Changes in libcfa/src/concurrency/kernel.cfa [e3fea42:8c50aed]

File:

• libcfa/src/concurrency/kernel.cfa (modified) (25 diffs)

libcfa/src/concurrency/kernel.cfa

@@ -10 +10 @@
 // Created On       : Tue Jan 17 12:27:26 2017
 // Last Modified By : Peter A. Buhr
-// Last Modified On : Tue Feb  4 13:03:15 2020
-// Update Count     : 58
+// Last Modified On : Thu Jan 30 22:55:50 2020
+// Update Count     : 56
 //
 
@@ -110 +110 @@
 //-----------------------------------------------------------------------------
 //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 ) ));
+static void __kernel_startup (void) __attribute__(( constructor( STARTUP_PRIORITY_KERNEL ) ));
+static void __kernel_shutdown(void) __attribute__(( destructor ( STARTUP_PRIORITY_KERNEL ) ));
 
 //-----------------------------------------------------------------------------
@@ -208 +208 @@
 }
 
-static void start(processor * this);
-void ?{}(processor & this, const char name[], cluster & cltr) with( this ) {
+static void * CtxInvokeProcessor(void * arg);
+
+void ?{}(processor & this, const char * name, cluster & cltr) with( this ) {
         this.name = name;
         this.cltr = &cltr;
         terminated{ 0 };
+        destroyer = 0p;
         do_terminate = false;
         preemption_alarm = 0p;
@@ -220 +222 @@
         idleLock{};
 
-        start( &this );
+        __cfaabi_dbg_print_safe("Kernel : Starting core %p\n", &this);
+
+        this.stack = __create_pthread( &this.kernel_thread, CtxInvokeProcessor, (void *)&this );
+
+        __cfaabi_dbg_print_safe("Kernel : core %p started\n", &this);
 }
 
@@ -238 +244 @@
 }
 
-void ?{}(cluster & this, const char name[], Duration preemption_rate) with( this ) {
+void ?{}(cluster & this, const char * name, Duration preemption_rate) with( this ) {
         this.name = name;
         this.preemption_rate = preemption_rate;
@@ -258 +264 @@
 // Kernel Scheduling logic
 //=============================================================================================
-static void runThread(processor * this, thread_desc * dst);
-static void finishRunning(processor * this);
-static void halt(processor * this);
+static thread_desc * __next_thread(cluster * this);
+static void __run_thread(processor * this, thread_desc * dst);
+static void __halt(processor * this);
 
 //Main of the processor contexts
@@ -283 +289 @@
                 thread_desc * readyThread = 0p;
                 for( unsigned int spin_count = 0; ! __atomic_load_n(&this->do_terminate, __ATOMIC_SEQ_CST); spin_count++ ) {
-                        readyThread = nextThread( this->cltr );
+                        readyThread = __next_thread( 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);
+                                /* paranoid */ verify( ! kernelTLS.preemption_state.enabled );
+                                /* paranoid */ verifyf( readyThread->state == Inactive || readyThread->state == Start || readyThread->preempted != __NO_PREEMPTION, "state : %d, preempted %d\n", readyThread->state, readyThread->preempted);
+                                /* paranoid */ verifyf( readyThread->next == 0p, "Expected null got %p", readyThread->next );
+
+                                __run_thread(this, readyThread);
+
+                                /* paranoid */ verify( ! kernelTLS.preemption_state.enabled );
 
