circuitpython/py/scheduler.c

/*
 * This file is part of the MicroPython project, http://micropython.org/
 *
 * The MIT License (MIT)
 *
 * SPDX-FileCopyrightText: Copyright (c) 2017 Damien P. George
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

#include <stdio.h>

#include "py/runtime.h"

// Schedules an exception on the main thread (for exceptions "thrown" by async
// sources such as interrupts and UNIX signal handlers).
void MICROPY_WRAP_MP_SCHED_EXCEPTION(mp_sched_exception)(mp_obj_t exc) {
    MP_STATE_MAIN_THREAD(mp_pending_exception) = exc;
    #if MICROPY_ENABLE_SCHEDULER
    if (MP_STATE_VM(sched_state) == MP_SCHED_IDLE) {
        MP_STATE_VM(sched_state) = MP_SCHED_PENDING;
    }
    #endif
}

#if MICROPY_KBD_EXCEPTION
// This function may be called asynchronously at any time so only do the bare minimum.
void MICROPY_WRAP_MP_SCHED_KEYBOARD_INTERRUPT(mp_sched_keyboard_interrupt)(void) {
    MP_STATE_VM(mp_kbd_exception).traceback = (mp_obj_traceback_t *)&mp_const_empty_traceback_obj;
    mp_sched_exception(MP_OBJ_FROM_PTR(&MP_STATE_VM(mp_kbd_exception)));
}
#endif

#if MICROPY_ENABLE_SCHEDULER

#define IDX_MASK(i) ((i) & (MICROPY_SCHEDULER_DEPTH - 1))

// This is a macro so it is guaranteed to be inlined in functions like
// mp_sched_schedule that may be located in a special memory region.
#define mp_sched_full() (mp_sched_num_pending() == MICROPY_SCHEDULER_DEPTH)

static inline bool mp_sched_empty(void) {
    MP_STATIC_ASSERT(MICROPY_SCHEDULER_DEPTH <= 255); // MICROPY_SCHEDULER_DEPTH must fit in 8 bits
    MP_STATIC_ASSERT((IDX_MASK(MICROPY_SCHEDULER_DEPTH) == 0)); // MICROPY_SCHEDULER_DEPTH must be a power of 2

    return mp_sched_num_pending() == 0;
}

// A variant of this is inlined in the VM at the pending exception check
void mp_handle_pending(bool raise_exc) {
    if (MP_STATE_VM(sched_state) == MP_SCHED_PENDING) {
        mp_uint_t atomic_state = MICROPY_BEGIN_ATOMIC_SECTION();
        // Re-check state is still pending now that we're in the atomic section.
        if (MP_STATE_VM(sched_state) == MP_SCHED_PENDING) {
            mp_obj_t obj = MP_STATE_THREAD(mp_pending_exception);
            if (obj != MP_OBJ_NULL) {
                MP_STATE_THREAD(mp_pending_exception) = MP_OBJ_NULL;
                if (!mp_sched_num_pending()) {
                    MP_STATE_VM(sched_state) = MP_SCHED_IDLE;
                }
                if (raise_exc) {
                    MICROPY_END_ATOMIC_SECTION(atomic_state);
                    nlr_raise(obj);
                }
            }
            mp_handle_pending_tail(atomic_state);
        } else {
            MICROPY_END_ATOMIC_SECTION(atomic_state);
        }
    }
}

// This function should only be called by mp_handle_pending,
// or by the VM's inlined version of that function.
void mp_handle_pending_tail(mp_uint_t atomic_state) {
    MP_STATE_VM(sched_state) = MP_SCHED_LOCKED;

    #if MICROPY_SCHEDULER_STATIC_NODES
    // Run all pending C callbacks.
    while (MP_STATE_VM(sched_head) != NULL) {
        mp_sched_node_t *node = MP_STATE_VM(sched_head);
        MP_STATE_VM(sched_head) = node->next;
        if (MP_STATE_VM(sched_head) == NULL) {
            MP_STATE_VM(sched_tail) = NULL;
        }
        mp_sched_callback_t callback = node->callback;
        node->callback = NULL;
        MICROPY_END_ATOMIC_SECTION(atomic_state);
        callback(node);
        atomic_state = MICROPY_BEGIN_ATOMIC_SECTION();
    }
    #endif

