blob: 862f0d0b001360ddb6ae312ce02570be6d1fde94 [file] [log] [blame]
/*
* Copyright (C) 2011 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "scoped_flock.h"
#include <sys/file.h>
#include <sys/stat.h>
#include "android-base/stringprintf.h"
#include "base/logging.h"
#include "base/unix_file/fd_file.h"
namespace art {
using android::base::StringPrintf;
bool ScopedFlock::Init(const char* filename, std::string* error_msg) {
return Init(filename, O_CREAT | O_RDWR, true, error_msg);
}
bool ScopedFlock::Init(const char* filename, int flags, bool block, std::string* error_msg) {
return Init(filename, flags, block, true, error_msg);
}
bool ScopedFlock::Init(const char* filename,
int flags,
bool block,
bool flush_on_close,
std::string* error_msg) {
flush_on_close_ = flush_on_close;
while (true) {
if (file_.get() != nullptr) {
UNUSED(file_->FlushCloseOrErase()); // Ignore result.
}
bool check_usage = flush_on_close; // Check usage only if we need to flush on close.
file_.reset(OS::OpenFileWithFlags(filename, flags, check_usage));
if (file_.get() == nullptr) {
*error_msg = StringPrintf("Failed to open file '%s': %s", filename, strerror(errno));
return false;
}
int operation = block ? LOCK_EX : (LOCK_EX | LOCK_NB);
int flock_result = TEMP_FAILURE_RETRY(flock(file_->Fd(), operation));
if (flock_result == EWOULDBLOCK) {
// File is locked by someone else and we are required not to block;
return false;
}
if (flock_result != 0) {
*error_msg = StringPrintf("Failed to lock file '%s': %s", filename, strerror(errno));
return false;
}
struct stat fstat_stat;
int fstat_result = TEMP_FAILURE_RETRY(fstat(file_->Fd(), &fstat_stat));
if (fstat_result != 0) {
*error_msg = StringPrintf("Failed to fstat file '%s': %s", filename, strerror(errno));
return false;
}
struct stat stat_stat;
int stat_result = TEMP_FAILURE_RETRY(stat(filename, &stat_stat));
if (stat_result != 0) {
PLOG(WARNING) << "Failed to stat, will retry: " << filename;
// ENOENT can happen if someone racing with us unlinks the file we created so just retry.
if (block) {
continue;
} else {
// Note that in theory we could race with someone here for a long time and end up retrying
// over and over again. This potential behavior does not fit well in the non-blocking
// semantics. Thus, if we are not require to block return failure when racing.
return false;
}
}
if (fstat_stat.st_dev != stat_stat.st_dev || fstat_stat.st_ino != stat_stat.st_ino) {
LOG(WARNING) << "File changed while locking, will retry: " << filename;
if (block) {
continue;
} else {
// See comment above.
return false;
}
}
return true;
}
}
bool ScopedFlock::Init(File* file, std::string* error_msg) {
flush_on_close_ = true;
file_.reset(new File(dup(file->Fd()), file->GetPath(), file->CheckUsage(), file->ReadOnlyMode()));
if (file_->Fd() == -1) {
file_.reset();
*error_msg = StringPrintf("Failed to duplicate open file '%s': %s",
file->GetPath().c_str(), strerror(errno));
return false;
}
if (0 != TEMP_FAILURE_RETRY(flock(file_->Fd(), LOCK_EX))) {
file_.reset();
*error_msg = StringPrintf(
"Failed to lock file '%s': %s", file->GetPath().c_str(), strerror(errno));
return false;
}
return true;
}
File* ScopedFlock::GetFile() const {
CHECK(file_.get() != nullptr);
return file_.get();
}
bool ScopedFlock::HasFile() {
return file_.get() != nullptr;
}
ScopedFlock::ScopedFlock() : flush_on_close_(true) { }
ScopedFlock::~ScopedFlock() {
if (file_.get() != nullptr) {
int flock_result = TEMP_FAILURE_RETRY(flock(file_->Fd(), LOCK_UN));
if (flock_result != 0) {
// Only printing a warning is okay since this is only used with either:
// 1) a non-blocking Init call, or
// 2) as a part of a seperate binary (eg dex2oat) which has it's own timeout logic to prevent
// deadlocks.
// This means we can be sure that the warning won't cause a deadlock.
PLOG(WARNING) << "Unable to unlock file " << file_->GetPath();
}
int close_result = -1;
if (file_->ReadOnlyMode() || !flush_on_close_) {
close_result = file_->Close();
} else {
close_result = file_->FlushCloseOrErase();
}
if (close_result != 0) {
PLOG(WARNING) << "Could not close scoped file lock file.";
}
}
}
} // namespace art