source: src/libcfa/concurrency/kernel.c@ db6f06a

//                              -*- Mode: CFA -*-
//
// 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 : Thierry Delisle
// Last Modified On : --
// Update Count     : 0
//

//Start and stop routine for the kernel, declared first to make sure they run first
void kernel_startup(void)  __attribute__((constructor(101)));
void kernel_shutdown(void) __attribute__((destructor(101)));

//Header
#include "kernel_private.h"

//C Includes
#include <stddef.h>
extern "C" {
#include <fenv.h>
#include <sys/resource.h>
}

//CFA Includes
#include "libhdr.h"

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

static volatile int lock;

void spin_lock( volatile int *lock ) {
        for ( unsigned int i = 1;; i += 1 ) {
          if ( *lock == 0 && __sync_lock_test_and_set_4( lock, 1 ) == 0 ) break;
        }
}

void spin_unlock( volatile int *lock ) {
        __sync_lock_release_4( lock );
}

//-----------------------------------------------------------------------------
// Kernel storage
#define KERNEL_STORAGE(T,X) static char X##_storage[sizeof(T)]

KERNEL_STORAGE(processorCtx_t, systemProcessorCtx);
KERNEL_STORAGE(cluster, systemCluster);
KERNEL_STORAGE(processor, systemProcessor);
KERNEL_STORAGE(thread, mainThread);
KERNEL_STORAGE(machine_context_t, mainThread_context);

cluster * systemCluster;
processor * systemProcessor;
thread * mainThread;

//-----------------------------------------------------------------------------
// Global state

thread_local processor * this_processor;

processor * get_this_processor() {
        return this_processor;
}

coroutine * this_coroutine(void) {
        return this_processor->current_coroutine;
}

thread * this_thread(void) {
        return this_processor->current_thread;
}

//-----------------------------------------------------------------------------
// Main thread construction
struct current_stack_info_t {
        machine_context_t ctx;  
        unsigned int size;              // size of stack
        void *base;                             // base of stack
        void *storage;                  // pointer to stack
        void *limit;                    // stack grows towards stack limit
        void *context;                  // address of cfa_context_t
        void *top;                              // address of top of storage
};

void ?{}( current_stack_info_t * this ) {
        CtxGet( &this->ctx );
        this->base = this->ctx.FP;
        this->storage = this->ctx.SP;

        rlimit r;
        getrlimit( RLIMIT_STACK, &r);
        this->size = r.rlim_cur;

        this->limit = (void *)(((intptr_t)this->base) - this->size);
        this->context = &mainThread_context_storage;
        this->top = this->base;
}

void ?{}( coStack_t * this, current_stack_info_t * info) {
        this->size = info->size;
        this->storage = info->storage;
        this->limit = info->limit;
        this->base = info->base;
        this->context = info->context;
        this->top = info->top;
        this->userStack = true;
}

void ?{}( coroutine * this, current_stack_info_t * info) {
        (&this->stack){ info }; 
        this->name = "Main Thread";
        this->errno_ = 0;
        this->state = Inactive;
        this->notHalted = true;
}

void ?{}( thread * this, current_stack_info_t * info) {
        (&this->c){ info };
}

//-----------------------------------------------------------------------------
// Processor coroutine
void ?{}(processorCtx_t * this, processor * proc) {
        (&this->c){};
        this->proc = proc;
        proc->runner = this;
}

void ?{}(processorCtx_t * this, processor * proc, current_stack_info_t * info) {
        (&this->c){ info };
        this->proc = proc;
        proc->runner = this;
}

void ?{}(processor * this) {
        this{ systemCluster };
}

void ?{}(processor * this, cluster * cltr) {
        this->cltr = cltr;
        this->current_coroutine = NULL;
        this->current_thread = NULL;
        (&this->terminated){};
        this->is_terminated = false;

        start( this );
}

void ?{}(processor * this, cluster * cltr, processorCtx_t * runner) {
        this->cltr = cltr;
        this->current_coroutine = NULL;
        this->current_thread = NULL;
        (&this->terminated){};
        this->is_terminated = false;

        this->runner = runner;
        LIB_DEBUG_PRINTF("Kernel : constructing processor context %p\n", runner);
        runner{ this };
}

