// Copyright 2019 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "sql/vfs_wrapper_fuchsia.h"
#include <string>
#include "base/check.h"
#include "base/check_op.h"
#include "base/containers/fixed_flat_set.h"
#include "base/containers/flat_map.h"
#include "base/containers/flat_set.h"
#include "base/logging.h"
#include "base/no_destructor.h"
#include "base/synchronization/lock.h"
#include "base/thread_annotations.h"
#include "sql/vfs_wrapper.h"
#include "third_party/sqlite/sqlite3.h"
namespace sql {
namespace {
struct FileLock {
int lock_level;
// Used to track the pointers to different VfsFile instances that hold shared
// locks on the same underlying file. The pointer is only used as a unique id
// for the VfsFile instance. The contents are never accessed.
base::flat_set<VfsFile*> readers = {};
// Used to track a VfsFile instance that holds a reserved/pending/exclusive
// lock for writing. The pointer is only used as a unique id for the VfsFile
// instance. The contents are never accessed.
VfsFile* writer = nullptr;
};
// Singleton that stores and mutates state as described in
// https://www.sqlite.org/lockingv3.html
class FuchsiaFileLockManager {
public:
FuchsiaFileLockManager() = default;
// Returns lock manager for the current process.
static FuchsiaFileLockManager* Instance() {
static base::NoDestructor<FuchsiaFileLockManager> lock_manager;
return lock_manager.get();
}
int Lock(VfsFile* vfs_file, int requested_lock) {
DCHECK_GT(requested_lock, SQLITE_LOCK_NONE)
<< "SQLITE_LOCK_NONE can only be set via Unlock";
base::AutoLock lock(lock_);
const auto file_lock_state = GetFileLockStateLocked(vfs_file);
// Allow any lock level since the lock isn't held.
if (file_lock_state.readers.empty() && file_lock_state.writer == nullptr) {
if (requested_lock == SQLITE_LOCK_SHARED) {
locked_files_[vfs_file->file_name] = {.lock_level = requested_lock,
.readers = {vfs_file}};
} else {
locked_files_[vfs_file->file_name] = {.lock_level = requested_lock,
.writer = vfs_file};
}
return SQLITE_OK;
}
if (requested_lock == SQLITE_LOCK_SHARED) {
if (file_lock_state.lock_level >= SQLITE_LOCK_PENDING) {
DVLOG(1) << "lock for file " << vfs_file->file_name
<< " is held by a writer and cannot be shared.";
return SQLITE_BUSY;
}
locked_files_[vfs_file->file_name].readers.insert(vfs_file);
return SQLITE_OK;
}
if (file_lock_state.writer != nullptr &&
file_lock_state.writer != vfs_file) {
DVLOG(1) << "lock for file " << vfs_file->file_name
<< " is already held by another writer.";
return SQLITE_BUSY;
}
if (requested_lock == SQLITE_LOCK_EXCLUSIVE &&
(file_lock_state.readers.size() > 1 ||
(file_lock_state.readers.size() == 1 &&
!file_lock_state.readers.contains(vfs_file)))) {
DVLOG(1) << "lock for file " << vfs_file->file_name
<< " is held by readers and can't yet be upgraded to exclusive.";
return SQLITE_BUSY;
}
DCHECK(file_lock_state.writer == nullptr ||
file_lock_state.writer == vfs_file);
locked_files_[vfs_file->file_name].lock_level = requested_lock;
locked_files_[vfs_file->file_name].writer = vfs_file;
locked_files_[vfs_file->file_name].readers.erase(vfs_file);
DCHECK(locked_files_[vfs_file->file_name].lock_level <
SQLITE_LOCK_EXCLUSIVE ||
locked_files_[vfs_file->file_name].readers.empty());
return SQLITE_OK;
}
int Unlock(VfsFile* vfs_file, int requested_lock) {
base::AutoLock lock(lock_);
const auto file_lock_state = GetFileLockStateLocked(vfs_file);
DCHECK_LE(requested_lock, file_lock_state.lock_level)
<< "Attempted to unlock to a higher lock level, unlock can only "
"decrement.";
// Shortcut if the caller doesn't currently hold a lock.
