Require C++20 (#13904)

Summary:
I am wanting to use std::counting_semaphore for something and the timing seems good to require C++20 support. The internets suggest:

* GCC >= 10 is adequate, >= 11 preferred
* Clang >= 10 is needed
* Visual Studio >= 2019 is adquate

And popular linux distributions look like this:
* CentOS Stream 9 -> GCC 11.2  (CentOS 8 is EOL)
* Ubuntu 22.04 LTS -> GCC 11.x  (Ubuntu 20 just ended standard support)
* Debian 12 (oldstable) -> GCC 12.2
  * (Debian 11 has ended security updates, uses GCC 10.2)

This required generating a new docker image based on Ubuntu 22 for CI using gcc. The existing Ubuntu 20 image works for covering appropriate clang versions (though we should maybe add a much later version as well, in the next increment of our Ubuntu 22 image; however the minimum available clang build from apt.llvm.org for Ubuntu 22 is clang 13).

Update to SetDumpFilter is to quiet a mysterious gcc-13 warning-as-error.

Removed --compile-no-warning-as-error from a cmake command line because cmake in the new docker image is too old for this option.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/13904

Test Plan: CI, one minor unit test added to verify std::counting_semaphor works

Reviewed By: xingbowang

Differential Revision: D81266435

Pulled By: pdillinger

fbshipit-source-id: 26040eeccca7004416e29a6ff4f6ea93f2052684

.github/workflows/nightly.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on:
       labels: 16-core-ubuntu
     container:
-      image: zjay437/rocksdb:0.6
+      image: ghcr.io/facebook/rocksdb_ubuntu:22.0
       options: --shm-size=16gb
     steps:
     - uses: actions/checkout@v4.1.0
@@ -32,7 +32,7 @@ jobs:
     runs-on:
       labels: 16-core-ubuntu
     container:
-      image: zjay437/rocksdb:0.6
+      image: ghcr.io/facebook/rocksdb_ubuntu:22.0
       options: --shm-size=16gb
     env:
       TEST_TMPDIR: "/tmp/rocksdb_test_tmp"
@@ -63,7 +63,7 @@ jobs:
     runs-on:
       labels: 16-core-ubuntu
     container:
-      image: zjay437/rocksdb:0.6
+      image: ghcr.io/facebook/rocksdb_ubuntu:22.0
       options: --shm-size=16gb
     steps:
     - uses: actions/checkout@v4.1.0
@@ -94,7 +94,7 @@ jobs:
     runs-on:
       labels: 4-core-ubuntu
     container:
-      image: zjay437/rocksdb:0.6
+      image: ghcr.io/facebook/rocksdb_ubuntu:22.0
       options: --shm-size=16gb
     steps:
     - uses: actions/checkout@v4.1.0
@@ -117,28 +117,13 @@ jobs:
     - name: Build fuzzers
       run: cd fuzz && make sst_file_writer_fuzzer db_fuzzer db_map_fuzzer
     - uses: "./.github/actions/post-steps"
-  build-linux-gcc-11-no_test_run:
-    if: ${{ github.repository_owner == 'facebook' }}
-    runs-on:
-      labels: 16-core-ubuntu
-    container:
-      image: zjay437/rocksdb:0.6
-      options: --shm-size=16gb
-    steps:
-    - uses: actions/checkout@v4.1.0
-    - uses: "./.github/actions/pre-steps"
-    - run: LIB_MODE=static CC=gcc-11 CXX=g++-11 V=1 make -j32 all microbench
-    - uses: "./.github/actions/post-steps"
   build-linux-cmake-with-folly-lite-no-test:
     if: ${{ github.repository_owner == 'facebook' }}
     runs-on:
       labels: 16-core-ubuntu
     container:
-      image: zjay437/rocksdb:0.6
+      image: ghcr.io/facebook/rocksdb_ubuntu:22.0
       options: --shm-size=16gb
-    env:
-      CC: gcc-10
-      CXX: g++-10
     steps:
     - uses: actions/checkout@v4.1.0
     - uses: "./.github/actions/pre-steps"

