source: libcfa/src/concurrency/kernel.cfa @ e8e457e

//
// Cforall Version 1.0.0 Copyright (C) 2016 University of Waterloo
//
// The contents of this file are covered under the licence agreement in the
// file "LICENCE" distributed with Cforall.
//
// kernel.c --
//
// Author           : Thierry Delisle
// Created On       : Tue Jan 17 12:27:26 2017
// Last Modified By : Peter A. Buhr
// Last Modified On : Mon Apr  9 16:11:46 2018
// Update Count     : 24
//

//C Includes
#include <stddef.h>
#include <errno.h>
#include <string.h>
extern "C" {
#include <stdio.h>
#include <fenv.h>
#include <sys/resource.h>
#include <signal.h>
#include <unistd.h>
}

//CFA Includes
#include "time.hfa"
#include "kernel_private.hfa"
#include "preemption.hfa"
#include "startup.hfa"

//Private includes
#define __CFA_INVOKE_PRIVATE__
#include "invoke.h"

//Start and stop routine for the kernel, declared first to make sure they run first
static void kernel_startup(void)  __attribute__(( constructor( STARTUP_PRIORITY_KERNEL ) ));
static void kernel_shutdown(void) __attribute__(( destructor ( STARTUP_PRIORITY_KERNEL ) ));

//-----------------------------------------------------------------------------
// Kernel storage
KERNEL_STORAGE(cluster,         mainCluster);
KERNEL_STORAGE(processor,       mainProcessor);
KERNEL_STORAGE(thread_desc,     mainThread);
KERNEL_STORAGE(__stack_t,       mainThreadCtx);

cluster     * mainCluster;
processor   * mainProcessor;
thread_desc * mainThread;

extern "C" {
struct { __dllist_t(cluster) list; __spinlock_t lock; } __cfa_dbg_global_clusters;
}

size_t __page_size = 0;

//-----------------------------------------------------------------------------
// Global state
thread_local struct KernelThreadData kernelTLS __attribute__ ((tls_model ( "initial-exec" ))) = {
        NULL,
        NULL,
        { 1, false, false }
};

//-----------------------------------------------------------------------------
// Struct to steal stack
struct current_stack_info_t {
        __stack_t * storage;            // pointer to stack object
        void *base;                             // base of stack
        void *limit;                    // stack grows towards stack limit
        void *context;                  // address of cfa_context_t
};

void ?{}( current_stack_info_t & this ) {
        __stack_context_t ctx;
        CtxGet( ctx );
        this.base = ctx.FP;

        rlimit r;
        getrlimit( RLIMIT_STACK, &r);
        size_t size = r.rlim_cur;

        this.limit = (void *)(((intptr_t)this.base) - size);
        this.context = &storage_mainThreadCtx;
}

//-----------------------------------------------------------------------------
// Main thread construction

void ?{}( coroutine_desc & this, current_stack_info_t * info) with( this ) {
        context.errno_ = 0;
        stack.storage = info->storage;
        with(*stack.storage) {
                limit     = info->limit;
                base      = info->base;
        }
        *((intptr_t*)&stack.storage) |= 0x1;
        name = "Main Thread";
        state = Start;
        starter = NULL;
        last = NULL;
        cancellation = NULL;
}

void ?{}( thread_desc & this, current_stack_info_t * info) with( this ) {
        state = Start;
        self_cor{ info };
        curr_cor = &self_cor;
        curr_cluster = mainCluster;
        self_mon.owner = &this;
        self_mon.recursion = 1;
        self_mon_p = &self_mon;
        next = NULL;

        node.next = NULL;
        node.prev = NULL;
        doregister(curr_cluster, this);

        monitors{ &self_mon_p, 1, (fptr_t)0 };
}

//-----------------------------------------------------------------------------
// Processor coroutine
void ?{}(processorCtx_t & this) {

