source: libcfa/src/concurrency/kernel.cfa @ 0cc43e1

//
// 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 Aug 31 07:08:20 2020
// Update Count     : 71
//

#define __cforall_thread__
// #define __CFA_DEBUG_PRINT_RUNTIME_CORE__

//C Includes
#include <errno.h>
#include <stdio.h>
#include <signal.h>
#include <unistd.h>

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

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


//-----------------------------------------------------------------------------
// Some assembly required
#if defined( __i386 )
        // mxcr : SSE Status and Control bits (control bits are preserved across function calls)
        // fcw  : X87 FPU control word (preserved across function calls)
        #define __x87_store         \
                uint32_t __mxcr;      \
                uint16_t __fcw;       \
                __asm__ volatile (    \
                        "stmxcsr %0\n"  \
                        "fnstcw  %1\n"  \
                        : "=m" (__mxcr),\
                                "=m" (__fcw)  \
                )

        #define __x87_load         \
                __asm__ volatile (   \
                        "fldcw  %1\n"  \
                        "ldmxcsr %0\n" \
                        ::"m" (__mxcr),\
                                "m" (__fcw)  \
                )

#elif defined( __x86_64 )
        #define __x87_store         \
                uint32_t __mxcr;      \
                uint16_t __fcw;       \
                __asm__ volatile (    \
                        "stmxcsr %0\n"  \
                        "fnstcw  %1\n"  \
                        : "=m" (__mxcr),\
                                "=m" (__fcw)  \
                )

        #define __x87_load          \
                __asm__ volatile (    \
                        "fldcw  %1\n"   \
                        "ldmxcsr %0\n"  \
                        :: "m" (__mxcr),\
                                "m" (__fcw)  \
                )

#elif defined( __arm__ )
        #define __x87_store
        #define __x87_load

#elif defined( __aarch64__ )
        #define __x87_store              \
                uint32_t __fpcntl[2];    \
                __asm__ volatile (    \
                        "mrs x9, FPCR\n" \
                        "mrs x10, FPSR\n"  \
                        "stp x9, x10, %0\n"  \
                        : "=m" (__fpcntl) : : "x9", "x10" \
                )

        #define __x87_load         \
                __asm__ volatile (    \
                        "ldp x9, x10, %0\n"  \
                        "msr FPSR, x10\n"  \
                        "msr FPCR, x9\n" \
                : "=m" (__fpcntl) : : "x9", "x10" \
                )

#else
        #error unsupported hardware architecture
#endif

extern $thread * mainThread;
extern processor * mainProcessor;

//-----------------------------------------------------------------------------
// Kernel Scheduling logic
static $thread * __next_thread(cluster * this);
static $thread * __next_thread_slow(cluster * this);
static void __run_thread(processor * this, $thread * dst);
static void __wake_one(cluster * cltr);

static void push  (__cluster_idles & idles, processor & proc);
static void remove(__cluster_idles & idles, processor & proc);
static [unsigned idle, unsigned total, * processor] query( & __cluster_idles idles );


//=============================================================================================
// Kernel Scheduling logic
//=============================================================================================
//Main of the processor contexts
void main(processorCtx_t & runner) {
        // Because of a bug, we couldn't initialized the seed on construction
        // Do it here
        __cfaabi_tls.rand_seed ^= rdtscl();
        __cfaabi_tls.ready_rng.fwd_seed = 25214903917_l64u * (rdtscl() ^ (uintptr_t)&runner);
        __tls_rand_advance_bck();

        processor * this = runner.proc;
        verify(this);

        __cfadbg_print_safe(runtime_core, "Kernel : core %p starting\n", this);
        #if !defined(__CFA_NO_STATISTICS__)
                if( this->print_halts ) {
                        __cfaabi_bits_print_safe( STDOUT_FILENO, "Processor : %d - %s (%p)\n", this->id, this->name, (void*)this);
                }
        #endif

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

                #if !defined(__CFA_NO_STATISTICS__)
                        unsigned long long last_tally = rdtscl();
                #endif


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

                $thread * readyThread = 0p;
                MAIN_LOOP:
                for() {
                        // Try to get the next thread
                        readyThread = __next_thread( this->cltr );

                        if( !readyThread ) {
                                readyThread = __next_thread_slow( this->cltr );
                        }