.github/workflows/pr-jobs.yml

@@ -66,7 +66,7 @@ jobs:
     runs-on:
       labels: 16-core-ubuntu
     container:
-      image: zjay437/rocksdb:0.6
+      image: ghcr.io/facebook/rocksdb_ubuntu:22.0
       options: --shm-size=16gb
     steps:
     - uses: actions/checkout@v4.1.0
@@ -78,7 +78,7 @@ jobs:
     runs-on:
       labels: 4-core-ubuntu
     container:
-      image: zjay437/rocksdb:0.6
+      image: ghcr.io/facebook/rocksdb_ubuntu:22.0
       options: --shm-size=16gb
     steps:
     - uses: actions/checkout@v4.1.0
@@ -97,11 +97,8 @@ jobs:
     runs-on:
       labels: 16-core-ubuntu
     container:
-      image: zjay437/rocksdb:0.6
+      image: ghcr.io/facebook/rocksdb_ubuntu:22.0
       options: --shm-size=16gb
-    env:
-      CC: gcc-10
-      CXX: g++-10
     steps:
     - uses: actions/checkout@v4.1.0
     - uses: "./.github/actions/pre-steps"
@@ -114,11 +111,8 @@ jobs:
     runs-on:
       labels: 16-core-ubuntu
     container:
-      image: zjay437/rocksdb:0.6
+      image: ghcr.io/facebook/rocksdb_ubuntu:22.0
       options: --shm-size=16gb
-    env:
-      CC: gcc-10
-      CXX: g++-10
     steps:
     - uses: actions/checkout@v4.1.0
     - uses: "./.github/actions/pre-steps"
@@ -131,11 +125,8 @@ jobs:
     runs-on:
       labels: 16-core-ubuntu
     container:
-      image: zjay437/rocksdb:0.6
+      image: ghcr.io/facebook/rocksdb_ubuntu:22.0
       options: --shm-size=16gb
-    env:
-      CC: gcc-10
-      CXX: g++-10
     steps:
     - uses: actions/checkout@v4.1.0
     - uses: "./.github/actions/pre-steps"
@@ -147,11 +138,8 @@ jobs:
     runs-on:
       labels: 16-core-ubuntu
     container:
-      image: zjay437/rocksdb:0.6
+      image: ghcr.io/facebook/rocksdb_ubuntu:22.0
       options: --shm-size=16gb
-    env:
-      CC: gcc-10
-      CXX: g++-10
     steps:
     - uses: actions/checkout@v4.1.0
     - uses: "./.github/actions/pre-steps"
@@ -164,7 +152,7 @@ jobs:
     runs-on:
       labels: 16-core-ubuntu
     container:
-      image: zjay437/rocksdb:0.6
+      image: ghcr.io/facebook/rocksdb_ubuntu:22.0
       options: --shm-size=16gb
     steps:
     - uses: actions/checkout@v4.1.0
@@ -176,7 +164,7 @@ jobs:
     runs-on:
       labels: 16-core-ubuntu
     container:
-      image: zjay437/rocksdb:0.6
+      image: ghcr.io/facebook/rocksdb_ubuntu:22.0
       options: --shm-size=16gb
     steps:
     - uses: actions/checkout@v4.1.0
@@ -190,7 +178,7 @@ jobs:
     runs-on:
       labels: 16-core-ubuntu
     container:
-      image: zjay437/rocksdb:0.6
+      image: ghcr.io/facebook/rocksdb_ubuntu:22.0
       options: --shm-size=16gb
     steps:
     - uses: actions/checkout@v4.1.0
@@ -236,29 +224,17 @@ jobs:
     - run: make clean
     - run: CC=clang-13 CXX=clang++-13 USE_CLANG=1 DEBUG_LEVEL=0 make -j32 release
     - uses: "./.github/actions/post-steps"
-  build-linux-gcc-8-no_test_run:
+  build-linux-gcc-13-no_test_run:
     if: ${{ github.repository_owner == 'facebook' }}
     runs-on:
       labels: 16-core-ubuntu
     container:
-      image: zjay437/rocksdb:0.6
+      image: ghcr.io/facebook/rocksdb_ubuntu:22.0
       options: --shm-size=16gb
     steps:
     - uses: actions/checkout@v4.1.0
     - uses: "./.github/actions/pre-steps"
-    - run: CC=gcc-8 CXX=g++-8 V=1 make -j32 all
-    - uses: "./.github/actions/post-steps"
-  build-linux-gcc-10-cxx20-no_test_run:
-    if: ${{ github.repository_owner == 'facebook' }}
-    runs-on:
-      labels: 16-core-ubuntu
-    container:
-      image: zjay437/rocksdb:0.6
-      options: --shm-size=16gb
-    steps:
-    - uses: actions/checkout@v4.1.0
-    - uses: "./.github/actions/pre-steps"
-    - run: CC=gcc-10 CXX=g++-10 V=1 ROCKSDB_CXX_STANDARD=c++20 make -j32 all
+    - run: CC=gcc-13 CXX=g++-13 V=1 make -j32 all microbench
     - uses: "./.github/actions/post-steps"
 
