source: libcfa/src/concurrency/preemption.cfa@ 4b30e8cc

ADT arm-eh ast-experimental enum forall-pointer-decay jacob/cs343-translation new-ast-unique-expr pthread-emulation qualifiedEnum
Last change on this file since 4b30e8cc was 4b30e8cc, checked in by Colby Alexander Parsons <caparsons@…>, 5 years ago

added callback support
  • Property mode set to 100644
File size: 17.4 KB
Line 
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 : Wed Aug 26 16:46:03 2020
13// Update Count : 53
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__ )
59#define CFA_REG_IP arm_pc
60#elif defined( __aarch64__ )
61#define CFA_REG_IP pc
62#else
63#error unsupported hardware architecture
64#endif
65
66KERNEL_STORAGE(event_kernel_t, event_kernel); // private storage for event kernel
67event_kernel_t * event_kernel; // kernel public handle to even kernel
68static pthread_t alarm_thread; // pthread handle to alarm thread
69static void * alarm_stack; // pthread stack for alarm thread
70
71static void ?{}(event_kernel_t & this) with( this ) {
72 alarms{};
73 lock{};
74}
75
76enum {
77 PREEMPT_NORMAL = 0,
78 PREEMPT_TERMINATE = 1,
79};
80
81//=============================================================================================
82// Kernel Preemption logic
83//=============================================================================================
84
85// Get next expired node
86static inline alarm_node_t * get_expired( alarm_list_t * alarms, Time currtime ) {
87 if( ! & (*alarms)`first ) return 0p; // If no alarms return null
88 if( (*alarms)`first.alarm >= currtime ) return 0p; // If alarms head not expired return null
89 return pop(alarms); // Otherwise just pop head
90}
91
92// Tick one frame of the Discrete Event Simulation for alarms
93static void tick_preemption( struct __processor_id_t * id ) {
94 alarm_node_t * node = 0p; // Used in the while loop but cannot be declared in the while condition
95 alarm_list_t * alarms = &event_kernel->alarms; // Local copy for ease of reading
96 Time currtime = __kernel_get_time(); // Check current time once so everything "happens at once"
97
98 //Loop throught every thing expired
99 while( node = get_expired( alarms, currtime ) ) {
100 // __cfaabi_dbg_print_buffer_decl( " KERNEL: preemption tick.\n" );
101 Duration period = node->period;
102 if( period == 0) {
103 node->set = false; // Node is one-shot, just mark it as not pending
104 }
105
106 // Check if this is a kernel
107 if( node->type == Kernel ) {
108 preempt( node->proc );
109 }
110 else if( node->type == User ) {
111 timeout( id, node->thrd );
112 }
113 else {
114 bool unpark_thd = node->callback(*node);
115 if (unpark_thd) timeout( id, node->thrd );
116 }
117
118 // Check if this is a periodic alarm
119 if( period > 0 ) {
120 // __cfaabi_dbg_print_buffer_local( " KERNEL: alarm period is %lu.\n", period.tv );
121 node->alarm = currtime + period; // Alarm is periodic, add currtime to it (used cached current time)
122 insert( alarms, node ); // Reinsert the node for the next time it triggers
123 }
124 }
125
126 // If there are still alarms pending, reset the timer
127 if( & (*alarms)`first ) {
128 __cfadbg_print_buffer_decl(preemption, " KERNEL: @%ju(%ju) resetting alarm to %ju.\n", currtime.tv, __kernel_get_time().tv, (alarms->head->alarm - currtime).tv);
129 Duration delta = (*alarms)`first.alarm - currtime;
130 Duration capped = max(delta, 50`us);
131 // itimerval tim = { caped };
132 // __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);
133
134 __kernel_set_timer( capped );
135 }
136}
137
138// Update the preemption of a processor and notify interested parties
139void update_preemption( processor * this, Duration duration ) {
140 alarm_node_t * alarm = this->preemption_alarm;
141
142 // Alarms need to be enabled
143 if ( duration > 0 && ! alarm->set ) {
144 alarm->alarm = __kernel_get_time() + duration;
145 alarm->period = duration;
146 register_self( alarm );
147 }
148 // Zero duration but alarm is set
149 else if ( duration == 0 && alarm->set ) {
150 unregister_self( alarm );
151 alarm->alarm = 0;
152 alarm->period = 0;
153 }
154 // If alarm is different from previous, change it
155 else if ( duration > 0 && alarm->period != duration ) {
156 unregister_self( alarm );
157 alarm->alarm = __kernel_get_time() + duration;
158 alarm->period = duration;
159 register_self( alarm );
160 }
161}
162
163//=============================================================================================
164// Kernel Signal Tools
165//=============================================================================================
166
167__cfaabi_dbg_debug_do( static thread_local void * last_interrupt = 0; )
168
169extern "C" {
170 // Disable interrupts by incrementing the counter
171 void disable_interrupts() {
172 with( kernelTLS.preemption_state ) {
173 #if GCC_VERSION > 50000
174 static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
175 #endif
176
177 // Set enabled flag to false
178 // should be atomic to avoid preemption in the middle of the operation.
