source: libcfa/src/concurrency/preemption.cfa @ 2026bb6

arm-ehjacob/cs343-translationjenkins-sandboxnew-astnew-ast-unique-expr
Last change on this file since 2026bb6 was 2026bb6, checked in by Thierry Delisle <tdelisle@…>, 3 years ago

More robust fix for optionally linking threads

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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 : Tue Jun  5 17:35:49 2018
13// Update Count     : 37
14//
15
16#define __cforall_thread__
17
18#include "preemption.hfa"
19#include <assert.h>
20
21extern "C" {
22#include <errno.h>
23#include <stdio.h>
24#include <string.h>
25#include <unistd.h>
26}
27
28#include "bits/signal.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( thread_desc * this );
41
42// FwdDeclarations : Signal handlers
43static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ );
44static void sigHandler_segv     ( __CFA_SIGPARMS__ );
45static void sigHandler_ill      ( __CFA_SIGPARMS__ );
46static void sigHandler_fpe      ( __CFA_SIGPARMS__ );
47static void sigHandler_abort    ( __CFA_SIGPARMS__ );
48
49// FwdDeclarations : alarm thread main
50static void * alarm_loop( __attribute__((unused)) void * args );
51
52// Machine specific register name
53#if   defined( __i386 )
54#define CFA_REG_IP gregs[REG_EIP]
55#elif defined( __x86_64 )
56#define CFA_REG_IP gregs[REG_RIP]
57#elif defined( __ARM_ARCH )
58#define CFA_REG_IP arm_pc
59#else
60#error unknown hardware architecture
61#endif
62
63KERNEL_STORAGE(event_kernel_t, event_kernel);         // private storage for event kernel
64event_kernel_t * event_kernel;                        // kernel public handle to even kernel
65static pthread_t alarm_thread;                        // pthread handle to alarm thread
66
67static void ?{}(event_kernel_t & this) with( this ) {
68        alarms{};
69        lock{};
70}
71
72enum {
73        PREEMPT_NORMAL    = 0,
74        PREEMPT_TERMINATE = 1,
75};
76
77//=============================================================================================
78// Kernel Preemption logic
79//=============================================================================================
80
81// Get next expired node
82static inline alarm_node_t * get_expired( alarm_list_t * alarms, Time currtime ) {
83        if( !alarms->head ) return NULL;                          // If no alarms return null
84        if( alarms->head->alarm >= currtime ) return NULL;        // If alarms head not expired return null
85        return pop(alarms);                                       // Otherwise just pop head
86}
87
88// Tick one frame of the Discrete Event Simulation for alarms
89static void tick_preemption() {
90        alarm_node_t * node = NULL;                     // Used in the while loop but cannot be declared in the while condition
91        alarm_list_t * alarms = &event_kernel->alarms;  // Local copy for ease of reading
92        Time currtime = __kernel_get_time();                    // Check current time once so we everything "happens at once"
93
94        //Loop throught every thing expired
95        while( node = get_expired( alarms, currtime ) ) {
96                // __cfaabi_dbg_print_buffer_decl( " KERNEL: preemption tick.\n" );
97
98                // Check if this is a kernel
99                if( node->kernel_alarm ) {
100                        preempt( node->proc );
101                }
102                else {
103                        timeout( node->thrd );
104                }
105
106                // Check if this is a periodic alarm
107                Duration period = node->period;
108                if( period > 0 ) {
109                        // __cfaabi_dbg_print_buffer_local( " KERNEL: alarm period is %lu.\n", period.tv );
110                        node->alarm = currtime + period;    // Alarm is periodic, add currtime to it (used cached current time)
111                        insert( alarms, node );             // Reinsert the node for the next time it triggers
112                }
113                else {
114                        node->set = false;                  // Node is one-shot, just mark it as not pending
115                }
116        }
117
118        // If there are still alarms pending, reset the timer
119        if( alarms->head ) {
120                __cfaabi_dbg_print_buffer_decl( " KERNEL: @%ju(%ju) resetting alarm to %ju.\n", currtime.tv, __kernel_get_time().tv, (alarms->head->alarm - currtime).tv);
121                Duration delta = alarms->head->alarm - currtime;
122                Duration caped = max(delta, 50`us);
123                // itimerval tim  = { caped };
124                // __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);
125
126                __kernel_set_timer( caped );
127        }
128}
129
130// Update the preemption of a processor and notify interested parties
131void update_preemption( processor * this, Duration duration ) {
132        alarm_node_t * alarm = this->preemption_alarm;
133
134        // Alarms need to be enabled
135        if ( duration > 0 && ! alarm->set ) {
136                alarm->alarm = __kernel_get_time() + duration;
137                alarm->period = duration;
138                register_self( alarm );
139        }
140        // Zero duration but alarm is set
141        else if ( duration == 0 && alarm->set ) {
142                unregister_self( alarm );
143                alarm->alarm = 0;
144                alarm->period = 0;
145        }
146        // If alarm is different from previous, change it
147        else if ( duration > 0 && alarm->period != duration ) {
148                unregister_self( alarm );
149                alarm->alarm = __kernel_get_time() + duration;
150                alarm->period = duration;
151                register_self( alarm );
152        }
153}
154
155//=============================================================================================
156// Kernel Signal Tools
157//=============================================================================================
158
159__cfaabi_dbg_debug_do( static thread_local void * last_interrupt = 0; )
160
161extern "C" {
162        // Disable interrupts by incrementing the counter
163        void disable_interrupts() {
164                with( kernelTLS.preemption_state ) {
165                        #if GCC_VERSION > 50000
166                        static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
167                        #endif
168
169                        // Set enabled flag to false
170                        // should be atomic to avoid preemption in the middle of the operation.