   # ======================== Linux Other Checks ======================= #
@@ -300,7 +276,7 @@ jobs:
     runs-on:
       labels: 4-core-ubuntu
     container:
-      image: zjay437/rocksdb:0.6
+      image: ghcr.io/facebook/rocksdb_ubuntu:22.0
       options: --shm-size=16gb
     steps:
     - uses: actions/checkout@v4.1.0
@@ -337,7 +313,7 @@ jobs:
     runs-on:
       labels: 16-core-ubuntu
     container:
-      image: zjay437/rocksdb:0.6
+      image: ghcr.io/facebook/rocksdb_ubuntu:22.0
       options: --shm-size=16gb
     steps:
     - uses: actions/checkout@v4.1.0
@@ -404,11 +380,13 @@ jobs:
     runs-on:
       labels: 4-core-ubuntu
     container:
-      image: evolvedbinary/rocksjava:centos7_x64-be
+      image: ghcr.io/facebook/rocksdb_ubuntu:22.0
       options: --shm-size=16gb
     steps:
     # The docker image is intentionally based on an OS that has an older GLIBC version.
     # That GLIBC is incompatibile with GitHub's actions/checkout. Thus we implement a manual checkout step.
+    # NOTE: replaced evolvedbinary/rocksjava:centos7_x64-be with ghcr.io/facebook/rocksdb_ubuntu:22.0
+    # until a more appropriate docker image with C++20 support is made.
     - name: Checkout
       env:
         GH_TOKEN: ${{ github.token }}
@@ -425,18 +403,21 @@ jobs:
         which java && java -version
         which javac && javac -version
     - name: Test RocksDBJava
-      run: scl enable devtoolset-7 'make V=1 J=8 -j8 jtest'
-    # NOTE: post-steps skipped because of compatibility issues with docker image
+    # NOTE: replaced scl enable devtoolset-7 'make V=1 J=8 -j8 jtest'
+      run: make V=1 J=8 -j8 jtest
+    # post-steps skipped because of compatibility issues with docker image
   build-linux-java-static:
     if: ${{ github.repository_owner == 'facebook' }}
     runs-on:
       labels: 4-core-ubuntu
     container:
-      image: evolvedbinary/rocksjava:centos7_x64-be
+      image: ghcr.io/facebook/rocksdb_ubuntu:22.0
       options: --shm-size=16gb
     steps:
     # The docker image is intentionally based on an OS that has an older GLIBC version.
     # That GLIBC is incompatibile with GitHub's actions/checkout. Thus we implement a manual checkout step.
+    # NOTE: replaced evolvedbinary/rocksjava:centos7_x64-be with ghcr.io/facebook/rocksdb_ubuntu:22.0
+    # until a more appropriate docker image with C++20 support is made.
     - name: Checkout
       env:
         GH_TOKEN: ${{ github.token }}
@@ -453,8 +434,9 @@ jobs:
         which java && java -version
         which javac && javac -version
     - name: Build RocksDBJava Static Library
-      run: scl enable devtoolset-7 'make V=1 J=8 -j8 rocksdbjavastatic'
-    # NOTE: post-steps skipped because of compatibility issues with docker image
+    # NOTE: replaced scl enable devtoolset-7 'make V=1 J=8 -j8 rocksdbjavastatic'
+      run: make V=1 J=8 -j8 rocksdbjavastatic
+    # post-steps skipped because of compatibility issues with docker image
   build-macos-java:
     if: ${{ github.repository_owner == 'facebook' }}
     runs-on: macos-13

CMakeLists.txt

@@ -27,7 +27,7 @@
 #
 # Linux:
 #
-# 1. Install a recent toolchain if you're on a older distro. C++17 required (GCC >= 7, Clang >= 5)
+# 1. Install a recent toolchain if you're on a older distro. C++20 required (GCC >= 11, Clang >= 10)
 # 2. mkdir build; cd build
 # 3. cmake ..
 # 4. make -j
@@ -100,7 +100,7 @@ endif()
 option(ROCKSDB_BUILD_SHARED "Build shared versions of the RocksDB libraries" ON)
 
 if( NOT DEFINED CMAKE_CXX_STANDARD )
-  set(CMAKE_CXX_STANDARD 17)
+  set(CMAKE_CXX_STANDARD 20)
 endif()
 
 include(CMakeDependentOption)
@@ -314,7 +314,6 @@ endif()
 
 # Check if -latomic is required or not
 if (NOT MSVC)
-  set(CMAKE_REQUIRED_FLAGS "--std=c++17")
   CHECK_CXX_SOURCE_COMPILES("
 #include <atomic>
 std::atomic<uint64_t> x(0);

INSTALL.md

@@ -6,7 +6,7 @@ than release mode.
 
 RocksDB's library should be able to compile without any dependency installed,
 although we recommend installing some compression libraries (see below).
-We do depend on newer gcc/clang with C++17 support (GCC >= 7, Clang >= 5).
+We do depend on newer gcc/clang with C++20 support (GCC >= 11, Clang >= 10).
 
