Summary: Pull Request resolved: https://github.com/facebook/rocksdb/pull/4124 Differential Revision: D8829910 Pulled By: siying fbshipit-source-id: f3e952ccf3a631071a5d77c48e327046f8abb560main
Siying Dong
6 years ago
committed by
Facebook Github Bot
parent
995fcf7573
commit
ddc07b40fc
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// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
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// This source code is licensed under both the GPLv2 (found in the
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// COPYING file in the root directory) and Apache 2.0 License
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// (found in the LICENSE.Apache file in the root directory).
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#ifndef ROCKSDB_LITE |
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#include "db/managed_iterator.h" |
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#include <limits> |
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#include <string> |
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#include <utility> |
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#include "db/column_family.h" |
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#include "db/db_impl.h" |
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#include "db/db_iter.h" |
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#include "db/dbformat.h" |
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#include "rocksdb/env.h" |
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#include "rocksdb/slice.h" |
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#include "rocksdb/slice_transform.h" |
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#include "table/merging_iterator.h" |
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namespace rocksdb { |
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namespace { |
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// Helper class that locks a mutex on construction and unlocks the mutex when
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// the destructor of the MutexLock object is invoked.
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//
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// Typical usage:
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//
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// void MyClass::MyMethod() {
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// MILock l(&mu_); // mu_ is an instance variable
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// ... some complex code, possibly with multiple return paths ...
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// }
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class MILock { |
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public: |
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explicit MILock(std::mutex* mu, ManagedIterator* mi) : mu_(mu), mi_(mi) { |
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this->mu_->lock(); |
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} |
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~MILock() { |
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this->mu_->unlock(); |
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} |
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ManagedIterator* GetManagedIterator() { return mi_; } |
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private: |
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std::mutex* const mu_; |
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ManagedIterator* mi_; |
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// No copying allowed
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MILock(const MILock&) = delete; |
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void operator=(const MILock&) = delete; |
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}; |
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} // anonymous namespace
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//
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// Synchronization between modifiers, releasers, creators
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// If iterator operation, wait till (!in_use), set in_use, do op, reset in_use
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// if modifying mutable_iter, atomically exchange in_use:
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// return if in_use set / otherwise set in use,
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// atomically replace new iter with old , reset in use
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// The releaser is the new operation and it holds a lock for a very short time
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// The existing non-const iterator operations are supposed to be single
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// threaded and hold the lock for the duration of the operation
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// The existing const iterator operations use the cached key/values
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// and don't do any locking.
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ManagedIterator::ManagedIterator(DBImpl* db, const ReadOptions& read_options, |
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ColumnFamilyData* cfd) |
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: db_(db), |
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read_options_(read_options), |
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cfd_(cfd), |
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svnum_(cfd->GetSuperVersionNumber()), |
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mutable_iter_(nullptr), |
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valid_(false), |
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snapshot_created_(false), |
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release_supported_(true) { |
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read_options_.managed = false; |
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if ((!read_options_.tailing) && (read_options_.snapshot == nullptr)) { |
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assert(nullptr != (read_options_.snapshot = db_->GetSnapshot())); |
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snapshot_created_ = true; |
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} |
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cfh_.SetCFD(cfd); |
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mutable_iter_ = unique_ptr<Iterator>(db->NewIterator(read_options_, &cfh_)); |
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} |
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ManagedIterator::~ManagedIterator() { |
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Lock(); |
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if (snapshot_created_) { |
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db_->ReleaseSnapshot(read_options_.snapshot); |
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snapshot_created_ = false; |
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read_options_.snapshot = nullptr; |
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} |
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UnLock(); |
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} |
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bool ManagedIterator::Valid() const { return valid_; } |
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void ManagedIterator::SeekToLast() { |
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MILock l(&in_use_, this); |
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if (NeedToRebuild()) { |
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RebuildIterator(); |
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} |
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assert(mutable_iter_ != nullptr); |
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mutable_iter_->SeekToLast(); |
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UpdateCurrent(); |
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} |
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void ManagedIterator::SeekToFirst() { |
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MILock l(&in_use_, this); |
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SeekInternal(Slice(), true); |
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} |
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void ManagedIterator::Seek(const Slice& user_key) { |
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MILock l(&in_use_, this); |
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SeekInternal(user_key, false); |
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} |
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void ManagedIterator::SeekForPrev(const Slice& user_key) { |
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MILock l(&in_use_, this); |
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if (NeedToRebuild()) { |
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RebuildIterator(); |
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} |
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assert(mutable_iter_ != nullptr); |
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mutable_iter_->SeekForPrev(user_key); |
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UpdateCurrent(); |
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} |
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void ManagedIterator::SeekInternal(const Slice& user_key, bool seek_to_first) { |
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if (NeedToRebuild()) { |
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RebuildIterator(); |
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} |
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assert(mutable_iter_ != nullptr); |
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if (seek_to_first) { |
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mutable_iter_->SeekToFirst(); |
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} else { |
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mutable_iter_->Seek(user_key); |
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} |
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UpdateCurrent(); |
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} |
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void ManagedIterator::Prev() { |
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if (!valid_) { |
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status_ = Status::InvalidArgument("Iterator value invalid"); |
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return; |
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} |
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MILock l(&in_use_, this); |
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if (NeedToRebuild()) { |
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RebuildIterator(true); |
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if (!valid_) { |
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return; |
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} |
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} |
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mutable_iter_->Prev(); |
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UpdateCurrent(); |
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} |
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void ManagedIterator::Next() { |
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if (!valid_) { |
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status_ = Status::InvalidArgument("Iterator value invalid"); |
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return; |
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} |
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MILock l(&in_use_, this); |
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if (NeedToRebuild()) { |
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RebuildIterator(true); |
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if (!valid_) { |
