source: libcfa/src/concurrency/preemption.cfa@ 5fe7322

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 5fe7322 was 97cba9f, checked in by Peter A. Buhr <pabuhr@…>, 5 years 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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