Changeset 957453d for src/libcfa/concurrency/preemption.c

Timestamp:

Jul 20, 2017, 2:05:44 PM (7 years ago)

Author:

Andrew Beach <ajbeach@…>

Branches:

ADT, aaron-thesis, arm-eh, ast-experimental, cleanup-dtors, deferred_resn, demangler, enum, forall-pointer-decay, jacob/cs343-translation, jenkins-sandbox, master, new-ast, new-ast-unique-expr, new-env, no_list, persistent-indexer, pthread-emulation, qualifiedEnum, resolv-new, with_gc

Children:

c72f9fd

Parents:

d49bfa8 (diff), 8b28a52 (diff)
Note: this is a merge changeset, the changes displayed below correspond to the merge itself.
Use the (diff) links above to see all the changes relative to each parent.

Message:

Merge branch 'master' of plg.uwaterloo.ca:software/cfa/cfa-cc

File:

• src/libcfa/concurrency/preemption.c (modified) (14 diffs)

src/libcfa/concurrency/preemption.c

@@ -34 +34 @@
 #endif
 
+//TODO move to defaults
 #define __CFA_DEFAULT_PREEMPTION__ 10000
 
+//TODO move to defaults
 __attribute__((weak)) unsigned int default_preemption() {
         return __CFA_DEFAULT_PREEMPTION__;
 }
 
+// Short hands for signal context information
 #define __CFA_SIGCXT__ ucontext_t *
 #define __CFA_SIGPARMS__ __attribute__((unused)) int sig, __attribute__((unused)) siginfo_t *sfp, __attribute__((unused)) __CFA_SIGCXT__ cxt
 
+// FwdDeclarations : timeout handlers
 static void preempt( processor   * this );
 static void timeout( thread_desc * this );
 
+// FwdDeclarations : Signal handlers
 void sigHandler_ctxSwitch( __CFA_SIGPARMS__ );
-void sigHandler_alarm    ( __CFA_SIGPARMS__ );
 void sigHandler_segv     ( __CFA_SIGPARMS__ );
 void sigHandler_abort    ( __CFA_SIGPARMS__ );
 
+// FwdDeclarations : sigaction wrapper
 static void __kernel_sigaction( int sig, void (*handler)(__CFA_SIGPARMS__), int flags );
-LIB_DEBUG_DO( bool validate( alarm_list_t * this ); )
-
+
+// FwdDeclarations : alarm thread main
+void * alarm_loop( __attribute__((unused)) void * args );
+
+// Machine specific register name
 #ifdef __x86_64__
 #define CFA_REG_IP REG_RIP
@@ -60 +68 @@
 #endif
 
+KERNEL_STORAGE(event_kernel_t, event_kernel);         // private storage for event kernel
+event_kernel_t * event_kernel;                        // kernel public handle to even kernel
+static pthread_t alarm_thread;                        // pthread handle to alarm thread
+
+void ?{}(event_kernel_t * this) {
+        (&this->alarms){};
+        (&this->lock){};
+}
 
 //=============================================================================================
@@ -65 +81 @@
 //=============================================================================================
 
+// Get next expired node
+static inline alarm_node_t * get_expired( alarm_list_t * alarms, __cfa_time_t currtime ) {
+        if( !alarms->head ) return NULL;                          // If no alarms return null
+        if( alarms->head->alarm >= currtime ) return NULL;        // If alarms head not expired return null
+        return pop(alarms);                                       // Otherwise just pop head
+}
+
+// Tick one frame of the Discrete Event Simulation for alarms
 void tick_preemption() {
-        alarm_list_t * alarms = &systemProcessor->alarms;
-        __cfa_time_t currtime = __kernel_get_time();
-
-        // LIB_DEBUG_PRINT_BUFFER_DECL( STDERR_FILENO, "Ticking preemption @ %llu\n", currtime );
-        while( alarms->head && alarms->head->alarm < currtime ) {
-                alarm_node_t * node = pop(alarms);
-                // LIB_DEBUG_PRINT_BUFFER_LOCAL( STDERR_FILENO, "Ticking %p\n", node );
-
+        alarm_node_t * node = NULL;                     // Used in the while loop but cannot be declared in the while condition
+        alarm_list_t * alarms = &event_kernel->alarms;  // Local copy for ease of reading
+        __cfa_time_t currtime = __kernel_get_time();    // Check current time once so we everything "happens at once"
+
+        //Loop throught every thing expired
+        while( node = get_expired( alarms, currtime ) ) {
+
+                // Check if this is a kernel
                 if( node->kernel_alarm ) {
                         preempt( node->proc );
@@ -81 +105 @@
                 }
 