void ^?{}(processor * this) {
        if( ! this->is_terminated ) {
                LIB_DEBUG_PRINTF("Kernel : core %p signaling termination\n", this);
                this->is_terminated = true;
                wait( &this->terminated );
        }
}

void ?{}(cluster * this) {
        ( &this->ready_queue ){};
        lock = 0;
}

void ^?{}(cluster * this) {
        
}

//=============================================================================================
// Kernel Scheduling logic
//=============================================================================================
//Main of the processor contexts
void main(processorCtx_t * runner) {
        processor * this = runner->proc;
        LIB_DEBUG_PRINTF("Kernel : core %p starting\n", this);

        thread * readyThread = NULL;
        for( unsigned int spin_count = 0; ! this->is_terminated; spin_count++ ) 
        {
                readyThread = nextThread( this->cltr );

                if(readyThread) 
                {
                        runThread(this, readyThread);

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

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

        LIB_DEBUG_PRINTF("Kernel : core %p unlocking thread\n", this);
        signal( &this->terminated );
        LIB_DEBUG_PRINTF("Kernel : core %p terminated\n", this);
}

// runThread runs a thread by context switching 
// from the processor coroutine to the target thread 
void runThread(processor * this, thread * dst) {
        coroutine * proc_cor = get_coroutine(this->runner);
        coroutine * thrd_cor = get_coroutine(dst);
        
        //Reset the terminating actions here
        this->finish.action_code = No_Action;

        //Update global state
        this->current_thread = dst;

        // Context Switch to the thread
        ThreadCtxSwitch(proc_cor, thrd_cor);
        // when ThreadCtxSwitch returns we are back in the processor coroutine
}

// Once a thread has finished running, some of 
// its final actions must be executed from the kernel
void finishRunning(processor * this) {
        if( this->finish.action_code == Release ) {
                unlock( this->finish.lock );
        }
        else if( this->finish.action_code == Schedule ) {
                ScheduleThread( this->finish.thrd );
        }
        else if( this->finish.action_code == Release_Schedule ) {
                unlock( this->finish.lock );            
                ScheduleThread( this->finish.thrd );
        }
        else {
                assert(this->finish.action_code == No_Action);
        }
}

// Handles spinning logic
// TODO : find some strategy to put cores to sleep after some time
void spin(processor * this, unsigned int * spin_count) {
        (*spin_count)++;
}

// Context invoker for processors
// This is the entry point for processors (kernel threads)
// It effectively constructs a coroutine by stealing the pthread stack
void * CtxInvokeProcessor(void * arg) {
        processor * proc = (processor *) arg;
        this_processor = proc;
        // 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;
        machine_context_t ctx;
        info.context = &ctx;
        processorCtx_t proc_cor_storage = { proc, &info };

        LIB_DEBUG_PRINTF("Coroutine : created stack %p\n", proc_cor_storage.c.stack.base);

        //Set global state
        proc->current_coroutine = &proc->runner->c;
        proc->current_thread = NULL;

        //We now have a proper context from which to schedule threads
        LIB_DEBUG_PRINTF("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.
        proc_cor_storage.c.state = Active;
      main( &proc_cor_storage );
      proc_cor_storage.c.state = Halt;
      proc_cor_storage.c.notHalted = false;

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

        return NULL;
}

void start(processor * this) {
        LIB_DEBUG_PRINTF("Kernel : Starting core %p\n", this);
        
        // pthread_attr_t attributes;
        // pthread_attr_init( &attributes );

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

        // pthread_attr_destroy( &attributes );

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

//-----------------------------------------------------------------------------
// Scheduler routines
void ScheduleThread( thread * thrd ) {
        assertf( thrd->next == NULL, "Expected null got %p", thrd->next );
        
        lock( &systemProcessor->cltr->lock );
        append( &systemProcessor->cltr->ready_queue, thrd );
        unlock( &systemProcessor->cltr->lock );
}

thread * nextThread(cluster * this) {
        lock( &this->lock );
        thread * head = pop_head( &this->ready_queue );
        unlock( &this->lock );
        return head;
}

void ScheduleInternal() {
        suspend();
}

void ScheduleInternal( spinlock * lock ) {
        get_this_processor()->finish.action_code = Release;
        get_this_processor()->finish.lock = lock;
        suspend();
}

void ScheduleInternal( thread * thrd ) {
        get_this_processor()->finish.action_code = Schedule;
        get_this_processor()->finish.thrd = thrd;
        suspend();
}

void ScheduleInternal( spinlock * lock, thread * thrd ) {
        get_this_processor()->finish.action_code = Release_Schedule;
        get_this_processor()->finish.lock = lock;
        get_this_processor()->finish.thrd = thrd;
        suspend();
}