 There are few options when compiling RocksDB:
 
@@ -60,7 +60,7 @@ most processors made since roughly 2013.
 ## Supported platforms
 
 * **Linux - Ubuntu**
-    * Upgrade your gcc to version at least 7 to get C++17 support.
+    * Upgrade your gcc to version at least 11 to get C++20 support.
     * Install gflags. First, try: `sudo apt-get install libgflags-dev`
       If this doesn't work and you're using Ubuntu, here's a nice tutorial:
       (http://askubuntu.com/questions/312173/installing-gflags-12-04)
@@ -72,7 +72,7 @@ most processors made since roughly 2013.
     * Install zstandard: `sudo apt-get install libzstd-dev`.
 
 * **Linux - CentOS / RHEL**
-    * Upgrade your gcc to version at least 7 to get C++17 support
+    * Upgrade your gcc to version at least 11 to get C++20 support
     * Install gflags:
 
               git clone https://github.com/gflags/gflags.git
@@ -122,7 +122,7 @@ most processors made since roughly 2013.
               make && sudo make install
 
 * **OS X**:
-    * Install latest C++ compiler that supports C++ 17:
+    * Install latest C++ compiler that supports C++20:
         * Update XCode:  run `xcode-select --install` (or install it from XCode App's settting).
         * Install via [homebrew](http://brew.sh/).
             * If you're first time developer in MacOS, you still need to run: `xcode-select --install` in your command line.
@@ -213,7 +213,7 @@ most processors made since roughly 2013.
              export PATH=/opt/freeware/bin:$PATH
 
 * **Solaris Sparc**
-    * Install GCC 7 and higher.
+    * Install GCC 11 and higher.
     * Use these environment variables:
 
              export CC=gcc

Makefile

@@ -148,10 +148,8 @@ ifeq ($(USE_COROUTINES), 1)
 	USE_FOLLY = 1
 	# glog/logging.h requires HAVE_CXX11_ATOMIC
 	OPT += -DUSE_COROUTINES -DHAVE_CXX11_ATOMIC
-	ROCKSDB_CXX_STANDARD = c++2a
 	USE_RTTI = 1
 ifneq ($(USE_CLANG), 1)
-	ROCKSDB_CXX_STANDARD = c++20
 	PLATFORM_CXXFLAGS += -fcoroutines
 endif
 endif
@@ -683,7 +681,7 @@ am__v_CCH_1 =
 # user build settings
 %.h.pub: %.h # .h.pub not actually created, so re-checked on each invocation
 	$(AM_V_CCH) cd include/ && echo '#include "$(patsubst include/%,%,$<)"' | \
-	  $(CXX) -I. -DROCKSDB_NAMESPACE=42 -x c++ -c - -o /dev/null
+	  $(CXX) -std=$(or $(ROCKSDB_CXX_STANDARD),c++20) -I. -DROCKSDB_NAMESPACE=42 -x c++ -c - -o /dev/null
 
 check-headers: $(HEADER_OK_FILES)
 
@@ -2251,7 +2249,7 @@ libsnappy.a: snappy-$(SNAPPY_VER).tar.gz
 	-rm -rf snappy-$(SNAPPY_VER)
 	tar xvzf snappy-$(SNAPPY_VER).tar.gz
 	mkdir snappy-$(SNAPPY_VER)/build
-	cd snappy-$(SNAPPY_VER)/build && CFLAGS='$(ARCHFLAG) ${JAVA_STATIC_DEPS_CCFLAGS} ${EXTRA_CFLAGS}' CXXFLAGS='$(ARCHFLAG) ${JAVA_STATIC_DEPS_CXXFLAGS} ${EXTRA_CXXFLAGS}' LDFLAGS='${JAVA_STATIC_DEPS_LDFLAGS} ${EXTRA_LDFLAGS}' cmake -DCMAKE_POSITION_INDEPENDENT_CODE=ON -DSNAPPY_BUILD_BENCHMARKS=OFF -DSNAPPY_BUILD_TESTS=OFF --compile-no-warning-as-error ${PLATFORM_CMAKE_FLAGS} .. && $(MAKE) ${SNAPPY_MAKE_TARGET}
+	cd snappy-$(SNAPPY_VER)/build && CFLAGS='$(ARCHFLAG) ${JAVA_STATIC_DEPS_CCFLAGS} ${EXTRA_CFLAGS}' CXXFLAGS='$(ARCHFLAG) ${JAVA_STATIC_DEPS_CXXFLAGS} ${EXTRA_CXXFLAGS}' LDFLAGS='${JAVA_STATIC_DEPS_LDFLAGS} ${EXTRA_LDFLAGS}' cmake -DCMAKE_POSITION_INDEPENDENT_CODE=ON -DSNAPPY_BUILD_BENCHMARKS=OFF -DSNAPPY_BUILD_TESTS=OFF ${PLATFORM_CMAKE_FLAGS} .. && $(MAKE) ${SNAPPY_MAKE_TARGET}
 	cp snappy-$(SNAPPY_VER)/build/libsnappy.a .
 