}

// Construct the processor context of non-main processors
static void ?{}(processorCtx_t & this, processor * proc, current_stack_info_t * info) {
        (this.__cor){ info };
        this.proc = proc;
}

static void start(processor * this);
void ?{}(processor & this, const char * name, cluster & cltr) with( this ) {
        this.name = name;
        this.cltr = &cltr;
        terminated{ 0 };
        do_terminate = false;
        preemption_alarm = NULL;
        pending_preemption = false;
        runner.proc = &this;

        idleLock{};

        start( &this );
}

void ^?{}(processor & this) with( this ){
        if( ! __atomic_load_n(&do_terminate, __ATOMIC_ACQUIRE) ) {
                __cfaabi_dbg_print_safe("Kernel : core %p signaling termination\n", &this);

                __atomic_store_n(&do_terminate, true, __ATOMIC_RELAXED);
                wake( &this );

                P( terminated );
                verify( kernelTLS.this_processor != &this);
        }

        pthread_join( kernel_thread, NULL );
}

void ?{}(cluster & this, const char * name, Duration preemption_rate) with( this ) {
        this.name = name;
        this.preemption_rate = preemption_rate;
        ready_queue{};
        ready_queue_lock{};

        procs{ __get };
        idles{ __get };
        threads{ __get };

        doregister(this);
}

void ^?{}(cluster & this) {
        unregister(this);
}

//=============================================================================================
// Kernel Scheduling logic
//=============================================================================================
static void runThread(processor * this, thread_desc * dst);
static void finishRunning(processor * this);
static void halt(processor * this);

//Main of the processor contexts
void main(processorCtx_t & runner) {
        processor * this = runner.proc;
        verify(this);

        __cfaabi_dbg_print_safe("Kernel : core %p starting\n", this);

        doregister(this->cltr, this);

        {
                // Setup preemption data
                preemption_scope scope = { this };

                __cfaabi_dbg_print_safe("Kernel : core %p started\n", this);

                thread_desc * readyThread = NULL;
                for( unsigned int spin_count = 0; ! __atomic_load_n(&this->do_terminate, __ATOMIC_SEQ_CST); spin_count++ )
                {
                        readyThread = nextThread( this->cltr );

                        if(readyThread)
                        {
                                verify( ! kernelTLS.preemption_state.enabled );

                                runThread(this, readyThread);

                                verify( ! kernelTLS.preemption_state.enabled );

                                //Some actions need to be taken from the kernel
                                finishRunning(this);

                                spin_count = 0;
                        }
                        else
                        {
                                // spin(this, &spin_count);
                                halt(this);
                        }
                }

                __cfaabi_dbg_print_safe("Kernel : core %p stopping\n", this);
        }

        unregister(this->cltr, this);

        V( this->terminated );

        __cfaabi_dbg_print_safe("Kernel : core %p terminated\n", this);
}

// KERNEL ONLY
// runThread runs a thread by context switching
// from the processor coroutine to the target thread
static void runThread(processor * this, thread_desc * thrd_dst) {
        coroutine_desc * proc_cor = get_coroutine(this->runner);

        // Reset the terminating actions here
        this->finish.action_code = No_Action;

        // Update global state
        kernelTLS.this_thread = thrd_dst;

        // set state of processor coroutine to inactive and the thread to active
        proc_cor->state = proc_cor->state == Halted ? Halted : Inactive;
        thrd_dst->state = Active;

        // set context switch to the thread that the processor is executing
        verify( thrd_dst->context.SP );
        CtxSwitch( &proc_cor->context, &thrd_dst->context );
        // when CtxSwitch returns we are back in the processor coroutine

        // set state of processor coroutine to active and the thread to inactive
        thrd_dst->state = thrd_dst->state == Halted ? Halted : Inactive;
        proc_cor->state = Active;
}

// KERNEL_ONLY
static void returnToKernel() {
        coroutine_desc * proc_cor = get_coroutine(kernelTLS.this_processor->runner);
        thread_desc * thrd_src = kernelTLS.this_thread;

        // set state of current coroutine to inactive
        thrd_src->state = thrd_src->state == Halted ? Halted : Inactive;
        proc_cor->state = Active;

        // set new coroutine that the processor is executing
        // and context switch to it
        verify( proc_cor->context.SP );
        CtxSwitch( &thrd_src->context, &proc_cor->context );

        // set state of new coroutine to active
        proc_cor->state = proc_cor->state == Halted ? Halted : Inactive;
        thrd_src->state = Active;
}

// KERNEL_ONLY
// Once a thread has finished running, some of
// its final actions must be executed from the kernel
static void finishRunning(processor * this) with( this->finish ) {
        verify( ! kernelTLS.preemption_state.enabled );
        choose( action_code ) {
        case No_Action:
                break;
        case Release:
                unlock( *lock );
        case Schedule:
                ScheduleThread( thrd );
        case Release_Schedule:
                unlock( *lock );
                ScheduleThread( thrd );
        case Release_Multi:
                for(int i = 0; i < lock_count; i++) {
                        unlock( *locks[i] );
                }
        case Release_Multi_Schedule:
                for(int i = 0; i < lock_count; i++) {
                        unlock( *locks[i] );
                }
                for(int i = 0; i < thrd_count; i++) {
                        ScheduleThread( thrds[i] );
                }
        case Callback:
                callback();
        default:
                abort("KERNEL ERROR: Unexpected action to run after thread");
        }
}

// KERNEL_ONLY
// Context invoker for processors
// This is the entry point for processors (kernel threads)
// It effectively constructs a coroutine by stealing the pthread stack
static void * CtxInvokeProcessor(void * arg) {
        processor * proc = (processor *) arg;
        kernelTLS.this_processor = proc;
        kernelTLS.this_thread    = NULL;
        kernelTLS.preemption_state.[enabled, disable_count] = [false, 1];
        // SKULLDUGGERY: We want to create a context for the processor coroutine
        // which is needed for the 2-step context switch. However, there is no reason
        // to waste the perfectly valid stack create by pthread.
        current_stack_info_t info;
        __stack_t ctx;
        info.storage = &ctx;
        (proc->runner){ proc, &info };

        __cfaabi_dbg_print_safe("Coroutine : created stack %p\n", get_coroutine(proc->runner)->stack.storage);

        //Set global state
        kernelTLS.this_thread    = NULL;

        //We now have a proper context from which to schedule threads
        __cfaabi_dbg_print_safe("Kernel : core %p created (%p, %p)\n", proc, &proc->runner, &ctx);

        // SKULLDUGGERY: Since the coroutine doesn't have its own stack, we can't
        // resume it to start it like it normally would, it will just context switch
        // back to here. Instead directly call the main since we already are on the
        // appropriate stack.
        get_coroutine(proc->runner)->state = Active;
        main( proc->runner );
        get_coroutine(proc->runner)->state = Halted;

        // Main routine of the core returned, the core is now fully terminated
        __cfaabi_dbg_print_safe("Kernel : core %p main ended (%p)\n", proc, &proc->runner);

        return NULL;
}

static void start(processor * this) {
        __cfaabi_dbg_print_safe("Kernel : Starting core %p\n", this);

        pthread_create( &this->kernel_thread, NULL, CtxInvokeProcessor, (void*)this );

        __cfaabi_dbg_print_safe("Kernel : core %p started\n", this);
}

// KERNEL_ONLY
void kernel_first_resume( processor * this ) {
        thread_desc * src = mainThread;
        coroutine_desc * dst = get_coroutine(this->runner);

        verify( ! kernelTLS.preemption_state.enabled );

        __stack_prepare( &dst->stack, 65000 );
        CtxStart(&this->runner, CtxInvokeCoroutine);

        verify( ! kernelTLS.preemption_state.enabled );

        dst->last = &src->self_cor;
        dst->starter = dst->starter ? dst->starter : &src->self_cor;

        // set state of current coroutine to inactive
        src->state = src->state == Halted ? Halted : Inactive;

        // SKULLDUGGERY normally interrupts are enable before leaving a coroutine ctxswitch.
        // Therefore, when first creating a coroutine, interrupts are enable before calling the main.
        // This is consistent with thread creation. However, when creating the main processor coroutine,
        // we wan't interrupts to be disabled. Therefore, we double-disable interrupts here so they will
        // stay disabled.
        disable_interrupts();

