问std::mutex是递归的(即不可重入的)吗？

EN

#include <iostream>
#include <mutex>

std::mutex g_mtx4val;
int g_val = 5;

void test() {
  std::lock_guard<std::mutex> lck(g_mtx4val);
  std::cout << "g_val=" << g_val << std::endl;
  if (g_val > 0) {
    --g_val;
    test();
  }
}

int main() {
  test();

  std::cout << "done ...." << std::endl;
  return 0;
}

peanut@peanut:~/demo$ g++ test.cpp 
peanut@peanut:~/demo$ ./a.out 
g_val=5
g_val=4
g_val=3
g_val=2
g_val=1
g_val=0
done ...

// Same code 1

int main() {
  std::thread t1(test);
  t1.join();

  std::cout << "done ...." << std::endl;
  return 0;
}

peanut@peanut:~/demo$ g++ test2.cpp -lpthread
peanut@peanut:~/demo$ ./a.out 
g_val=5
^C
peanut@peanut:~/demo$