source: src/libcfa/concurrency/preemption.c@ a43c561

ADT aaron-thesis arm-eh ast-experimental cleanup-dtors deferred_resn demangler enum forall-pointer-decay jacob/cs343-translation jenkins-sandbox new-ast new-ast-unique-expr new-env no_list persistent-indexer pthread-emulation qualifiedEnum with_gc
Last change on this file since a43c561 was a43c561, checked in by Thierry Delisle <tdelisle@…>, 7 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 : Tue Jun 5 17:35:49 2018
13// Update Count : 37
14//
15
16#include "preemption.h"
17#include <assert.h>
18
19extern "C" {
20#include <errno.h>
21#include <stdio.h>
22#include <string.h>
23#include <unistd.h>
24}
25
26#include "bits/signal.h"
27
28#if !defined(__CFA_DEFAULT_PREEMPTION__)
29#define __CFA_DEFAULT_PREEMPTION__ 10`ms
30#endif
31
32Duration default_preemption() __attribute__((weak)) {
33 return __CFA_DEFAULT_PREEMPTION__;
34}
35
36// FwdDeclarations : timeout handlers
37static void preempt( processor * this );
38static void timeout( thread_desc * this );
39
40// FwdDeclarations : Signal handlers
41void sigHandler_ctxSwitch( __CFA_SIGPARMS__ );
42void sigHandler_segv ( __CFA_SIGPARMS__ );
43void sigHandler_ill ( __CFA_SIGPARMS__ );
44void sigHandler_fpe ( __CFA_SIGPARMS__ );
45void sigHandler_abort ( __CFA_SIGPARMS__ );
46
47// FwdDeclarations : alarm thread main
48void * alarm_loop( __attribute__((unused)) void * args );
49
50// Machine specific register name
51#if defined( __i386 )
52#define CFA_REG_IP gregs[REG_EIP]
53#elif defined( __x86_64 )
54#define CFA_REG_IP gregs[REG_RIP]
55#elif defined( __ARM_ARCH )
56#define CFA_REG_IP arm_pc
57#else
58#error unknown hardware architecture
59#endif
60
61KERNEL_STORAGE(event_kernel_t, event_kernel); // private storage for event kernel
62event_kernel_t * event_kernel; // kernel public handle to even kernel
63static pthread_t alarm_thread; // pthread handle to alarm thread
64
65void ?{}(event_kernel_t & this) with( this ) {
66 alarms{};
67 lock{};
68}
69
70enum {
71 PREEMPT_NORMAL = 0,
72 PREEMPT_TERMINATE = 1,
73};
74
75//=============================================================================================
76// Kernel Preemption logic
77//=============================================================================================
78
79// Get next expired node
80static inline alarm_node_t * get_expired( alarm_list_t * alarms, Time currtime ) {
81 if( !alarms->head ) return NULL; // If no alarms return null
82 if( alarms->head->alarm >= currtime ) return NULL; // If alarms head not expired return null
83 return pop(alarms); // Otherwise just pop head
84}
85
86// Tick one frame of the Discrete Event Simulation for alarms
87void tick_preemption() {
88 alarm_node_t * node = NULL; // Used in the while loop but cannot be declared in the while condition
89 alarm_list_t * alarms = &event_kernel->alarms; // Local copy for ease of reading
90 Time currtime = __kernel_get_time(); // Check current time once so we everything "happens at once"
91
92 //Loop throught every thing expired
93 while( node = get_expired( alarms, currtime ) ) {
94 // __cfaabi_dbg_print_buffer_decl( " KERNEL: preemption tick.\n" );
95
96 // Check if this is a kernel
97 if( node->kernel_alarm ) {
98 preempt( node->proc );
99 }
100 else {
101 timeout( node->thrd );
102 }
103
104 // Check if this is a periodic alarm
105 Duration period = node->period;
106 if( period > 0 ) {
107 // __cfaabi_dbg_print_buffer_local( " KERNEL: alarm period is %lu.\n", period.tv );
108 node->alarm = currtime + period; // Alarm is periodic, add currtime to it (used cached current time)
109 insert( alarms, node ); // Reinsert the node for the next time it triggers
110 }
111 else {
112 node->set = false; // Node is one-shot, just mark it as not pending
113 }
114 }
115
116 // If there are still alarms pending, reset the timer
117 if( alarms->head ) {
118 __cfaabi_dbg_print_buffer_decl( " KERNEL: @%ju(%ju) resetting alarm to %ju.\n", currtime.tv, __kernel_get_time().tv, (alarms->head->alarm - currtime).tv);
119 Duration delta = alarms->head->alarm - currtime;
120 Duration caped = max(delta, 50`us);
121 // itimerval tim = { caped };
122 // __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);
123
124 __kernel_set_timer( caped );
125 }
126}
127
128// Update the preemption of a processor and notify interested parties
129void update_preemption( processor * this, Duration duration ) {
130 alarm_node_t * alarm = this->preemption_alarm;
131
132 // Alarms need to be enabled
133 if ( duration > 0 && ! alarm->set ) {
134 alarm->alarm = __kernel_get_time() + duration;
135 alarm->period = duration;
136 register_self( alarm );
137 }
138 // Zero duration but alarm is set
139 else if ( duration == 0 && alarm->set ) {
140 unregister_self( alarm );
141 alarm->alarm = 0;
142 alarm->period = 0;
143 }
144 // If alarm is different from previous, change it
145 else if ( duration > 0 && alarm->period != duration ) {
146 unregister_self( alarm );
147 alarm->alarm = __kernel_get_time() + duration;
148 alarm->period = duration;
149 register_self( alarm );
150 }
151}
152
153//=============================================================================================
154// Kernel Signal Tools
155//=============================================================================================
156
157__cfaabi_dbg_debug_do( static thread_local void * last_interrupt = 0; )
158
159extern "C" {
160 // Disable interrupts by incrementing the counter
161 void disable_interrupts() {
162 with( kernelTLS.preemption_state ) {
163 #if GCC_VERSION > 50000
164 static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
165 #endif
166
167 // Set enabled flag to false
168 // should be atomic to avoid preemption in the middle of the operation.
