cosmopolitan/third_party/nsync/mem/nsync_counter.c

/*-*- mode:c;indent-tabs-mode:t;c-basic-offset:8;tab-width:8;coding:utf-8   -*-│
│vi: set et ft=c ts=8 tw=8 fenc=utf-8                                       :vi│
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 2016 Google Inc.                                                   │
│                                                                              │
│ 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.                                               │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/mem/mem.h"
#include "libc/str/str.h"
#include "third_party/nsync/atomic.h"
#include "third_party/nsync/atomic.internal.h"
#include "third_party/nsync/common.internal.h"
#include "third_party/nsync/counter.h"
#include "third_party/nsync/dll.h"
#include "third_party/nsync/mu_semaphore.h"
#include "third_party/nsync/races.internal.h"
#include "third_party/nsync/wait_s.internal.h"
#include "third_party/nsync/waiter.h"

asm(".ident\t\"\\n\\n\
*NSYNC (Apache 2.0)\\n\
Copyright 2016 Google, Inc.\\n\
https://github.com/google/nsync\"");
// clang-format off

/* Internal details of nsync_counter. */
struct nsync_counter_s_ {
        nsync_atomic_uint32_ waited;    /* wait has been called */
        nsync_mu counter_mu;         /* protects fields below except reads of "value" */
        nsync_atomic_uint32_ value;     /* value of counter */
        struct nsync_dll_element_s_ *waiters;  /* list of waiters */
};

nsync_counter nsync_counter_new (uint32_t value) {
	nsync_counter c = (nsync_counter) malloc (sizeof (*c));
	if (c != NULL) {
		memset ((void *) c, 0, sizeof (*c));
		ATM_STORE (&c->value, value);
	}
	return (c);
}

void nsync_counter_free (nsync_counter c) {
	nsync_mu_lock (&c->counter_mu);
	ASSERT (nsync_dll_is_empty_ (c->waiters));
	nsync_mu_unlock (&c->counter_mu);
	free (c);
}

uint32_t nsync_counter_add (nsync_counter c, int32_t delta) {
	uint32_t value;
	IGNORE_RACES_START ();
	if (delta == 0) {
		value = ATM_LOAD_ACQ (&c->value);
	} else {
		nsync_mu_lock (&c->counter_mu);
		do {
			value = ATM_LOAD (&c->value);
		} while (!ATM_CAS_RELACQ (&c->value, value, value+delta));
		value += delta;
		if (delta > 0) {
			/* It's illegal to increase the count from zero if
			   there has been a waiter. */
			ASSERT (value != (uint32_t) delta || !ATM_LOAD (&c->waited));
			ASSERT (value > value - delta); /* Crash on overflow. */
		} else {
			ASSERT (value < value - delta); /* Crash on overflow. */
		}
		if (value == 0) {
			nsync_dll_element_ *p;
			while ((p = nsync_dll_first_ (c->waiters)) != NULL) {
				struct nsync_waiter_s *nw = DLL_NSYNC_WAITER (p);
				c->waiters = nsync_dll_remove_ (c->waiters, p);
				ATM_STORE_REL (&nw->waiting, 0);
				nsync_mu_semaphore_v (nw->sem);
			}
		}
		nsync_mu_unlock (&c->counter_mu);
	}
	IGNORE_RACES_END ();
	return (value);
}

uint32_t nsync_counter_value (nsync_counter c) {
	uint32_t result;
	IGNORE_RACES_START ();
	result = ATM_LOAD_ACQ (&c->value);
	IGNORE_RACES_END ();
	return (result);
}

uint32_t nsync_counter_wait (nsync_counter c, nsync_time abs_deadline) {
	struct nsync_waitable_s waitable;
	struct nsync_waitable_s *pwaitable = &waitable;
	uint32_t result = 0;
	waitable.v = c;
	waitable.funcs = &nsync_counter_waitable_funcs;
	if (nsync_wait_n (NULL, NULL, NULL, abs_deadline, 1, &pwaitable) != 0) {
		IGNORE_RACES_START ();
		result = ATM_LOAD_ACQ (&c->value);
		IGNORE_RACES_END ();
	}
	return (result);
}

static nsync_time counter_ready_time (void *v, struct nsync_waiter_s *nw) {
	nsync_counter c = (nsync_counter) v;
	nsync_time r;
	ATM_STORE (&c->waited, 1);
	r = (ATM_LOAD_ACQ (&c->value) == 0? nsync_time_zero : nsync_time_no_deadline);
	return (r);
}

static int counter_enqueue (void *v, struct nsync_waiter_s *nw) {
	nsync_counter c = (nsync_counter) v;
	int32_t value;
	nsync_mu_lock (&c->counter_mu);
	value = ATM_LOAD_ACQ (&c->value);
	if (value != 0) {
		c->waiters = nsync_dll_make_last_in_list_ (c->waiters, &nw->q);
		ATM_STORE (&nw->waiting, 1);
	} else {
		ATM_STORE (&nw->waiting, 0);
	}
	nsync_mu_unlock (&c->counter_mu);
	return (value != 0);
}

static int counter_dequeue (void *v, struct nsync_waiter_s *nw) {
	nsync_counter c = (nsync_counter) v;
	int32_t value;
	nsync_mu_lock (&c->counter_mu);
	value = ATM_LOAD_ACQ (&c->value);
	if (ATM_LOAD_ACQ (&nw->waiting) != 0) {
		c->waiters = nsync_dll_remove_ (c->waiters, &nw->q);
		ATM_STORE (&nw->waiting, 0);
	}
	nsync_mu_unlock (&c->counter_mu);
	return (value != 0);
}

const struct nsync_waitable_funcs_s nsync_counter_waitable_funcs = {
	&counter_ready_time,
	&counter_enqueue,
	&counter_dequeue
};