                        HALT:
                        if( !readyThread ) {
                                // Don't block if we are done
                                if( __atomic_load_n(&this->do_terminate, __ATOMIC_SEQ_CST) ) break MAIN_LOOP;

                                #if !defined(__CFA_NO_STATISTICS__)
                                        __tls_stats()->ready.sleep.halts++;
                                #endif

                                // Push self to idle stack
                                push(this->cltr->idles, * this);

                                // Confirm the ready-queue is empty
                                readyThread = __next_thread_slow( this->cltr );
                                if( readyThread ) {
                                        // A thread was found, cancel the halt
                                        remove(this->cltr->idles, * this);

                                        #if !defined(__CFA_NO_STATISTICS__)
                                                __tls_stats()->ready.sleep.cancels++;
                                        #endif

                                        // continue the mai loop
                                        break HALT;
                                }

                                #if !defined(__CFA_NO_STATISTICS__)
                                        if(this->print_halts) {
                                                __cfaabi_bits_print_safe( STDOUT_FILENO, "PH:%d - %lld 0\n", this->id, rdtscl());
                                        }
                                #endif

                                wait( this->idle );

                                #if !defined(__CFA_NO_STATISTICS__)
                                        if(this->print_halts) {
                                                __cfaabi_bits_print_safe( STDOUT_FILENO, "PH:%d - %lld 1\n", this->id, rdtscl());
                                        }
                                #endif

                                // We were woken up, remove self from idle
                                remove(this->cltr->idles, * this);

                                // DON'T just proceed, start looking again
                                continue MAIN_LOOP;
                        }

                        /* paranoid */ verify( readyThread );

                        // We found a thread run it
                        __run_thread(this, readyThread);

                        // Are we done?
                        if( __atomic_load_n(&this->do_terminate, __ATOMIC_SEQ_CST) ) break MAIN_LOOP;

                        #if !defined(__CFA_NO_STATISTICS__)
                                unsigned long long curr = rdtscl();
                                if(curr > (last_tally + 500000000)) {
                                        __tally_stats(this->cltr->stats, __cfaabi_tls.this_stats);
                                        last_tally = curr;
                                }
                        #endif
                }

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

        V( this->terminated );

        if(this == mainProcessor) {
                // HACK : the coroutine context switch expects this_thread to be set
                // and it make sense for it to be set in all other cases except here
                // fake it
                __cfaabi_tls.this_thread = mainThread;
        }

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

static int * __volatile_errno() __attribute__((noinline));
static int * __volatile_errno() { asm(""); return &errno; }

// KERNEL ONLY
// runThread runs a thread by context switching
// from the processor coroutine to the target thread
static void __run_thread(processor * this, $thread * thrd_dst) {
        /* paranoid */ verify( ! __preemption_enabled() );
        /* paranoid */ verifyf( thrd_dst->state == Ready || thrd_dst->preempted != __NO_PREEMPTION, "state : %d, preempted %d\n", thrd_dst->state, thrd_dst->preempted);
        /* paranoid */ verifyf( thrd_dst->link.next == 0p, "Expected null got %p", thrd_dst->link.next );
        __builtin_prefetch( thrd_dst->context.SP );

        $coroutine * proc_cor = get_coroutine(this->runner);

        // set state of processor coroutine to inactive
        verify(proc_cor->state == Active);
        proc_cor->state = Blocked;

        // Actually run the thread
        RUNNING:  while(true) {
                thrd_dst->preempted = __NO_PREEMPTION;
                thrd_dst->state = Active;

                // Update global state
                kernelTLS().this_thread = thrd_dst;

                /* paranoid */ verify( ! __preemption_enabled() );
                /* paranoid */ verify( kernelTLS().this_thread == thrd_dst );
                /* paranoid */ verify( thrd_dst->curr_cluster == this->cltr );
                /* paranoid */ verify( thrd_dst->context.SP );
                /* paranoid */ verify( thrd_dst->state != Halted );
                /* paranoid */ verifyf( ((uintptr_t)thrd_dst->context.SP) < ((uintptr_t)__get_stack(thrd_dst->curr_cor)->base ) || thrd_dst->curr_cor == proc_cor, "ERROR : Destination $thread %p has been corrupted.\n StackPointer too small.\n", thrd_dst ); // add escape condition if we are setting up the processor
                /* paranoid */ verifyf( ((uintptr_t)thrd_dst->context.SP) > ((uintptr_t)__get_stack(thrd_dst->curr_cor)->limit) || thrd_dst->curr_cor == proc_cor, "ERROR : Destination $thread %p has been corrupted.\n StackPointer too large.\n", thrd_dst ); // add escape condition if we are setting up the processor
                /* paranoid */ verify( 0x0D15EA5E0D15EA5Ep == thrd_dst->canary );