if (!file_lock_state.readers.contains(vfs_file) &&
file_lock_state.writer != vfs_file) {
DVLOG(1) << "caller can't unlock because it doesn't currently "
<< "hold a lock for file " << vfs_file->file_name;
return SQLITE_OK;
}
if (requested_lock == SQLITE_LOCK_NONE) {
locked_files_[vfs_file->file_name].readers.erase(vfs_file);
} else if (requested_lock == SQLITE_LOCK_SHARED) {
locked_files_[vfs_file->file_name].readers.insert(vfs_file);
}
if (requested_lock < SQLITE_LOCK_RESERVED &&
file_lock_state.writer == vfs_file) {
locked_files_[vfs_file->file_name].writer = nullptr;
}
// Check that `vfs_file` is correctly tracked given the `requested_lock`.
DCHECK(requested_lock == SQLITE_LOCK_SHARED ||
!locked_files_[vfs_file->file_name].readers.contains(vfs_file));
DCHECK_EQ(requested_lock > SQLITE_LOCK_SHARED,
locked_files_[vfs_file->file_name].writer == vfs_file);
// Mark lock level as shared if there are only shared usages.
if (!file_lock_state.readers.empty() && file_lock_state.writer == nullptr) {
locked_files_[vfs_file->file_name].lock_level = SQLITE_LOCK_SHARED;
return SQLITE_OK;
}
// Remove lock if there are no usages left.
if (file_lock_state.readers.empty() && file_lock_state.writer == nullptr) {
DCHECK_EQ(requested_lock, SQLITE_LOCK_NONE);
locked_files_.erase(vfs_file->file_name);
return SQLITE_OK;
}
if (file_lock_state.writer != vfs_file) {
DCHECK_GE(file_lock_state.lock_level, SQLITE_LOCK_RESERVED);
DCHECK_LE(requested_lock, SQLITE_LOCK_SHARED);
return SQLITE_OK;
}
locked_files_[vfs_file->file_name].lock_level = requested_lock;
return SQLITE_OK;
}
int CheckReservedLock(VfsFile* vfs_file, int* result) {
base::AutoLock lock(lock_);
const auto file_lock_state = GetFileLockStateLocked(vfs_file);
switch (file_lock_state.lock_level) {
case SQLITE_LOCK_NONE:
case SQLITE_LOCK_SHARED:
*result = 0;
return SQLITE_OK;
case SQLITE_LOCK_RESERVED:
case SQLITE_LOCK_PENDING:
case SQLITE_LOCK_EXCLUSIVE:
*result = 1;
return SQLITE_OK;
default:
return SQLITE_IOERR_CHECKRESERVEDLOCK;
}
}
private:
~FuchsiaFileLockManager() = delete;
const FileLock& GetFileLockStateLocked(VfsFile* vfs_file)
EXCLUSIVE_LOCKS_REQUIRED(lock_) {
static const FileLock kUnlockedFileLock = {.lock_level = SQLITE_LOCK_NONE};
const auto file_lock_state_iter = locked_files_.find(vfs_file->file_name);
if (file_lock_state_iter == locked_files_.end()) {
return kUnlockedFileLock;
}
return file_lock_state_iter->second;
}
base::Lock lock_;
// Set of all currently locked files.
base::flat_map<std::string, FileLock> locked_files_ GUARDED_BY(lock_);
};
} // namespace
int Lock(sqlite3_file* sqlite_file, int file_lock) {
DCHECK(file_lock == SQLITE_LOCK_SHARED || file_lock == SQLITE_LOCK_RESERVED ||
file_lock == SQLITE_LOCK_PENDING ||
file_lock == SQLITE_LOCK_EXCLUSIVE);
auto* vfs_file = reinterpret_cast<VfsFile*>(sqlite_file);
return FuchsiaFileLockManager::Instance()->Lock(vfs_file, file_lock);
}
int Unlock(sqlite3_file* sqlite_file, int file_lock) {
auto* vfs_file = reinterpret_cast<VfsFile*>(sqlite_file);
return FuchsiaFileLockManager::Instance()->Unlock(vfs_file, file_lock);
}
int CheckReservedLock(sqlite3_file* sqlite_file, int* result) {
auto* vfs_file = reinterpret_cast<VfsFile*>(sqlite_file);
return FuchsiaFileLockManager::Instance()->CheckReservedLock(vfs_file,
result);
}
} // namespace sql
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