source: libcfa/src/concurrency/preemption.cfa @ 97cba9f

arm-ehjacob/cs343-translationnew-ast-unique-expr
Last change on this file since 97cba9f was 97cba9f, checked in by Peter A. Buhr <pabuhr@…>, 16 months ago

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1//
2// Cforall Version 1.0.0 Copyright (C) 2016 University of Waterloo
3//
4// The contents of this file are covered under the licence agreement in the
5// file "LICENCE" distributed with Cforall.
6//
7// signal.c --
8//
9// Author           : Thierry Delisle
10// Created On       : Mon Jun 5 14:20:42 2017
11// Last Modified By : Peter A. Buhr
12// Last Modified On : Fri Aug 21 13:45:32 2020
13// Update Count     : 52
14//
15
16#define __cforall_thread__
17
18#include "preemption.hfa"
19#include <assert.h>
20
21#include <errno.h>
22#include <stdio.h>
23#include <string.h>
24#include <unistd.h>
25#include <limits.h>                                                                             // PTHREAD_STACK_MIN
26
27#include "bits/signal.hfa"
28#include "kernel_private.hfa"
29
30#if !defined(__CFA_DEFAULT_PREEMPTION__)
31#define __CFA_DEFAULT_PREEMPTION__ 10`ms
32#endif
33
34Duration default_preemption() __attribute__((weak)) {
35        return __CFA_DEFAULT_PREEMPTION__;
36}
37
38// FwdDeclarations : timeout handlers
39static void preempt( processor   * this );
40static void timeout( struct __processor_id_t * id, $thread * this );
41
42// FwdDeclarations : Signal handlers
43static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ );
44static void sigHandler_alarm    ( __CFA_SIGPARMS__ );
45static void sigHandler_segv     ( __CFA_SIGPARMS__ );
46static void sigHandler_ill      ( __CFA_SIGPARMS__ );
47static void sigHandler_fpe      ( __CFA_SIGPARMS__ );
48static void sigHandler_abort    ( __CFA_SIGPARMS__ );
49
50// FwdDeclarations : alarm thread main
51static void * alarm_loop( __attribute__((unused)) void * args );
52
53// Machine specific register name
54#if   defined( __i386 )
55#define CFA_REG_IP gregs[REG_EIP]
56#elif defined( __x86_64 )
57#define CFA_REG_IP gregs[REG_RIP]
58#elif defined( __ARM_ARCH )
59#define CFA_REG_IP pc
60#else
61#error unknown hardware architecture
62#endif
63
64KERNEL_STORAGE(event_kernel_t, event_kernel);         // private storage for event kernel
65event_kernel_t * event_kernel;                        // kernel public handle to even kernel
66static pthread_t alarm_thread;                        // pthread handle to alarm thread
67static void * alarm_stack;                                                        // pthread stack for alarm thread
68
69static void ?{}(event_kernel_t & this) with( this ) {
70        alarms{};
71        lock{};
72}
73
74enum {
75        PREEMPT_NORMAL    = 0,
76        PREEMPT_TERMINATE = 1,
77};
78
79//=============================================================================================
80// Kernel Preemption logic
81//=============================================================================================
82
83// Get next expired node
84static inline alarm_node_t * get_expired( alarm_list_t * alarms, Time currtime ) {
85        if( ! & (*alarms)`first ) return 0p;                                            // If no alarms return null
86        if( (*alarms)`first.alarm >= currtime ) return 0p;      // If alarms head not expired return null
87        return pop(alarms);                                                                     // Otherwise just pop head
88}
89
90// Tick one frame of the Discrete Event Simulation for alarms
91static void tick_preemption( struct __processor_id_t * id ) {
92        alarm_node_t * node = 0p;                                                       // Used in the while loop but cannot be declared in the while condition
93        alarm_list_t * alarms = &event_kernel->alarms;          // Local copy for ease of reading
94        Time currtime = __kernel_get_time();                            // Check current time once so everything "happens at once"
95
96        //Loop throught every thing expired
97        while( node = get_expired( alarms, currtime ) ) {
98                // __cfaabi_dbg_print_buffer_decl( " KERNEL: preemption tick.\n" );
99                Duration period = node->period;
100                if( period == 0) {
101                        node->set = false;                  // Node is one-shot, just mark it as not pending
102                }
103
104                // Check if this is a kernel
105                if( node->kernel_alarm ) {
106                        preempt( node->proc );
107                }
108                else {
109                        timeout( id, node->thrd );
110                }
111
112                // Check if this is a periodic alarm
113                if( period > 0 ) {