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

                /* paranoid */ verify( 0x0D15EA5E0D15EA5Ep == thrd_dst->canary );
                /* paranoid */ verifyf( ((uintptr_t)thrd_dst->context.SP) > ((uintptr_t)__get_stack(thrd_dst->curr_cor)->limit), "ERROR : Destination $thread %p has been corrupted.\n StackPointer too large.\n", thrd_dst );
                /* paranoid */ verifyf( ((uintptr_t)thrd_dst->context.SP) < ((uintptr_t)__get_stack(thrd_dst->curr_cor)->base ), "ERROR : Destination $thread %p has been corrupted.\n StackPointer too small.\n", thrd_dst );
                /* paranoid */ verify( thrd_dst->context.SP );
                /* paranoid */ verify( thrd_dst->curr_cluster == this->cltr );
                /* paranoid */ verify( kernelTLS().this_thread == thrd_dst );
                /* paranoid */ verify( ! __preemption_enabled() );

                // Reset global state
                kernelTLS().this_thread = 0p;

                // We just finished running a thread, there are a few things that could have happened.
                // 1 - Regular case : the thread has blocked and now one has scheduled it yet.
                // 2 - Racy case    : the thread has blocked but someone has already tried to schedule it.
                // 4 - Preempted
                // In case 1, we may have won a race so we can't write to the state again.
                // In case 2, we lost the race so we now own the thread.

                if(unlikely(thrd_dst->preempted != __NO_PREEMPTION)) {
                        // The thread was preempted, reschedule it and reset the flag
                        __schedule_thread( thrd_dst );
                        break RUNNING;
                }

                if(unlikely(thrd_dst->state == Halting)) {
                        // The thread has halted, it should never be scheduled/run again
                        // finish the thread
                        __thread_finish( thrd_dst );
                        break RUNNING;
                }

                /* paranoid */ verify( thrd_dst->state == Active );
                thrd_dst->state = Blocked;

                // set state of processor coroutine to active and the thread to inactive
                int old_ticket = __atomic_fetch_sub(&thrd_dst->ticket, 1, __ATOMIC_SEQ_CST);
                switch(old_ticket) {
                        case TICKET_RUNNING:
                                // This is case 1, the regular case, nothing more is needed
                                break RUNNING;
                        case TICKET_UNBLOCK:
                                // This is case 2, the racy case, someone tried to run this thread before it finished blocking
                                // In this case, just run it again.
                                continue RUNNING;
                        default:
                                // This makes no sense, something is wrong abort
                                abort();
                }
        }

        // Just before returning to the processor, set the processor coroutine to active
        proc_cor->state = Active;

        /* paranoid */ verify( ! __preemption_enabled() );
}

// KERNEL_ONLY
void returnToKernel() {
        /* paranoid */ verify( ! __preemption_enabled() );
        $coroutine * proc_cor = get_coroutine(kernelTLS().this_processor->runner);
        $thread * thrd_src = kernelTLS().this_thread;

        #if !defined(__CFA_NO_STATISTICS__)
                struct processor * last_proc = kernelTLS().this_processor;
        #endif

        // Run the thread on this processor
        {
                int local_errno = *__volatile_errno();
                #if defined( __i386 ) || defined( __x86_64 )
                        __x87_store;
                #endif
                /* paranoid */ verify( proc_cor->context.SP );
                /* paranoid */ verify( 0x0D15EA5E0D15EA5Ep == thrd_src->canary );
                __cfactx_switch( &thrd_src->context, &proc_cor->context );
                /* paranoid */ verify( 0x0D15EA5E0D15EA5Ep == thrd_src->canary );
                #if defined( __i386 ) || defined( __x86_64 )
                        __x87_load;
                #endif
                *__volatile_errno() = local_errno;
        }

        #if !defined(__CFA_NO_STATISTICS__)
                if(last_proc != kernelTLS().this_processor) {
                        __tls_stats()->ready.threads.migration++;
                }
        #endif

