source: libcfa/src/concurrency/preemption.cfa@ b0a0ee4

ADT arm-eh ast-experimental enum forall-pointer-decay jacob/cs343-translation new-ast new-ast-unique-expr pthread-emulation qualifiedEnum
Last change on this file since b0a0ee4 was 8e9e9a2, checked in by Thierry Delisle <tdelisle@…>, 5 years ago

Added assert to check for non-processors enabling preemption.
  • Property mode set to 100644
File size: 17.1 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 Jun 17 11:36:25 2020
13// Update Count : 46
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
29#if !defined(__CFA_DEFAULT_PREEMPTION__)
30#define __CFA_DEFAULT_PREEMPTION__ 10`ms
31#endif
32
33Duration default_preemption() __attribute__((weak)) {
34 return __CFA_DEFAULT_PREEMPTION__;
35}
36
37// FwdDeclarations : timeout handlers
38static void preempt( processor * this );
39static void timeout( struct __processor_id_t * id, $thread * this );
40
41// FwdDeclarations : Signal handlers
42static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ );
43static void sigHandler_alarm ( __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
66static void * alarm_stack; // pthread stack for alarm thread
67
68static void ?{}(event_kernel_t & this) with( this ) {
69 alarms{};
70 lock{};
71}
72
73enum {
74 PREEMPT_NORMAL = 0,
75 PREEMPT_TERMINATE = 1,
76};
77
78//=============================================================================================
79// Kernel Preemption logic
80//=============================================================================================
81
82// Get next expired node
83static inline alarm_node_t * get_expired( alarm_list_t * alarms, Time currtime ) {
84 if( ! & (*alarms)`first ) return 0p; // If no alarms return null
85 if( (*alarms)`first.alarm >= currtime ) return 0p; // If alarms head not expired return null
86 return pop(alarms); // Otherwise just pop head
87}
88
89// Tick one frame of the Discrete Event Simulation for alarms
90static void tick_preemption( struct __processor_id_t * id ) {
91 alarm_node_t * node = 0p; // Used in the while loop but cannot be declared in the while condition
92 alarm_list_t * alarms = &event_kernel->alarms; // Local copy for ease of reading
93 Time currtime = __kernel_get_time(); // Check current time once so everything "happens at once"
94
95 //Loop throught every thing expired
96 while( node = get_expired( alarms, currtime ) ) {
97 // __cfaabi_dbg_print_buffer_decl( " KERNEL: preemption tick.\n" );
98 Duration period = node->period;
99 if( period == 0) {
100 node->set = false; // Node is one-shot, just mark it as not pending
101 }
102
103 // Check if this is a kernel
104 if( node->kernel_alarm ) {
105 preempt( node->proc );
106 }
107 else {
108 timeout( id, node->thrd );
109 }
110
111 // Check if this is a periodic alarm
112 if( period > 0 ) {
113 // __cfaabi_dbg_print_buffer_local( " KERNEL: alarm period is %lu.\n", period.tv );
114 node->alarm = currtime + period; // Alarm is periodic, add currtime to it (used cached current time)
115 insert( alarms, node ); // Reinsert the node for the next time it triggers
116 }
117 }
118
119 // If there are still alarms pending, reset the timer
120 if( & (*alarms)`first ) {
121 __cfadbg_print_buffer_decl(preemption, " KERNEL: @%ju(%ju) resetting alarm to %ju.\n", currtime.tv, __kernel_get_time().tv, (alarms->head->alarm - currtime).tv);
122 Duration delta = (*alarms)`first.alarm - currtime;
123 Duration capped = max(delta, 50`us);
124 // itimerval tim = { caped };
125 // __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);
126
127 __kernel_set_timer( capped );
128 }
129}
130
131// Update the preemption of a processor and notify interested parties
132void update_preemption( processor * this, Duration duration ) {
133 alarm_node_t * alarm = this->preemption_alarm;
134
135 // Alarms need to be enabled
136 if ( duration > 0 && ! alarm->set ) {
137 alarm->alarm = __kernel_get_time() + duration;
138 alarm->period = duration;
139 register_self( alarm );
140 }
141 // Zero duration but alarm is set
142 else if ( duration == 0 && alarm->set ) {
143 unregister_self( alarm );
144 alarm->alarm = 0;
145 alarm->period = 0;
146 }
147 // If alarm is different from previous, change it
148 else if ( duration > 0 && alarm->period != duration ) {
149 unregister_self( alarm );
150 alarm->alarm = __kernel_get_time() + duration;
151 alarm->period = duration;
152 register_self( alarm );
153 }
154}
155
156//=============================================================================================
157// Kernel Signal Tools
158//=============================================================================================
159
160__cfaabi_dbg_debug_do( static thread_local void * last_interrupt = 0; )
161
162extern "C" {
163 // Disable interrupts by incrementing the counter
164 void disable_interrupts() {
165 with( kernelTLS.preemption_state ) {
166 #if GCC_VERSION > 50000
167 static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
168 #endif
169
170 // Set enabled flag to false
171 // should be atomic to avoid preemption in the middle of the operation.
