Run JDK check for Linux clock monotonicity manually

check_clock.c

// gcc check_clock.c -ldl -o check_clock
// ripped from http://hg.openjdk.java.net/jdk8u/jdk8u-gate/hotspot/file/9c2ddd17626e/src/os/linux/vm/os_linux.cpp

#include <dlfcn.h>
#include <stdio.h>
#include <linux/time.h>

typedef int clockid_t;

int main(int argc, const char* argv[]) {
  // we do dlopen's in this particular order due to bug in linux
  // dynamical loader (see 6348968) leading to crash on exit
  void* handle = dlopen("librt.so.1", RTLD_LAZY);
  if (handle == NULL) {
    handle = dlopen("librt.so", RTLD_LAZY);
  }

  if (handle) {
    int (*clock_getres_func)(clockid_t, struct timespec*) =
           (int(*)(clockid_t, struct timespec*))dlsym(handle, "clock_getres");
    int (*clock_gettime_func)(clockid_t, struct timespec*) =
           (int(*)(clockid_t, struct timespec*))dlsym(handle, "clock_gettime");
    if (clock_getres_func && clock_gettime_func) {
      // See if monotonic clock is supported by the kernel. Note that some
      // early implementations simply return kernel jiffies (updated every
      // 1/100 or 1/1000 second). It would be bad to use such a low res clock
      // for nano time (though the monotonic property is still nice to have).
      // It's fixed in newer kernels, however clock_getres() still returns
      // 1/HZ. We check if clock_getres() works, but will ignore its reported
      // resolution for now. Hopefully as people move to new kernels, this
      // won't be a problem.
      struct timespec res;
      struct timespec tp;
      if (clock_getres_func (CLOCK_MONOTONIC, &res) == 0 &&
          clock_gettime_func(CLOCK_MONOTONIC, &tp)  == 0) {
        printf("monotonic clock supported\n");
        return;
      } else {
        printf("monotonic clock NOT supported\n");
        // close librt if there is no monotonic clock
        dlclose(handle);
      }
    }
  }
}