source: libcfa/src/concurrency/preemption.cfa@ 16ba4a6f

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 16ba4a6f was eeb5023, checked in by Colby Alexander Parsons <caparsons@…>, 5 years ago

added full timeout functionality to unified condition variables
  • Property mode set to 100644
File size: 17.3 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( $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(void) {
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( node->thrd );
112 }
113 else {
114 node->callback(*node);
115 }
116
117 // Check if this is a periodic alarm
118 if( period > 0 ) {
119 // __cfaabi_dbg_print_buffer_local( " KERNEL: alarm period is %lu.\n", period.tv );
120 node->alarm = currtime + period; // Alarm is periodic, add currtime to it (used cached current time)
121 insert( alarms, node ); // Reinsert the node for the next time it triggers
122 }
123 }
124
125 // If there are still alarms pending, reset the timer
126 if( & (*alarms)`first ) {
127 __cfadbg_print_buffer_decl(preemption, " KERNEL: @%ju(%ju) resetting alarm to %ju.\n", currtime.tv, __kernel_get_time().tv, (alarms->head->alarm - currtime).tv);
128 Duration delta = (*alarms)`first.alarm - currtime;
129 Duration capped = max(delta, 50`us);
130 // itimerval tim = { caped };
131 // __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);
132
133 __kernel_set_timer( capped );
134 }
135}
136
137// Update the preemption of a processor and notify interested parties
138void update_preemption( processor * this, Duration duration ) {
139 alarm_node_t * alarm = this->preemption_alarm;
140
141 // Alarms need to be enabled
142 if ( duration > 0 && ! alarm->set ) {
143 alarm->alarm = __kernel_get_time() + duration;
144 alarm->period = duration;
145 register_self( alarm );
146 }
147 // Zero duration but alarm is set
148 else if ( duration == 0 && alarm->set ) {
149 unregister_self( alarm );
150 alarm->alarm = 0;
151 alarm->period = 0;
152 }
153 // If alarm is different from previous, change it
154 else if ( duration > 0 && alarm->period != duration ) {
155 unregister_self( alarm );
156 alarm->alarm = __kernel_get_time() + duration;
157 alarm->period = duration;
158 register_self( alarm );
159 }
160}
161
162//=============================================================================================
163// Kernel Signal Tools
164//=============================================================================================
165
166__cfaabi_dbg_debug_do( static thread_local void * last_interrupt = 0; )
167
168extern "C" {
169 // Disable interrupts by incrementing the counter
170 void disable_interrupts() {
171 with( kernelTLS.preemption_state ) {
172 #if GCC_VERSION > 50000
173 static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
174 #endif
175
176 // Set enabled flag to false
177 // should be atomic to avoid preemption in the middle of the operation.
178 // use memory order RELAXED since there is no inter-thread on this variable requirements
179 __atomic_store_n(&enabled, false, __ATOMIC_RELAXED);
180
181 // Signal the compiler that a fence is needed but only for signal handlers
182 __atomic_signal_fence(__ATOMIC_ACQUIRE);
183
184 __attribute__((unused)) unsigned short new_val = disable_count + 1;
185 disable_count = new_val;
186 verify( new_val < 65_000u ); // If this triggers someone is disabling interrupts without enabling them
187 }
188 }
189
190 // Enable interrupts by decrementing the counter
191 // If counter reaches 0, execute any pending __cfactx_switch
192 void enable_interrupts( __cfaabi_dbg_ctx_param ) {
193 processor * proc = kernelTLS.this_processor; // Cache the processor now since interrupts can start happening after the atomic store
194 /* paranoid */ verify( proc );
195
196 with( kernelTLS.preemption_state ){
197 unsigned short prev = disable_count;
198 disable_count -= 1;
199 verify( prev != 0u ); // If this triggers someone is enabled already enabled interruptsverify( prev != 0u );
200
201 // Check if we need to prempt the thread because an interrupt was missed
202 if( prev == 1 ) {
203 #if GCC_VERSION > 50000
204 static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
205 #endif
206
207 // Set enabled flag to true
208 // should be atomic to avoid preemption in the middle of the operation.
209 // use memory order RELAXED since there is no inter-thread on this variable requirements
210 __atomic_store_n(&enabled, true, __ATOMIC_RELAXED);
211
212 // Signal the compiler that a fence is needed but only for signal handlers
213 __atomic_signal_fence(__ATOMIC_RELEASE);
214 if( proc->pending_preemption ) {
215 proc->pending_preemption = false;
216 force_yield( __POLL_PREEMPTION );
217 }
218 }
219 }
220
221 // For debugging purposes : keep track of the last person to enable the interrupts
222 __cfaabi_dbg_debug_do( proc->last_enable = caller; )
223 }
224
225 // Disable interrupts by incrementint the counter
226 // Don't execute any pending __cfactx_switch even if counter reaches 0
227 void enable_interrupts_noPoll() {
228 unsigned short prev = kernelTLS.preemption_state.disable_count;
229 kernelTLS.preemption_state.disable_count -= 1;
230 verifyf( prev != 0u, "Incremented from %u\n", prev ); // If this triggers someone is enabled already enabled interrupts
231 if( prev == 1 ) {
232 #if GCC_VERSION > 50000
233 static_assert(__atomic_always_lock_free(sizeof(kernelTLS.preemption_state.enabled), &kernelTLS.preemption_state.enabled), "Must be lock-free");
234 #endif
235 // Set enabled flag to true
236 // should be atomic to avoid preemption in the middle of the operation.
237 // use memory order RELAXED since there is no inter-thread on this variable requirements
238 __atomic_store_n(&kernelTLS.preemption_state.enabled, true, __ATOMIC_RELAXED);
239
240 // Signal the compiler that a fence is needed but only for signal handlers
241 __atomic_signal_fence(__ATOMIC_RELEASE);
242 }
243 }
244}
245
246// sigprocmask wrapper : unblock a single signal
247static inline void signal_unblock( int sig ) {
248 sigset_t mask;
249 sigemptyset( &mask );
250 sigaddset( &mask, sig );
251
252 if ( pthread_sigmask( SIG_UNBLOCK, &mask, 0p ) == -1 ) {
253 abort( "internal error, pthread_sigmask" );
254 }
255}
256
257// sigprocmask wrapper : block a single signal
258static inline void signal_block( int sig ) {
259 sigset_t mask;
260 sigemptyset( &mask );
261 sigaddset( &mask, sig );
262
263 if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
264 abort( "internal error, pthread_sigmask" );
265 }
266}
267
268// kill wrapper : signal a processor
269static void preempt( processor * this ) {
270 sigval_t value = { PREEMPT_NORMAL };
271 pthread_sigqueue( this->kernel_thread, SIGUSR1, value );
272}
273
274// reserved for future use
275static void timeout( $thread * this ) {
276 #if !defined( __CFA_NO_STATISTICS__ )
277 kernelTLS.this_stats = this->curr_cluster->stats;
278 #endif
279 unpark( this );
280}
281
282// KERNEL ONLY
283// Check if a __cfactx_switch signal handler shoud defer
284// If true : preemption is safe
285// If false : preemption is unsafe and marked as pending
286static inline bool preemption_ready() {
287 // Check if preemption is safe
288 bool ready = kernelTLS.preemption_state.enabled && ! kernelTLS.preemption_state.in_progress;
289
290 // Adjust the pending flag accordingly
291 kernelTLS.this_processor->pending_preemption = !ready;
292 return ready;
293}
294
295//=============================================================================================
296// Kernel Signal Startup/Shutdown logic
297//=============================================================================================
298
299// Startup routine to activate preemption
300// Called from kernel_startup
301void __kernel_alarm_startup() {
302 __cfaabi_dbg_print_safe( "Kernel : Starting preemption\n" );
303
304 // Start with preemption disabled until ready
305 kernelTLS.preemption_state.enabled = false;
306 kernelTLS.preemption_state.disable_count = 1;
307
308 // Initialize the event kernel
309 event_kernel = (event_kernel_t *)&storage_event_kernel;
310 (*event_kernel){};
311
312 // Setup proper signal handlers
313 __cfaabi_sigaction( SIGUSR1, sigHandler_ctxSwitch, SA_SIGINFO | SA_RESTART ); // __cfactx_switch handler
314 __cfaabi_sigaction( SIGALRM, sigHandler_alarm , SA_SIGINFO | SA_RESTART ); // debug handler
315
316 signal_block( SIGALRM );
317
318 alarm_stack = __create_pthread( &alarm_thread, alarm_loop, 0p );
319}
320
321// Shutdown routine to deactivate preemption
322// Called from kernel_shutdown
323void __kernel_alarm_shutdown() {
324 __cfaabi_dbg_print_safe( "Kernel : Preemption stopping\n" );
325
326 // Block all signals since we are already shutting down
327 sigset_t mask;
328 sigfillset( &mask );
329 sigprocmask( SIG_BLOCK, &mask, 0p );
330
331 // Notify the alarm thread of the shutdown
332 sigval val = { 1 };
333 pthread_sigqueue( alarm_thread, SIGALRM, val );
334
335 // Wait for the preemption thread to finish
336
337 pthread_join( alarm_thread, 0p );
338 free( alarm_stack );
339
340 // Preemption is now fully stopped
341
342 __cfaabi_dbg_print_safe( "Kernel : Preemption stopped\n" );
343}
344
345// Raii ctor/dtor for the preemption_scope
346// Used by thread to control when they want to receive preemption signals
347void ?{}( preemption_scope & this, processor * proc ) {
348 (this.alarm){ proc, (Time){ 0 }, 0`s };
349 this.proc = proc;
350 this.proc->preemption_alarm = &this.alarm;
351
352 update_preemption( this.proc, this.proc->cltr->preemption_rate );
353}
354
355void ^?{}( preemption_scope & this ) {
356 disable_interrupts();
357
358 update_preemption( this.proc, 0`s );
359}
360
361//=============================================================================================
362// Kernel Signal Handlers
363//=============================================================================================
364
365// Context switch signal handler
366// Receives SIGUSR1 signal and causes the current thread to yield
367static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ ) {
368 __cfaabi_dbg_debug_do( last_interrupt = (void *)(cxt->uc_mcontext.CFA_REG_IP); )
369
370 // SKULLDUGGERY: if a thread creates a processor and the immediately deletes it,
371 // the interrupt that is supposed to force the kernel thread to preempt might arrive
372 // before the kernel thread has even started running. When that happens, an interrupt
373 // with a null 'this_processor' will be caught, just ignore it.
374 if(! kernelTLS.this_processor ) return;
375
376 choose(sfp->si_value.sival_int) {
377 case PREEMPT_NORMAL : ;// Normal case, nothing to do here
378 case PREEMPT_TERMINATE: verify( __atomic_load_n( &kernelTLS.this_processor->do_terminate, __ATOMIC_SEQ_CST ) );
379 default:
380 abort( "internal error, signal value is %d", sfp->si_value.sival_int );
381 }
382
383 // Check if it is safe to preempt here
384 if( !preemption_ready() ) { return; }
385
386 __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) );
387
388 // Sync flag : prevent recursive calls to the signal handler
389 kernelTLS.preemption_state.in_progress = true;
390
391 // Clear sighandler mask before context switching.
392 #if GCC_VERSION > 50000
393 static_assert( sizeof( sigset_t ) == sizeof( cxt->uc_sigmask ), "Expected cxt->uc_sigmask to be of sigset_t" );
394 #endif
395 if ( pthread_sigmask( SIG_SETMASK, (sigset_t *)&(cxt->uc_sigmask), 0p ) == -1 ) {
396 abort( "internal error, sigprocmask" );
397 }
398
399 // TODO: this should go in finish action
400 // Clear the in progress flag
401 kernelTLS.preemption_state.in_progress = false;
402
403 // Preemption can occur here
404
405 force_yield( __ALARM_PREEMPTION ); // Do the actual __cfactx_switch
406}
407
408static void sigHandler_alarm( __CFA_SIGPARMS__ ) {
409 abort("SIGALRM should never reach the signal handler");
410}
411
412// Main of the alarm thread
413// Waits on SIGALRM and send SIGUSR1 to whom ever needs it
414static void * alarm_loop( __attribute__((unused)) void * args ) {
415 __processor_id_t id;
416 id.full_proc = false;
417 id.id = doregister(&id);
418 kernelTLS.this_proc_id = &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();
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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