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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     file_.reset(OS::OpenFileWithFlags(filename, O_CREAT | O_RDWR));
     31     if (file_.get() == NULL) {
     32       *error_msg = StringPrintf("Failed to open file '%s': %s", filename, strerror(errno));
     33       return false;
     34     }
     35     int flock_result = TEMP_FAILURE_RETRY(flock(file_->Fd(), LOCK_EX));
     36     if (flock_result != 0) {
     37       *error_msg = StringPrintf("Failed to lock file '%s': %s", filename, strerror(errno));
     38       return false;
     39     }
     40     struct stat fstat_stat;
     41     int fstat_result = TEMP_FAILURE_RETRY(fstat(file_->Fd(), &fstat_stat));
     42     if (fstat_result != 0) {
     43       *error_msg = StringPrintf("Failed to fstat file '%s': %s", filename, strerror(errno));
     44       return false;
     45     }
     46     struct stat stat_stat;
     47     int stat_result = TEMP_FAILURE_RETRY(stat(filename, &stat_stat));
     48     if (stat_result != 0) {
     49       PLOG(WARNING) << "Failed to stat, will retry: " << filename;
     50       // ENOENT can happen if someone racing with us unlinks the file we created so just retry.
     51       continue;
     52     }
     53     if (fstat_stat.st_dev != stat_stat.st_dev || fstat_stat.st_ino != stat_stat.st_ino) {
     54       LOG(WARNING) << "File changed while locking, will retry: " << filename;
     55       continue;
     56     }
     57     return true;
     58   }
     59 }
     60 
     61 bool ScopedFlock::Init(File* file, std::string* error_msg) {
     62   file_.reset(new File(dup(file->Fd())));
     63   if (file_->Fd() == -1) {
     64     file_.reset();
     65     *error_msg = StringPrintf("Failed to duplicate open file '%s': %s",
     66                               file->GetPath().c_str(), strerror(errno));
     67     return false;
     68   }
     69   if (0 != TEMP_FAILURE_RETRY(flock(file_->Fd(), LOCK_EX))) {
     70     file_.reset();
     71     *error_msg = StringPrintf("Failed to lock file '%s': %s", file->GetPath().c_str(), strerror(errno));
     72     return false;
     73   }
     74   return true;
     75 }
     76 
     77 File* ScopedFlock::GetFile() {
     78   CHECK(file_.get() != NULL);
     79   return file_.get();
     80 }
     81 
     82 bool ScopedFlock::HasFile() {
     83   return file_.get() != nullptr;
     84 }
     85 
     86 ScopedFlock::ScopedFlock() { }
     87 
     88 ScopedFlock::~ScopedFlock() {
     89   if (file_.get() != NULL) {
     90     int flock_result = TEMP_FAILURE_RETRY(flock(file_->Fd(), LOCK_UN));
     91     CHECK_EQ(0, flock_result);
     92   }
     93 }
     94 
     95 }  // namespace art
     96