source: libcfa/src/concurrency/preemption.cfa @ 8c01e1b

arm-ehcleanup-dtorsjacob/cs343-translationjenkins-sandboxnew-astnew-ast-unique-expr
Last change on this file since 8c01e1b was 73abe95, checked in by Thierry Delisle <tdelisle@…>, 3 years ago

Replace extension-less headers with .hfa

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