-                verify( validate( alarms ) );
-
+                // Check if this is a periodic alarm
                 __cfa_time_t period = node->period;
                 if( period > 0 ) {
-                        node->alarm = currtime + period;
-                        // LIB_DEBUG_PRINT_BUFFER_LOCAL( STDERR_FILENO, "Reinsert %p @ %llu (%llu + %llu)\n", node, node->alarm, currtime, period );
-                        insert( alarms, node );
+                        node->alarm = currtime + period;    // Alarm is periodic, add currtime to it (used cached current time)
+                        insert( alarms, node );             // Reinsert the node for the next time it triggers
                 }
                 else {
-                        node->set = false;
-                }
-        }
-
-        if( alarms->head ) {
-                __kernel_set_timer( alarms->head->alarm - currtime );
-        }
-
-        verify( validate( alarms ) );
-        // LIB_DEBUG_PRINT_BUFFER_LOCAL( STDERR_FILENO, "Ticking preemption done\n" );
-}
-
+                        node->set = false;                  // Node is one-shot, just mark it as not pending
+                }
+        }
+
+        // If there are still alarms pending, reset the timer
+        if( alarms->head ) { __kernel_set_timer( alarms->head->alarm - currtime ); }
+}
+
+// Update the preemption of a processor and notify interested parties
 void update_preemption( processor * this, __cfa_time_t duration ) {
-        LIB_DEBUG_PRINT_BUFFER_DECL( STDERR_FILENO, "Processor : %p updating preemption to %llu\n", this, duration );
-
         alarm_node_t * alarm = this->preemption_alarm;
-        duration *= 1000;
 
         // Alarms need to be enabled
@@ -136 +152 @@
 
 extern "C" {
+        // Disable interrupts by incrementing the counter
         void disable_interrupts() {
                 __attribute__((unused)) unsigned short new_val = __atomic_add_fetch_2( &disable_preempt_count, 1, __ATOMIC_SEQ_CST );
-                verify( new_val < (unsigned short)65_000 );
-                verify( new_val != (unsigned short) 0 );
-        }
-
-        void enable_interrupts_noRF() {
-                __attribute__((unused)) unsigned short prev = __atomic_fetch_add_2( &disable_preempt_count, -1, __ATOMIC_SEQ_CST );
-                verify( prev != (unsigned short) 0 );
-        }
-
+                verify( new_val < 65_000u );              // If this triggers someone is disabling interrupts without enabling them
+        }
+
+        // Enable interrupts by decrementing the counter
+        // If counter reaches 0, execute any pending CtxSwitch
         void enable_interrupts( DEBUG_CTX_PARAM ) {
-                processor * proc   = this_processor;
-                thread_desc * thrd = this_thread;
+                processor * proc   = this_processor;      // Cache the processor now since interrupts can start happening after the atomic add
+                thread_desc * thrd = this_thread;         // Cache the thread now since interrupts can start happening after the atomic add
+
                 unsigned short prev = __atomic_fetch_add_2( &disable_preempt_count, -1, __ATOMIC_SEQ_CST );
-                verify( prev != (unsigned short) 0 );
+                verify( prev != 0u );                     // If this triggers someone is enabled already enabled interruptsverify( prev != 0u );
+
+                // Check if we need to prempt the thread because an interrupt was missed
                 if( prev == 1 && proc->pending_preemption ) {
                         proc->pending_preemption = false;
@@ -157 +173 @@
                 }
 