172 // use memory order RELAXED since there is no inter-thread on this variable requirements
173 __atomic_store_n(&enabled, false, __ATOMIC_RELAXED);
174
175 // Signal the compiler that a fence is needed but only for signal handlers
176 __atomic_signal_fence(__ATOMIC_ACQUIRE);
177
178 __attribute__((unused)) unsigned short new_val = disable_count + 1;
179 disable_count = new_val;
180 verify( new_val < 65_000u ); // If this triggers someone is disabling interrupts without enabling them
181 }
182 }
183
184 // Enable interrupts by decrementing the counter
185 // If counter reaches 0, execute any pending __cfactx_switch
186 void enable_interrupts( __cfaabi_dbg_ctx_param ) {
187 processor * proc = kernelTLS.this_processor; // Cache the processor now since interrupts can start happening after the atomic store
188 /* paranoid */ verify( proc );
189
190 with( kernelTLS.preemption_state ){
191 unsigned short prev = disable_count;
192 disable_count -= 1;
193 verify( prev != 0u ); // If this triggers someone is enabled already enabled interruptsverify( prev != 0u );
194
195 // Check if we need to prempt the thread because an interrupt was missed
196 if( prev == 1 ) {
197 #if GCC_VERSION > 50000
198 static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
199 #endif
200
201 // Set enabled flag to true
202 // should be atomic to avoid preemption in the middle of the operation.
203 // use memory order RELAXED since there is no inter-thread on this variable requirements
204 __atomic_store_n(&enabled, true, __ATOMIC_RELAXED);
205
206 // Signal the compiler that a fence is needed but only for signal handlers
207 __atomic_signal_fence(__ATOMIC_RELEASE);
208 if( proc->pending_preemption ) {
209 proc->pending_preemption = false;
210 force_yield( __POLL_PREEMPTION );
211 }
212 }
213 }
214
215 // For debugging purposes : keep track of the last person to enable the interrupts
216 __cfaabi_dbg_debug_do( proc->last_enable = caller; )
217 }
218
219 // Disable interrupts by incrementint the counter
220 // Don't execute any pending __cfactx_switch even if counter reaches 0
221 void enable_interrupts_noPoll() {
222 unsigned short prev = kernelTLS.preemption_state.disable_count;
223 kernelTLS.preemption_state.disable_count -= 1;
224 verifyf( prev != 0u, "Incremented from %u\n", prev ); // If this triggers someone is enabled already enabled interrupts
225 if( prev == 1 ) {
226 #if GCC_VERSION > 50000
227 static_assert(__atomic_always_lock_free(sizeof(kernelTLS.preemption_state.enabled), &kernelTLS.preemption_state.enabled), "Must be lock-free");
228 #endif
229 // Set enabled flag to true
230 // should be atomic to avoid preemption in the middle of the operation.