 lz4-$(LZ4_VER).tar.gz:

build_tools/build_detect_platform

@@ -45,11 +45,11 @@ if test -z "$OUTPUT"; then
   exit 1
 fi
 
-# we depend on C++17, but should be compatible with newer standards
+# we depend on C++20, but should be compatible with newer standards
 if [ "$ROCKSDB_CXX_STANDARD" ]; then
   PLATFORM_CXXFLAGS="-std=$ROCKSDB_CXX_STANDARD"
 else
-  PLATFORM_CXXFLAGS="-std=c++17"
+  PLATFORM_CXXFLAGS="-std=c++20"
 fi
 
 # we currently depend on POSIX platform

build_tools/ubuntu22_image/Dockerfile

@@ -0,0 +1,80 @@
+# INSTRUCTIONS:
+# I was not about to build docker images on an isolated devserver because of
+# issues with proxy internet access. Use a public cloud or other Linux system.
+# (I used a Debian system after installing docker features, adding my user to
+# the docker and docker-registry groups, and logging out and back in to pick
+# those up.)
+#
+# Follow https://docs.github.com/en/packages/working-with-a-github-packages-registry/working-with-the-container-registry#authenticating-with-a-personal-access-token-classic
+# to login with your GitHub credentials, as in
+#
+# $ docker login ghcr.io -u pdillinger
+#
+# and paste the limited-purpose GitHub token into the terminal.
+#
+# Then in the build_tools/ubuntu22_image directory, (bump minor version for
+# random docker file updates, major version tracks Ubuntu release)
+#
+# $ docker build -t ghcr.io/facebook/rocksdb_ubuntu:22.0
+# $ docker push ghcr.io/facebook/rocksdb_ubuntu:22.0
+#
+# Might need to change visibility to public through
+# https://github.com/orgs/facebook/packages/container/rocksdb_ubuntu/settings
+# or similar.
+
+# from official ubuntu 22.04
+FROM ubuntu:22.04
+# update system
+RUN apt-get update
+RUN apt-get upgrade -y
+# install basic tools
+RUN apt-get install -y vim wget curl
+# install tzdata noninteractive
+RUN DEBIAN_FRONTEND=noninteractive TZ=Etc/UTC apt-get -y install tzdata
+# install git and default compilers
+RUN apt-get install -y git gcc g++ clang clang-tools
+# install basic package
+RUN apt-get install -y lsb-release software-properties-common gnupg
+# install gflags, tbb
+RUN apt-get install -y libgflags-dev libtbb-dev
+# install compression libs
+RUN apt-get install -y libsnappy-dev zlib1g-dev libbz2-dev liblz4-dev libzstd-dev
+# install cmake
+RUN apt-get install -y cmake
+RUN apt-get install -y libssl-dev
+# install clang-13
+WORKDIR /root
+RUN wget https://apt.llvm.org/llvm.sh
+RUN chmod +x llvm.sh
+RUN ./llvm.sh 13 all
+# install gcc-10 and more, default is 11
+RUN apt-get install -y gcc-10 g++-10
+RUN add-apt-repository -y ppa:ubuntu-toolchain-r/test
+RUN apt-get install -y gcc-13 g++-13
+# install apt-get install -y valgrind
+RUN apt-get install -y valgrind
+# install folly depencencies
+RUN apt-get install -y libunwind-dev libgoogle-glog-dev
+# install openjdk 8
+RUN apt-get install -y openjdk-8-jdk
+ENV JAVA_HOME /usr/lib/jvm/java-1.8.0-openjdk-amd64
+# install mingw
+RUN apt-get install -y mingw-w64
+
+# install gtest-parallel package
+RUN git clone --single-branch --branch master --depth 1 https://github.com/google/gtest-parallel.git ~/gtest-parallel
+ENV PATH $PATH:/root/gtest-parallel
+
+# install libprotobuf for fuzzers test
+RUN apt-get install -y ninja-build binutils liblzma-dev libz-dev pkg-config autoconf libtool
+RUN git clone --branch v1.0 https://github.com/google/libprotobuf-mutator.git ~/libprotobuf-mutator && cd ~/libprotobuf-mutator && git checkout ffd86a32874e5c08a143019aad1aaf0907294c9f && mkdir build && cd build && cmake .. -GNinja -DCMAKE_C_COMPILER=clang-13 -DCMAKE_CXX_COMPILER=clang++-13 -DCMAKE_BUILD_TYPE=Release -DLIB_PROTO_MUTATOR_DOWNLOAD_PROTOBUF=ON && ninja && ninja install
+ENV PKG_CONFIG_PATH /usr/local/OFF/:/root/libprotobuf-mutator/build/external.protobuf/lib/pkgconfig/
+ENV PROTOC_BIN /root/libprotobuf-mutator/build/external.protobuf/bin/protoc
+
+# install the latest google benchmark
+RUN git clone --depth 1 --branch v1.7.0 https://github.com/google/benchmark.git ~/benchmark
+RUN cd ~/benchmark && mkdir build && cd build && cmake .. -GNinja -DCMAKE_BUILD_TYPE=Release -DBENCHMARK_ENABLE_GTEST_TESTS=0 && ninja && ninja install
+
+# clean up
+RUN rm -rf /var/lib/apt/lists/*
+RUN rm -rf /root/benchmark

db/db_impl/db_impl.cc

@@ -1245,13 +1245,11 @@ Status DBImpl::SetOptions(
           WriteOptionsFile(write_options, true /*db_mutex_already_held*/);
       bg_cv_.SignalAll();
 
