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54cb9c77d9
Summary: The following are risks associated with pointer-to-pointer reinterpret_cast: * Can produce the "wrong result" (crash or memory corruption). IIRC, in theory this can happen for any up-cast or down-cast for a non-standard-layout type, though in practice would only happen for multiple inheritance cases (where the base class pointer might be "inside" the derived object). We don't use multiple inheritance a lot, but we do. * Can mask useful compiler errors upon code change, including converting between unrelated pointer types that you are expecting to be related, and converting between pointer and scalar types unintentionally. I can only think of some obscure cases where static_cast could be troublesome when it compiles as a replacement: * Going through `void*` could plausibly cause unnecessary or broken pointer arithmetic. Suppose we have `struct Derived: public Base1, public Base2`. If we have `Derived*` -> `void*` -> `Base2*` -> `Derived*` through reinterpret casts, this could plausibly work (though technical UB) assuming the `Base2*` is not dereferenced. Changing to static cast could introduce breaking pointer arithmetic. * Unnecessary (but safe) pointer arithmetic could arise in a case like `Derived*` -> `Base2*` -> `Derived*` where before the Base2 pointer might not have been dereferenced. This could potentially affect performance. With some light scripting, I tried replacing pointer-to-pointer reinterpret_casts with static_cast and kept the cases that still compile. Most occurrences of reinterpret_cast have successfully been changed (except for java/ and third-party/). 294 changed, 257 remain. A couple of related interventions included here: * Previously Cache::Handle was not actually derived from in the implementations and just used as a `void*` stand-in with reinterpret_cast. Now there is a relationship to allow static_cast. In theory, this could introduce pointer arithmetic (as described above) but is unlikely without multiple inheritance AND non-empty Cache::Handle. * Remove some unnecessary casts to void* as this is allowed to be implicit (for better or worse). Most of the remaining reinterpret_casts are for converting to/from raw bytes of objects. We could consider better idioms for these patterns in follow-up work. I wish there were a way to implement a template variant of static_cast that would only compile if no pointer arithmetic is generated, but best I can tell, this is not possible. AFAIK the best you could do is a dynamic check that the void* conversion after the static cast is unchanged. Pull Request resolved: https://github.com/facebook/rocksdb/pull/12308 Test Plan: existing tests, CI Reviewed By: ltamasi Differential Revision: D53204947 Pulled By: pdillinger fbshipit-source-id: 9de23e618263b0d5b9820f4e15966876888a16e2
113 lines
3.9 KiB
C++
113 lines
3.9 KiB
C++
// 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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#include "utilities/transactions/optimistic_transaction_db_impl.h"
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#include <string>
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#include <vector>
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#include "db/db_impl/db_impl.h"
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#include "rocksdb/db.h"
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#include "rocksdb/options.h"
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#include "rocksdb/utilities/optimistic_transaction_db.h"
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#include "utilities/transactions/optimistic_transaction.h"
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namespace ROCKSDB_NAMESPACE {
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std::shared_ptr<OccLockBuckets> MakeSharedOccLockBuckets(size_t bucket_count,
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bool cache_aligned) {
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if (cache_aligned) {
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return std::make_shared<OccLockBucketsImpl<true>>(bucket_count);
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} else {
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return std::make_shared<OccLockBucketsImpl<false>>(bucket_count);
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}
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}
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Transaction* OptimisticTransactionDBImpl::BeginTransaction(
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const WriteOptions& write_options,
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const OptimisticTransactionOptions& txn_options, Transaction* old_txn) {
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if (old_txn != nullptr) {
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ReinitializeTransaction(old_txn, write_options, txn_options);
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return old_txn;
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} else {
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return new OptimisticTransaction(this, write_options, txn_options);
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}
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}
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Status OptimisticTransactionDB::Open(const Options& options,
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const std::string& dbname,
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OptimisticTransactionDB** dbptr) {
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DBOptions db_options(options);
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ColumnFamilyOptions cf_options(options);
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std::vector<ColumnFamilyDescriptor> column_families;
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column_families.push_back(
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ColumnFamilyDescriptor(kDefaultColumnFamilyName, cf_options));
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std::vector<ColumnFamilyHandle*> handles;
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Status s = Open(db_options, dbname, column_families, &handles, dbptr);
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if (s.ok()) {
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assert(handles.size() == 1);
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// i can delete the handle since DBImpl is always holding a reference to
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// default column family
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delete handles[0];
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}
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return s;
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}
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Status OptimisticTransactionDB::Open(
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const DBOptions& db_options, const std::string& dbname,
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const std::vector<ColumnFamilyDescriptor>& column_families,
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std::vector<ColumnFamilyHandle*>* handles,
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OptimisticTransactionDB** dbptr) {
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return OptimisticTransactionDB::Open(db_options,
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OptimisticTransactionDBOptions(), dbname,
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column_families, handles, dbptr);
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}
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Status OptimisticTransactionDB::Open(
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const DBOptions& db_options,
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const OptimisticTransactionDBOptions& occ_options,
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const std::string& dbname,
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const std::vector<ColumnFamilyDescriptor>& column_families,
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std::vector<ColumnFamilyHandle*>* handles,
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OptimisticTransactionDB** dbptr) {
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Status s;
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DB* db;
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std::vector<ColumnFamilyDescriptor> column_families_copy = column_families;
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// Enable MemTable History if not already enabled
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for (auto& column_family : column_families_copy) {
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ColumnFamilyOptions* options = &column_family.options;
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if (options->max_write_buffer_size_to_maintain == 0 &&
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options->max_write_buffer_number_to_maintain == 0) {
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// Setting to -1 will set the History size to
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// max_write_buffer_number * write_buffer_size.
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options->max_write_buffer_size_to_maintain = -1;
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}
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}
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s = DB::Open(db_options, dbname, column_families_copy, handles, &db);
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if (s.ok()) {
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*dbptr = new OptimisticTransactionDBImpl(db, occ_options);
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}
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return s;
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}
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void OptimisticTransactionDBImpl::ReinitializeTransaction(
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Transaction* txn, const WriteOptions& write_options,
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const OptimisticTransactionOptions& txn_options) {
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assert(dynamic_cast<OptimisticTransaction*>(txn) != nullptr);
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auto txn_impl = static_cast<OptimisticTransaction*>(txn);
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txn_impl->Reinitialize(this, write_options, txn_options);
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}
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} // namespace ROCKSDB_NAMESPACE
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