rocksdb/db/managed_iterator.cc

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// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
// This source code is licensed under the BSD-style license found in the
// LICENSE file in the root directory of this source tree. An additional grant
// of patent rights can be found in the PATENTS file in the same directory.
#ifndef ROCKSDB_LITE
#include "db/managed_iterator.h"
#include <limits>
#include <string>
#include <utility>
#include "db/column_family.h"
#include "db/db_impl.h"
#include "db/db_iter.h"
#include "db/dbformat.h"
#include "rocksdb/env.h"
#include "rocksdb/slice.h"
#include "rocksdb/slice_transform.h"
#include "table/merging_iterator.h"
namespace rocksdb {
namespace {
// Helper class that locks a mutex on construction and unlocks the mutex when
// the destructor of the MutexLock object is invoked.
//
// Typical usage:
//
// void MyClass::MyMethod() {
// MILock l(&mu_); // mu_ is an instance variable
// ... some complex code, possibly with multiple return paths ...
// }
class MILock {
public:
explicit MILock(std::mutex* mu, ManagedIterator* mi) : mu_(mu), mi_(mi) {
this->mu_->lock();
}
~MILock() {
this->mu_->unlock();
}
ManagedIterator* GetManagedIterator() { return mi_; }
private:
std::mutex* const mu_;
ManagedIterator* mi_;
// No copying allowed
MILock(const MILock&) = delete;
void operator=(const MILock&) = delete;
};
} // anonymous namespace
//
// Synchronization between modifiers, releasers, creators
// If iterator operation, wait till (!in_use), set in_use, do op, reset in_use
// if modifying mutable_iter, atomically exchange in_use:
// return if in_use set / otherwise set in use,
// atomically replace new iter with old , reset in use
// The releaser is the new operation and it holds a lock for a very short time
// The existing non-const iterator operations are supposed to be single
// threaded and hold the lock for the duration of the operation
// The existing const iterator operations use the cached key/values
// and don't do any locking.
ManagedIterator::ManagedIterator(DBImpl* db, const ReadOptions& read_options,
ColumnFamilyData* cfd)
: db_(db),
read_options_(read_options),
cfd_(cfd),
svnum_(cfd->GetSuperVersionNumber()),
mutable_iter_(nullptr),
valid_(false),
snapshot_created_(false),
release_supported_(true) {
read_options_.managed = false;
if ((!read_options_.tailing) && (read_options_.snapshot == nullptr)) {
assert(nullptr != (read_options_.snapshot = db_->GetSnapshot()));
snapshot_created_ = true;
}
cfh_.SetCFD(cfd);
mutable_iter_ = unique_ptr<Iterator>(db->NewIterator(read_options_, &cfh_));
}
ManagedIterator::~ManagedIterator() {
Lock();
if (snapshot_created_) {
db_->ReleaseSnapshot(read_options_.snapshot);
snapshot_created_ = false;
read_options_.snapshot = nullptr;
}
UnLock();
}
bool ManagedIterator::Valid() const { return valid_; }
void ManagedIterator::SeekToLast() {
MILock l(&in_use_, this);
if (NeedToRebuild()) {
RebuildIterator();
}
assert(mutable_iter_ != nullptr);
mutable_iter_->SeekToLast();
if (mutable_iter_->status().ok()) {
UpdateCurrent();
}
}
void ManagedIterator::SeekToFirst() {
MILock l(&in_use_, this);
SeekInternal(Slice(), true);
}
void ManagedIterator::Seek(const Slice& user_key) {
MILock l(&in_use_, this);
SeekInternal(user_key, false);
}
void ManagedIterator::SeekForPrev(const Slice& user_key) {
MILock l(&in_use_, this);
if (NeedToRebuild()) {
RebuildIterator();
}
assert(mutable_iter_ != nullptr);
mutable_iter_->SeekForPrev(user_key);
UpdateCurrent();
}
void ManagedIterator::SeekInternal(const Slice& user_key, bool seek_to_first) {
if (NeedToRebuild()) {
RebuildIterator();
}
assert(mutable_iter_ != nullptr);
if (seek_to_first) {
mutable_iter_->SeekToFirst();
} else {
mutable_iter_->Seek(user_key);
}
UpdateCurrent();
}
void ManagedIterator::Prev() {
if (!valid_) {
status_ = Status::InvalidArgument("Iterator value invalid");
return;
}
MILock l(&in_use_, this);
if (NeedToRebuild()) {
std::string current_key = key().ToString();
Slice old_key(current_key);
RebuildIterator();
SeekInternal(old_key, false);
UpdateCurrent();
if (!valid_) {
return;
}
if (key().compare(old_key) != 0) {
valid_ = false;
status_ = Status::Incomplete("Cannot do Prev now");
return;
}
}
mutable_iter_->Prev();
if (mutable_iter_->status().ok()) {
UpdateCurrent();
status_ = Status::OK();
} else {
status_ = mutable_iter_->status();
}
}
void ManagedIterator::Next() {
if (!valid_) {
status_ = Status::InvalidArgument("Iterator value invalid");
return;
}
MILock l(&in_use_, this);
if (NeedToRebuild()) {
std::string current_key = key().ToString();
Slice old_key(current_key.data(), cached_key_.Size());
RebuildIterator();
SeekInternal(old_key, false);
UpdateCurrent();
if (!valid_) {
return;
}
if (key().compare(old_key) != 0) {
valid_ = false;
status_ = Status::Incomplete("Cannot do Next now");
return;
}
}
mutable_iter_->Next();
UpdateCurrent();
}
Slice ManagedIterator::key() const {
assert(valid_);
return cached_key_.GetKey();
}
Slice ManagedIterator::value() const {
assert(valid_);
return cached_value_.GetKey();
}
Status ManagedIterator::status() const { return status_; }
void ManagedIterator::RebuildIterator() {
svnum_ = cfd_->GetSuperVersionNumber();
mutable_iter_ = unique_ptr<Iterator>(db_->NewIterator(read_options_, &cfh_));
}
void ManagedIterator::UpdateCurrent() {
assert(mutable_iter_ != nullptr);
valid_ = mutable_iter_->Valid();
if (!valid_) {
status_ = mutable_iter_->status();
return;
}
status_ = Status::OK();
cached_key_.SetKey(mutable_iter_->key());
cached_value_.SetKey(mutable_iter_->value());
}
void ManagedIterator::ReleaseIter(bool only_old) {
if ((mutable_iter_ == nullptr) || (!release_supported_)) {
return;
}
if (svnum_ != cfd_->GetSuperVersionNumber() || !only_old) {
if (!TryLock()) { // Don't release iter if in use
return;
}
mutable_iter_ = nullptr; // in_use for a very short time
UnLock();
}
}
bool ManagedIterator::NeedToRebuild() {
if ((mutable_iter_ == nullptr) || (status_.IsIncomplete()) ||
(!only_drop_old_ && (svnum_ != cfd_->GetSuperVersionNumber()))) {
return true;
}
return false;
}
void ManagedIterator::Lock() {
in_use_.lock();
return;
}
bool ManagedIterator::TryLock() { return in_use_.try_lock(); }
void ManagedIterator::UnLock() {
in_use_.unlock();
}
} // namespace rocksdb
#endif // ROCKSDB_LITE