-#if __cplusplus >= 202002L
       assert(new_options_copy == cfd->GetLatestMutableCFOptions());
       assert(cfd->GetLatestMutableCFOptions() ==
              cfd->GetCurrentMutableCFOptions());
       assert(cfd->GetCurrentMutableCFOptions() ==
              cfd->current()->GetMutableCFOptions());
-#endif
     }
   }
   sv_context.Clean();

examples/Makefile

@@ -19,16 +19,16 @@ CFLAGS += -Wstrict-prototypes
 all: simple_example column_families_example compact_files_example c_simple_example optimistic_transaction_example transaction_example compaction_filter_example options_file_example rocksdb_backup_restore_example
 
 simple_example: librocksdb simple_example.cc
-	$(CXX) $(CXXFLAGS) $@.cc -o$@ ../librocksdb.a -I../include -O2 -std=c++17 $(PLATFORM_LDFLAGS) $(PLATFORM_CXXFLAGS) $(EXEC_LDFLAGS)
+	$(CXX) $(CXXFLAGS) $@.cc -o$@ ../librocksdb.a -I../include -O2 -std=c++20 $(PLATFORM_LDFLAGS) $(PLATFORM_CXXFLAGS) $(EXEC_LDFLAGS)
 
 column_families_example: librocksdb column_families_example.cc
-	$(CXX) $(CXXFLAGS) $@.cc -o$@ ../librocksdb.a -I../include -O2 -std=c++17 $(PLATFORM_LDFLAGS) $(PLATFORM_CXXFLAGS) $(EXEC_LDFLAGS)
+	$(CXX) $(CXXFLAGS) $@.cc -o$@ ../librocksdb.a -I../include -O2 -std=c++20 $(PLATFORM_LDFLAGS) $(PLATFORM_CXXFLAGS) $(EXEC_LDFLAGS)
 
 compaction_filter_example: librocksdb compaction_filter_example.cc
-	$(CXX) $(CXXFLAGS) $@.cc -o$@ ../librocksdb.a -I../include -O2 -std=c++17 $(PLATFORM_LDFLAGS) $(PLATFORM_CXXFLAGS) $(EXEC_LDFLAGS)
+	$(CXX) $(CXXFLAGS) $@.cc -o$@ ../librocksdb.a -I../include -O2 -std=c++20 $(PLATFORM_LDFLAGS) $(PLATFORM_CXXFLAGS) $(EXEC_LDFLAGS)
 
 compact_files_example: librocksdb compact_files_example.cc
-	$(CXX) $(CXXFLAGS) $@.cc -o$@ ../librocksdb.a -I../include -O2 -std=c++17 $(PLATFORM_LDFLAGS) $(PLATFORM_CXXFLAGS) $(EXEC_LDFLAGS)
+	$(CXX) $(CXXFLAGS) $@.cc -o$@ ../librocksdb.a -I../include -O2 -std=c++20 $(PLATFORM_LDFLAGS) $(PLATFORM_CXXFLAGS) $(EXEC_LDFLAGS)
 
 .c.o:
 	$(CC) $(CFLAGS) -c $< -o $@ -I../include
@@ -37,19 +37,19 @@ c_simple_example: librocksdb c_simple_example.o
 	$(CXX) $@.o -o$@ ../librocksdb.a $(PLATFORM_LDFLAGS) $(EXEC_LDFLAGS)
 
 optimistic_transaction_example: librocksdb optimistic_transaction_example.cc
-	$(CXX) $(CXXFLAGS) $@.cc -o$@ ../librocksdb.a -I../include -O2 -std=c++17 $(PLATFORM_LDFLAGS) $(PLATFORM_CXXFLAGS) $(EXEC_LDFLAGS)
+	$(CXX) $(CXXFLAGS) $@.cc -o$@ ../librocksdb.a -I../include -O2 -std=c++20 $(PLATFORM_LDFLAGS) $(PLATFORM_CXXFLAGS) $(EXEC_LDFLAGS)
 