        // context switch to specified coroutine
        verify( dst->context.SP );
        CtxSwitch( &src->context, &dst->context );
        // when CtxSwitch returns we are back in the src coroutine

        // set state of new coroutine to active
        src->state = Active;

        verify( ! kernelTLS.preemption_state.enabled );
}

// KERNEL_ONLY
void kernel_last_resume( processor * this ) {
        coroutine_desc * src = &mainThread->self_cor;
        coroutine_desc * dst = get_coroutine(this->runner);

        verify( ! kernelTLS.preemption_state.enabled );
        verify( dst->starter == src );
        verify( dst->context.SP );

        // context switch to the processor
        CtxSwitch( &src->context, &dst->context );
}

//-----------------------------------------------------------------------------
// Scheduler routines

// KERNEL ONLY
void ScheduleThread( thread_desc * thrd ) {
        verify( thrd );
        verify( thrd->state != Halted );

        verify( ! kernelTLS.preemption_state.enabled );

        verifyf( thrd->next == NULL, "Expected null got %p", thrd->next );

        with( *thrd->curr_cluster ) {
                lock  ( ready_queue_lock __cfaabi_dbg_ctx2 );
                bool was_empty = !(ready_queue != 0);
                append( ready_queue, thrd );
                unlock( ready_queue_lock );

                if(was_empty) {
                        lock      (proc_list_lock __cfaabi_dbg_ctx2);
                        if(idles) {
                                wake_fast(idles.head);
                        }
                        unlock    (proc_list_lock);
                }
                else if( struct processor * idle = idles.head ) {
                        wake_fast(idle);
                }

        }

        verify( ! kernelTLS.preemption_state.enabled );
}

// KERNEL ONLY
thread_desc * nextThread(cluster * this) with( *this ) {
        verify( ! kernelTLS.preemption_state.enabled );
        lock( ready_queue_lock __cfaabi_dbg_ctx2 );
        thread_desc * head = pop_head( ready_queue );
        unlock( ready_queue_lock );
        verify( ! kernelTLS.preemption_state.enabled );
        return head;
}

void BlockInternal() {
        disable_interrupts();
        verify( ! kernelTLS.preemption_state.enabled );
        returnToKernel();
        verify( ! kernelTLS.preemption_state.enabled );
        enable_interrupts( __cfaabi_dbg_ctx );
}

void BlockInternal( __spinlock_t * lock ) {
        disable_interrupts();
        with( *kernelTLS.this_processor ) {
                finish.action_code = Release;
                finish.lock        = lock;
        }

        verify( ! kernelTLS.preemption_state.enabled );
        returnToKernel();
        verify( ! kernelTLS.preemption_state.enabled );

        enable_interrupts( __cfaabi_dbg_ctx );
}

void BlockInternal( thread_desc * thrd ) {
        disable_interrupts();
        with( * kernelTLS.this_processor ) {
                finish.action_code = Schedule;
                finish.thrd        = thrd;
        }

        verify( ! kernelTLS.preemption_state.enabled );
        returnToKernel();
        verify( ! kernelTLS.preemption_state.enabled );

        enable_interrupts( __cfaabi_dbg_ctx );
}

void BlockInternal( __spinlock_t * lock, thread_desc * thrd ) {
        assert(thrd);
        disable_interrupts();
        with( * kernelTLS.this_processor ) {
                finish.action_code = Release_Schedule;
                finish.lock        = lock;
                finish.thrd        = thrd;
        }

        verify( ! kernelTLS.preemption_state.enabled );
        returnToKernel();
        verify( ! kernelTLS.preemption_state.enabled );

        enable_interrupts( __cfaabi_dbg_ctx );
}

void BlockInternal(__spinlock_t * locks [], unsigned short count) {
        disable_interrupts();
        with( * kernelTLS.this_processor ) {
                finish.action_code = Release_Multi;
                finish.locks       = locks;
                finish.lock_count  = count;
        }

