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      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.
     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.
     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:
     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