 transaction_example: librocksdb transaction_example.cc
-	$(CXX) $(CXXFLAGS) $@.cc -o$@ ../librocksdb.a -I../include -O2 -std=c++17 $(PLATFORM_LDFLAGS) $(PLATFORM_CXXFLAGS) $(EXEC_LDFLAGS)
+	$(CXX) $(CXXFLAGS) $@.cc -o$@ ../librocksdb.a -I../include -O2 -std=c++20 $(PLATFORM_LDFLAGS) $(PLATFORM_CXXFLAGS) $(EXEC_LDFLAGS)
 
 options_file_example: librocksdb options_file_example.cc
-	$(CXX) $(CXXFLAGS) $@.cc -o$@ ../librocksdb.a -I../include -O2 -std=c++17 $(PLATFORM_LDFLAGS) $(PLATFORM_CXXFLAGS) $(EXEC_LDFLAGS)
+	$(CXX) $(CXXFLAGS) $@.cc -o$@ ../librocksdb.a -I../include -O2 -std=c++20 $(PLATFORM_LDFLAGS) $(PLATFORM_CXXFLAGS) $(EXEC_LDFLAGS)
 
 multi_processes_example: librocksdb multi_processes_example.cc
-	$(CXX) $(CXXFLAGS) $@.cc -o$@ ../librocksdb.a -I../include -O2 -std=c++17 $(PLATFORM_LDFLAGS) $(PLATFORM_CXXFLAGS) $(EXEC_LDFLAGS)
+	$(CXX) $(CXXFLAGS) $@.cc -o$@ ../librocksdb.a -I../include -O2 -std=c++20 $(PLATFORM_LDFLAGS) $(PLATFORM_CXXFLAGS) $(EXEC_LDFLAGS)
 
 rocksdb_backup_restore_example: librocksdb rocksdb_backup_restore_example.cc
-	$(CXX) $(CXXFLAGS) $@.cc -o$@ ../librocksdb.a -I../include -O2 -std=c++17 $(PLATFORM_LDFLAGS) $(PLATFORM_CXXFLAGS) $(EXEC_LDFLAGS)
+	$(CXX) $(CXXFLAGS) $@.cc -o$@ ../librocksdb.a -I../include -O2 -std=c++20 $(PLATFORM_LDFLAGS) $(PLATFORM_CXXFLAGS) $(EXEC_LDFLAGS)
 
 clean:
 	rm -rf ./simple_example ./column_families_example ./compact_files_example ./compaction_filter_example ./c_simple_example c_simple_example.o ./optimistic_transaction_example ./transaction_example ./options_file_example ./multi_processes_example ./rocksdb_backup_restore_example

include/rocksdb/advanced_options.h

@@ -64,9 +64,7 @@ enum CompactionPri : char {
 struct FileTemperatureAge {
   Temperature temperature = Temperature::kUnknown;
   uint64_t age = 0;
-#if __cplusplus >= 202002L
   bool operator==(const FileTemperatureAge& rhs) const = default;
-#endif
 };
 
 struct CompactionOptionsFIFO {
@@ -135,9 +133,7 @@ struct CompactionOptionsFIFO {
       : max_table_files_size(_max_table_files_size),
         allow_compaction(_allow_compaction) {}
 
-#if __cplusplus >= 202002L
   bool operator==(const CompactionOptionsFIFO& rhs) const = default;
-#endif
 };
 
 // The control option of how the cache tiers will be used. Currently rocksdb

include/rocksdb/compression_type.h

@@ -313,9 +313,7 @@ struct CompressionOptions {
     max_compressed_bytes_per_kb = static_cast<int>(1024.0 / min_ratio + 0.5);
   }
 
-#if __cplusplus >= 202002L
   bool operator==(const CompressionOptions& rhs) const = default;
-#endif
 };
 
 // See advanced_compression.h

include/rocksdb/slice.h

@@ -24,7 +24,7 @@
 #include <cstdio>
 #include <cstring>
 #include <string>
-#include <string_view>  // RocksDB now requires C++17 support
+#include <string_view>
 
 #include "rocksdb/cleanable.h"
 

include/rocksdb/universal_compaction.h

@@ -144,9 +144,7 @@ class CompactionOptionsUniversal {
         incremental(false),
         reduce_file_locking(false) {}
 
-#if __cplusplus >= 202002L
   bool operator==(const CompactionOptionsUniversal& rhs) const = default;
-#endif
 };
 
 }  // namespace ROCKSDB_NAMESPACE

include/rocksdb/utilities/cache_dump_load.h

@@ -90,7 +90,7 @@ class CacheDumper {
  public:
   virtual ~CacheDumper() = default;
   // Only dump the blocks in the block cache that belong to the DBs in this list
-  virtual Status SetDumpFilter(std::vector<DB*> db_list) {
+  virtual Status SetDumpFilter(const std::vector<DB*>& db_list) {
     (void)db_list;
     return Status::NotSupported("SetDumpFilter is not supported");
   }

options/cf_options.h

@@ -257,9 +257,7 @@ struct MutableCFOptions {
 
   void Dump(Logger* log) const;
 
