Use CREATE_ALWAYS instead of CREATE_NEW

[cloudwu]

CREATE_ALWAYS is better than CREATE_NEW for dir locking IMHO, because lockfile.lfs may be not deleted in some cases.

[coveralls]

Coverage increased (+0.1%) to 80.244% when pulling 1f298b1 on cloudwu:patch-1 into 1dfb8c4 on keplerproject:master.

[coveralls]

Coverage remained the same at 82.227% when pulling cea32e6 on cloudwu:patch-1 into 6048863 on keplerproject:master.

[hishamhm]

@cloudwu I'm not too familiar with the Windows API, but from what I'm reading here my understanding is that the use of CREATE_NEW is deliberate, in order to fail in case a lockfile from another concurrent execution already exists. If we used CREATE_ALWAYS here, then two concurrent executions would be able to acquire the lock.

I'm closing this for now, but feel free to reopen if my understanding is not correct.

[cloudwu]

The exclusive here is guaranteed by GENERIC_WRITE rather than the existence of the file "lockfile.lfs" . windows doesn't allow two or more concurrent execution open the file with GENERIC_WRITE at the same time.

It's easier to fail to delete the file "lockfile.lfs" in windows, although we set FILE_FLAG_DELETE_ON_CLOSE. I found many times my app can't delete the file "lockfile.lfs" in windows after exit , so I think we should change CREATE_NEW to CREATE_ALWAYS (or OPEN_ALWAYS) . The lock can still work whether we delete "lockfile.lfs" last time.

[hishamhm]

@cloudwu Thank you for the clarification! I fixed the conflict and merged your commit manually!