179 // use memory order RELAXED since there is no inter-thread on this variable requirements
180 __atomic_store_n(&enabled, false, __ATOMIC_RELAXED);
181
182 // Signal the compiler that a fence is needed but only for signal handlers
183 __atomic_signal_fence(__ATOMIC_ACQUIRE);
184
185 __attribute__((unused)) unsigned short new_val = disable_count + 1;
186 disable_count = new_val;
187 verify( new_val < 65_000u ); // If this triggers someone is disabling interrupts without enabling them
188 }
189 }
190
191 // Enable interrupts by decrementing the counter
192 // If counter reaches 0, execute any pending __cfactx_switch
193 void enable_interrupts( __cfaabi_dbg_ctx_param ) {
194 processor * proc = kernelTLS.this_processor; // Cache the processor now since interrupts can start happening after the atomic store
195 /* paranoid */ verify( proc );
196
197 with( kernelTLS.preemption_state ){
198 unsigned short prev = disable_count;
199 disable_count -= 1;
200 verify( prev != 0u ); // If this triggers someone is enabled already enabled interruptsverify( prev != 0u );
201
202 // Check if we need to prempt the thread because an interrupt was missed
203 if( prev == 1 ) {
204 #if GCC_VERSION > 50000
205 static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
206 #endif
207
208 // Set enabled flag to true
209 // should be atomic to avoid preemption in the middle of the operation.
210 // use memory order RELAXED since there is no inter-thread on this variable requirements
211 __atomic_store_n(&enabled, true, __ATOMIC_RELAXED);
212
213 // Signal the compiler that a fence is needed but only for signal handlers
214 __atomic_signal_fence(__ATOMIC_RELEASE);
215 if( proc->pending_preemption ) {
216 proc->pending_preemption = false;
217 force_yield( __POLL_PREEMPTION );
218 }
219 }
220 }
221
222 // For debugging purposes : keep track of the last person to enable the interrupts
223 __cfaabi_dbg_debug_do( proc->last_enable = caller; )
224 }
225
226 // Disable interrupts by incrementint the counter
227 // Don't execute any pending __cfactx_switch even if counter reaches 0
228 void enable_interrupts_noPoll() {
229 unsigned short prev = kernelTLS.preemption_state.disable_count;
230 kernelTLS.preemption_state.disable_count -= 1;
231 verifyf( prev != 0u, "Incremented from %u\n", prev ); // If this triggers someone is enabled already enabled interrupts
232 if( prev == 1 ) {
233 #if GCC_VERSION > 50000
234 static_assert(__atomic_always_lock_free(sizeof(kernelTLS.preemption_state.enabled), &kernelTLS.preemption_state.enabled), "Must be lock-free");
235 #endif
236 // Set enabled flag to true
237 // should be atomic to avoid preemption in the middle of the operation.