-#if __cplusplus >= 202002L
   bool operator==(const MutableCFOptions& rhs) const = default;
-#endif
 
   // Memtable related options
   size_t write_buffer_size;

unreleased_history/public_api_changes/cplusplus20.md

@@ -0,0 +1 @@
+* RocksDB now requires a C++20 compatible compiler (GCC >= 11, Clang >= 10, Visual Studio >= 2019), including for any code using RocksDB headers.

util/slice_test.cc

@@ -7,6 +7,8 @@
 
 #include <gtest/gtest.h>
 
+#include <semaphore>
+
 #include "port/port.h"
 #include "port/stack_trace.h"
 #include "rocksdb/data_structure.h"
@@ -422,6 +424,24 @@ TEST(ToBaseCharsStringTest, Tests) {
   ASSERT_EQ(ToBaseCharsString<32>(2, 255, false), "7v");
 }
 
+TEST(SemaphoreTest, BasicStdCountingSemaphore) {
+  // Verify the C++20 API is available and apparently working
+  std::counting_semaphore sem{0};
+  int kCount = 5;
+  std::vector<std::thread> threads;
+  for (int i = 0; i < kCount; ++i) {
+    threads.emplace_back([&sem] { sem.release(); });
+  }
+  for (int i = 0; i < kCount; ++i) {
+    threads.emplace_back([&sem] { sem.acquire(); });
+  }
+  for (auto& t : threads) {
+    t.join();
+  }
+  // Nothing left on the semaphore
+  ASSERT_FALSE(sem.try_acquire());
+}
+
 }  // namespace ROCKSDB_NAMESPACE
 
 int main(int argc, char** argv) {

util/string_util.cc

@@ -20,20 +20,6 @@
 #include "port/sys_time.h"
 #include "rocksdb/slice.h"
 
-#ifndef __has_cpp_attribute
-#define ROCKSDB_HAS_CPP_ATTRIBUTE(x) 0
-#else
-#define ROCKSDB_HAS_CPP_ATTRIBUTE(x) __has_cpp_attribute(x)
-#endif
-
-#if ROCKSDB_HAS_CPP_ATTRIBUTE(maybe_unused) && __cplusplus >= 201703L
-#define ROCKSDB_MAYBE_UNUSED [[maybe_unused]]
-#elif ROCKSDB_HAS_CPP_ATTRIBUTE(gnu::unused) || __GNUC__
-#define ROCKSDB_MAYBE_UNUSED [[gnu::unused]]
-#else
-#define ROCKSDB_MAYBE_UNUSED
-#endif
-
 namespace ROCKSDB_NAMESPACE {
 
 const std::string kNullptrString = "nullptr";
@@ -501,7 +487,7 @@ bool TryParseTimeRangeString(const std::string& value, int& start_time,
 // selects proper function.
 
 #if !(defined(_WIN32) && (defined(__MINGW32__) || defined(_MSC_VER)))
-ROCKSDB_MAYBE_UNUSED
+[[maybe_unused]]
 static std::string invoke_strerror_r(int (*strerror_r)(int, char*, size_t),
                                      int err, char* buf, size_t buflen) {
   // Using XSI-compatible strerror_r
@@ -515,7 +501,7 @@ static std::string invoke_strerror_r(int (*strerror_r)(int, char*, size_t),
   return buf;
 }
 
-ROCKSDB_MAYBE_UNUSED
+[[maybe_unused]]
 static std::string invoke_strerror_r(char* (*strerror_r)(int, char*, size_t),
                                      int err, char* buf, size_t buflen) {
   // Using GNU strerror_r

utilities/cache_dump_load_impl.cc

@@ -24,7 +24,7 @@ namespace ROCKSDB_NAMESPACE {
 // DBs and we may only want to dump out the blocks belonging to certain DB(s).
 // Therefore, a filter is need to decide if the key of the block satisfy the
 // requirement.
-Status CacheDumperImpl::SetDumpFilter(std::vector<DB*> db_list) {
+Status CacheDumperImpl::SetDumpFilter(const std::vector<DB*>& db_list) {
   Status s = Status::OK();
   dump_all_keys_ = false;
   for (size_t i = 0; i < db_list.size(); i++) {

utilities/cache_dump_load_impl.h

@@ -100,7 +100,7 @@ class CacheDumperImpl : public CacheDumper {
     dumped_size_bytes_ = 0;
   }
   ~CacheDumperImpl() { writer_.reset(); }
-  Status SetDumpFilter(std::vector<DB*> db_list) override;
+  Status SetDumpFilter(const std::vector<DB*>& db_list) override;
   IOStatus DumpCacheEntriesToWriter() override;
 
  private: