source: libcfa/src/concurrency/preemption.cfa@ d65f92c

ADT arm-eh ast-experimental enum forall-pointer-decay jacob/cs343-translation jenkins-sandbox new-ast new-ast-unique-expr pthread-emulation qualifiedEnum
Last change on this file since d65f92c was 2026bb6, checked in by Thierry Delisle <tdelisle@…>, 6 years ago

More robust fix for optionally linking threads
  • Property mode set to 100644
File size: 16.6 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 : Tue Jun 5 17:35:49 2018
13// Update Count : 37
14//
15
16#define __cforall_thread__
17
18#include "preemption.hfa"
19#include <assert.h>
20
21extern "C" {
22#include <errno.h>
23#include <stdio.h>
24#include <string.h>
25#include <unistd.h>
26}
27
28#include "bits/signal.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_desc * this );
41
42// FwdDeclarations : Signal handlers
43static void sigHandler_ctxSwitch( __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
66
67static void ?{}(event_kernel_t & this) with( this ) {
68 alarms{};
69 lock{};
70}
71
72enum {
73 PREEMPT_NORMAL = 0,
74 PREEMPT_TERMINATE = 1,
75};
76
77//=============================================================================================
78// Kernel Preemption logic
79//=============================================================================================
80
81// Get next expired node
82static inline alarm_node_t * get_expired( alarm_list_t * alarms, Time currtime ) {
83 if( !alarms->head ) return NULL; // If no alarms return null
84 if( alarms->head->alarm >= currtime ) return NULL; // If alarms head not expired return null
85 return pop(alarms); // Otherwise just pop head
86}
87
88// Tick one frame of the Discrete Event Simulation for alarms
89static void tick_preemption() {
90 alarm_node_t * node = NULL; // Used in the while loop but cannot be declared in the while condition
91 alarm_list_t * alarms = &event_kernel->alarms; // Local copy for ease of reading
92 Time currtime = __kernel_get_time(); // Check current time once so we everything "happens at once"
93
94 //Loop throught every thing expired
95 while( node = get_expired( alarms, currtime ) ) {
96 // __cfaabi_dbg_print_buffer_decl( " KERNEL: preemption tick.\n" );
97
98 // Check if this is a kernel
99 if( node->kernel_alarm ) {
100 preempt( node->proc );
101 }
102 else {
103 timeout( node->thrd );
104 }
105
106 // Check if this is a periodic alarm
107 Duration period = node->period;
108 if( period > 0 ) {
109 // __cfaabi_dbg_print_buffer_local( " KERNEL: alarm period is %lu.\n", period.tv );
110 node->alarm = currtime + period; // Alarm is periodic, add currtime to it (used cached current time)
111 insert( alarms, node ); // Reinsert the node for the next time it triggers
112 }
113 else {
114 node->set = false; // Node is one-shot, just mark it as not pending
115 }
116 }
117
118 // If there are still alarms pending, reset the timer
119 if( alarms->head ) {
120 __cfaabi_dbg_print_buffer_decl( " KERNEL: @%ju(%ju) resetting alarm to %ju.\n", currtime.tv, __kernel_get_time().tv, (alarms->head->alarm - currtime).tv);
121 Duration delta = alarms->head->alarm - currtime;
122 Duration caped = max(delta, 50`us);
123 // itimerval tim = { caped };
124 // __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);
125
126 __kernel_set_timer( caped );
127 }
128}
129
130// Update the preemption of a processor and notify interested parties
131void update_preemption( processor * this, Duration duration ) {
132 alarm_node_t * alarm = this->preemption_alarm;
133
134 // Alarms need to be enabled
135 if ( duration > 0 && ! alarm->set ) {
136 alarm->alarm = __kernel_get_time() + duration;
137 alarm->period = duration;
138 register_self( alarm );
139 }
140 // Zero duration but alarm is set
141 else if ( duration == 0 && alarm->set ) {
142 unregister_self( alarm );
143 alarm->alarm = 0;
144 alarm->period = 0;
145 }
146 // If alarm is different from previous, change it
147 else if ( duration > 0 && alarm->period != duration ) {
148 unregister_self( alarm );
149 alarm->alarm = __kernel_get_time() + duration;
150 alarm->period = duration;
151 register_self( alarm );
152 }
153}
154
155//=============================================================================================
156// Kernel Signal Tools
157//=============================================================================================
158
159__cfaabi_dbg_debug_do( static thread_local void * last_interrupt = 0; )
160
161extern "C" {
162 // Disable interrupts by incrementing the counter
163 void disable_interrupts() {
164 with( kernelTLS.preemption_state ) {
165 #if GCC_VERSION > 50000
166 static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
167 #endif
168
169 // Set enabled flag to false
170 // should be atomic to avoid preemption in the middle of the operation.
