github.com/pingcap/ticdc@v0.0.0-20220526033649-485a10ef2652/pkg/filelock/filelock.go (about)

     1  // Copyright 2021 PingCAP, Inc.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // See the License for the specific language governing permissions and
    12  // limitations under the License.
    13  
    14  package filelock
    15  
    16  import (
    17  	"os"
    18  	"syscall"
    19  
    20  	"github.com/pingcap/errors"
    21  	cerrors "github.com/pingcap/ticdc/pkg/errors"
    22  )
    23  
    24  // FileLock represents a file lock created by `flock`.
    25  // For more on the system call `flock`, read:
    26  // https://linux.die.net/man/2/flock
    27  type FileLock struct {
    28  	fd *os.File
    29  }
    30  
    31  // NewFileLock creates a new file lock on the file described in filePath.
    32  func NewFileLock(filePath string) (*FileLock, error) {
    33  	file, err := os.OpenFile(filePath, os.O_RDWR|os.O_CREATE|syscall.O_NONBLOCK, 0o666)
    34  	if err != nil {
    35  		return nil, errors.Trace(err)
    36  	}
    37  
    38  	return &FileLock{fd: file}, nil
    39  }
    40  
    41  // Lock places a lock on the file
    42  func (fl *FileLock) Lock() error {
    43  	fdInt := fl.fd.Fd()
    44  	err := syscall.Flock(int(fdInt), syscall.LOCK_EX|syscall.LOCK_NB)
    45  	if err != nil {
    46  		if err == syscall.EAGAIN {
    47  			return cerrors.ErrConflictingFileLocks.Wrap(err).GenWithStackByArgs(fl.fd.Name())
    48  		}
    49  		return errors.Trace(err)
    50  	}
    51  	return nil
    52  }
    53  
    54  // Unlock unlocks the file lock
    55  func (fl *FileLock) Unlock() error {
    56  	fdInt := fl.fd.Fd()
    57  	err := syscall.Flock(int(fdInt), syscall.LOCK_UN)
    58  	if err != nil {
    59  		return errors.Trace(err)
    60  	}
    61  	return nil
    62  }
    63  
    64  // Close closes the underlying file.
    65  // NOTE: this function will unlock the lock as well.
    66  func (fl *FileLock) Close() error {
    67  	err := fl.fd.Close()
    68  	if err != nil {
    69  		return errors.Trace(err)
    70  	}
    71  	return nil
    72  }
    73  
    74  // IsLocked checks whether the file is currently locked
    75  func (fl *FileLock) IsLocked() (bool, error) {
    76  	fdInt := fl.fd.Fd()
    77  	err := syscall.Flock(int(fdInt), syscall.LOCK_SH|syscall.LOCK_NB)
    78  	if err == syscall.EAGAIN {
    79  		return true, nil
    80  	} else if err != nil {
    81  		return false, errors.Trace(err)
    82  	} else {
    83  		return false, nil
    84  	}
    85  }