171                        // use memory order RELAXED since there is no inter-thread on this variable requirements
172                        __atomic_store_n(&enabled, false, __ATOMIC_RELAXED);
173
174                        // Signal the compiler that a fence is needed but only for signal handlers
175                        __atomic_signal_fence(__ATOMIC_ACQUIRE);
176
177                        __attribute__((unused)) unsigned short new_val = disable_count + 1;
178                        disable_count = new_val;
179                        verify( new_val < 65_000u );              // If this triggers someone is disabling interrupts without enabling them
180                }
181        }
182
183        // Enable interrupts by decrementing the counter
184        // If counter reaches 0, execute any pending CtxSwitch
185        void enable_interrupts( __cfaabi_dbg_ctx_param ) {
186                processor   * proc = kernelTLS.this_processor; // Cache the processor now since interrupts can start happening after the atomic store
187                thread_desc * thrd = kernelTLS.this_thread;       // Cache the thread now since interrupts can start happening after the atomic store
188
189                with( kernelTLS.preemption_state ){
190                        unsigned short prev = disable_count;
191                        disable_count -= 1;
192                        verify( prev != 0u );                     // If this triggers someone is enabled already enabled interruptsverify( prev != 0u );
193
194                        // Check if we need to prempt the thread because an interrupt was missed
195                        if( prev == 1 ) {
196                                #if GCC_VERSION > 50000
197                                static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
198                                #endif
199
200                                // Set enabled flag to true
201                                // should be atomic to avoid preemption in the middle of the operation.
202                                // use memory order RELAXED since there is no inter-thread on this variable requirements
203                                __atomic_store_n(&enabled, true, __ATOMIC_RELAXED);
204
205                                // Signal the compiler that a fence is needed but only for signal handlers
206                                __atomic_signal_fence(__ATOMIC_RELEASE);
207                                if( proc->pending_preemption ) {
208                                        proc->pending_preemption = false;
209                                        BlockInternal( thrd );
210                                }
211                        }
212                }
213
214                // For debugging purposes : keep track of the last person to enable the interrupts
215                __cfaabi_dbg_debug_do( proc->last_enable = caller; )
216        }
217
218        // Disable interrupts by incrementint the counter
219        // Don't execute any pending CtxSwitch even if counter reaches 0
220        void enable_interrupts_noPoll() {
221                unsigned short prev = kernelTLS.preemption_state.disable_count;
222                kernelTLS.preemption_state.disable_count -= 1;
223                verifyf( prev != 0u, "Incremented from %u\n", prev );                     // If this triggers someone is enabled already enabled interrupts
224                if( prev == 1 ) {
225                        #if GCC_VERSION > 50000
226                        static_assert(__atomic_always_lock_free(sizeof(kernelTLS.preemption_state.enabled), &kernelTLS.preemption_state.enabled), "Must be lock-free");
227                        #endif
228                        // Set enabled flag to true
229                        // should be atomic to avoid preemption in the middle of the operation.