114                        // __cfaabi_dbg_print_buffer_local( " KERNEL: alarm period is %lu.\n", period.tv );
115                        node->alarm = currtime + period;    // Alarm is periodic, add currtime to it (used cached current time)
116                        insert( alarms, node );             // Reinsert the node for the next time it triggers
117                }
118        }
119
120        // If there are still alarms pending, reset the timer
121        if( & (*alarms)`first ) {
122                __cfadbg_print_buffer_decl(preemption, " KERNEL: @%ju(%ju) resetting alarm to %ju.\n", currtime.tv, __kernel_get_time().tv, (alarms->head->alarm - currtime).tv);
123                Duration delta = (*alarms)`first.alarm - currtime;
124                Duration capped = max(delta, 50`us);
125                // itimerval tim  = { caped };
126                // __cfaabi_dbg_print_buffer_local( "    Values are %lu, %lu, %lu %lu.\n", delta.tv, caped.tv, tim.it_value.tv_sec, tim.it_value.tv_usec);
127
128                __kernel_set_timer( capped );
129        }
130}
131
132// Update the preemption of a processor and notify interested parties
133void update_preemption( processor * this, Duration duration ) {
134        alarm_node_t * alarm = this->preemption_alarm;
135
136        // Alarms need to be enabled
137        if ( duration > 0 && ! alarm->set ) {
138                alarm->alarm = __kernel_get_time() + duration;
139                alarm->period = duration;
140                register_self( alarm );
141        }
142        // Zero duration but alarm is set
143        else if ( duration == 0 && alarm->set ) {
144                unregister_self( alarm );
145                alarm->alarm = 0;
146                alarm->period = 0;
147        }
148        // If alarm is different from previous, change it
149        else if ( duration > 0 && alarm->period != duration ) {
150                unregister_self( alarm );
151                alarm->alarm = __kernel_get_time() + duration;
152                alarm->period = duration;
153                register_self( alarm );
154        }
155}
156
157//=============================================================================================
158// Kernel Signal Tools
159//=============================================================================================
160
161__cfaabi_dbg_debug_do( static thread_local void * last_interrupt = 0; )
162
163extern "C" {
164        // Disable interrupts by incrementing the counter
165        void disable_interrupts() {
166                with( kernelTLS.preemption_state ) {
167                        #if GCC_VERSION > 50000
168                        static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
169                        #endif
170
171                        // Set enabled flag to false
172                        // should be atomic to avoid preemption in the middle of the operation.
173                        // use memory order RELAXED since there is no inter-thread on this variable requirements
174                        __atomic_store_n(&enabled, false, __ATOMIC_RELAXED);
175
176                        // Signal the compiler that a fence is needed but only for signal handlers
177                        __atomic_signal_fence(__ATOMIC_ACQUIRE);
178
179                        __attribute__((unused)) unsigned short new_val = disable_count + 1;
180                        disable_count = new_val;
181                        verify( new_val < 65_000u );              // If this triggers someone is disabling interrupts without enabling them
182                }
183        }
184
185        // Enable interrupts by decrementing the counter
186        // If counter reaches 0, execute any pending __cfactx_switch
187        void enable_interrupts( __cfaabi_dbg_ctx_param ) {
188                processor   * proc = kernelTLS.this_processor; // Cache the processor now since interrupts can start happening after the atomic store
189                /* paranoid */ verify( proc );
190
191                with( kernelTLS.preemption_state ){
192                        unsigned short prev = disable_count;
193                        disable_count -= 1;
194                        verify( prev != 0u );                     // If this triggers someone is enabled already enabled interruptsverify( prev != 0u );
195
196                        // Check if we need to prempt the thread because an interrupt was missed
197                        if( prev == 1 ) {
198                                #if GCC_VERSION > 50000
199                                static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
200                                #endif
201
202                                // Set enabled flag to true
203                                // should be atomic to avoid preemption in the middle of the operation.
