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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
133 lines
3.9 KiB
C++
133 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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#ifndef GFLAGS
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#include <cstdio>
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int main() {
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fprintf(stderr, "Please install gflags to run rocksdb tools\n");
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return 1;
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}
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#else
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#include <atomic>
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#include <cstdio>
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#include "db/write_batch_internal.h"
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#include "rocksdb/db.h"
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#include "rocksdb/types.h"
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#include "test_util/testutil.h"
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#include "util/gflags_compat.h"
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// Run a thread to perform Put's.
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// Another thread uses GetUpdatesSince API to keep getting the updates.
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// options :
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// --num_inserts = the num of inserts the first thread should perform.
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// --wal_ttl = the wal ttl for the run.
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DEFINE_uint64(num_inserts, 1000,
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"the num of inserts the first thread should"
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" perform.");
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DEFINE_uint64(wal_ttl_seconds, 1000, "the wal ttl for the run(in seconds)");
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DEFINE_uint64(wal_size_limit_MB, 10,
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"the wal size limit for the run"
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"(in MB)");
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using ROCKSDB_NAMESPACE::BatchResult;
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using ROCKSDB_NAMESPACE::DB;
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using ROCKSDB_NAMESPACE::DestroyDB;
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using ROCKSDB_NAMESPACE::Env;
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using ROCKSDB_NAMESPACE::Options;
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using ROCKSDB_NAMESPACE::Random;
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using ROCKSDB_NAMESPACE::SequenceNumber;
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using ROCKSDB_NAMESPACE::Slice;
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using ROCKSDB_NAMESPACE::Status;
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using ROCKSDB_NAMESPACE::TransactionLogIterator;
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using ROCKSDB_NAMESPACE::WriteOptions;
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using GFLAGS_NAMESPACE::ParseCommandLineFlags;
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using GFLAGS_NAMESPACE::SetUsageMessage;
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struct DataPumpThread {
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DB* db; // Assumption DB is Open'ed already.
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};
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static void DataPumpThreadBody(void* arg) {
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DataPumpThread* t = static_cast<DataPumpThread*>(arg);
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DB* db = t->db;
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Random rnd(301);
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uint64_t i = 0;
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while (i++ < FLAGS_num_inserts) {
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if (!db->Put(WriteOptions(), Slice(rnd.RandomString(500)),
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Slice(rnd.RandomString(500)))
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.ok()) {
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fprintf(stderr, "Error in put\n");
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exit(1);
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}
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}
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}
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int main(int argc, const char** argv) {
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SetUsageMessage(
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std::string("\nUSAGE:\n") + std::string(argv[0]) +
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" --num_inserts=<num_inserts> --wal_ttl_seconds=<WAL_ttl_seconds>" +
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" --wal_size_limit_MB=<WAL_size_limit_MB>");
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ParseCommandLineFlags(&argc, const_cast<char***>(&argv), true);
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Env* env = Env::Default();
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std::string default_db_path;
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env->GetTestDirectory(&default_db_path);
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default_db_path += "db_repl_stress";
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Options options;
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options.create_if_missing = true;
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options.WAL_ttl_seconds = FLAGS_wal_ttl_seconds;
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options.WAL_size_limit_MB = FLAGS_wal_size_limit_MB;
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DB* db;
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DestroyDB(default_db_path, options);
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Status s = DB::Open(options, default_db_path, &db);
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if (!s.ok()) {
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fprintf(stderr, "Could not open DB due to %s\n", s.ToString().c_str());
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exit(1);
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}
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DataPumpThread dataPump;
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dataPump.db = db;
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env->StartThread(DataPumpThreadBody, &dataPump);
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std::unique_ptr<TransactionLogIterator> iter;
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SequenceNumber currentSeqNum = 1;
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uint64_t num_read = 0;
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for (;;) {
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iter.reset();
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// Continue to probe a bit more after all received
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size_t probes = 0;
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while (!db->GetUpdatesSince(currentSeqNum, &iter).ok()) {
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probes++;
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if (probes > 100 && num_read >= FLAGS_num_inserts) {
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if (num_read > FLAGS_num_inserts) {
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fprintf(stderr, "Too many updates read: %ld expected: %ld\n",
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(long)num_read, (long)FLAGS_num_inserts);
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exit(1);
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}
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fprintf(stderr, "Successful!\n");
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return 0;
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}
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}
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fprintf(stderr, "Refreshing iterator\n");
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for (; iter->Valid(); iter->Next(), num_read++, currentSeqNum++) {
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BatchResult res = iter->GetBatch();
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if (res.sequence != currentSeqNum) {
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fprintf(stderr, "Missed a seq no. b/w %ld and %ld\n",
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(long)currentSeqNum, (long)res.sequence);
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exit(1);
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}
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}
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}
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}
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#endif // GFLAGS
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