        verify( ! kernelTLS.preemption_state.enabled );
        returnToKernel();
        verify( ! kernelTLS.preemption_state.enabled );

        enable_interrupts( __cfaabi_dbg_ctx );
}

void BlockInternal(__spinlock_t * locks [], unsigned short lock_count, thread_desc * thrds [], unsigned short thrd_count) {
        disable_interrupts();
        with( *kernelTLS.this_processor ) {
                finish.action_code = Release_Multi_Schedule;
                finish.locks       = locks;
                finish.lock_count  = lock_count;
                finish.thrds       = thrds;
                finish.thrd_count  = thrd_count;
        }

        verify( ! kernelTLS.preemption_state.enabled );
        returnToKernel();
        verify( ! kernelTLS.preemption_state.enabled );

        enable_interrupts( __cfaabi_dbg_ctx );
}

void BlockInternal(__finish_callback_fptr_t callback) {
        disable_interrupts();
        with( *kernelTLS.this_processor ) {
                finish.action_code = Callback;
                finish.callback    = callback;
        }

        verify( ! kernelTLS.preemption_state.enabled );
        returnToKernel();
        verify( ! kernelTLS.preemption_state.enabled );

        enable_interrupts( __cfaabi_dbg_ctx );
}

// KERNEL ONLY
void LeaveThread(__spinlock_t * lock, thread_desc * thrd) {
        verify( ! kernelTLS.preemption_state.enabled );
        with( * kernelTLS.this_processor ) {
                finish.action_code = thrd ? Release_Schedule : Release;
                finish.lock        = lock;
                finish.thrd        = thrd;
        }

        returnToKernel();
}

//=============================================================================================
// Kernel Setup logic
//=============================================================================================
//-----------------------------------------------------------------------------
// Kernel boot procedures
static void kernel_startup(void) {
        verify( ! kernelTLS.preemption_state.enabled );
        __cfaabi_dbg_print_safe("Kernel : Starting\n");

        __page_size = sysconf( _SC_PAGESIZE );

        __cfa_dbg_global_clusters.list{ __get };
        __cfa_dbg_global_clusters.lock{};

        // Initialize the main cluster
        mainCluster = (cluster *)&storage_mainCluster;
        (*mainCluster){"Main Cluster"};

        __cfaabi_dbg_print_safe("Kernel : Main cluster ready\n");

        // Start by initializing the main thread
        // SKULLDUGGERY: the mainThread steals the process main thread
        // which will then be scheduled by the mainProcessor normally
        mainThread = (thread_desc *)&storage_mainThread;
        current_stack_info_t info;
        info.storage = (__stack_t*)&storage_mainThreadCtx;
        (*mainThread){ &info };

        __cfaabi_dbg_print_safe("Kernel : Main thread ready\n");



        // Construct the processor context of the main processor
        void ?{}(processorCtx_t & this, processor * proc) {
                (this.__cor){ "Processor" };
                this.__cor.starter = NULL;
                this.proc = proc;
        }

        void ?{}(processor & this) with( this ) {
                name = "Main Processor";
                cltr = mainCluster;
                terminated{ 0 };
                do_terminate = false;
                preemption_alarm = NULL;
                pending_preemption = false;
                kernel_thread = pthread_self();

                runner{ &this };
                __cfaabi_dbg_print_safe("Kernel : constructed main processor context %p\n", &runner);
        }

        // Initialize the main processor and the main processor ctx
        // (the coroutine that contains the processing control flow)
        mainProcessor = (processor *)&storage_mainProcessor;
        (*mainProcessor){};

        //initialize the global state variables
        kernelTLS.this_processor = mainProcessor;
        kernelTLS.this_thread    = mainThread;

        // Enable preemption
        kernel_start_preemption();

        // Add the main thread to the ready queue
        // once resume is called on mainProcessor->runner the mainThread needs to be scheduled like any normal thread
        ScheduleThread(mainThread);

        // SKULLDUGGERY: Force a context switch to the main processor to set the main thread's context to the current UNIX
        // context. Hence, the main thread does not begin through CtxInvokeThread, like all other threads. The trick here is that
        // mainThread is on the ready queue when this call is made.
        kernel_first_resume( kernelTLS.this_processor );



