1/*
2 * Copyright (C) 2011 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17#ifndef ART_LIBARTBASE_BASE_SCOPED_FLOCK_H_
18#define ART_LIBARTBASE_BASE_SCOPED_FLOCK_H_
19
20#include <memory>
21#include <string>
22
23#include <android-base/unique_fd.h>
24
25#include "base/macros.h"
26#include "base/os.h"
27#include "base/unix_file/fd_file.h"
28
29namespace art {
30
31class LockedFile;
32class LockedFileCloseNoFlush;
33
34// A scoped File object that calls Close without flushing.
35typedef std::unique_ptr<LockedFile, LockedFileCloseNoFlush> ScopedFlock;
36
37class LockedFile : public unix_file::FdFile {
38 public:
39  // Attempts to acquire an exclusive file lock (see flock(2)) on the file
40  // at filename, and blocks until it can do so.
41  //
42  // It is an error if its inode changed (usually due to a new file being
43  // created at the same path) between attempts to lock it. In blocking mode,
44  // locking will be retried if the file changed. In non-blocking mode, false
45  // is returned and no attempt is made to re-acquire the lock.
46  //
47  // The file is opened with the provided flags.
48  static ScopedFlock Open(const char* filename, int flags, bool block,
49                          std::string* error_msg);
50
51  // Calls Open(filename, O_CREAT | O_RDWR, true, errror_msg)
52  static ScopedFlock Open(const char* filename, std::string* error_msg);
53
54  // Attempt to acquire an exclusive file lock (see flock(2)) on 'file'.
55  // Returns true if the lock could be acquired or false if an error
56  // occured.
57  static ScopedFlock DupOf(const int fd, const std::string& path,
58                           const bool read_only_mode, std::string* error_message);
59
60  // Release a lock held on this file, if any.
61  void ReleaseLock();
62
63 private:
64  // Constructors should not be invoked directly, use one of the factory
65  // methods instead.
66  explicit LockedFile(FdFile&& other) : FdFile(std::move(other)) {
67  }
68
69  // Constructors should not be invoked directly, use one of the factory
70  // methods instead.
71  LockedFile(int fd, const std::string& path, bool check_usage, bool read_only_mode)
72      : FdFile(fd, path, check_usage, read_only_mode) {
73  }
74};
75
76class LockedFileCloseNoFlush {
77 public:
78  void operator()(LockedFile* ptr) {
79    ptr->ReleaseLock();
80    UNUSED(ptr->Close());
81
82    delete ptr;
83  }
84};
85
86}  // namespace art
87
88#endif  // ART_LIBARTBASE_BASE_SCOPED_FLOCK_H_
89