+                // For debugging purposes : keep track of the last person to enable the interrupts
                 LIB_DEBUG_DO( proc->last_enable = caller; )
         }
-}
-
+
+        // Disable interrupts by incrementint the counter
+        // Don't execute any pending CtxSwitch even if counter reaches 0
+        void enable_interrupts_noPoll() {
+                __attribute__((unused)) unsigned short prev = __atomic_fetch_add_2( &disable_preempt_count, -1, __ATOMIC_SEQ_CST );
+                verify( prev != 0u );                     // If this triggers someone is enabled already enabled interrupts
+        }
+}
+
+// sigprocmask wrapper : unblock a single signal
 static inline void signal_unblock( int sig ) {
         sigset_t mask;
@@ -171 +196 @@
 }
 
+// sigprocmask wrapper : block a single signal
 static inline void signal_block( int sig ) {
         sigset_t mask;
@@ -181 +207 @@
 }
 
-static inline bool preemption_ready() {
-        return disable_preempt_count == 0 && !preemption_in_progress;
-}
-
-static inline void defer_ctxSwitch() {
-        this_processor->pending_preemption = true;
-}
-
-static inline void defer_alarm() {
-        systemProcessor->pending_alarm = true;
-}
-
+// kill wrapper : signal a processor
 static void preempt( processor * this ) {
         pthread_kill( this->kernel_thread, SIGUSR1 );
 }
 
+// reserved for future use
 static void timeout( thread_desc * this ) {
         //TODO : implement waking threads
 }
 
+
+// Check if a CtxSwitch signal handler shoud defer
+// If true  : preemption is safe
+// If false : preemption is unsafe and marked as pending
+static inline bool preemption_ready() {
+        bool ready = disable_preempt_count == 0 && !preemption_in_progress; // Check if preemption is safe
+        this_processor->pending_preemption = !ready;                        // Adjust the pending flag accordingly
+        return ready;
+}
+
 //=============================================================================================
 // Kernel Signal Startup/Shutdown logic
 //=============================================================================================
 
-static pthread_t alarm_thread;
-void * alarm_loop( __attribute__((unused)) void * args );
-
+// Startup routine to activate preemption
+// Called from kernel_startup
 void kernel_start_preemption() {
         LIB_DEBUG_PRINT_SAFE("Kernel : Starting preemption\n");
-        __kernel_sigaction( SIGUSR1, sigHandler_ctxSwitch, SA_SIGINFO );
-        // __kernel_sigaction( SIGSEGV, sigHandler_segv     , SA_SIGINFO );
-        // __kernel_sigaction( SIGBUS , sigHandler_segv     , SA_SIGINFO );
+
+        // Start with preemption disabled until ready
+        disable_preempt_count = 1;
+
+        // Initialize the event kernel
+        event_kernel = (event_kernel_t *)&storage_event_kernel;
+        event_kernel{};
+
+        // Setup proper signal handlers
+        __kernel_sigaction( SIGUSR1, sigHandler_ctxSwitch, SA_SIGINFO );         // CtxSwitch handler
+        // __kernel_sigaction( SIGSEGV, sigHandler_segv     , SA_SIGINFO );      // Failure handler
+        // __kernel_sigaction( SIGBUS , sigHandler_segv     , SA_SIGINFO );      // Failure handler
 
         signal_block( SIGALRM );
@@ -219 +253 @@
 }
 
+// Shutdown routine to deactivate preemption
+// Called from kernel_shutdown
 void kernel_stop_preemption() {
         LIB_DEBUG_PRINT_SAFE("Kernel : Preemption stopping\n");
 
+        // Block all signals since we are already shutting down
         sigset_t mask;
         sigfillset( &mask );
         sigprocmask( SIG_BLOCK, &mask, NULL );
 
+        // Notify the alarm thread of the shutdown
         sigval val = { 1 };
         pthread_sigqueue( alarm_thread, SIGALRM, val );
+
+        // Wait for the preemption thread to finish
         pthread_join( alarm_thread, NULL );
+
+        // Preemption is now fully stopped
+
         LIB_DEBUG_PRINT_SAFE("Kernel : Preemption stopped\n");
 }
 