//-----------------------------------------------------------------------------
// Kernel boot procedures
void kernel_startup(void) {
        LIB_DEBUG_PRINTF("Kernel : Starting\n");        

        // Start by initializing the main thread
        // SKULLDUGGERY: the mainThread steals the process main thread 
        // which will then be scheduled by the systemProcessor normally
        mainThread = (thread *)&mainThread_storage;
        current_stack_info_t info;
        mainThread{ &info };

        // Initialize the system cluster
        systemCluster = (cluster *)&systemCluster_storage;
        systemCluster{};

        // Initialize the system processor and the system processor ctx
        // (the coroutine that contains the processing control flow)
        systemProcessor = (processor *)&systemProcessor_storage;
        systemProcessor{ systemCluster, (processorCtx_t *)&systemProcessorCtx_storage };

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

        //initialize the global state variables
        this_processor = systemProcessor;
        this_processor->current_thread = mainThread;
        this_processor->current_coroutine = &mainThread->c;

        // SKULLDUGGERY: Force a context switch to the system 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. 
        resume(systemProcessor->runner);



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

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

        // SKULLDUGGERY: Notify the systemProcessor it needs to terminates.
        // When its coroutine terminates, it return control to the mainThread
        // which is currently here
        systemProcessor->is_terminated = true;
        suspend();

        // THE SYSTEM IS NOW COMPLETELY STOPPED

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

        // 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){};

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

//-----------------------------------------------------------------------------
// Locks
// void ?{}( simple_lock * this ) {
//      ( &this->blocked ){};
// }

// void ^?{}( simple_lock * this ) {

// }

// void lock( simple_lock * this ) {
//      {
//              spin_lock( &lock );
//              append( &this->blocked, this_thread() );
//              spin_unlock( &lock );
//      }
//      ScheduleInternal();
// }

// void lock( simple_lock * this, spinlock * to_release ) {
//      {
//              spin_lock( &lock );
//              append( &this->blocked, this_thread() );
//              spin_unlock( &lock );
//      }
//      ScheduleInternal( to_release );
//      lock( to_release );
// }

// void unlock( simple_lock * this ) {
//      thread * it;
//      while( it = pop_head( &this->blocked) ) {
//              ScheduleThread( it );
//      }
// }

void ?{}( spinlock * this ) {
        this->lock = 0;
}
void ^?{}( spinlock * this ) {

}

void lock( spinlock * this ) {
        for ( unsigned int i = 1;; i += 1 ) {
                if ( this->lock == 0 && __sync_lock_test_and_set_4( &this->lock, 1 ) == 0 ) break;
        }
}

void unlock( spinlock * this ) {
        __sync_lock_release_4( &this->lock );
}

void ?{}( signal_once * this ) {
        this->condition = false;
}
void ^?{}( signal_once * this ) {

}

void wait( signal_once * this ) {
        lock( &this->lock );
        if( !this->condition ) {
                append( &this->blocked, this_thread() );
                ScheduleInternal( &this->lock );
                lock( &this->lock );
        }
        unlock( &this->lock );
}

void signal( signal_once * this ) {
        lock( &this->lock );
        {
                this->condition = true;

                thread * it;
                while( it = pop_head( &this->blocked) ) {
                        ScheduleThread( it );
                }
        }
        unlock( &this->lock );
}

//-----------------------------------------------------------------------------
// Queues
void ?{}( simple_thread_list * this ) {
        this->head = NULL;
        this->tail = &this->head;
}

void append( simple_thread_list * this, thread * t ) {
        assert( t->next == NULL );
        *this->tail = t;
        this->tail = &t->next;
}

thread * pop_head( simple_thread_list * this ) {
        thread * head = this->head;
        if( head ) {
                this->head = head->next;
                if( !head->next ) {
                        this->tail = &this->head;
                }
                head->next = NULL;
        }       
        
        return head;
}
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