230                        // use memory order RELAXED since there is no inter-thread on this variable requirements
231                        __atomic_store_n(&kernelTLS.preemption_state.enabled, true, __ATOMIC_RELAXED);
232
233                        // Signal the compiler that a fence is needed but only for signal handlers
234                        __atomic_signal_fence(__ATOMIC_RELEASE);
235                }
236        }
237}
238
239// sigprocmask wrapper : unblock a single signal
240static inline void signal_unblock( int sig ) {
241        sigset_t mask;
242        sigemptyset( &mask );
243        sigaddset( &mask, sig );
244
245        if ( pthread_sigmask( SIG_UNBLOCK, &mask, NULL ) == -1 ) {
246            abort( "internal error, pthread_sigmask" );
247        }
248}
249
250// sigprocmask wrapper : block a single signal
251static inline void signal_block( int sig ) {
252        sigset_t mask;
253        sigemptyset( &mask );
254        sigaddset( &mask, sig );
255
256        if ( pthread_sigmask( SIG_BLOCK, &mask, NULL ) == -1 ) {
257            abort( "internal error, pthread_sigmask" );
258        }
259}
260
261// kill wrapper : signal a processor
262static void preempt( processor * this ) {
263        sigval_t value = { PREEMPT_NORMAL };
264        pthread_sigqueue( this->kernel_thread, SIGUSR1, value );
265}
266
267// reserved for future use
268static void timeout( thread_desc * this ) {
269        //TODO : implement waking threads
270}
271
272// KERNEL ONLY
273// Check if a CtxSwitch signal handler shoud defer
274// If true  : preemption is safe
275// If false : preemption is unsafe and marked as pending
276static inline bool preemption_ready() {
277        // Check if preemption is safe
278        bool ready = kernelTLS.preemption_state.enabled && ! kernelTLS.preemption_state.in_progress;
279
280        // Adjust the pending flag accordingly
281        kernelTLS.this_processor->pending_preemption = !ready;
282        return ready;
283}
284
285//=============================================================================================
286// Kernel Signal Startup/Shutdown logic
287//=============================================================================================
288
289// Startup routine to activate preemption
290// Called from kernel_startup
291void kernel_start_preemption() {
292        __cfaabi_dbg_print_safe( "Kernel : Starting preemption\n" );
293
294        // Start with preemption disabled until ready
295        kernelTLS.preemption_state.enabled = false;
296        kernelTLS.preemption_state.disable_count = 1;
297
298        // Initialize the event kernel
299        event_kernel = (event_kernel_t *)&storage_event_kernel;
300        (*event_kernel){};
301
302        // Setup proper signal handlers
303        __cfaabi_sigaction( SIGUSR1, sigHandler_ctxSwitch, SA_SIGINFO | SA_RESTART );         // CtxSwitch handler
304
305        signal_block( SIGALRM );
306
307        pthread_create( &alarm_thread, NULL, alarm_loop, NULL );
308}
309
310// Shutdown routine to deactivate preemption
311// Called from kernel_shutdown
312void kernel_stop_preemption() {
313        __cfaabi_dbg_print_safe( "Kernel : Preemption stopping\n" );
314
315        // Block all signals since we are already shutting down
316        sigset_t mask;
317        sigfillset( &mask );
318        sigprocmask( SIG_BLOCK, &mask, NULL );
319
320        // Notify the alarm thread of the shutdown
321        sigval val = { 1 };
322        pthread_sigqueue( alarm_thread, SIGALRM, val );
323
324        // Wait for the preemption thread to finish
325        pthread_join( alarm_thread, NULL );
326
327        // Preemption is now fully stopped
328
329        __cfaabi_dbg_print_safe( "Kernel : Preemption stopped\n" );
330}
331
332// Raii ctor/dtor for the preemption_scope
333// Used by thread to control when they want to receive preemption signals
334void ?{}( preemption_scope & this, processor * proc ) {
335        (this.alarm){ proc, (Time){ 0 }, 0`s };
336        this.proc = proc;
337        this.proc->preemption_alarm = &this.alarm;
338
339        update_preemption( this.proc, this.proc->cltr->preemption_rate );
340}
341
342void ^?{}( preemption_scope & this ) {
343        disable_interrupts();
344
345        update_preemption( this.proc, 0`s );
346}
347
348//=============================================================================================
349// Kernel Signal Handlers
350//=============================================================================================
351
352// Context switch signal handler
353// Receives SIGUSR1 signal and causes the current thread to yield
354static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ ) {
355        __cfaabi_dbg_debug_do( last_interrupt = (void *)(cxt->uc_mcontext.CFA_REG_IP); )
356
357        // SKULLDUGGERY: if a thread creates a processor and the immediately deletes it,
358        // the interrupt that is supposed to force the kernel thread to preempt might arrive
359        // before the kernel thread has even started running. When that happens an iterrupt
360        // we a null 'this_processor' will be caught, just ignore it.