                                 spin_count = 0;
                         } else {
                                 // spin(this, &spin_count);
-                                halt(this);
+                                __halt(this);
                         }
                 }
@@ -318 +323 @@
 // runThread runs a thread by context switching
 // from the processor coroutine to the target thread
-static void runThread(processor * this, thread_desc * thrd_dst) {
+static void __run_thread(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;
+        // set state of processor coroutine to inactive
+        verify(proc_cor->state == Active);
+        proc_cor->state = Inactive;
+
+        // Actually run the thread
+        RUNNING:  while(true) {
+                if(unlikely(thrd_dst->preempted)) {
+                        thrd_dst->preempted = __NO_PREEMPTION;
+                        verify(thrd_dst->state == Active || thrd_dst->state == Rerun);
+                } else {
+                        verify(thrd_dst->state == Start || thrd_dst->state == Primed || thrd_dst->state == Inactive);
+                        thrd_dst->state = Active;
+                }
+
+                /* paranoid */ verify( ! kernelTLS.preemption_state.enabled );
+
+                // 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
+
+                /* paranoid */ verify( ! kernelTLS.preemption_state.enabled );
+
+
+                // 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.
+                // 3 - Polite Racy case : the thread has blocked, someone has already tried to schedule it, but the thread is nice and wants to go through the ready-queue any way
+                // 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.
+                // In case 3, we lost the race but can just reschedule 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;
+                }
+
+                // set state of processor coroutine to active and the thread to inactive
+                static_assert(sizeof(thrd_dst->state) == sizeof(int));
+                enum coroutine_state old_state = __atomic_exchange_n(&thrd_dst->state, Inactive, __ATOMIC_SEQ_CST);
+                switch(old_state) {
+                        case Halted:
+                                // The thread has halted, it should never be scheduled/run again, leave it back to Halted and move on
+                                thrd_dst->state = Halted;
+
+                                // We may need to wake someone up here since
+                                unpark( this->destroyer );
+                                this->destroyer = 0p;
+                                break RUNNING;
+                        case Active:
+                                // This is case 1, the regular case, nothing more is needed
+                                break RUNNING;
+                        case Rerun:
+                                // 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("Finished running a thread that was Inactive/Start/Primed %d\n", old_state);
+                }
+        }
+
+        // Just before returning to the processor, set the processor coroutine to active
         proc_cor->state = Active;
 }
 
 // KERNEL_ONLY
-static void returnToKernel() {
+void returnToKernel() {
+        /* paranoid */ verify( ! kernelTLS.preemption_state.enabled );
         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;
-        int local_errno = *__volatile_errno();
-        #if defined( __i386 ) || defined( __x86_64 )
-                __x87_store;
-        #endif
-
-        // 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;
-
-        #if defined( __i386 ) || defined( __x86_64 )
-                __x87_load;
-        #endif
-        *__volatile_errno() = local_errno;
-}
-
-// 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");
-        }
+        // Run the thread on this processor
+        {
+                int local_errno = *__volatile_errno();
+                #if defined( __i386 ) || defined( __x86_64 )
+                        __x87_store;
+                #endif
+                verify( proc_cor->context.SP );
+                CtxSwitch( &thrd_src->context, &proc_cor->context );
+                #if defined( __i386 ) || defined( __x86_64 )
+                        __x87_load;
+                #endif
+                *__volatile_errno() = local_errno;
+        }
+
+        /* paranoid */ verify( ! kernelTLS.preemption_state.enabled );
 }
 
@@ -441 +459 @@
 }
 
-static void Abort( int ret, const char func[] ) {
+static void Abort( int ret, const char * func ) {
         if ( ret ) {                                                                            // pthread routines return errno values
                 abort( "%s : internal error, error(%d) %s.", func, ret, strerror( ret ) );
@@ -447 +465 @@
 } // Abort
 
-void * create_pthread( pthread_t * pthread, void * (*start)(void *), void * arg ) {
+void * __create_pthread( pthread_t * pthread, void * (*start)(void *), void * arg ) {
         pthread_attr_t attr;
 
@@ -469 +487 @@
         );
 
-        Abort( pthread_attr_setstack( &attr, stack, stacksize ), "pthread_attr_setstack" ); 
+        Abort( pthread_attr_setstack( &attr, stack, stacksize ), "pthread_attr_setstack" );
 
         Abort( pthread_create( pthread, &attr, start, arg ), "pthread_create" );
@@ -475 +493 @@
 }
 