204                                // use memory order RELAXED since there is no inter-thread on this variable requirements
205                                __atomic_store_n(&enabled, true, __ATOMIC_RELAXED);
206
207                                // Signal the compiler that a fence is needed but only for signal handlers
208                                __atomic_signal_fence(__ATOMIC_RELEASE);
209                                if( proc->pending_preemption ) {
210                                        proc->pending_preemption = false;
211                                        force_yield( __POLL_PREEMPTION );
212                                }
213                        }
214                }
215
216                // For debugging purposes : keep track of the last person to enable the interrupts
217                __cfaabi_dbg_debug_do( proc->last_enable = caller; )
218        }
219
220        // Disable interrupts by incrementint the counter
221        // Don't execute any pending __cfactx_switch even if counter reaches 0
222        void enable_interrupts_noPoll() {
223                unsigned short prev = kernelTLS.preemption_state.disable_count;
224                kernelTLS.preemption_state.disable_count -= 1;
225                verifyf( prev != 0u, "Incremented from %u\n", prev );                     // If this triggers someone is enabled already enabled interrupts
226                if( prev == 1 ) {
227                        #if GCC_VERSION > 50000
228                        static_assert(__atomic_always_lock_free(sizeof(kernelTLS.preemption_state.enabled), &kernelTLS.preemption_state.enabled), "Must be lock-free");
229                        #endif
230                        // Set enabled flag to true
231                        // should be atomic to avoid preemption in the middle of the operation.
232                        // use memory order RELAXED since there is no inter-thread on this variable requirements
233                        __atomic_store_n(&kernelTLS.preemption_state.enabled, true, __ATOMIC_RELAXED);
234
235                        // Signal the compiler that a fence is needed but only for signal handlers
236                        __atomic_signal_fence(__ATOMIC_RELEASE);
237                }
238        }
239}
240
241// sigprocmask wrapper : unblock a single signal
242static inline void signal_unblock( int sig ) {
243        sigset_t mask;
244        sigemptyset( &mask );
245        sigaddset( &mask, sig );
246
247        if ( pthread_sigmask( SIG_UNBLOCK, &mask, 0p ) == -1 ) {
248            abort( "internal error, pthread_sigmask" );
249        }
250}
251
252// sigprocmask wrapper : block a single signal
253static inline void signal_block( int sig ) {
254        sigset_t mask;
255        sigemptyset( &mask );
256        sigaddset( &mask, sig );
257
258        if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
259                abort( "internal error, pthread_sigmask" );
260        }
261}
262
263// kill wrapper : signal a processor
264static void preempt( processor * this ) {
265        sigval_t value = { PREEMPT_NORMAL };
266        pthread_sigqueue( this->kernel_thread, SIGUSR1, value );
267}
268
269// reserved for future use
270static void timeout( struct __processor_id_t * id, $thread * this ) {
271        #if !defined( __CFA_NO_STATISTICS__ )
272                kernelTLS.this_stats = this->curr_cluster->stats;
273        #endif
274        __unpark( id, this __cfaabi_dbg_ctx2 );
275}
276
277// KERNEL ONLY
278// Check if a __cfactx_switch signal handler shoud defer
279// If true  : preemption is safe
280// If false : preemption is unsafe and marked as pending
281static inline bool preemption_ready() {
282        // Check if preemption is safe
283        bool ready = kernelTLS.preemption_state.enabled && ! kernelTLS.preemption_state.in_progress;
284
285        // Adjust the pending flag accordingly
286        kernelTLS.this_processor->pending_preemption = !ready;
287        return ready;
288}
289
290//=============================================================================================
291// Kernel Signal Startup/Shutdown logic