    // Run at most one pending Python callback.
    if (!mp_sched_empty()) {
        mp_sched_item_t item = MP_STATE_VM(sched_queue)[MP_STATE_VM(sched_idx)];
        MP_STATE_VM(sched_idx) = IDX_MASK(MP_STATE_VM(sched_idx) + 1);
        --MP_STATE_VM(sched_len);
        MICROPY_END_ATOMIC_SECTION(atomic_state);
        mp_call_function_1_protected(item.func, item.arg);
    } else {
        MICROPY_END_ATOMIC_SECTION(atomic_state);
    }

    mp_sched_unlock();
}

void mp_sched_lock(void) {
    mp_uint_t atomic_state = MICROPY_BEGIN_ATOMIC_SECTION();
    if (MP_STATE_VM(sched_state) < 0) {
        --MP_STATE_VM(sched_state);
    } else {
        MP_STATE_VM(sched_state) = MP_SCHED_LOCKED;
    }
    MICROPY_END_ATOMIC_SECTION(atomic_state);
}

void mp_sched_unlock(void) {
    mp_uint_t atomic_state = MICROPY_BEGIN_ATOMIC_SECTION();
    assert(MP_STATE_VM(sched_state) < 0);
    if (++MP_STATE_VM(sched_state) == 0) {
        // vm became unlocked
        if (MP_STATE_THREAD(mp_pending_exception) != MP_OBJ_NULL
            #if MICROPY_SCHEDULER_STATIC_NODES
            || MP_STATE_VM(sched_head) != NULL
            #endif
            || mp_sched_num_pending()) {
            MP_STATE_VM(sched_state) = MP_SCHED_PENDING;
        } else {
            MP_STATE_VM(sched_state) = MP_SCHED_IDLE;
        }
    }
    MICROPY_END_ATOMIC_SECTION(atomic_state);
}

bool MICROPY_WRAP_MP_SCHED_SCHEDULE(mp_sched_schedule)(mp_obj_t function, mp_obj_t arg) {
    mp_uint_t atomic_state = MICROPY_BEGIN_ATOMIC_SECTION();
    bool ret;
    if (!mp_sched_full()) {
        if (MP_STATE_VM(sched_state) == MP_SCHED_IDLE) {
            MP_STATE_VM(sched_state) = MP_SCHED_PENDING;
        }
        uint8_t iput = IDX_MASK(MP_STATE_VM(sched_idx) + MP_STATE_VM(sched_len)++);
        MP_STATE_VM(sched_queue)[iput].func = function;
        MP_STATE_VM(sched_queue)[iput].arg = arg;
        MICROPY_SCHED_HOOK_SCHEDULED;
        ret = true;
    } else {
        // schedule queue is full
        ret = false;
    }
    MICROPY_END_ATOMIC_SECTION(atomic_state);
    return ret;
}

#if MICROPY_SCHEDULER_STATIC_NODES
bool mp_sched_schedule_node(mp_sched_node_t *node, mp_sched_callback_t callback) {
    mp_uint_t atomic_state = MICROPY_BEGIN_ATOMIC_SECTION();
    bool ret;
    if (node->callback == NULL) {
        if (MP_STATE_VM(sched_state) == MP_SCHED_IDLE) {
            MP_STATE_VM(sched_state) = MP_SCHED_PENDING;
        }
        node->callback = callback;
        node->next = NULL;
        if (MP_STATE_VM(sched_tail) == NULL) {
            MP_STATE_VM(sched_head) = node;
        } else {
            MP_STATE_VM(sched_tail)->next = node;
        }
        MP_STATE_VM(sched_tail) = node;
        MICROPY_SCHED_HOOK_SCHEDULED;
        ret = true;
    } else {
        // already scheduled
        ret = false;
    }
    MICROPY_END_ATOMIC_SECTION(atomic_state);
    return ret;
}
#endif

#else // MICROPY_ENABLE_SCHEDULER

// A variant of this is inlined in the VM at the pending exception check
void mp_handle_pending(bool raise_exc) {
    if (MP_STATE_THREAD(mp_pending_exception) != MP_OBJ_NULL) {
        mp_obj_t obj = MP_STATE_THREAD(mp_pending_exception);
        MP_STATE_THREAD(mp_pending_exception) = MP_OBJ_NULL;
        if (raise_exc) {
            nlr_raise(obj);
        }
    }
}

#endif // MICROPY_ENABLE_SCHEDULER