Windows / speeup: dynamically load libraries on startup and never again

[giampaolo]

This is kinda big. It encapsulates the logic for dynamically loading libraries at runtime instead of on each function call. Undocumented / private Windows APIs are now loaded globally on import. In doing so I refactored a lot of stuff and didn't test this on Win XP, which I am tempted to keep alive. I also removed MinGW related cruft, so this probably deserves a major version bump.

EDIT: benchmark script including timings and the APIs involved:

API                                      BEFORE     AFTER   DIFF
psutil.boot_time()                       0.018      0.008   +76%
psutil.cpu_count(logical=False)          0.055      0.033   +50%
psutil.cpu_count(logical=True)           0.041      0.025   +48%
psutil.cpu_stats()                       0.379      0.157   +82%
psutil.cpu_times(percpu=True)            0.341      0.066   +135%
psutil.disk_io_counters()                0.945      0.921   +2%
psutil.users()                           5.671      5.466   +3%
proc.ionice()                            0.056      0.047   +17%
proc.ionice(0)                           0.061      0.051   +18%
proc.open_files()   (too slow)
proc.connections()  (too slow)

Benchmark script:

from __future__ import print_function
import sys
import timeit
import psutil

ITERATIONS = 10000
apis = [
    'psutil.boot_time()',
    'psutil.disk_io_counters()',
    'psutil.cpu_count(logical=False)',
    'psutil.cpu_count(logical=True)',
    'psutil.cpu_times(percpu=True)',
    'psutil.users()',
    'psutil.cpu_stats()',
    # 'psutil.net_connections(kind="inet4")',  # slow
    'proc.ionice()',
    'proc.ionice(0)',
    # 'proc.open_files()',  # slow
]
apis = sorted(set(apis))
setup = "import psutil; proc = psutil.Process()"

def main():
    if not psutil.WINDOWS:
        sys.exit("Windows only")
    for api in apis:
        elapsed = timeit.timeit(api, setup=setup, number=ITERATIONS)
        print("%-40s %.3f" % (api, elapsed))


if __name__ == '__main__':
    main()

[giampaolo]

Attaching benchmarks in the first message.