292//=============================================================================================
293
294// Startup routine to activate preemption
295// Called from kernel_startup
296void __kernel_alarm_startup() {
297        __cfaabi_dbg_print_safe( "Kernel : Starting preemption\n" );
298
299        // Start with preemption disabled until ready
300        kernelTLS.preemption_state.enabled = false;
301        kernelTLS.preemption_state.disable_count = 1;
302
303        // Initialize the event kernel
304        event_kernel = (event_kernel_t *)&storage_event_kernel;
305        (*event_kernel){};
306
307        // Setup proper signal handlers
308        __cfaabi_sigaction( SIGUSR1, sigHandler_ctxSwitch, SA_SIGINFO | SA_RESTART ); // __cfactx_switch handler
309        __cfaabi_sigaction( SIGALRM, sigHandler_alarm    , SA_SIGINFO | SA_RESTART ); // debug handler
310
311        signal_block( SIGALRM );
312
313        alarm_stack = __create_pthread( &alarm_thread, alarm_loop, 0p );
314}
315
316// Shutdown routine to deactivate preemption
317// Called from kernel_shutdown
318void __kernel_alarm_shutdown() {
319        __cfaabi_dbg_print_safe( "Kernel : Preemption stopping\n" );
320
321        // Block all signals since we are already shutting down
322        sigset_t mask;
323        sigfillset( &mask );
324        sigprocmask( SIG_BLOCK, &mask, 0p );
325
326        // Notify the alarm thread of the shutdown
327        sigval val = { 1 };
328        pthread_sigqueue( alarm_thread, SIGALRM, val );
329
330        // Wait for the preemption thread to finish
331
332        pthread_join( alarm_thread, 0p );
333        free( alarm_stack );
334
335        // Preemption is now fully stopped
336
337        __cfaabi_dbg_print_safe( "Kernel : Preemption stopped\n" );
338}
339
340// Raii ctor/dtor for the preemption_scope
341// Used by thread to control when they want to receive preemption signals
342void ?{}( preemption_scope & this, processor * proc ) {
343        (this.alarm){ proc, (Time){ 0 }, 0`s };
344        this.proc = proc;
345        this.proc->preemption_alarm = &this.alarm;
346
347        update_preemption( this.proc, this.proc->cltr->preemption_rate );
348}
349
350void ^?{}( preemption_scope & this ) {
351        disable_interrupts();
352
353        update_preemption( this.proc, 0`s );
354}
355
356//=============================================================================================
357// Kernel Signal Handlers
358//=============================================================================================
359
360// Context switch signal handler
361// Receives SIGUSR1 signal and causes the current thread to yield
362static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ ) {
363        __cfaabi_dbg_debug_do( last_interrupt = (void *)(cxt->uc_mcontext.CFA_REG_IP); )
364
365        // SKULLDUGGERY: if a thread creates a processor and the immediately deletes it,
366        // the interrupt that is supposed to force the kernel thread to preempt might arrive
367        // before the kernel thread has even started running. When that happens, an interrupt
368        // with a null 'this_processor' will be caught, just ignore it.
369        if(! kernelTLS.this_processor ) return;
370
371        choose(sfp->si_value.sival_int) {
372                case PREEMPT_NORMAL   : ;// Normal case, nothing to do here
373                case PREEMPT_TERMINATE: verify( __atomic_load_n( &kernelTLS.this_processor->do_terminate, __ATOMIC_SEQ_CST ) );
374                default:
375                        abort( "internal error, signal value is %d", sfp->si_value.sival_int );
376        }
377
378        // Check if it is safe to preempt here
379        if( !preemption_ready() ) { return; }
380
381        __cfaabi_dbg_print_buffer_decl( " KERNEL: preempting core %p (%p @ %p).\n", kernelTLS.this_processor, kernelTLS.this_thread, (void *)(cxt->uc_mcontext.CFA_REG_IP) );
382
383        // Sync flag : prevent recursive calls to the signal handler
384        kernelTLS.preemption_state.in_progress = true;
385
386        // Clear sighandler mask before context switching.
