src/core/util/linux/cpu.cc

//
//
// Copyright 2015 gRPC authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
//

#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif  // _GNU_SOURCE

#include <grpc/support/port_platform.h>

#ifdef GPR_CPU_LINUX

#include <errno.h>
#include <sched.h>
#include <string.h>
#include <unistd.h>

#include <grpc/support/cpu.h>
#include <grpc/support/log.h>
#include <grpc/support/sync.h>

#include "src/core/lib/gprpp/crash.h"
#include "src/core/lib/gprpp/strerror.h"

static int ncpus = 0;

static void init_num_cpus() {
#ifndef GPR_MUSL_LIBC_COMPAT
  if (sched_getcpu() < 0) {
    gpr_log(GPR_ERROR, "Error determining current CPU: %s\n",
            grpc_core::StrError(errno).c_str());
    ncpus = 1;
    return;
  }
#endif
  // This must be signed. sysconf returns -1 when the number cannot be
  // determined
  ncpus = static_cast<int>(sysconf(_SC_NPROCESSORS_CONF));
  if (ncpus < 1) {
    gpr_log(GPR_ERROR, "Cannot determine number of CPUs: assuming 1");
    ncpus = 1;
  }
}

unsigned gpr_cpu_num_cores(void) {
  static gpr_once once = GPR_ONCE_INIT;
  gpr_once_init(&once, init_num_cpus);
  return static_cast<unsigned>(ncpus);
}

unsigned gpr_cpu_current_cpu(void) {
#ifdef GPR_MUSL_LIBC_COMPAT
  // sched_getcpu() is undefined on musl
  return 0;
#else
  if (gpr_cpu_num_cores() == 1) {
    return 0;
  }
  int cpu = sched_getcpu();
  if (cpu < 0) {
    gpr_log(GPR_ERROR, "Error determining current CPU: %s\n",
            grpc_core::StrError(errno).c_str());
    return 0;
  }
  if (static_cast<unsigned>(cpu) >= gpr_cpu_num_cores()) {
    gpr_log(GPR_DEBUG, "Cannot handle hot-plugged CPUs");
    return 0;
  }
  return static_cast<unsigned>(cpu);
#endif
}

#endif  // GPR_CPU_LINUX