C++17 thread guard implementation for RAII strategy

main.cpp

#include <iostream>
#include <thread>
#include <mutex>

#include "thread_guard.h"

int main() {
    auto x = 0u;
    auto m = std::mutex();
    {
        const auto tg = thread_guard(std::thread([](unsigned int &x, std::mutex &m){ const std::lock_guard<std::mutex> lock(m);  ++x; }, std::ref(x), std::ref(m)));
        std::cout << "computing x" << std::endl;
    }
    std::cout << x << std::endl;
    return 0;
}

Makefile

CXX?=g++
BIN?=main
EXT?=cpp
LINKS?=pthread

CXXSTD?=c++17

SRCS=$(shell find . -name "*."$(EXT))
DIRS=$(shell find ./* -type d)
OBJS=$(patsubst %.$(EXT),%.o,$(SRCS))
INCS=$(addprefix -I, $(DIRS))

CXXFLAGS+=-std=$(CXXSTD) -Wall $(INCS)
LDFLAGS+=$(addprefix -l, $(LINKS))

.PHONY: all run clean

all: $(BIN)

$(EXT).o: $(SRCS)
        $(CXX) $(CPPFLAGS) -c $<

$(BIN): $(OBJS)
        $(CXX) $(CXXFLAGS) -o $(BIN) $(notdir $(OBJS)) $(LDFLAGS)

run: all
        -./$(BIN)

clean:
        -rm -f $(notdir $(OBJS)) $(BIN)

thread_guard.h

#ifndef THREAD_GUARD
#define THREAD_GUARD

class thread_guard final {
private:
    std::thread th_;

public:
    explicit thread_guard(std::thread th) : th_{std::move(th)} {}

    ~thread_guard() {
        join();
    }

    void join() {
        if (th_.joinable()) {
            th_.join();
        }
    }

    thread_guard(const thread_guard &) = delete;

    thread_guard &operator=(const thread_guard &) = delete;

    thread_guard(thread_guard &&) = default;

    thread_guard &operator=(thread_guard &&) = default;
};

#endif // THREAD_GUARD