Changeset 9f575ea

Timestamp:

Feb 6, 2020, 10:23:27 AM (5 years ago)

Author:

Thierry Delisle <tdelisle@…>

Branches:

ADT, arm-eh, ast-experimental, enum, forall-pointer-decay, jacob/cs343-translation, jenkins-sandbox, master, new-ast, new-ast-unique-expr, pthread-emulation, qualifiedEnum

Children:

3381ed7

Parents:

4f7b418

Message:

First attempt at park/unpark

Location:

libcfa/src/concurrency

Files:

• invoke.h (modified) (2 diffs)
• kernel.cfa (modified) (12 diffs)
• kernel_private.hfa (modified) (1 diff)
• monitor.cfa (modified) (1 diff)
• mutex.cfa (modified) (4 diffs)
• preemption.cfa (modified) (1 diff)
• thread.cfa (modified) (1 diff)

libcfa/src/concurrency/invoke.h

@@ -92 +92 @@
         };
 
-        enum coroutine_state { Halted, Start, Inactive, Active, Primed };
+        enum coroutine_state { Halted, Start, Primed, Inactive, Active, Rerun, Reschedule };
 
         struct coroutine_desc {
@@ -164 +164 @@
 
                 // current execution status for coroutine
-                enum coroutine_state state;
+                volatile int state;
+                int preempted;
 
                 //SKULLDUGGERY errno is not save in the thread data structure because returnToKernel appears to be the only function to require saving and restoring it

libcfa/src/concurrency/kernel.cfa

@@ -327 +327 @@
         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 inactive
+        verify(proc_cor->state == Active);
+        proc_cor->state = Inactive;
+
+        // Actually run the thread
+        RUN:
+        {
+                if(unlikely(thrd_dst->preempted)) {
+                        thrd_dst->preempted = false;
+                } else {
+                        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
+        }
+
+        // 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)) {
+                // The thread was preempted, reschedule it and reset the flag
+                ScheduleThread( thrd_dst );
+
+                // Just before returning to the processor, set the processor coroutine to active
+                proc_cor->state = Active;
+                return;
+        }
 
         // set state of processor coroutine to active and the thread to inactive
-        thrd_dst->state = thrd_dst->state == Halted ? Halted : Inactive;
+        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;
+                        break;
+                case Active:
+                        // This is case 1, the regular case, nothing more is needed
+                        break;
+                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.
+                        goto RUN;
+                case Reschedule:
+                        // This is case 3, someone tried to run this before it finished blocking
+                        // but it must go through the ready-queue
+                        thrd_dst->state = Inactive;  /*restore invariant */
+                        ScheduleThread( thrd_dst );
+                        break;
+                case Inactive:
+                case Start:
+                case Primed:
+                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;
 }
@@ -343 +398 @@
 // KERNEL_ONLY
 static void returnToKernel() {
+        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;
+        // 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;
+        }
+
+        verify( ! kernelTLS.preemption_state.enabled );
 }
 
@@ -374 +424 @@
 static void finishRunning(processor * this) with( this->finish ) {
         verify( ! kernelTLS.preemption_state.enabled );
+        verify( action_code == No_Action );
         choose( action_code ) {
         case No_Action:
@@ -532 +583 @@
 
 // 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 ScheduleThread( thread_desc * thrd ) with( *thrd->curr_cluster ) {
+        /* paranoid */ verify( ! kernelTLS.preemption_state.enabled );
+        /* paranoid */ verifyf( thrd->state == Inactive || thrd->state == Start || thrd->preempted, "state : %d, preempted %d\n", thrd->state, thrd->preempted);
+        /* 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 );
 }
 
@@ -582 +627 @@
 void BlockInternal( __spinlock_t * lock ) {
         disable_interrupts();
-        with( *kernelTLS.this_processor ) {
-                finish.action_code = Release;
-                finish.lock        = lock;
-        }
+        unlock( *lock );
 
         verify( ! kernelTLS.preemption_state.enabled );
@@ -596 +638 @@
 void BlockInternal( thread_desc * thrd ) {
         disable_interrupts();
-        with( * kernelTLS.this_processor ) {
-                finish.action_code = Schedule;
-                finish.thrd        = thrd;
-        }
+        WakeThread( thrd, false );
 
         verify( ! kernelTLS.preemption_state.enabled );
@@ -609 +648 @@
 
 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;
-        }
+        unlock( *lock );
+        WakeThread( thrd, false );
 
         verify( ! kernelTLS.preemption_state.enabled );
@@ -626 +661 @@
 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;
+        for(int i = 0; i < count; i++) {
+                unlock( *locks[i] );
         }
 