361        if(! kernelTLS.this_processor ) return;
362
363        choose(sfp->si_value.sival_int) {
364                case PREEMPT_NORMAL   : ;// Normal case, nothing to do here
365                case PREEMPT_TERMINATE: verify( __atomic_load_n( &kernelTLS.this_processor->do_terminate, __ATOMIC_SEQ_CST ) );
366                default:
367                        abort( "internal error, signal value is %d", sfp->si_value.sival_int );
368        }
369
370        // Check if it is safe to preempt here
371        if( !preemption_ready() ) { return; }
372
373        __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) );
374
375        // Sync flag : prevent recursive calls to the signal handler
376        kernelTLS.preemption_state.in_progress = true;
377
378        // Clear sighandler mask before context switching.
379        #if GCC_VERSION > 50000
380        static_assert( sizeof( sigset_t ) == sizeof( cxt->uc_sigmask ), "Expected cxt->uc_sigmask to be of sigset_t" );
381        #endif
382        if ( pthread_sigmask( SIG_SETMASK, (sigset_t *)&(cxt->uc_sigmask), NULL ) == -1 ) {
383                abort( "internal error, sigprocmask" );
384        }
385
386        // TODO: this should go in finish action
387        // Clear the in progress flag
388        kernelTLS.preemption_state.in_progress = false;
389
390        // Preemption can occur here
391
392        BlockInternal( kernelTLS.this_thread ); // Do the actual CtxSwitch
393}
394
395// Main of the alarm thread
396// Waits on SIGALRM and send SIGUSR1 to whom ever needs it
397static void * alarm_loop( __attribute__((unused)) void * args ) {
398        // Block sigalrms to control when they arrive
399        sigset_t mask;
400        sigfillset(&mask);
401        if ( pthread_sigmask( SIG_BLOCK, &mask, NULL ) == -1 ) {
402            abort( "internal error, pthread_sigmask" );
403        }
404
405        sigemptyset( &mask );
406        sigaddset( &mask, SIGALRM );
407
408        // Main loop
409        while( true ) {
410                // Wait for a sigalrm
411                siginfo_t info;
412                int sig = sigwaitinfo( &mask, &info );
413
414                if( sig < 0 ) {
415                        //Error!
416                        int err = errno;
417                        switch( err ) {
418                                case EAGAIN :
419                                case EINTR :
420                                        {__cfaabi_dbg_print_buffer_decl( " KERNEL: Spurious wakeup %d.\n", err );}
421                                        continue;
422                        case EINVAL :
423                                        abort( "Timeout was invalid." );
424                                default:
425                                        abort( "Unhandled error %d", err);
426                        }
427                }
428
429                // If another signal arrived something went wrong
430                assertf(sig == SIGALRM, "Kernel Internal Error, sigwait: Unexpected signal %d (%d : %d)\n", sig, info.si_code, info.si_value.sival_int);
431
432                // __cfaabi_dbg_print_safe( "Kernel : Caught alarm from %d with %d\n", info.si_code, info.si_value.sival_int );
433                // Switch on the code (a.k.a. the sender) to
434                switch( info.si_code )
435                {
436                // Timers can apparently be marked as sent for the kernel
437                // In either case, tick preemption
438                case SI_TIMER:
439                case SI_KERNEL:
440                        // __cfaabi_dbg_print_safe( "Kernel : Preemption thread tick\n" );
441                        lock( event_kernel->lock __cfaabi_dbg_ctx2 );
442                        tick_preemption();
443                        unlock( event_kernel->lock );
444                        break;
445                // Signal was not sent by the kernel but by an other thread
446                case SI_QUEUE:
447                        // For now, other thread only signal the alarm thread to shut it down
448                        // If this needs to change use info.si_value and handle the case here
449                        goto EXIT;
450                }
451        }
452
453EXIT:
454        __cfaabi_dbg_print_safe( "Kernel : Preemption thread stopping\n" );
455        return NULL;
456}
457
458//=============================================================================================
459// Kernel Signal Debug
460//=============================================================================================
461
462void __cfaabi_check_preemption() {
463        bool ready = kernelTLS.preemption_state.enabled;
464        if(!ready) { abort("Preemption should be ready"); }
465
466        sigset_t oldset;
467        int ret;
468        ret = pthread_sigmask(0, NULL, &oldset);
469        if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
470
471        ret = sigismember(&oldset, SIGUSR1);
472        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
473        if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
474
475        ret = sigismember(&oldset, SIGALRM);
476        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
477        if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
478
479        ret = sigismember(&oldset, SIGTERM);
480        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
481        if(ret == 1) { abort("ERROR SIGTERM is disabled"); }
482}
483
484#ifdef __CFA_WITH_VERIFY__
485bool __cfaabi_dbg_in_kernel() {
486        return !kernelTLS.preemption_state.enabled;
487}
488#endif
489
490// Local Variables: //
491// mode: c //
492// tab-width: 4 //
493// End: //
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