-static void start(processor * this) {
-        __cfaabi_dbg_print_safe("Kernel : Starting core %p\n", this);
-
-        this->stack = create_pthread( &this->kernel_thread, CtxInvokeProcessor, (void *)this );
-
-        __cfaabi_dbg_print_safe("Kernel : core %p started\n", this);
-}
-
 // KERNEL_ONLY
-void kernel_first_resume( processor * this ) {
+static void __kernel_first_resume( processor * this ) {
         thread_desc * src = mainThread;
         coroutine_desc * dst = get_coroutine(this->runner);
@@ -490 +500 @@
         verify( ! kernelTLS.preemption_state.enabled );
 
+        kernelTLS.this_thread->curr_cor = dst;
         __stack_prepare( &dst->stack, 65000 );
-        CtxStart(&this->runner, CtxInvokeCoroutine);
+        CtxStart(main, dst, this->runner, CtxInvokeCoroutine);
 
         verify( ! kernelTLS.preemption_state.enabled );
@@ -506 +517 @@
         // when CtxSwitch returns we are back in the src coroutine
 
+        mainThread->curr_cor = &mainThread->self_cor;
+
         // set state of new coroutine to active
         src->state = Active;
@@ -513 +526 @@
 
 // KERNEL_ONLY
-void kernel_last_resume( processor * this ) {
+static void __kernel_last_resume( processor * this ) {
         coroutine_desc * src = &mainThread->self_cor;
         coroutine_desc * dst = get_coroutine(this->runner);
@@ -527 +540 @@
 //-----------------------------------------------------------------------------
 // Scheduler routines
-
 // KERNEL ONLY
-void ScheduleThread( thread_desc * thrd ) {
-        verify( thrd );
-        verify( thrd->state != Halted );
-
-        verify( ! kernelTLS.preemption_state.enabled );
-
-        verifyf( thrd->next == 0p, "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);
+void __schedule_thread( thread_desc * thrd ) with( *thrd->curr_cluster ) {
+        /* paranoid */ verify( ! kernelTLS.preemption_state.enabled );
+        /* paranoid */ #if defined( __CFA_WITH_VERIFY__ )
+        /* paranoid */ if( thrd->state == Inactive || 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 || thrd->state == Rerun,
+                          "Error preempted thread marked as not currently running, state %d, preemption %d\n", thrd->state, thrd->preempted );
+        /* paranoid */ #endif
+        /* paranoid */ verifyf( thrd->next == 0p, "Expected null got %p", thrd->next );
+
+        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);
                 }
-                else if( struct processor * idle = idles.head ) {
-                        wake_fast(idle);
-                }
-
-        }
-
-        verify( ! kernelTLS.preemption_state.enabled );
+                unlock    (proc_list_lock);
+        }
+        else if( struct processor * idle = idles.head ) {
+                wake_fast(idle);
+        }
+
+        /* paranoid */ verify( ! kernelTLS.preemption_state.enabled );
 }
 
 // KERNEL ONLY
-thread_desc * nextThread(cluster * this) with( *this ) {
-        verify( ! kernelTLS.preemption_state.enabled );
+static thread_desc * __next_thread(cluster * this) with( *this ) {
+        /* paranoid */ 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 );
+
+        /* paranoid */ verify( ! kernelTLS.preemption_state.enabled );
         return head;
 }
 