171 // use memory order RELAXED since there is no inter-thread on this variable requirements
172 __atomic_store_n(&enabled, false, __ATOMIC_RELAXED);
173
174 // Signal the compiler that a fence is needed but only for signal handlers
175 __atomic_signal_fence(__ATOMIC_ACQUIRE);
176
177 __attribute__((unused)) unsigned short new_val = disable_count + 1;
178 disable_count = new_val;
179 verify( new_val < 65_000u ); // If this triggers someone is disabling interrupts without enabling them
180 }
181 }
182
183 // Enable interrupts by decrementing the counter
184 // If counter reaches 0, execute any pending CtxSwitch
185 void enable_interrupts( __cfaabi_dbg_ctx_param ) {
186 processor * proc = kernelTLS.this_processor; // Cache the processor now since interrupts can start happening after the atomic store
187 thread_desc * thrd = kernelTLS.this_thread; // Cache the thread now since interrupts can start happening after the atomic store
188
189 with( kernelTLS.preemption_state ){
190 unsigned short prev = disable_count;
191 disable_count -= 1;
192 verify( prev != 0u ); // If this triggers someone is enabled already enabled interruptsverify( prev != 0u );
193
194 // Check if we need to prempt the thread because an interrupt was missed
195 if( prev == 1 ) {
196 #if GCC_VERSION > 50000
197 static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
198 #endif
199
200 // Set enabled flag to true
201 // should be atomic to avoid preemption in the middle of the operation.
202 // use memory order RELAXED since there is no inter-thread on this variable requirements
203 __atomic_store_n(&enabled, true, __ATOMIC_RELAXED);
204
205 // Signal the compiler that a fence is needed but only for signal handlers
206 __atomic_signal_fence(__ATOMIC_RELEASE);
207 if( proc->pending_preemption ) {
208 proc->pending_preemption = false;
209 BlockInternal( thrd );
210 }
211 }
212 }
213
214 // For debugging purposes : keep track of the last person to enable the interrupts
215 __cfaabi_dbg_debug_do( proc->last_enable = caller; )
216 }
217
218 // Disable interrupts by incrementint the counter
219 // Don't execute any pending CtxSwitch even if counter reaches 0
220 void enable_interrupts_noPoll() {
221 unsigned short prev = kernelTLS.preemption_state.disable_count;
222 kernelTLS.preemption_state.disable_count -= 1;
223 verifyf( prev != 0u, "Incremented from %u\n", prev ); // If this triggers someone is enabled already enabled interrupts
224 if( prev == 1 ) {
225 #if GCC_VERSION > 50000
226 static_assert(__atomic_always_lock_free(sizeof(kernelTLS.preemption_state.enabled), &kernelTLS.preemption_state.enabled), "Must be lock-free");
227 #endif
228 // Set enabled flag to true
229 // should be atomic to avoid preemption in the middle of the operation.