387        #if GCC_VERSION > 50000
388        static_assert( sizeof( sigset_t ) == sizeof( cxt->uc_sigmask ), "Expected cxt->uc_sigmask to be of sigset_t" );
389        #endif
390        if ( pthread_sigmask( SIG_SETMASK, (sigset_t *)&(cxt->uc_sigmask), 0p ) == -1 ) {
391                abort( "internal error, sigprocmask" );
392        }
393
394        // TODO: this should go in finish action
395        // Clear the in progress flag
396        kernelTLS.preemption_state.in_progress = false;
397
398        // Preemption can occur here
399
400        force_yield( __ALARM_PREEMPTION ); // Do the actual __cfactx_switch
401}
402
403static void sigHandler_alarm( __CFA_SIGPARMS__ ) {
404        abort("SIGALRM should never reach the signal handler");
405}
406
407// Main of the alarm thread
408// Waits on SIGALRM and send SIGUSR1 to whom ever needs it
409static void * alarm_loop( __attribute__((unused)) void * args ) {
410        __processor_id_t id;
411        id.id = doregister(&id);
412
413        // Block sigalrms to control when they arrive
414        sigset_t mask;
415        sigfillset(&mask);
416        if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
417            abort( "internal error, pthread_sigmask" );
418        }
419
420        sigemptyset( &mask );
421        sigaddset( &mask, SIGALRM );
422
423        // Main loop
424        while( true ) {
425                // Wait for a sigalrm
426                siginfo_t info;
427                int sig = sigwaitinfo( &mask, &info );
428
429                if( sig < 0 ) {
430                        //Error!
431                        int err = errno;
432                        switch( err ) {
433                                case EAGAIN :
434                                case EINTR :
435                                        {__cfaabi_dbg_print_buffer_decl( " KERNEL: Spurious wakeup %d.\n", err );}
436                                        continue;
437                                case EINVAL :
438                                        abort( "Timeout was invalid." );
439                                default:
440                                        abort( "Unhandled error %d", err);
441                        }
442                }
443
444                // If another signal arrived something went wrong
445                assertf(sig == SIGALRM, "Kernel Internal Error, sigwait: Unexpected signal %d (%d : %d)\n", sig, info.si_code, info.si_value.sival_int);
446
447                // __cfaabi_dbg_print_safe( "Kernel : Caught alarm from %d with %d\n", info.si_code, info.si_value.sival_int );
448                // Switch on the code (a.k.a. the sender) to
449                switch( info.si_code )
450                {
451                // Timers can apparently be marked as sent for the kernel
452                // In either case, tick preemption
453                case SI_TIMER:
454                case SI_KERNEL:
455                        // __cfaabi_dbg_print_safe( "Kernel : Preemption thread tick\n" );
456                        lock( event_kernel->lock __cfaabi_dbg_ctx2 );
457                        tick_preemption( &id );
458                        unlock( event_kernel->lock );
459                        break;
460                // Signal was not sent by the kernel but by an other thread
461                case SI_QUEUE:
462                        // For now, other thread only signal the alarm thread to shut it down
463                        // If this needs to change use info.si_value and handle the case here
464                        goto EXIT;
465                }
466        }
467
468EXIT:
469        __cfaabi_dbg_print_safe( "Kernel : Preemption thread stopping\n" );
470        unregister(&id);
471        return 0p;
472}
473
474//=============================================================================================
475// Kernel Signal Debug
476//=============================================================================================
477
478void __cfaabi_check_preemption() {
479        bool ready = kernelTLS.preemption_state.enabled;
480        if(!ready) { abort("Preemption should be ready"); }
481
482        sigset_t oldset;
483        int ret;
484        ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset);  // workaround trac#208: cast should be unnecessary
485        if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
486
487        ret = sigismember(&oldset, SIGUSR1);
488        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
489        if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
490
491        ret = sigismember(&oldset, SIGALRM);
492        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
493        if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
494
495        ret = sigismember(&oldset, SIGTERM);
496        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
497        if(ret == 1) { abort("ERROR SIGTERM is disabled"); }
498}
499
500#ifdef __CFA_WITH_VERIFY__
501bool __cfaabi_dbg_in_kernel() {
502        return !kernelTLS.preemption_state.enabled;
503}
504#endif
505
506// Local Variables: //
507// mode: c //
508// tab-width: 4 //
509// End: //
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