        /* paranoid */ verify( ! __preemption_enabled() );
        /* paranoid */ verifyf( ((uintptr_t)thrd_src->context.SP) < ((uintptr_t)__get_stack(thrd_src->curr_cor)->base ), "ERROR : Returning $thread %p has been corrupted.\n StackPointer too small.\n", thrd_src );
        /* paranoid */ verifyf( ((uintptr_t)thrd_src->context.SP) > ((uintptr_t)__get_stack(thrd_src->curr_cor)->limit), "ERROR : Returning $thread %p has been corrupted.\n StackPointer too large.\n", thrd_src );
}

//-----------------------------------------------------------------------------
// Scheduler routines
// KERNEL ONLY
void __schedule_thread( $thread * thrd ) {
        /* paranoid */ verify( ! __preemption_enabled() );
        /* paranoid */ verify( kernelTLS().this_proc_id );
        /* paranoid */ verify( thrd );
        /* paranoid */ verify( thrd->state != Halted );
        /* paranoid */ verify( thrd->curr_cluster );
        /* paranoid */ #if defined( __CFA_WITH_VERIFY__ )
        /* paranoid */  if( thrd->state == Blocked || thrd->state == Start ) assertf( thrd->preempted == __NO_PREEMPTION,
                                        "Error inactive thread marked as preempted, state %d, preemption %d\n", thrd->state, thrd->preempted );
        /* paranoid */  if( thrd->preempted != __NO_PREEMPTION ) assertf(thrd->state == Active,
                                        "Error preempted thread marked as not currently running, state %d, preemption %d\n", thrd->state, thrd->preempted );
        /* paranoid */ #endif
        /* paranoid */ verifyf( thrd->link.next == 0p, "Expected null got %p", thrd->link.next );
        /* paranoid */ verify( 0x0D15EA5E0D15EA5Ep == thrd->canary );


        if (thrd->preempted == __NO_PREEMPTION) thrd->state = Ready;

        ready_schedule_lock();
                // Dereference the thread now because once we push it, there is not guaranteed it's still valid.
                struct cluster * cl = thrd->curr_cluster;

                // push the thread to the cluster ready-queue
                push( cl, thrd );

                // variable thrd is no longer safe to use

                // wake the cluster using the save variable.
                __wake_one( cl );
        ready_schedule_unlock();

        /* paranoid */ verify( ! __preemption_enabled() );
}

// KERNEL ONLY
static inline $thread * __next_thread(cluster * this) with( *this ) {
        /* paranoid */ verify( ! __preemption_enabled() );
        /* paranoid */ verify( kernelTLS().this_proc_id );

        ready_schedule_lock();
                $thread * thrd = pop( this );
        ready_schedule_unlock();

        /* paranoid */ verify( kernelTLS().this_proc_id );
        /* paranoid */ verify( ! __preemption_enabled() );
        return thrd;
}

// KERNEL ONLY
static inline $thread * __next_thread_slow(cluster * this) with( *this ) {
        /* paranoid */ verify( ! __preemption_enabled() );
        /* paranoid */ verify( kernelTLS().this_proc_id );

        ready_schedule_lock();
                $thread * thrd = pop_slow( this );
        ready_schedule_unlock();

        /* paranoid */ verify( kernelTLS().this_proc_id );
        /* paranoid */ verify( ! __preemption_enabled() );
        return thrd;
}

void unpark( $thread * thrd ) {
        if( !thrd ) return;

        int old_ticket = __atomic_fetch_add(&thrd->ticket, 1, __ATOMIC_SEQ_CST);
        switch(old_ticket) {
                case TICKET_RUNNING:
                        // Wake won the race, the thread will reschedule/rerun itself
                        break;
                case TICKET_BLOCKED:
                        /* paranoid */ verify( ! thrd->preempted != __NO_PREEMPTION );
                        /* paranoid */ verify( thrd->state == Blocked );

                        {
                                /* paranoid */ verify( publicTLS_get(this_proc_id) );
                                bool full = publicTLS_get(this_proc_id)->full_proc;
                                if(full) disable_interrupts();

                                /* paranoid */ verify( ! __preemption_enabled() );

                                // Wake lost the race,
                                __schedule_thread( thrd );

                                /* paranoid */ verify( ! __preemption_enabled() );

                                if(full) enable_interrupts( __cfaabi_dbg_ctx );
                                /* paranoid */ verify( publicTLS_get(this_proc_id) );
                        }

