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// SPDX-License-Identifier: GPL-2.0-only
/*
* Copyright (C) 2021 Ahmad Fatoum, Pengutronix
* Copyright (C) 2025 Linaro Limited
*
* An implementation of cooperative multi-tasking inspired from barebox threads
* https://github.com/barebox/barebox/blob/master/common/bthread.c
*/
#include <compiler.h>
#include <linux/errno.h>
#include <linux/kernel.h>
#include <linux/list.h>
#include <malloc.h>
#include <setjmp.h>
#include <stdint.h>
#include <uthread.h>
static struct uthread main_thread = {
.list = LIST_HEAD_INIT(main_thread.list),
};
static struct uthread *current = &main_thread;
/**
* uthread_trampoline() - Call the current thread's entry point then resume the
* main thread.
*
* This is a helper function which is used as the @func argument to the
* initjmp() function, and ultimately invoked via setjmp(). It does not return
* but instead longjmp()'s back to the main thread.
*/
static void __noreturn uthread_trampoline(void)
{
struct uthread *curr = current;
curr->fn(curr->arg);
curr->done = true;
current = &main_thread;
longjmp(current->ctx, 1);
/* Not reached */
while (true)
;
}
/**
* uthread_free() - Free memory used by a uthread object.
*/
static void uthread_free(struct uthread *uthread)
{
if (!uthread)
return;
free(uthread->stack);
free(uthread);
}
int uthread_create(struct uthread *uthr, void (*fn)(void *), void *arg,
size_t stack_sz, unsigned int grp_id)
{
bool user_allocated = false;
if (!stack_sz)
stack_sz = CONFIG_UTHREAD_STACK_SIZE;
if (uthr) {
user_allocated = true;
} else {
uthr = calloc(1, sizeof(*uthr));
if (!uthr)
return -1;
}
uthr->stack = memalign(16, stack_sz);
if (!uthr->stack)
goto err;
uthr->fn = fn;
uthr->arg = arg;
uthr->grp_id = grp_id;
list_add_tail(&uthr->list, ¤t->list);
initjmp(uthr->ctx, uthread_trampoline, uthr->stack, stack_sz);
return 0;
err:
if (!user_allocated)
free(uthr);
return -1;
}
/**
* uthread_resume() - switch execution to a given thread
*
* @uthread: the thread object that should be resumed
*/
static void uthread_resume(struct uthread *uthread)
{
if (!setjmp(current->ctx)) {
current = uthread;
longjmp(uthread->ctx, 1);
}
}
bool uthread_schedule(void)
{
struct uthread *next;
struct uthread *tmp;
list_for_each_entry_safe(next, tmp, ¤t->list, list) {
if (!next->done) {
uthread_resume(next);
return true;
}
/* Found a 'done' thread, free its resources */
list_del(&next->list);
uthread_free(next);
}
return false;
}
unsigned int uthread_grp_new_id(void)
{
static unsigned int id;
return ++id;
}
bool uthread_grp_done(unsigned int grp_id)
{
struct uthread *next;
list_for_each_entry(next, &main_thread.list, list) {
if (next->grp_id == grp_id && !next->done)
return false;
}
return true;
}
int uthread_mutex_lock(struct uthread_mutex *mutex)
{
while (mutex->state == UTHREAD_MUTEX_LOCKED)
uthread_schedule();
mutex->state = UTHREAD_MUTEX_LOCKED;
return 0;
}
int uthread_mutex_trylock(struct uthread_mutex *mutex)
{
if (mutex->state == UTHREAD_MUTEX_UNLOCKED) {
mutex->state = UTHREAD_MUTEX_LOCKED;
return 0;
}
return -EBUSY;
}
int uthread_mutex_unlock(struct uthread_mutex *mutex)
{
mutex->state = UTHREAD_MUTEX_UNLOCKED;
return 0;
}
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