        // THE SYSTEM IS NOW COMPLETELY RUNNING
        __cfaabi_dbg_print_safe("Kernel : Started\n--------------------------------------------------\n\n");

        verify( ! kernelTLS.preemption_state.enabled );
        enable_interrupts( __cfaabi_dbg_ctx );
        verify( TL_GET( preemption_state.enabled ) );
}

static void kernel_shutdown(void) {
        __cfaabi_dbg_print_safe("\n--------------------------------------------------\nKernel : Shutting down\n");

        verify( TL_GET( preemption_state.enabled ) );
        disable_interrupts();
        verify( ! kernelTLS.preemption_state.enabled );

        // SKULLDUGGERY: Notify the mainProcessor it needs to terminates.
        // When its coroutine terminates, it return control to the mainThread
        // which is currently here
        __atomic_store_n(&mainProcessor->do_terminate, true, __ATOMIC_RELEASE);
        kernel_last_resume( kernelTLS.this_processor );
        mainThread->self_cor.state = Halted;

        // THE SYSTEM IS NOW COMPLETELY STOPPED

        // Disable preemption
        kernel_stop_preemption();

        // Destroy the main processor and its context in reverse order of construction
        // These were manually constructed so we need manually destroy them
        ^(mainProcessor->runner){};
        ^(mainProcessor){};

        // Final step, destroy the main thread since it is no longer needed
        // Since we provided a stack to this taxk it will not destroy anything
        ^(mainThread){};

        ^(__cfa_dbg_global_clusters.list){};
        ^(__cfa_dbg_global_clusters.lock){};

        __cfaabi_dbg_print_safe("Kernel : Shutdown complete\n");
}

//=============================================================================================
// Kernel Quiescing
//=============================================================================================
static void halt(processor * this) with( *this ) {
        // verify( ! __atomic_load_n(&do_terminate, __ATOMIC_SEQ_CST) );

        with( *cltr ) {
                lock      (proc_list_lock __cfaabi_dbg_ctx2);
                remove    (procs, *this);
                push_front(idles, *this);
                unlock    (proc_list_lock);
        }

        __cfaabi_dbg_print_safe("Kernel : Processor %p ready to sleep\n", this);

        wait( idleLock );

        __cfaabi_dbg_print_safe("Kernel : Processor %p woke up and ready to run\n", this);

        with( *cltr ) {
                lock      (proc_list_lock __cfaabi_dbg_ctx2);
                remove    (idles, *this);
                push_front(procs, *this);
                unlock    (proc_list_lock);
        }
}

//=============================================================================================
// Unexpected Terminating logic
//=============================================================================================
static __spinlock_t kernel_abort_lock;
static bool kernel_abort_called = false;

void * kernel_abort(void) __attribute__ ((__nothrow__)) {
        // abort cannot be recursively entered by the same or different processors because all signal handlers return when
        // the globalAbort flag is true.
        lock( kernel_abort_lock __cfaabi_dbg_ctx2 );

        // first task to abort ?
        if ( kernel_abort_called ) {                    // not first task to abort ?
                unlock( kernel_abort_lock );

                sigset_t mask;
                sigemptyset( &mask );
                sigaddset( &mask, SIGALRM );            // block SIGALRM signals
                sigsuspend( &mask );                    // block the processor to prevent further damage during abort
                _exit( EXIT_FAILURE );                  // if processor unblocks before it is killed, terminate it
        }
        else {
                kernel_abort_called = true;
                unlock( kernel_abort_lock );
        }

        return kernelTLS.this_thread;
}

void kernel_abort_msg( void * kernel_data, char * abort_text, int abort_text_size ) {
        thread_desc * thrd = kernel_data;

        if(thrd) {
                int len = snprintf( abort_text, abort_text_size, "Error occurred while executing thread %.256s (%p)", thrd->self_cor.name, thrd );
                __cfaabi_dbg_bits_write( abort_text, len );

