129 lines
4.2 KiB
C++
129 lines
4.2 KiB
C++
/*
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* Copyright (C) 2011 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include "scoped_flock.h"
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#include <sys/file.h>
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#include <sys/stat.h>
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#include "base/logging.h"
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#include "base/stringprintf.h"
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#include "base/unix_file/fd_file.h"
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namespace art {
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bool ScopedFlock::Init(const char* filename, std::string* error_msg) {
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return Init(filename, O_CREAT | O_RDWR, true, error_msg);
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}
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bool ScopedFlock::Init(const char* filename, int flags, bool block, std::string* error_msg) {
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while (true) {
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if (file_.get() != nullptr) {
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UNUSED(file_->FlushCloseOrErase()); // Ignore result.
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}
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file_.reset(OS::OpenFileWithFlags(filename, flags));
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if (file_.get() == nullptr) {
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*error_msg = StringPrintf("Failed to open file '%s': %s", filename, strerror(errno));
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return false;
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}
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int operation = block ? LOCK_EX : (LOCK_EX | LOCK_NB);
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int flock_result = TEMP_FAILURE_RETRY(flock(file_->Fd(), operation));
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if (flock_result == EWOULDBLOCK) {
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// File is locked by someone else and we are required not to block;
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return false;
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}
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if (flock_result != 0) {
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*error_msg = StringPrintf("Failed to lock file '%s': %s", filename, strerror(errno));
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return false;
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}
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struct stat fstat_stat;
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int fstat_result = TEMP_FAILURE_RETRY(fstat(file_->Fd(), &fstat_stat));
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if (fstat_result != 0) {
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*error_msg = StringPrintf("Failed to fstat file '%s': %s", filename, strerror(errno));
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return false;
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}
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struct stat stat_stat;
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int stat_result = TEMP_FAILURE_RETRY(stat(filename, &stat_stat));
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if (stat_result != 0) {
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PLOG(WARNING) << "Failed to stat, will retry: " << filename;
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// ENOENT can happen if someone racing with us unlinks the file we created so just retry.
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if (block) {
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continue;
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} else {
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// Note that in theory we could race with someone here for a long time and end up retrying
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// over and over again. This potential behavior does not fit well in the non-blocking
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// semantics. Thus, if we are not require to block return failure when racing.
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return false;
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}
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}
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if (fstat_stat.st_dev != stat_stat.st_dev || fstat_stat.st_ino != stat_stat.st_ino) {
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LOG(WARNING) << "File changed while locking, will retry: " << filename;
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if (block) {
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continue;
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} else {
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// See comment above.
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return false;
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}
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}
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return true;
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}
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}
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bool ScopedFlock::Init(File* file, std::string* error_msg) {
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file_.reset(new File(dup(file->Fd()), file->GetPath(), file->CheckUsage(), file->ReadOnlyMode()));
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if (file_->Fd() == -1) {
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file_.reset();
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*error_msg = StringPrintf("Failed to duplicate open file '%s': %s",
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file->GetPath().c_str(), strerror(errno));
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return false;
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}
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if (0 != TEMP_FAILURE_RETRY(flock(file_->Fd(), LOCK_EX))) {
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file_.reset();
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*error_msg = StringPrintf(
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"Failed to lock file '%s': %s", file->GetPath().c_str(), strerror(errno));
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return false;
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}
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return true;
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}
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File* ScopedFlock::GetFile() const {
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CHECK(file_.get() != nullptr);
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return file_.get();
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}
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bool ScopedFlock::HasFile() {
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return file_.get() != nullptr;
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}
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ScopedFlock::ScopedFlock() { }
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ScopedFlock::~ScopedFlock() {
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if (file_.get() != nullptr) {
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int flock_result = TEMP_FAILURE_RETRY(flock(file_->Fd(), LOCK_UN));
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CHECK_EQ(0, flock_result);
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int close_result = -1;
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if (file_->ReadOnlyMode()) {
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close_result = file_->Close();
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} else {
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close_result = file_->FlushCloseOrErase();
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}
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if (close_result != 0) {
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PLOG(WARNING) << "Could not close scoped file lock file.";
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}
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}
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}
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} // namespace art
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