-void BlockInternal() {
+void unpark( thread_desc * thrd ) {
+        if( !thrd ) return;
+
         disable_interrupts();
-        verify( ! kernelTLS.preemption_state.enabled );
+        static_assert(sizeof(thrd->state) == sizeof(int));
+        enum coroutine_state old_state = __atomic_exchange_n(&thrd->state, Rerun, __ATOMIC_SEQ_CST);
+        switch(old_state) {
+                case Active:
+                        // Wake won the race, the thread will reschedule/rerun itself
+                        break;
+                case Inactive:
+                        /* paranoid */ verify( ! thrd->preempted != __NO_PREEMPTION );
+
+                        // Wake lost the race,
+                        thrd->state = Inactive;
+                        __schedule_thread( thrd );
+                        break;
+                case Rerun:
+                        abort("More than one thread attempted to schedule thread %p\n", thrd);
+                        break;
+                case Halted:
+                case Start:
+                case Primed:
+                default:
+                        // This makes no sense, something is wrong abort
+                        abort();
+        }
+        enable_interrupts( __cfaabi_dbg_ctx );
+}
+
+void park( void ) {
+        /* paranoid */ verify( kernelTLS.preemption_state.enabled );
+        disable_interrupts();
+        /* paranoid */ verify( ! kernelTLS.preemption_state.enabled );
+        /* paranoid */ verify( kernelTLS.this_thread->preempted == __NO_PREEMPTION );
+
         returnToKernel();
-        verify( ! kernelTLS.preemption_state.enabled );
+
+        /* paranoid */ verify( ! kernelTLS.preemption_state.enabled );
         enable_interrupts( __cfaabi_dbg_ctx );
-}
-
-void BlockInternal( __spinlock_t * lock ) {
+        /* paranoid */ verify( kernelTLS.preemption_state.enabled );
+
+}
+
+// KERNEL ONLY
+void __leave_thread() {
+        /* paranoid */ verify( ! kernelTLS.preemption_state.enabled );
+        returnToKernel();
+        abort();
+}
+
+// KERNEL ONLY
+bool force_yield( __Preemption_Reason reason ) {
+        /* paranoid */ verify( kernelTLS.preemption_state.enabled );
         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();
+        /* paranoid */ verify( ! kernelTLS.preemption_state.enabled );
+
+        thread_desc * thrd = kernelTLS.this_thread;
+        /* paranoid */ verify(thrd->state == Active || thrd->state == Rerun);
+
+        // 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->next == 0p) {
+                preempted = true;
+                thrd->preempted = reason;
+                returnToKernel();
+        }
+
+        /* paranoid */ verify( ! kernelTLS.preemption_state.enabled );
+        enable_interrupts_noPoll();
+        /* paranoid */ verify( kernelTLS.preemption_state.enabled );
+
+        return preempted;
 }
 
@@ -684 +665 @@
 //-----------------------------------------------------------------------------
 // Kernel boot procedures
-static void kernel_startup(void) {
+static void __kernel_startup(void) {
         verify( ! kernelTLS.preemption_state.enabled );
         __cfaabi_dbg_print_safe("Kernel : Starting\n");
@@ -745 +726 @@
         // 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);
+        __schedule_thread(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 );
+        __kernel_first_resume( kernelTLS.this_processor );
 
 
@@ -762 +743 @@
 }
 
-static void kernel_shutdown(void) {
+static void __kernel_shutdown(void) {
         __cfaabi_dbg_print_safe("\n--------------------------------------------------\nKernel : Shutting down\n");
 
@@ -773 +754 @@
         // which is currently here
         __atomic_store_n(&mainProcessor->do_terminate, true, __ATOMIC_RELEASE);
-        kernel_last_resume( kernelTLS.this_processor );
+        __kernel_last_resume( kernelTLS.this_processor );
         mainThread->self_cor.state = Halted;
 
@@ -799 +780 @@
 // Kernel Quiescing
 //=============================================================================================
-static void halt(processor * this) with( *this ) {
+static void __halt(processor * this) with( *this ) {
         // verify( ! __atomic_load_n(&do_terminate, __ATOMIC_SEQ_CST) );
 
@@ -910 +891 @@
 
                 // atomically release spin lock and block
-                BlockInternal( &lock );
+                unlock( lock );
+                park();
         }
         else {
@@ -929 +911 @@
 
         // make new owner
-        WakeThread( thrd );
+        unpark( thrd );
 }
 
@@ -978 +960 @@
 __cfaabi_dbg_debug_do(
         extern "C" {
-                void __cfaabi_dbg_record(__spinlock_t & this, const char prev_name[]) {
+                void __cfaabi_dbg_record(__spinlock_t & this, const char * prev_name) {
                         this.prev_name = prev_name;
                         this.prev_thrd = kernelTLS.this_thread;
@@ -987 +969 @@
 //-----------------------------------------------------------------------------
 // Debug
-bool threading_enabled(void) {
+bool threading_enabled(void) __attribute__((const)) {
         return true;
 }