231 // use memory order RELAXED since there is no inter-thread on this variable requirements
232 __atomic_store_n(&kernelTLS.preemption_state.enabled, true, __ATOMIC_RELAXED);
233
234 // Signal the compiler that a fence is needed but only for signal handlers
235 __atomic_signal_fence(__ATOMIC_RELEASE);
236 }
237 }
238}
239
240// sigprocmask wrapper : unblock a single signal
241static inline void signal_unblock( int sig ) {
242 sigset_t mask;
243 sigemptyset( &mask );
244 sigaddset( &mask, sig );
245
246 if ( pthread_sigmask( SIG_UNBLOCK, &mask, 0p ) == -1 ) {
247 abort( "internal error, pthread_sigmask" );
248 }
249}
250
251// sigprocmask wrapper : block a single signal
252static inline void signal_block( int sig ) {
253 sigset_t mask;
254 sigemptyset( &mask );
255 sigaddset( &mask, sig );
256
257 if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
258 abort( "internal error, pthread_sigmask" );
259 }
260}
261
262// kill wrapper : signal a processor
263static void preempt( processor * this ) {
264 sigval_t value = { PREEMPT_NORMAL };
265 pthread_sigqueue( this->kernel_thread, SIGUSR1, value );
266}
267
268// reserved for future use
269static void timeout( struct __processor_id_t * id, $thread * this ) {
270 #if !defined( __CFA_NO_STATISTICS__ )
271 kernelTLS.this_stats = this->curr_cluster->stats;
272 #endif
273 __unpark( id, this __cfaabi_dbg_ctx2 );
274}
275
276// KERNEL ONLY
277// Check if a __cfactx_switch signal handler shoud defer
278// If true : preemption is safe
279// If false : preemption is unsafe and marked as pending
280static inline bool preemption_ready() {
281 // Check if preemption is safe
282 bool ready = kernelTLS.preemption_state.enabled && ! kernelTLS.preemption_state.in_progress;
283
284 // Adjust the pending flag accordingly
285 kernelTLS.this_processor->pending_preemption = !ready;
286 return ready;
287}
288
289//=============================================================================================
290// Kernel Signal Startup/Shutdown logic
291//=============================================================================================
292
293// Startup routine to activate preemption
294// Called from kernel_startup
295void kernel_start_preemption() {
296 __cfaabi_dbg_print_safe( "Kernel : Starting preemption\n" );
297
298 // Start with preemption disabled until ready
299 kernelTLS.preemption_state.enabled = false;
300 kernelTLS.preemption_state.disable_count = 1;
301
302 // Initialize the event kernel
303 event_kernel = (event_kernel_t *)&storage_event_kernel;
304 (*event_kernel){};
305
306 // Setup proper signal handlers
307 __cfaabi_sigaction( SIGUSR1, sigHandler_ctxSwitch, SA_SIGINFO | SA_RESTART ); // __cfactx_switch handler
308 __cfaabi_sigaction( SIGALRM, sigHandler_alarm , SA_SIGINFO | SA_RESTART ); // debug handler
309
310 signal_block( SIGALRM );
311
312 alarm_stack = __create_pthread( &alarm_thread, alarm_loop, 0p );
313}
314
315// Shutdown routine to deactivate preemption
316// Called from kernel_shutdown
317void kernel_stop_preemption() {
318 __cfaabi_dbg_print_safe( "Kernel : Preemption stopping\n" );
319
320 // Block all signals since we are already shutting down
321 sigset_t mask;
322 sigfillset( &mask );
323 sigprocmask( SIG_BLOCK, &mask, 0p );
324
325 // Notify the alarm thread of the shutdown
326 sigval val = { 1 };
327 pthread_sigqueue( alarm_thread, SIGALRM, val );
328
329 // Wait for the preemption thread to finish
330
331 pthread_join( alarm_thread, 0p );
332 free( alarm_stack );
333
334 // Preemption is now fully stopped
335
336 __cfaabi_dbg_print_safe( "Kernel : Preemption stopped\n" );
337}
338
339// Raii ctor/dtor for the preemption_scope
340// Used by thread to control when they want to receive preemption signals
341void ?{}( preemption_scope & this, processor * proc ) {
342 (this.alarm){ proc, (Time){ 0 }, 0`s };
343 this.proc = proc;
344 this.proc->preemption_alarm = &this.alarm;
345
346 update_preemption( this.proc, this.proc->cltr->preemption_rate );
347}
348
349void ^?{}( preemption_scope & this ) {
350 disable_interrupts();
351
352 update_preemption( this.proc, 0`s );
353}
354
355//=============================================================================================
356// Kernel Signal Handlers
357//=============================================================================================
358
359// Context switch signal handler
360// Receives SIGUSR1 signal and causes the current thread to yield
361static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ ) {
362 __cfaabi_dbg_debug_do( last_interrupt = (void *)(cxt->uc_mcontext.CFA_REG_IP); )
363
364 // SKULLDUGGERY: if a thread creates a processor and the immediately deletes it,
365 // the interrupt that is supposed to force the kernel thread to preempt might arrive
366 // before the kernel thread has even started running. When that happens an iterrupt
367 // we a null 'this_processor' will be caught, just ignore it.
368 if(! kernelTLS.this_processor ) return;
369
370 choose(sfp->si_value.sival_int) {
371 case PREEMPT_NORMAL : ;// Normal case, nothing to do here
372 case PREEMPT_TERMINATE: verify( __atomic_load_n( &kernelTLS.this_processor->do_terminate, __ATOMIC_SEQ_CST ) );
373 default:
374 abort( "internal error, signal value is %d", sfp->si_value.sival_int );
375 }
376
377 // Check if it is safe to preempt here
378 if( !preemption_ready() ) { return; }
379
380 __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) );
381
382 // Sync flag : prevent recursive calls to the signal handler
383 kernelTLS.preemption_state.in_progress = true;
384
385 // Clear sighandler mask before context switching.