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return; |
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} |
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} |
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mutable_iter_->Next(); |
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UpdateCurrent(); |
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} |
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Slice ManagedIterator::key() const { |
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assert(valid_); |
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return cached_key_.GetUserKey(); |
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} |
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Slice ManagedIterator::value() const { |
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assert(valid_); |
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return cached_value_.GetUserKey(); |
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} |
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Status ManagedIterator::status() const { return status_; } |
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void ManagedIterator::RebuildIterator(bool reseek) { |
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std::string current_key; |
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if (reseek) { |
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current_key = key().ToString(); |
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} |
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svnum_ = cfd_->GetSuperVersionNumber(); |
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mutable_iter_ = unique_ptr<Iterator>(db_->NewIterator(read_options_, &cfh_)); |
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if (reseek) { |
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Slice old_key(current_key.data(), current_key.size()); |
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SeekInternal(old_key, false); |
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UpdateCurrent(); |
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if (!valid_ || key().compare(old_key) != 0) { |
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valid_ = false; |
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status_ = Status::Incomplete( |
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"Next/Prev failed because current key has " |
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"been removed"); |
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} |
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} |
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} |
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void ManagedIterator::UpdateCurrent() { |
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assert(mutable_iter_ != nullptr); |
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valid_ = mutable_iter_->Valid(); |
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status_ = mutable_iter_->status(); |
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if (!valid_) { |
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return; |
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} |
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cached_key_.SetUserKey(mutable_iter_->key()); |
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cached_value_.SetUserKey(mutable_iter_->value()); |
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} |
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void ManagedIterator::ReleaseIter(bool only_old) { |
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if ((mutable_iter_ == nullptr) || (!release_supported_)) { |
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return; |
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} |
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if (svnum_ != cfd_->GetSuperVersionNumber() || !only_old) { |
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if (!TryLock()) { // Don't release iter if in use
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return; |
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} |
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mutable_iter_ = nullptr; // in_use for a very short time
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UnLock(); |
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} |
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} |
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bool ManagedIterator::NeedToRebuild() { |
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if ((mutable_iter_ == nullptr) || (status_.IsIncomplete()) || |
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(!only_drop_old_ && (svnum_ != cfd_->GetSuperVersionNumber()))) { |
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return true; |
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} |
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return false; |
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} |
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void ManagedIterator::Lock() { |
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in_use_.lock(); |
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return; |
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} |
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bool ManagedIterator::TryLock() { return in_use_.try_lock(); } |
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void ManagedIterator::UnLock() { |
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in_use_.unlock(); |
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} |
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} // namespace rocksdb
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#endif // ROCKSDB_LITE
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@ -1,85 +0,0 @@ |
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// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
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// This source code is licensed under both the GPLv2 (found in the
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// COPYING file in the root directory) and Apache 2.0 License
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// (found in the LICENSE.Apache file in the root directory).
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#pragma once |
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#ifndef ROCKSDB_LITE |
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#include <mutex> |
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#include <queue> |
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#include <string> |
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#include <vector> |
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#include "db/column_family.h" |
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#include "rocksdb/db.h" |
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#include "rocksdb/iterator.h" |
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#include "rocksdb/options.h" |
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#include "util/arena.h" |
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namespace rocksdb { |
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class DBImpl; |
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struct SuperVersion; |
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class ColumnFamilyData; |
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/**
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* ManagedIterator is a special type of iterator that supports freeing the |
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* underlying iterator and still being able to access the current key/value |
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* pair. This is done by copying the key/value pair so that clients can |
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* continue to access the data without getting a SIGSEGV. |
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* The underlying iterator can be freed manually through the call to |
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* ReleaseIter or automatically (as needed on space pressure or age.) |
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* The iterator is recreated using the saved original arguments. |
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*/ |
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class ManagedIterator : public Iterator { |
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public: |
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ManagedIterator(DBImpl* db, const ReadOptions& read_options, |
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ColumnFamilyData* cfd); |
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virtual ~ManagedIterator(); |
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virtual void SeekToLast() override; |
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virtual void Prev() override; |
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virtual bool Valid() const override; |
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void SeekToFirst() override; |
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virtual void Seek(const Slice& target) override; |
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virtual void SeekForPrev(const Slice& target) override; |
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virtual void Next() override; |
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virtual Slice key() const override; |
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virtual Slice value() const override; |
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virtual Status status() const override; |
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void ReleaseIter(bool only_old); |
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void SetDropOld(bool only_old) { |
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only_drop_old_ = read_options_.tailing || only_old; |
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} |
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private: |
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void RebuildIterator(bool reseek = false); |
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void UpdateCurrent(); |
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void SeekInternal(const Slice& user_key, bool seek_to_first); |
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bool NeedToRebuild(); |
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void Lock(); |
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bool TryLock(); |
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void UnLock(); |
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DBImpl* const db_; |
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ReadOptions read_options_; |
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ColumnFamilyData* const cfd_; |
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ColumnFamilyHandleInternal cfh_; |
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uint64_t svnum_; |
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std::unique_ptr<Iterator> mutable_iter_; |
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// internal iterator status
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Status status_; |
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bool valid_; |
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IterKey cached_key_; |
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IterKey cached_value_; |
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bool only_drop_old_ = true; |
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bool snapshot_created_; |
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bool release_supported_; |
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std::mutex in_use_; // is managed iterator in use
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}; |
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} // namespace rocksdb
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#endif // !ROCKSDB_LITE
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