230 // use memory order RELAXED since there is no inter-thread on this variable requirements
231 __atomic_store_n(&kernelTLS.preemption_state.enabled, true, __ATOMIC_RELAXED);
232
233 // Signal the compiler that a fence is needed but only for signal handlers
234 __atomic_signal_fence(__ATOMIC_RELEASE);
235 }
236 }
237}
238
239// sigprocmask wrapper : unblock a single signal
240static inline void signal_unblock( int sig ) {
241 sigset_t mask;
242 sigemptyset( &mask );
243 sigaddset( &mask, sig );
244
245 if ( pthread_sigmask( SIG_UNBLOCK, &mask, NULL ) == -1 ) {
246 abort( "internal error, pthread_sigmask" );
247 }
248}
249
250// sigprocmask wrapper : block a single signal
251static inline void signal_block( int sig ) {
252 sigset_t mask;
253 sigemptyset( &mask );
254 sigaddset( &mask, sig );
255
256 if ( pthread_sigmask( SIG_BLOCK, &mask, NULL ) == -1 ) {
257 abort( "internal error, pthread_sigmask" );
258 }
259}
260
261// kill wrapper : signal a processor
262static void preempt( processor * this ) {
263 sigval_t value = { PREEMPT_NORMAL };
264 pthread_sigqueue( this->kernel_thread, SIGUSR1, value );
265}
266
267// reserved for future use
268static void timeout( thread_desc * this ) {
269 //TODO : implement waking threads
270}
271
272// KERNEL ONLY
273// Check if a CtxSwitch signal handler shoud defer
274// If true : preemption is safe
275// If false : preemption is unsafe and marked as pending
276static inline bool preemption_ready() {
277 // Check if preemption is safe
278 bool ready = kernelTLS.preemption_state.enabled && ! kernelTLS.preemption_state.in_progress;
279
280 // Adjust the pending flag accordingly
281 kernelTLS.this_processor->pending_preemption = !ready;
282 return ready;
283}
284
285//=============================================================================================
286// Kernel Signal Startup/Shutdown logic
287//=============================================================================================
288
289// Startup routine to activate preemption
290// Called from kernel_startup
291void kernel_start_preemption() {
292 __cfaabi_dbg_print_safe( "Kernel : Starting preemption\n" );
293
294 // Start with preemption disabled until ready
295 kernelTLS.preemption_state.enabled = false;
296 kernelTLS.preemption_state.disable_count = 1;
297
298 // Initialize the event kernel
299 event_kernel = (event_kernel_t *)&storage_event_kernel;
300 (*event_kernel){};
301
302 // Setup proper signal handlers
303 __cfaabi_sigaction( SIGUSR1, sigHandler_ctxSwitch, SA_SIGINFO | SA_RESTART ); // CtxSwitch handler
304
305 signal_block( SIGALRM );
306
307 pthread_create( &alarm_thread, NULL, alarm_loop, NULL );
308}
309
310// Shutdown routine to deactivate preemption
311// Called from kernel_shutdown
312void kernel_stop_preemption() {
313 __cfaabi_dbg_print_safe( "Kernel : Preemption stopping\n" );
314
315 // Block all signals since we are already shutting down
316 sigset_t mask;
317 sigfillset( &mask );
318 sigprocmask( SIG_BLOCK, &mask, NULL );
319
320 // Notify the alarm thread of the shutdown
321 sigval val = { 1 };
322 pthread_sigqueue( alarm_thread, SIGALRM, val );
323
324 // Wait for the preemption thread to finish
325 pthread_join( alarm_thread, NULL );
326
327 // Preemption is now fully stopped
328
329 __cfaabi_dbg_print_safe( "Kernel : Preemption stopped\n" );
330}
331
332// Raii ctor/dtor for the preemption_scope
333// Used by thread to control when they want to receive preemption signals
334void ?{}( preemption_scope & this, processor * proc ) {
335 (this.alarm){ proc, (Time){ 0 }, 0`s };
336 this.proc = proc;
337 this.proc->preemption_alarm = &this.alarm;
338
339 update_preemption( this.proc, this.proc->cltr->preemption_rate );
340}
341
342void ^?{}( preemption_scope & this ) {
343 disable_interrupts();
344
345 update_preemption( this.proc, 0`s );
346}
347
348//=============================================================================================
349// Kernel Signal Handlers
350//=============================================================================================
351
352// Context switch signal handler
353// Receives SIGUSR1 signal and causes the current thread to yield
354static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ ) {
355 __cfaabi_dbg_debug_do( last_interrupt = (void *)(cxt->uc_mcontext.CFA_REG_IP); )
356
357 // SKULLDUGGERY: if a thread creates a processor and the immediately deletes it,
358 // the interrupt that is supposed to force the kernel thread to preempt might arrive
359 // before the kernel thread has even started running. When that happens an iterrupt
360 // we a null 'this_processor' will be caught, just ignore it.
361 if(! kernelTLS.this_processor ) return;
362
363 choose(sfp->si_value.sival_int) {
364 case PREEMPT_NORMAL : ;// Normal case, nothing to do here
365 case PREEMPT_TERMINATE: verify( __atomic_load_n( &kernelTLS.this_processor->do_terminate, __ATOMIC_SEQ_CST ) );
366 default:
367 abort( "internal error, signal value is %d", sfp->si_value.sival_int );
368 }
369
370 // Check if it is safe to preempt here
371 if( !preemption_ready() ) { return; }
372
373 __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) );
374
375 // Sync flag : prevent recursive calls to the signal handler
376 kernelTLS.preemption_state.in_progress = true;
377
378 // Clear sighandler mask before context switching.