                        break;
                default:
                        // This makes no sense, something is wrong abort
                        abort("Thread %p (%s) has mismatch park/unpark\n", thrd, thrd->self_cor.name);
        }
}

void park( void ) {
        /* paranoid */ verify( __preemption_enabled() );
        disable_interrupts();
        /* paranoid */ verify( ! __preemption_enabled() );
        /* paranoid */ verify( kernelTLS().this_thread->preempted == __NO_PREEMPTION );

        returnToKernel();

        /* paranoid */ verify( ! __preemption_enabled() );
        enable_interrupts( __cfaabi_dbg_ctx );
        /* paranoid */ verify( __preemption_enabled() );

}

extern "C" {
        // Leave the thread monitor
        // last routine called by a thread.
        // Should never return
        void __cfactx_thrd_leave() {
                $thread * thrd = active_thread();
                $monitor * this = &thrd->self_mon;

                // Lock the monitor now
                lock( this->lock __cfaabi_dbg_ctx2 );

                disable_interrupts();

                /* paranoid */ verify( ! __preemption_enabled() );
                /* paranoid */ verify( thrd->state == Active );
                /* paranoid */ verify( 0x0D15EA5E0D15EA5Ep == thrd->canary );
                /* paranoid */ verify( kernelTLS().this_thread == thrd );
                /* paranoid */ verify( thrd->context.SP );
                /* paranoid */ verifyf( ((uintptr_t)thrd->context.SP) > ((uintptr_t)__get_stack(thrd->curr_cor)->limit), "ERROR : $thread %p has been corrupted.\n StackPointer too large.\n", thrd );
                /* paranoid */ verifyf( ((uintptr_t)thrd->context.SP) < ((uintptr_t)__get_stack(thrd->curr_cor)->base ), "ERROR : $thread %p has been corrupted.\n StackPointer too small.\n", thrd );

                thrd->state = Halting;
                if( TICKET_RUNNING != thrd->ticket ) { abort( "Thread terminated with pending unpark" ); }
                if( thrd != this->owner ) { abort( "Thread internal monitor has incorrect owner" ); }
                if( this->recursion != 1) { abort( "Thread internal monitor has unbalanced recursion" ); }

                // Leave the thread
                returnToKernel();

                // Control flow should never reach here!
                abort();
        }
}

// KERNEL ONLY
bool force_yield( __Preemption_Reason reason ) {
        /* paranoid */ verify( __preemption_enabled() );
        disable_interrupts();
        /* paranoid */ verify( ! __preemption_enabled() );

        $thread * thrd = kernelTLS().this_thread;
        /* paranoid */ verify(thrd->state == Active);

        // SKULLDUGGERY: It is possible that we are preempting this thread just before
        // it was going to park itself. If that is the case and it is already using the
        // intrusive fields then we can't use them to preempt the thread
        // If that is the case, abandon the preemption.
        bool preempted = false;
        if(thrd->link.next == 0p) {
                preempted = true;
                thrd->preempted = reason;
                returnToKernel();
        }

        /* paranoid */ verify( ! __preemption_enabled() );
        enable_interrupts_noPoll();
        /* paranoid */ verify( __preemption_enabled() );

        return preempted;
}

//=============================================================================================
// Kernel Idle Sleep
//=============================================================================================
// Wake a thread from the front if there are any
static void __wake_one(cluster * this) {
        /* paranoid */ verify( ! __preemption_enabled() );
        /* paranoid */ verify( ready_schedule_islocked() );

        // Check if there is a sleeping processor
        processor * p;
        unsigned idle;
        unsigned total;
        [idle, total, p] = query(this->idles);

        // If no one is sleeping, we are done
        if( idle == 0 ) return;

        // We found a processor, wake it up
        post( p->idle );

        #if !defined(__CFA_NO_STATISTICS__)
                __tls_stats()->ready.sleep.wakes++;
        #endif

