source: mainline/kernel/generic/src/preempt/preemption.c@ 935e28c

/*
 * Copyright (c) 2005 Jakub Jermar
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/** @addtogroup generic
 * @{
 */

/**
 * @file preemption.c
 * @brief Preemption control.
 */

#include <preemption.h>
#include <proc/scheduler.h>


/** Determines if we are executing an exception/interrupt handler. */
static bool in_exc_handler(void)
{
        /* Err on the safe side until all exception processing code is audited. */
        return true;
}

/** Preemption was enabled. Calls scheduler(). */
void preemption_enabled_scheduler(void)
{
        ASSERT(PREEMPTION_ENABLED);
        ASSERT(PREEMPTION_NEEDED);
        
        /* 
         * Avoid a race between a thread about to invoke the scheduler() 
         * after checking THREAD->need_resched and an interrupt that
         * occurs right after the check.
         * 
         * Also ensures that code that relies on disabled interrupts
         * to suppress preemption continues to work.
         */
        if (!interrupts_disabled() && !in_exc_handler()) {
                preemption_clear_needed();
                /* We may be preempted here, so we'll scheduler() again. Too bad. */
                scheduler();
        } 
}

/** Sets a flag to reschedule the next time preemption is enabled. */
void preemption_set_needed(void)
{
        /* No need to disable interrupts. */
        THE->preemption |= PREEMPTION_NEEDED_FLAG;
}

/** Instructs not to reschedule immediately when preemption is enabled. */
void preemption_clear_needed(void)
{
        /* No need to disable interrupts. */
        THE->preemption &= ~PREEMPTION_NEEDED_FLAG;
}

/** @}
 */