# Copyright 2014 The Chromium Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

"""Computes and prints the default number of concurrent links.

Computes the number of concurrent links to be run in the build, as a function
of machine spec. Based on GetDefaultConcurrentLinks in GYP.
"""

import ctypes
import optparse
import os
import re
import subprocess
import sys


def _GetTotalMemoryInBytes():
  """Gets the total amount of virtual memory in bytes.

  Returns:
    See above
  """
  if sys.platform in ('win32', 'cygwin'):

    class MEMORYSTATUSEX(ctypes.Structure):
      _fields_ = [
          ('dwLength', ctypes.c_ulong),
          ('dwMemoryLoad', ctypes.c_ulong),
          ('ullTotalPhys', ctypes.c_ulonglong),
          ('ullAvailPhys', ctypes.c_ulonglong),
          ('ullTotalPageFile', ctypes.c_ulonglong),
          ('ullAvailPageFile', ctypes.c_ulonglong),
          ('ullTotalVirtual', ctypes.c_ulonglong),
          ('ullAvailVirtual', ctypes.c_ulonglong),
          ('sullAvailExtendedVirtual', ctypes.c_ulonglong),
      ]

    stat = MEMORYSTATUSEX(dwLength=ctypes.sizeof(MEMORYSTATUSEX))
    ctypes.windll.kernel32.GlobalMemoryStatusEx(ctypes.byref(stat))
    return stat.ullTotalPhys
  elif sys.platform.startswith('linux'):
    if os.path.exists('/proc/meminfo'):
      with open('/proc/meminfo') as meminfo:
        memtotal_re = re.compile(r'^MemTotal:\s*(\d*)\s*kB')
        for line in meminfo:
          match = memtotal_re.match(line)
          if not match:
            continue
          return float(match.group(1)) * 2**10
  elif sys.platform == 'darwin':
    try:
      return int(subprocess.check_output(['sysctl', '-n', 'hw.memsize']))
    except subprocess.CalledProcessError:
      return 0
  # TODO: Implement this for other platforms.
  return 0


def _GetDefaultConcurrentLinks(mem_per_link_gb, reserve_mem_gb):
  # Inherit the legacy environment variable for people that have set it in GYP.
  pool_size = int(os.getenv('GYP_LINK_CONCURRENCY', 0))
  if pool_size:
    return pool_size

  mem_total_bytes = _GetTotalMemoryInBytes()
  mem_total_bytes = max(0, mem_total_bytes - reserve_mem_gb * 2**30)
  num_concurrent_links = int(max(1, mem_total_bytes / mem_per_link_gb / 2**30))
  hard_cap = max(1, int(os.getenv('GYP_LINK_CONCURRENCY_MAX', 2**32)))
  return min(num_concurrent_links, hard_cap)


def main():
  parser = optparse.OptionParser()
  parser.add_option('--mem_per_link_gb', action='store', type='int', default=6)
  parser.add_option('--reserve_mem_gb', action='store', type='int', default=0)
  parser.disable_interspersed_args()
  options, _ = parser.parse_args()

  print _GetDefaultConcurrentLinks(options.mem_per_link_gb,
                                   options.reserve_mem_gb)
  return 0

if __name__ == '__main__':
  sys.exit(main())