386 #if GCC_VERSION > 50000
387 static_assert( sizeof( sigset_t ) == sizeof( cxt->uc_sigmask ), "Expected cxt->uc_sigmask to be of sigset_t" );
388 #endif
389 if ( pthread_sigmask( SIG_SETMASK, (sigset_t *)&(cxt->uc_sigmask), 0p ) == -1 ) {
390 abort( "internal error, sigprocmask" );
391 }
392
393 // TODO: this should go in finish action
394 // Clear the in progress flag
395 kernelTLS.preemption_state.in_progress = false;
396
397 // Preemption can occur here
398
399 force_yield( __ALARM_PREEMPTION ); // Do the actual __cfactx_switch
400}
401
402static void sigHandler_alarm( __CFA_SIGPARMS__ ) {
403 abort("SIGALRM should never reach the signal handler");
404}
405
406// Main of the alarm thread
407// Waits on SIGALRM and send SIGUSR1 to whom ever needs it
408static void * alarm_loop( __attribute__((unused)) void * args ) {
409 __processor_id_t id;
410 id.id = doregister(&id);
411
412 // Block sigalrms to control when they arrive
413 sigset_t mask;
414 sigfillset(&mask);
415 if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
416 abort( "internal error, pthread_sigmask" );
417 }
418
419 sigemptyset( &mask );
420 sigaddset( &mask, SIGALRM );
421
422 // Main loop
423 while( true ) {
424 // Wait for a sigalrm
425 siginfo_t info;
426 int sig = sigwaitinfo( &mask, &info );
427
428 if( sig < 0 ) {
429 //Error!
430 int err = errno;
431 switch( err ) {
432 case EAGAIN :
433 case EINTR :
434 {__cfaabi_dbg_print_buffer_decl( " KERNEL: Spurious wakeup %d.\n", err );}
435 continue;
436 case EINVAL :
437 abort( "Timeout was invalid." );
438 default:
439 abort( "Unhandled error %d", err);
440 }
441 }
442
443 // If another signal arrived something went wrong
444 assertf(sig == SIGALRM, "Kernel Internal Error, sigwait: Unexpected signal %d (%d : %d)\n", sig, info.si_code, info.si_value.sival_int);
445
446 // __cfaabi_dbg_print_safe( "Kernel : Caught alarm from %d with %d\n", info.si_code, info.si_value.sival_int );
447 // Switch on the code (a.k.a. the sender) to
448 switch( info.si_code )
449 {
450 // Timers can apparently be marked as sent for the kernel
451 // In either case, tick preemption
452 case SI_TIMER:
453 case SI_KERNEL:
454 // __cfaabi_dbg_print_safe( "Kernel : Preemption thread tick\n" );
455 lock( event_kernel->lock __cfaabi_dbg_ctx2 );
456 tick_preemption( &id );
457 unlock( event_kernel->lock );
458 break;
459 // Signal was not sent by the kernel but by an other thread
460 case SI_QUEUE:
461 // For now, other thread only signal the alarm thread to shut it down
462 // If this needs to change use info.si_value and handle the case here
463 goto EXIT;
464 }
465 }
466
467EXIT:
468 __cfaabi_dbg_print_safe( "Kernel : Preemption thread stopping\n" );
469 unregister(&id);
470 return 0p;
471}
472
473//=============================================================================================
474// Kernel Signal Debug
475//=============================================================================================
476
477void __cfaabi_check_preemption() {
478 bool ready = kernelTLS.preemption_state.enabled;
479 if(!ready) { abort("Preemption should be ready"); }
480
481 sigset_t oldset;
482 int ret;
483 ret = pthread_sigmask(0, 0p, &oldset);
484 if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
485
486 ret = sigismember(&oldset, SIGUSR1);
487 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
488 if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
489
490 ret = sigismember(&oldset, SIGALRM);
491 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
492 if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
493
494 ret = sigismember(&oldset, SIGTERM);
495 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
496 if(ret == 1) { abort("ERROR SIGTERM is disabled"); }
497}
498
499#ifdef __CFA_WITH_VERIFY__
500bool __cfaabi_dbg_in_kernel() {
501 return !kernelTLS.preemption_state.enabled;
502}
503#endif
504
505// Local Variables: //
506// mode: c //
507// tab-width: 4 //
508// End: //
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