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_RUNTIME_BASE_SCOPED_FLOCK_H_ 18 #define ART_RUNTIME_BASE_SCOPED_FLOCK_H_ 19 20 #include <memory> 21 #include <string> 22 23 #include "android-base/unique_fd.h" 24 25 #include "base/logging.h" 26 #include "base/macros.h" 27 #include "base/unix_file/fd_file.h" 28 #include "os.h" 29 30 namespace art { 31 32 class LockedFile; 33 class LockedFileCloseNoFlush; 34 35 // A scoped File object that calls Close without flushing. 36 typedef std::unique_ptr<LockedFile, LockedFileCloseNoFlush> ScopedFlock; 37 38 class LockedFile : public unix_file::FdFile { 39 public: 40 // Attempts to acquire an exclusive file lock (see flock(2)) on the file 41 // at filename, and blocks until it can do so. 42 // 43 // It is an error if its inode changed (usually due to a new file being 44 // created at the same path) between attempts to lock it. In blocking mode, 45 // locking will be retried if the file changed. In non-blocking mode, false 46 // is returned and no attempt is made to re-acquire the lock. 47 // 48 // The file is opened with the provided flags. 49 static ScopedFlock Open(const char* filename, int flags, bool block, 50 std::string* error_msg); 51 52 // Calls Open(filename, O_CREAT | O_RDWR, true, errror_msg) 53 static ScopedFlock Open(const char* filename, std::string* error_msg); 54 55 // Attempt to acquire an exclusive file lock (see flock(2)) on 'file'. 56 // Returns true if the lock could be acquired or false if an error 57 // occured. 58 static ScopedFlock DupOf(const int fd, const std::string& path, 59 const bool read_only_mode, std::string* error_message); 60 61 // Release a lock held on this file, if any. 62 void ReleaseLock(); 63 64 private: 65 // Constructors should not be invoked directly, use one of the factory 66 // methods instead. LockedFile(FdFile && other)67 explicit LockedFile(FdFile&& other) : FdFile(std::move(other)) { 68 } 69 70 // Constructors should not be invoked directly, use one of the factory 71 // methods instead. LockedFile(int fd,const std::string & path,bool check_usage,bool read_only_mode)72 LockedFile(int fd, const std::string& path, bool check_usage, bool read_only_mode) 73 : FdFile(fd, path, check_usage, read_only_mode) { 74 } 75 }; 76 77 class LockedFileCloseNoFlush { 78 public: operator()79 void operator()(LockedFile* ptr) { 80 ptr->ReleaseLock(); 81 UNUSED(ptr->Close()); 82 83 delete ptr; 84 } 85 }; 86 87 } // namespace art 88 89 #endif // ART_RUNTIME_BASE_SCOPED_FLOCK_H_ 90