_SETLK, &lock);if(result<0){perror("lockR:");}return result;}int FileMutex::lockW(int offset, int len) {struct flock lock;lock.l_start = offset;lock.l_len = len;lock.l_type = F_WRLCK;lock.l_whence = SEEK_SET;return fcntl(fd, F_SETLK, &lock);}int FileMutex::lockRWait(int offset, int len, int millseconds) {struct flock lock;lock.l_start = offset;lock.l_len = len;lock.l_type = F_RDLCK;lock.l_whence = SEEK_SET;return fcntl(fd, F_SETLKW, &lock);}int FileMutex::lockWWait(int offset, int len, int millseconds) {struct flock lock;lock.l_start = offset;lock.l_len = len;lock.l_type = F_WRLCK;lock.l_whence = SEEK_SET;return fcntl(fd, F_SETLKW, &lock);}int FileMutex::unlock(int offset, int len) {struct flock lock;lock.l_start = offset;lock.l_len = len;lock.l_type = F_UNLCK;lock.l_whence = SEEK_SET;return fcntl(fd, F_SETLK, &lock);}const option options[] = { { "file", required_argument, NULL, 'f' }, { "type", required_argument, NULL, 't' }, {"offset", required_argument, NULL, 'o' }, { "len", required_argument, NULL, 'l' }, { 0, 0, 0, 0 } };int main(int argc, char **argv) {char cFileName[128];int type;int offset;int len;int ch;while ((ch = getopt_long(argc, argv, ":f:t:o:l:", options, NULL)) != -1) {switch (ch) {case 'f':strcpy(cFileName, optarg);break;case 't':type = atoi(optarg);break;case 'o':offset = atoi(optarg);break;case 'l':len = atoi(optarg);break;default:break;}}cout << "FileName:" << cFileName << " type:" << type << " offset:" << offset << " len:" << len << endl;FileMutex mutex(cFileName);int lockResult;if (type == 0) {lockResult = mutex.lockR(offset, len);}if (type == 1) {lockResult = mutex.lockW(offset, len);}cout << lockResult << endl;pause();}

Run:

./Mutex -- file = lock1 -- type = 0 -- offset = 0 -- Len = 10

./Mutex -- file = lock1 -- type = 0 -- offset = 10 -- Len = 10

Two read locks can coexist.

./Mutex -- file = lock1 -- type = 0 -- offset = 0 -- Len = 10

./Mutex -- file = lock1 -- type = 1 -- offset = 10 -- Len = 10

The read/write locks and read/write locks must be in the same region.

./Mutex -- file = lock1 -- type = 0 -- offset = 0 -- Len = 10

./Mutex -- file = lock1 -- type = 1 -- offset = 11 -- Len = 10

Areas do not overlap and can coexist