238 // use memory order RELAXED since there is no inter-thread on this variable requirements
239 __atomic_store_n(&kernelTLS.preemption_state.enabled, true, __ATOMIC_RELAXED);
240
241 // Signal the compiler that a fence is needed but only for signal handlers
242 __atomic_signal_fence(__ATOMIC_RELEASE);
243 }
244 }
245}
246
247// sigprocmask wrapper : unblock a single signal
248static inline void signal_unblock( int sig ) {
249 sigset_t mask;
250 sigemptyset( &mask );
251 sigaddset( &mask, sig );
252
253 if ( pthread_sigmask( SIG_UNBLOCK, &mask, 0p ) == -1 ) {
254 abort( "internal error, pthread_sigmask" );
255 }
256}
257
258// sigprocmask wrapper : block a single signal
259static inline void signal_block( int sig ) {
260 sigset_t mask;
261 sigemptyset( &mask );
262 sigaddset( &mask, sig );
263
264 if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
265 abort( "internal error, pthread_sigmask" );
266 }
267}
268
269// kill wrapper : signal a processor
270static void preempt( processor * this ) {
271 sigval_t value = { PREEMPT_NORMAL };
272 pthread_sigqueue( this->kernel_thread, SIGUSR1, value );
273}
274
275// reserved for future use
276static void timeout( struct __processor_id_t * id, $thread * this ) {
277 #if !defined( __CFA_NO_STATISTICS__ )
278 kernelTLS.this_stats = this->curr_cluster->stats;
279 #endif
280 __unpark( id, this );
281}
282
283// KERNEL ONLY
284// Check if a __cfactx_switch signal handler shoud defer
285// If true : preemption is safe
286// If false : preemption is unsafe and marked as pending
287static inline bool preemption_ready() {
288 // Check if preemption is safe
289 bool ready = kernelTLS.preemption_state.enabled && ! kernelTLS.preemption_state.in_progress;
290
291 // Adjust the pending flag accordingly
292 kernelTLS.this_processor->pending_preemption = !ready;
293 return ready;
294}
295
296//=============================================================================================
297// Kernel Signal Startup/Shutdown logic
298//=============================================================================================
299
300// Startup routine to activate preemption
301// Called from kernel_startup
302void __kernel_alarm_startup() {
303 __cfaabi_dbg_print_safe( "Kernel : Starting preemption\n" );
304
305 // Start with preemption disabled until ready
306 kernelTLS.preemption_state.enabled = false;
307 kernelTLS.preemption_state.disable_count = 1;
308
309 // Initialize the event kernel
310 event_kernel = (event_kernel_t *)&storage_event_kernel;
311 (*event_kernel){};
312
313 // Setup proper signal handlers
314 __cfaabi_sigaction( SIGUSR1, sigHandler_ctxSwitch, SA_SIGINFO | SA_RESTART ); // __cfactx_switch handler
315 __cfaabi_sigaction( SIGALRM, sigHandler_alarm , SA_SIGINFO | SA_RESTART ); // debug handler
316
317 signal_block( SIGALRM );
318
319 alarm_stack = __create_pthread( &alarm_thread, alarm_loop, 0p );
320}
321
322// Shutdown routine to deactivate preemption
323// Called from kernel_shutdown
324void __kernel_alarm_shutdown() {
325 __cfaabi_dbg_print_safe( "Kernel : Preemption stopping\n" );
326
327 // Block all signals since we are already shutting down
328 sigset_t mask;
329 sigfillset( &mask );
330 sigprocmask( SIG_BLOCK, &mask, 0p );
331
332 // Notify the alarm thread of the shutdown
333 sigval val = { 1 };
334 pthread_sigqueue( alarm_thread, SIGALRM, val );
335
336 // Wait for the preemption thread to finish
337
338 pthread_join( alarm_thread, 0p );
339 free( alarm_stack );
340
341 // Preemption is now fully stopped
342
343 __cfaabi_dbg_print_safe( "Kernel : Preemption stopped\n" );
344}
345
346// Raii ctor/dtor for the preemption_scope
347// Used by thread to control when they want to receive preemption signals
348void ?{}( preemption_scope & this, processor * proc ) {
349 (this.alarm){ proc, (Time){ 0 }, 0`s };
350 this.proc = proc;
351 this.proc->preemption_alarm = &this.alarm;
352
353 update_preemption( this.proc, this.proc->cltr->preemption_rate );
354}
355
356void ^?{}( preemption_scope & this ) {
357 disable_interrupts();
358
359 update_preemption( this.proc, 0`s );
360}
361
362//=============================================================================================
363// Kernel Signal Handlers
364//=============================================================================================
365
366// Context switch signal handler
367// Receives SIGUSR1 signal and causes the current thread to yield
368static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ ) {
369 __cfaabi_dbg_debug_do( last_interrupt = (void *)(cxt->uc_mcontext.CFA_REG_IP); )
370
371 // SKULLDUGGERY: if a thread creates a processor and the immediately deletes it,
372 // the interrupt that is supposed to force the kernel thread to preempt might arrive
373 // before the kernel thread has even started running. When that happens, an interrupt
374 // with a null 'this_processor' will be caught, just ignore it.
375 if(! kernelTLS.this_processor ) return;
376
377 choose(sfp->si_value.sival_int) {
378 case PREEMPT_NORMAL : ;// Normal case, nothing to do here
379 case PREEMPT_TERMINATE: verify( __atomic_load_n( &kernelTLS.this_processor->do_terminate, __ATOMIC_SEQ_CST ) );
380 default:
381 abort( "internal error, signal value is %d", sfp->si_value.sival_int );
382 }
383
384 // Check if it is safe to preempt here
385 if( !preemption_ready() ) { return; }
386
387 __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) );
388
389 // Sync flag : prevent recursive calls to the signal handler
390 kernelTLS.preemption_state.in_progress = true;
391
392 // Clear sighandler mask before context switching.
