"""
Global Interpreter Lock.
"""

# This module adds a global lock to an object space.
# If multiple threads try to execute simultaneously in this space,
# all but one will be blocked.  The other threads get a chance to run
# from time to time, using the hook yield_thread().

from pypy.module.thread import ll_thread as thread
from pypy.module.thread.error import wrap_thread_error
from pypy.interpreter.executioncontext import PeriodicAsyncAction
from pypy.module.thread.threadlocals import OSThreadLocals
from pypy.rlib.objectmodel import invoke_around_extcall
from pypy.rlib.rposix import get_errno, set_errno

class GILThreadLocals(OSThreadLocals):
    """A version of OSThreadLocals that enforces a GIL."""
    ll_GIL = thread.null_ll_lock

    def initialize(self, space):
        # add the GIL-releasing callback as an action on the space
        space.actionflag.register_action(GILReleaseAction(space))

    def setup_threads(self, space):
        """Enable threads in the object space, if they haven't already been."""
        if not self.ll_GIL:
            try:
                self.ll_GIL = thread.allocate_ll_lock()
            except thread.error:
                raise wrap_thread_error(space, "can't allocate GIL")
            thread.acquire_NOAUTO(self.ll_GIL, True)
            self.enter_thread(space)   # setup the main thread
            result = True
        else:
            result = False      # already set up

        # add the GIL-releasing callback around external function calls.
        #
        # XXX we assume a single space, but this is not quite true during
        # testing; for example, if you run the whole of test_lock you get
        # a deadlock caused by the first test's space being reused by
        # test_lock_again after the global state was cleared by
        # test_compile_lock.  As a workaround, we repatch these global
        # fields systematically.
        spacestate.ll_GIL = self.ll_GIL
        spacestate.actionflag = space.actionflag
        invoke_around_extcall(before_external_call, after_external_call)
        return result

    def yield_thread(self):
        thread.yield_thread()  # explicitly release the gil (used by test_gil)


class GILReleaseAction(PeriodicAsyncAction):
    """An action called every sys.checkinterval bytecodes.  It releases
    the GIL to give some other thread a chance to run.
    """

    def perform(self, executioncontext, frame):
        # Other threads can run between the release() and the acquire()
        # implicit in the following external function call (which has
        # otherwise no effect).
        thread.yield_thread()


class SpaceState:

    def _freeze_(self):
        self.ll_GIL = thread.null_ll_lock
        self.actionflag = None
        self.set_actionflag_bit_after_thread_switch = 0
        return False

    def after_thread_switch(self):
        # this is support logic for the signal module, to help it deliver
        # signals to the main thread.
        actionflag = self.actionflag
        if actionflag is not None:
            flag = actionflag.get()
            flag |= self.set_actionflag_bit_after_thread_switch
            actionflag.set(flag)

spacestate = SpaceState()
spacestate._freeze_()

# Fragile code below.  We have to preserve the C-level errno manually...

def before_external_call():
    # this function must not raise, in such a way that the exception
    # transformer knows that it cannot raise!
    e = get_errno()
    thread.release_NOAUTO(spacestate.ll_GIL)
    set_errno(e)
before_external_call._gctransformer_hint_cannot_collect_ = True

def after_external_call():
    e = get_errno()
    thread.acquire_NOAUTO(spacestate.ll_GIL, True)
    thread.gc_thread_run()
    spacestate.after_thread_switch()
    set_errno(e)
after_external_call._gctransformer_hint_cannot_collect_ = True

# The _gctransformer_hint_cannot_collect_ hack is needed for
# translations in which the *_external_call() functions are not inlined.
# They tell the gctransformer not to save and restore the local GC
# pointers in the shadow stack.  This is necessary because the GIL is
# not held after the call to before_external_call() or before the call
# to after_external_call().