        /* paranoid */ verify( ready_schedule_islocked() );
        /* paranoid */ verify( ! __preemption_enabled() );

        return;
}

// Unconditionnaly wake a thread
void __wake_proc(processor * this) {
        __cfadbg_print_safe(runtime_core, "Kernel : waking Processor %p\n", this);

        disable_interrupts();
                /* paranoid */ verify( ! __preemption_enabled() );
                post( this->idle );
        enable_interrupts( __cfaabi_dbg_ctx );
}

static void push  (__cluster_idles & this, processor & proc) {
        /* paranoid */ verify( ! __preemption_enabled() );
        lock( this );
                this.idle++;
                /* paranoid */ verify( this.idle <= this.total );

                insert_first(this.list, proc);
        unlock( this );
        /* paranoid */ verify( ! __preemption_enabled() );
}

static void remove(__cluster_idles & this, processor & proc) {
        /* paranoid */ verify( ! __preemption_enabled() );
        lock( this );
                this.idle--;
                /* paranoid */ verify( this.idle >= 0 );

                remove(proc);
        unlock( this );
        /* paranoid */ verify( ! __preemption_enabled() );
}

static [unsigned idle, unsigned total, * processor] query( & __cluster_idles this ) {
        for() {
                uint64_t l = __atomic_load_n(&this.lock, __ATOMIC_SEQ_CST);
                if( 1 == (l % 2) ) { Pause(); continue; }
                unsigned idle    = this.idle;
                unsigned total   = this.total;
                processor * proc = &this.list`first;
                // Compiler fence is unnecessary, but gcc-8 and older incorrectly reorder code without it
                asm volatile("": : :"memory");
                if(l != __atomic_load_n(&this.lock, __ATOMIC_SEQ_CST)) { Pause(); continue; }
                return [idle, total, proc];
        }
}

//=============================================================================================
// Unexpected Terminating logic
//=============================================================================================

extern "C" {
        extern void __cfaabi_real_abort(void);
}
static volatile 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.
        bool first = __atomic_test_and_set( &kernel_abort_called, __ATOMIC_SEQ_CST);

        // first task to abort ?
        if ( !first ) {
                // We aren't the first to abort.
                // I give up, just let C handle it
                __cfaabi_real_abort();
        }

        // disable interrupts, it no longer makes sense to try to interrupt this processor
        disable_interrupts();

        return __cfaabi_tls.this_thread;
}

void kernel_abort_msg( void * kernel_data, char * abort_text, int abort_text_size ) {
        $thread * thrd = ( $thread * ) 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_bits_write( STDERR_FILENO, 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_bits_write( STDERR_FILENO, abort_text, len );
                }
                else {
                        __cfaabi_bits_write( STDERR_FILENO, ".\n", 2 );
                }
        }
        else {
                int len = snprintf( abort_text, abort_text_size, "Error occurred outside of any thread.\n" );
                __cfaabi_bits_write( STDERR_FILENO, 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_bits_acquire() {
                lock( kernel_debug_lock __cfaabi_dbg_ctx2 );
        }

        void __cfaabi_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) {}

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

                // atomically release spin lock and block
                unlock( lock );
                park();
                return true;
        }
        else {
            unlock( lock );
            return false;
        }
}

bool V(semaphore & this) with( this ) {
        $thread * thrd = 0p;
        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
        unpark( thrd );

        return thrd != 0p;
}

bool V(semaphore & this, unsigned diff) with( this ) {
        $thread * thrd = 0p;
        lock( lock __cfaabi_dbg_ctx2 );
        int release = max(-count, (int)diff);
        count += diff;
        for(release) {
                unpark( pop_head( waiting ) );
        }

        unlock( lock );

        return thrd != 0p;
}

//-----------------------------------------------------------------------------
// Debug
__cfaabi_dbg_debug_do(
        extern "C" {
                void __cfaabi_dbg_record_lock(__spinlock_t & this, const char prev_name[]) {
                        this.prev_name = prev_name;
                        this.prev_thrd = kernelTLS().this_thread;
                }
        }
)

//-----------------------------------------------------------------------------
// Debug
bool threading_enabled(void) __attribute__((const)) {
        return true;
}

//-----------------------------------------------------------------------------
// Statistics
#if !defined(__CFA_NO_STATISTICS__)
        void print_halts( processor & this ) {
                this.print_halts = true;
        }

        void print_stats_now( cluster & this, int flags ) {
                __print_stats( this.stats, this.print_stats, "Cluster", this.name, (void*)&this );
        }

        extern int __print_alarm_stats;
        void print_alarm_stats() {
                __print_alarm_stats = -1;
        }
#endif
// Local Variables: //
// mode: c //
// tab-width: 4 //
// End: //