393 #if GCC_VERSION > 50000
394 static_assert( sizeof( sigset_t ) == sizeof( cxt->uc_sigmask ), "Expected cxt->uc_sigmask to be of sigset_t" );
395 #endif
396 if ( pthread_sigmask( SIG_SETMASK, (sigset_t *)&(cxt->uc_sigmask), 0p ) == -1 ) {
397 abort( "internal error, sigprocmask" );
398 }
399
400 // TODO: this should go in finish action
401 // Clear the in progress flag
402 kernelTLS.preemption_state.in_progress = false;
403
404 // Preemption can occur here
405
406 force_yield( __ALARM_PREEMPTION ); // Do the actual __cfactx_switch
407}
408
409static void sigHandler_alarm( __CFA_SIGPARMS__ ) {
410 abort("SIGALRM should never reach the signal handler");
411}
412
413// Main of the alarm thread
414// Waits on SIGALRM and send SIGUSR1 to whom ever needs it
415static void * alarm_loop( __attribute__((unused)) void * args ) {
416 __processor_id_t id;
417 id.full_proc = false;
418 id.id = doregister(&id);
419
420 // Block sigalrms to control when they arrive
421 sigset_t mask;
422 sigfillset(&mask);
423 if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
424 abort( "internal error, pthread_sigmask" );
425 }
426
427 sigemptyset( &mask );
428 sigaddset( &mask, SIGALRM );
429
430 // Main loop
431 while( true ) {
432 // Wait for a sigalrm
433 siginfo_t info;
434 int sig = sigwaitinfo( &mask, &info );
435
436 if( sig < 0 ) {
437 //Error!
438 int err = errno;
439 switch( err ) {
440 case EAGAIN :
441 case EINTR :
442 {__cfaabi_dbg_print_buffer_decl( " KERNEL: Spurious wakeup %d.\n", err );}
443 continue;
444 case EINVAL :
445 abort( "Timeout was invalid." );
446 default:
447 abort( "Unhandled error %d", err);
448 }
449 }
450
451 // If another signal arrived something went wrong
452 assertf(sig == SIGALRM, "Kernel Internal Error, sigwait: Unexpected signal %d (%d : %d)\n", sig, info.si_code, info.si_value.sival_int);
453
454 // __cfaabi_dbg_print_safe( "Kernel : Caught alarm from %d with %d\n", info.si_code, info.si_value.sival_int );
455 // Switch on the code (a.k.a. the sender) to
456 switch( info.si_code )
457 {
458 // Timers can apparently be marked as sent for the kernel
459 // In either case, tick preemption
460 case SI_TIMER:
461 case SI_KERNEL:
462 // __cfaabi_dbg_print_safe( "Kernel : Preemption thread tick\n" );
463 lock( event_kernel->lock __cfaabi_dbg_ctx2 );
464 tick_preemption( &id );
465 unlock( event_kernel->lock );
466 break;
467 // Signal was not sent by the kernel but by an other thread
468 case SI_QUEUE:
469 // For now, other thread only signal the alarm thread to shut it down
470 // If this needs to change use info.si_value and handle the case here
471 goto EXIT;
472 }
473 }
474
475EXIT:
476 __cfaabi_dbg_print_safe( "Kernel : Preemption thread stopping\n" );
477 unregister(&id);
478 return 0p;
479}
480
481//=============================================================================================
482// Kernel Signal Debug
483//=============================================================================================
484
485void __cfaabi_check_preemption() {
486 bool ready = kernelTLS.preemption_state.enabled;
487 if(!ready) { abort("Preemption should be ready"); }
488
489 sigset_t oldset;
490 int ret;
491 ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset); // workaround trac#208: cast should be unnecessary
492 if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
493
494 ret = sigismember(&oldset, SIGUSR1);
495 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
496 if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
497
498 ret = sigismember(&oldset, SIGALRM);
499 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
500 if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
501
502 ret = sigismember(&oldset, SIGTERM);
503 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
504 if(ret == 1) { abort("ERROR SIGTERM is disabled"); }
505}
506
507#ifdef __CFA_WITH_VERIFY__
508bool __cfaabi_dbg_in_kernel() {
509 return !kernelTLS.preemption_state.enabled;
510}
511#endif
512
513// Local Variables: //
514// mode: c //
515// tab-width: 4 //
516// End: //
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