@@ -641 +674 @@
 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;
+        for(int i = 0; i < lock_count; i++) {
+                unlock( *locks[i] );
+        }
+        for(int i = 0; i < thrd_count; i++) {
+                WakeThread( thrds[i], false );
         }
 
@@ -658 +690 @@
 void BlockInternal(__finish_callback_fptr_t callback) {
         disable_interrupts();
-        with( *kernelTLS.this_processor ) {
-                finish.action_code = Callback;
-                finish.callback    = callback;
-        }
+        callback();
 
         verify( ! kernelTLS.preemption_state.enabled );
@@ -673 +702 @@
 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;
-        }
+        unlock( *lock );
+        WakeThread( thrd, false );
 
         returnToKernel();
@@ -932 +958 @@
 
         // make new owner
-        WakeThread( thrd );
+        WakeThread( thrd, false );
 }
 

libcfa/src/concurrency/kernel_private.hfa

@@ -31 +31 @@
 }
 
-void ScheduleThread( thread_desc * );
-static inline void WakeThread( thread_desc * thrd ) {
+void ScheduleThread( thread_desc * ) __attribute__((nonnull (1)));
+static inline void WakeThread( thread_desc * thrd, bool must_yield ) {
         if( !thrd ) return;
 
-        verify(thrd->state == Inactive);
+        enum coroutine_state new_state = must_yield ? Reschedule : Rerun;
 
         disable_interrupts();
-        ScheduleThread( thrd );
+        static_assert(sizeof(thrd->state) == sizeof(int));
+        enum coroutine_state old_state = (enum coroutine_state)__atomic_exchange_n((volatile int *)&thrd->state, (int)new_state, __ATOMIC_SEQ_CST);
+        switch(old_state) {
+                case Active:
+                        // Wake won the race, the thread will reschedule/rerun itself
+                        break;
+                case Inactive:
+                        // Wake lost the race,
+                        thrd->state = Inactive;
+                        ScheduleThread( thrd );
+                        break;
+                case Rerun:
+                case Reschedule:
+                        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 );
 }

libcfa/src/concurrency/monitor.cfa

@@ -225 +225 @@
 
                 //We need to wake-up the thread
-                WakeThread( new_owner );
+                WakeThread( new_owner, false );
         }
 

libcfa/src/concurrency/mutex.cfa

@@ -63 +63 @@
         this.is_locked = (this.blocked_threads != 0);
         WakeThread(
-                pop_head( this.blocked_threads )
+                pop_head( this.blocked_threads ), false
         );
         unlock( this.lock );
@@ -121 +121 @@
                 owner = thrd;
                 recursion_count = (thrd ? 1 : 0);
-                WakeThread( thrd );
+                WakeThread( thrd, false );
         }
         unlock( lock );
@@ -139 +139 @@
         lock( lock __cfaabi_dbg_ctx2 );
         WakeThread(
-                pop_head( this.blocked_threads )
+                pop_head( this.blocked_threads ), false
         );
         unlock( lock );
@@ -148 +148 @@
         while(this.blocked_threads) {
                 WakeThread(
-                        pop_head( this.blocked_threads )
+                        pop_head( this.blocked_threads ), false
                 );
         }

libcfa/src/concurrency/preemption.cfa

@@ -394 +394 @@
         // Preemption can occur here
 
-        BlockInternal( kernelTLS.this_thread ); // Do the actual CtxSwitch
+        kernelTLS.this_thread->preempted = true;
+        BlockInternal(); // Do the actual CtxSwitch
 }
 

libcfa/src/concurrency/thread.cfa

@@ -36 +36 @@
         self_cor{ name, storage, storageSize };
         state = Start;
+        preempted = false;
         curr_cor = &self_cor;
         self_mon.owner = &this;