# 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.

# This script computs the number of concurrent links we want to run in the build
# as a function of machine spec. It's based on GetDefaultConcurrentLinks in GYP.

import os
import re
import subprocess
import sys


def GetDefaultConcurrentLinks():
    # 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

    if sys.platform in ('win32', 'cygwin'):
        import ctypes

        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))

        mem_limit = max(1, stat.ullTotalPhys // (4 * (2**30)))  # total / 4GB
        hard_cap = max(1, int(os.getenv('GYP_LINK_CONCURRENCY_MAX', 2**32)))
        return min(mem_limit, hard_cap)
    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
                    # Allow 8Gb per link on Linux because Gold is quite memory hungry
                    return max(1, int(match.group(1)) // (8 * (2**20)))
        return 1
    elif sys.platform == 'darwin':
        try:
            avail_bytes = int(
                subprocess.check_output(['sysctl', '-n', 'hw.memsize']))
            # A static library debug build of Chromium's unit_tests takes ~2.7GB, so
            # 4GB per ld process allows for some more bloat.
            return max(1, avail_bytes // (4 * (2**30)))  # total / 4GB
        except Exception:
            return 1
    else:
        # TODO(scottmg): Implement this for other platforms.
        return 1


print(GetDefaultConcurrentLinks())