                if ( &thrd->self_cor != thrd->curr_cor ) {
                        len = snprintf( abort_text, abort_text_size, " in coroutine %.256s (%p).\n", thrd->curr_cor->name, thrd->curr_cor );
                        __cfaabi_dbg_bits_write( abort_text, len );
                }
                else {
                        __cfaabi_dbg_bits_write( ".\n", 2 );
                }
        }
        else {
                int len = snprintf( abort_text, abort_text_size, "Error occurred outside of any thread.\n" );
                __cfaabi_dbg_bits_write( abort_text, len );
        }
}

int kernel_abort_lastframe( void ) __attribute__ ((__nothrow__)) {
        return get_coroutine(kernelTLS.this_thread) == get_coroutine(mainThread) ? 4 : 2;
}

static __spinlock_t kernel_debug_lock;

extern "C" {
        void __cfaabi_dbg_bits_acquire() {
                lock( kernel_debug_lock __cfaabi_dbg_ctx2 );
        }

        void __cfaabi_dbg_bits_release() {
                unlock( kernel_debug_lock );
        }
}

//=============================================================================================
// Kernel Utilities
//=============================================================================================
//-----------------------------------------------------------------------------
// Locks
void  ?{}( semaphore & this, int count = 1 ) {
        (this.lock){};
        this.count = count;
        (this.waiting){};
}
void ^?{}(semaphore & this) {}

void P(semaphore & this) with( this ){
        lock( lock __cfaabi_dbg_ctx2 );
        count -= 1;
        if ( count < 0 ) {
                // queue current task
                append( waiting, kernelTLS.this_thread );

                // atomically release spin lock and block
                BlockInternal( &lock );
        }
        else {
            unlock( lock );
        }
}

void V(semaphore & this) with( this ) {
        thread_desc * thrd = NULL;
        lock( lock __cfaabi_dbg_ctx2 );
        count += 1;
        if ( count <= 0 ) {
                // remove task at head of waiting list
                thrd = pop_head( waiting );
        }

        unlock( lock );

        // make new owner
        WakeThread( thrd );
}

//-----------------------------------------------------------------------------
// Global Queues
void doregister( cluster     & cltr ) {
        lock      ( __cfa_dbg_global_clusters.lock __cfaabi_dbg_ctx2);
        push_front( __cfa_dbg_global_clusters.list, cltr );
        unlock    ( __cfa_dbg_global_clusters.lock );
}

void unregister( cluster     & cltr ) {
        lock  ( __cfa_dbg_global_clusters.lock __cfaabi_dbg_ctx2);
        remove( __cfa_dbg_global_clusters.list, cltr );
        unlock( __cfa_dbg_global_clusters.lock );
}

void doregister( cluster * cltr, thread_desc & thrd ) {
        lock      (cltr->thread_list_lock __cfaabi_dbg_ctx2);
        push_front(cltr->threads, thrd);
        unlock    (cltr->thread_list_lock);
}

void unregister( cluster * cltr, thread_desc & thrd ) {
        lock  (cltr->thread_list_lock __cfaabi_dbg_ctx2);
        remove(cltr->threads, thrd );
        unlock(cltr->thread_list_lock);
}

void doregister( cluster * cltr, processor * proc ) {
        lock      (cltr->proc_list_lock __cfaabi_dbg_ctx2);
        push_front(cltr->procs, *proc);
        unlock    (cltr->proc_list_lock);
}

void unregister( cluster * cltr, processor * proc ) {
        lock  (cltr->proc_list_lock __cfaabi_dbg_ctx2);
        remove(cltr->procs, *proc );
        unlock(cltr->proc_list_lock);
}

//-----------------------------------------------------------------------------
// Debug
__cfaabi_dbg_debug_do(
        extern "C" {
                void __cfaabi_dbg_record(__spinlock_t & this, const char * prev_name) {
                        this.prev_name = prev_name;
                        this.prev_thrd = kernelTLS.this_thread;
                }
        }
)
// Local Variables: //
// mode: c //
// tab-width: 4 //
// End: //