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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 #include "scoped_flock.h"
     18 
     19 #include <sys/file.h>
     20 #include <sys/stat.h>
     21 
     22 #include "base/logging.h"
     23 #include "base/stringprintf.h"
     24 #include "base/unix_file/fd_file.h"
     25 
     26 namespace art {
     27 
     28 bool ScopedFlock::Init(const char* filename, std::string* error_msg) {
     29   while (true) {
     30     if (file_.get() != nullptr) {
     31       UNUSED(file_->FlushCloseOrErase());  // Ignore result.
     32     }
     33     file_.reset(OS::OpenFileWithFlags(filename, O_CREAT | O_RDWR));
     34     if (file_.get() == nullptr) {
     35       *error_msg = StringPrintf("Failed to open file '%s': %s", filename, strerror(errno));
     36       return false;
     37     }
     38     int flock_result = TEMP_FAILURE_RETRY(flock(file_->Fd(), LOCK_EX));
     39     if (flock_result != 0) {
     40       *error_msg = StringPrintf("Failed to lock file '%s': %s", filename, strerror(errno));
     41       return false;
     42     }
     43     struct stat fstat_stat;
     44     int fstat_result = TEMP_FAILURE_RETRY(fstat(file_->Fd(), &fstat_stat));
     45     if (fstat_result != 0) {
     46       *error_msg = StringPrintf("Failed to fstat file '%s': %s", filename, strerror(errno));
     47       return false;
     48     }
     49     struct stat stat_stat;
     50     int stat_result = TEMP_FAILURE_RETRY(stat(filename, &stat_stat));
     51     if (stat_result != 0) {
     52       PLOG(WARNING) << "Failed to stat, will retry: " << filename;
     53       // ENOENT can happen if someone racing with us unlinks the file we created so just retry.
     54       continue;
     55     }
     56     if (fstat_stat.st_dev != stat_stat.st_dev || fstat_stat.st_ino != stat_stat.st_ino) {
     57       LOG(WARNING) << "File changed while locking, will retry: " << filename;
     58       continue;
     59     }
     60     return true;
     61   }
     62 }
     63 
     64 bool ScopedFlock::Init(File* file, std::string* error_msg) {
     65   file_.reset(new File(dup(file->Fd()), true));
     66   if (file_->Fd() == -1) {
     67     file_.reset();
     68     *error_msg = StringPrintf("Failed to duplicate open file '%s': %s",
     69                               file->GetPath().c_str(), strerror(errno));
     70     return false;
     71   }
     72   if (0 != TEMP_FAILURE_RETRY(flock(file_->Fd(), LOCK_EX))) {
     73     file_.reset();
     74     *error_msg = StringPrintf(
     75         "Failed to lock file '%s': %s", file->GetPath().c_str(), strerror(errno));
     76     return false;
     77   }
     78   return true;
     79 }
     80 
     81 File* ScopedFlock::GetFile() {
     82   CHECK(file_.get() != nullptr);
     83   return file_.get();
     84 }
     85 
     86 bool ScopedFlock::HasFile() {
     87   return file_.get() != nullptr;
     88 }
     89 
     90 ScopedFlock::ScopedFlock() { }
     91 
     92 ScopedFlock::~ScopedFlock() {
     93   if (file_.get() != nullptr) {
     94     int flock_result = TEMP_FAILURE_RETRY(flock(file_->Fd(), LOCK_UN));
     95     CHECK_EQ(0, flock_result);
     96     if (file_->FlushCloseOrErase() != 0) {
     97       PLOG(WARNING) << "Could not close scoped file lock file.";
     98     }
     99   }
    100 }
    101 
    102 }  // namespace art
    103