379 #if GCC_VERSION > 50000
380 static_assert( sizeof( sigset_t ) == sizeof( cxt->uc_sigmask ), "Expected cxt->uc_sigmask to be of sigset_t" );
381 #endif
382 if ( pthread_sigmask( SIG_SETMASK, (sigset_t *)&(cxt->uc_sigmask), NULL ) == -1 ) {
383 abort( "internal error, sigprocmask" );
384 }
385
386 // TODO: this should go in finish action
387 // Clear the in progress flag
388 kernelTLS.preemption_state.in_progress = false;
389
390 // Preemption can occur here
391
392 BlockInternal( kernelTLS.this_thread ); // Do the actual CtxSwitch
393}
394
395// Main of the alarm thread
396// Waits on SIGALRM and send SIGUSR1 to whom ever needs it
397static void * alarm_loop( __attribute__((unused)) void * args ) {
398 // Block sigalrms to control when they arrive
399 sigset_t mask;
400 sigfillset(&mask);
401 if ( pthread_sigmask( SIG_BLOCK, &mask, NULL ) == -1 ) {
402 abort( "internal error, pthread_sigmask" );
403 }
404
405 sigemptyset( &mask );
406 sigaddset( &mask, SIGALRM );
407
408 // Main loop
409 while( true ) {
410 // Wait for a sigalrm
411 siginfo_t info;
412 int sig = sigwaitinfo( &mask, &info );
413
414 if( sig < 0 ) {
415 //Error!
416 int err = errno;
417 switch( err ) {
418 case EAGAIN :
419 case EINTR :
420 {__cfaabi_dbg_print_buffer_decl( " KERNEL: Spurious wakeup %d.\n", err );}
421 continue;
422 case EINVAL :
423 abort( "Timeout was invalid." );
424 default:
425 abort( "Unhandled error %d", err);
426 }
427 }
428
429 // If another signal arrived something went wrong
430 assertf(sig == SIGALRM, "Kernel Internal Error, sigwait: Unexpected signal %d (%d : %d)\n", sig, info.si_code, info.si_value.sival_int);
431
432 // __cfaabi_dbg_print_safe( "Kernel : Caught alarm from %d with %d\n", info.si_code, info.si_value.sival_int );
433 // Switch on the code (a.k.a. the sender) to
434 switch( info.si_code )
435 {
436 // Timers can apparently be marked as sent for the kernel
437 // In either case, tick preemption
438 case SI_TIMER:
439 case SI_KERNEL:
440 // __cfaabi_dbg_print_safe( "Kernel : Preemption thread tick\n" );
441 lock( event_kernel->lock __cfaabi_dbg_ctx2 );
442 tick_preemption();
443 unlock( event_kernel->lock );
444 break;
445 // Signal was not sent by the kernel but by an other thread
446 case SI_QUEUE:
447 // For now, other thread only signal the alarm thread to shut it down
448 // If this needs to change use info.si_value and handle the case here
449 goto EXIT;
450 }
451 }
452
453EXIT:
454 __cfaabi_dbg_print_safe( "Kernel : Preemption thread stopping\n" );
455 return NULL;
456}
457
458//=============================================================================================
459// Kernel Signal Debug
460//=============================================================================================
461
462void __cfaabi_check_preemption() {
463 bool ready = kernelTLS.preemption_state.enabled;
464 if(!ready) { abort("Preemption should be ready"); }
465
466 sigset_t oldset;
467 int ret;
468 ret = pthread_sigmask(0, NULL, &oldset);
469 if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
470
471 ret = sigismember(&oldset, SIGUSR1);
472 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
473 if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
474
475 ret = sigismember(&oldset, SIGALRM);
476 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
477 if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
478
479 ret = sigismember(&oldset, SIGTERM);
480 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
481 if(ret == 1) { abort("ERROR SIGTERM is disabled"); }
482}
483
484#ifdef __CFA_WITH_VERIFY__
485bool __cfaabi_dbg_in_kernel() {
486 return !kernelTLS.preemption_state.enabled;
487}
488#endif
489
490// Local Variables: //
491// mode: c //
492// tab-width: 4 //
493// End: //
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