Home | History | Annotate | Download | only in base 
      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   return Init(filename, O_CREAT | O_RDWR, true, error_msg);
     30 }
     31 
     32 bool ScopedFlock::Init(const char* filename, int flags, bool block, std::string* error_msg) {
     33   while (true) {
     34     if (file_.get() != nullptr) {
     35       UNUSED(file_->FlushCloseOrErase());  // Ignore result.
     36     }
     37     file_.reset(OS::OpenFileWithFlags(filename, flags));
     38     if (file_.get() == nullptr) {
     39       *error_msg = StringPrintf("Failed to open file '%s': %s", filename, strerror(errno));
     40       return false;
     41     }
     42     int operation = block ? LOCK_EX : (LOCK_EX | LOCK_NB);
     43     int flock_result = TEMP_FAILURE_RETRY(flock(file_->Fd(), operation));
     44     if (flock_result == EWOULDBLOCK) {
     45       // File is locked by someone else and we are required not to block;
     46       return false;
     47     }
     48     if (flock_result != 0) {
     49       *error_msg = StringPrintf("Failed to lock file '%s': %s", filename, strerror(errno));
     50       return false;
     51     }
     52     struct stat fstat_stat;
     53     int fstat_result = TEMP_FAILURE_RETRY(fstat(file_->Fd(), &fstat_stat));
     54     if (fstat_result != 0) {
     55       *error_msg = StringPrintf("Failed to fstat file '%s': %s", filename, strerror(errno));
     56       return false;
     57     }
     58     struct stat stat_stat;
     59     int stat_result = TEMP_FAILURE_RETRY(stat(filename, &stat_stat));
     60     if (stat_result != 0) {
     61       PLOG(WARNING) << "Failed to stat, will retry: " << filename;
     62       // ENOENT can happen if someone racing with us unlinks the file we created so just retry.
     63       if (block) {
     64         continue;
     65       } else {
     66         // Note that in theory we could race with someone here for a long time and end up retrying
     67         // over and over again. This potential behavior does not fit well in the non-blocking
     68         // semantics. Thus, if we are not require to block return failure when racing.
     69         return false;
     70       }
     71     }
     72     if (fstat_stat.st_dev != stat_stat.st_dev || fstat_stat.st_ino != stat_stat.st_ino) {
     73       LOG(WARNING) << "File changed while locking, will retry: " << filename;
     74       if (block) {
     75         continue;
     76       } else {
     77         // See comment above.
     78         return false;
     79       }
     80     }
     81     return true;
     82   }
     83 }
     84 
     85 bool ScopedFlock::Init(File* file, std::string* error_msg) {
     86   file_.reset(new File(dup(file->Fd()), file->GetPath(), file->CheckUsage(), file->ReadOnlyMode()));
     87   if (file_->Fd() == -1) {
     88     file_.reset();
     89     *error_msg = StringPrintf("Failed to duplicate open file '%s': %s",
     90                               file->GetPath().c_str(), strerror(errno));
     91     return false;
     92   }
     93   if (0 != TEMP_FAILURE_RETRY(flock(file_->Fd(), LOCK_EX))) {
     94     file_.reset();
     95     *error_msg = StringPrintf(
     96         "Failed to lock file '%s': %s", file->GetPath().c_str(), strerror(errno));
     97     return false;
     98   }
     99   return true;
    100 }
    101 
    102 File* ScopedFlock::GetFile() const {
    103   CHECK(file_.get() != nullptr);
    104   return file_.get();
    105 }
    106 
    107 bool ScopedFlock::HasFile() {
    108   return file_.get() != nullptr;
    109 }
    110 
    111 ScopedFlock::ScopedFlock() { }
    112 
    113 ScopedFlock::~ScopedFlock() {
    114   if (file_.get() != nullptr) {
    115     int flock_result = TEMP_FAILURE_RETRY(flock(file_->Fd(), LOCK_UN));
    116     CHECK_EQ(0, flock_result);
    117     int close_result = -1;
    118     if (file_->ReadOnlyMode()) {
    119       close_result = file_->Close();
    120     } else {
    121       close_result = file_->FlushCloseOrErase();
    122     }
    123     if (close_result != 0) {
    124       PLOG(WARNING) << "Could not close scoped file lock file.";
    125     }
    126   }
    127 }
    128 
    129 }  // namespace art
    130