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 29 namespace art { 30 31 class LockedFile; 32 class LockedFileCloseNoFlush; 33 34 // A scoped File object that calls Close without flushing. 35 typedef std::unique_ptr<LockedFile, LockedFileCloseNoFlush> ScopedFlock; 36 37 class 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 76 class 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