+// Raii ctor/dtor for the preemption_scope
+// Used by thread to control when they want to receive preemption signals
 void ?{}( preemption_scope * this, processor * proc ) {
-        (&this->alarm){ proc };
+        (&this->alarm){ proc, zero_time, zero_time };
         this->proc = proc;
         this->proc->preemption_alarm = &this->alarm;
-        update_preemption( this->proc, this->proc->preemption );
+
+        update_preemption( this->proc, from_us(this->proc->cltr->preemption) );
 }
 
@@ -242 +288 @@
         disable_interrupts();
 
-        update_preemption( this->proc, 0 );
+        update_preemption( this->proc, zero_time );
 }
 
@@ -249 +295 @@
 //=============================================================================================
 
+// Context switch signal handler
+// Receives SIGUSR1 signal and causes the current thread to yield
 void sigHandler_ctxSwitch( __CFA_SIGPARMS__ ) {
         LIB_DEBUG_DO( last_interrupt = (void *)(cxt->uc_mcontext.gregs[CFA_REG_IP]); )
-        if( preemption_ready() ) {
-                preemption_in_progress = true;
-                signal_unblock( SIGUSR1 );
-                this_processor->pending_preemption = false;
-                preemption_in_progress = false;
-                BlockInternal( (thread_desc*)this_thread );
-        }
-        else {
-                defer_ctxSwitch();
-        }
-}
-
+
+        // Check if it is safe to preempt here
+        if( !preemption_ready() ) { return; }
+
+        preemption_in_progress = true;                      // Sync flag : prevent recursive calls to the signal handler
+        signal_unblock( SIGUSR1 );                          // We are about to CtxSwitch out of the signal handler, let other handlers in
+        preemption_in_progress = false;                     // Clear the in progress flag
+
+        // Preemption can occur here
+
+        BlockInternal( (thread_desc*)this_thread );         // Do the actual CtxSwitch
+}
+
+// Main of the alarm thread
+// Waits on SIGALRM and send SIGUSR1 to whom ever needs it
 void * alarm_loop( __attribute__((unused)) void * args ) {
+        // Block sigalrms to control when they arrive
         sigset_t mask;
         sigemptyset( &mask );
@@ -272 +324 @@
         }
 
+        // Main loop
         while( true ) {
+                // Wait for a sigalrm
                 siginfo_t info;
                 int sig = sigwaitinfo( &mask, &info );
+
+                // If another signal arrived something went wrong
                 assertf(sig == SIGALRM, "Kernel Internal Error, sigwait: Unexpected signal %d (%d : %d)\n", sig, info.si_code, info.si_value.sival_int);
 
                 LIB_DEBUG_PRINT_SAFE("Kernel : Caught alarm from %d with %d\n", info.si_code, info.si_value.sival_int );
+                // Switch on the code (a.k.a. the sender) to
                 switch( info.si_code )
                 {
+                // Timers can apparently be marked as sent for the kernel
+                // In either case, tick preemption
                 case SI_TIMER:
                 case SI_KERNEL:
                         LIB_DEBUG_PRINT_SAFE("Kernel : Preemption thread tick\n");
-                        lock( &systemProcessor->alarm_lock DEBUG_CTX2 );
+                        lock( &event_kernel->lock DEBUG_CTX2 );
                         tick_preemption();
-                        unlock( &systemProcessor->alarm_lock );
+                        unlock( &event_kernel->lock );
                         break;
+                // Signal was not sent by the kernel but by an other thread
                 case SI_QUEUE:
+                        // For now, other thread only signal the alarm thread to shut it down
+                        // If this needs to change use info.si_value and handle the case here
                         goto EXIT;
                 }
@@ -297 +359 @@
 }
 
+// Sigaction wrapper : register an signal handler
 static void __kernel_sigaction( int sig, void (*handler)(__CFA_SIGPARMS__), int flags ) {
         struct sigaction act;
@@ -312 +375 @@
 }
 
-typedef void (*sa_handler_t)(int);
-
+// Sigaction wrapper : restore default handler
 static void __kernel_sigdefault( int sig ) {
         struct sigaction act;
 
-        // act.sa_handler = SIG_DFL;
+        act.sa_handler = SIG_DFL;
         act.sa_flags = 0;
         sigemptyset( &act.sa_mask );