169 // use memory order RELAXED since there is no inter-thread on this variable requirements
170 __atomic_store_n(&enabled, false, __ATOMIC_RELAXED);
171
172 // Signal the compiler that a fence is needed but only for signal handlers
173 __atomic_signal_fence(__ATOMIC_ACQUIRE);
174
175 __attribute__((unused)) unsigned short new_val = disable_count + 1;
176 disable_count = new_val;
177 verify( new_val < 65_000u ); // If this triggers someone is disabling interrupts without enabling them
178 }
179 }
180
181 // Enable interrupts by decrementing the counter
182 // If counter reaches 0, execute any pending CtxSwitch
183 void enable_interrupts( __cfaabi_dbg_ctx_param ) {
184 processor * proc = kernelTLS.this_processor; // Cache the processor now since interrupts can start happening after the atomic store
185 thread_desc * thrd = kernelTLS.this_thread; // Cache the thread now since interrupts can start happening after the atomic store
186
187 with( kernelTLS.preemption_state ){
188 unsigned short prev = disable_count;
189 disable_count -= 1;
190 verify( prev != 0u ); // If this triggers someone is enabled already enabled interruptsverify( prev != 0u );
191
192 // Check if we need to prempt the thread because an interrupt was missed
193 if( prev == 1 ) {
194 #if GCC_VERSION > 50000
195 static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
196 #endif
197
198 // Set enabled flag to true
199 // should be atomic to avoid preemption in the middle of the operation.
200 // use memory order RELAXED since there is no inter-thread on this variable requirements
201 __atomic_store_n(&enabled, true, __ATOMIC_RELAXED);
202
203 // Signal the compiler that a fence is needed but only for signal handlers
204 __atomic_signal_fence(__ATOMIC_RELEASE);
205 if( proc->pending_preemption ) {
206 proc->pending_preemption = false;
207 BlockInternal( thrd );
208 }
209 }
210 }
211
212 // For debugging purposes : keep track of the last person to enable the interrupts
213 __cfaabi_dbg_debug_do( proc->last_enable = caller; )
214 }
215
216 // Disable interrupts by incrementint the counter
217 // Don't execute any pending CtxSwitch even if counter reaches 0
218 void enable_interrupts_noPoll() {
219 unsigned short prev = kernelTLS.preemption_state.disable_count;
220 kernelTLS.preemption_state.disable_count -= 1;
221 verifyf( prev != 0u, "Incremented from %u\n", prev ); // If this triggers someone is enabled already enabled interrupts
222 if( prev == 1 ) {
223 #if GCC_VERSION > 50000
224 static_assert(__atomic_always_lock_free(sizeof(kernelTLS.preemption_state.enabled), &kernelTLS.preemption_state.enabled), "Must be lock-free");
225 #endif
226 // Set enabled flag to true
227 // should be atomic to avoid preemption in the middle of the operation.
228 // use memory order RELAXED since there is no inter-thread on this variable requirements
229 __atomic_store_n(&kernelTLS.preemption_state.enabled, true, __ATOMIC_RELAXED);
230
231 // Signal the compiler that a fence is needed but only for signal handlers
232 __atomic_signal_fence(__ATOMIC_RELEASE);
233 }
234 }
235}
236
237// sigprocmask wrapper : unblock a single signal
238static inline void signal_unblock( int sig ) {
239 sigset_t mask;
240 sigemptyset( &mask );
241 sigaddset( &mask, sig );
242
243 if ( pthread_sigmask( SIG_UNBLOCK, &mask, NULL ) == -1 ) {
244 abort( "internal error, pthread_sigmask" );
245 }
246}
247
248// sigprocmask wrapper : block a single signal
249static inline void signal_block( int sig ) {
250 sigset_t mask;
251 sigemptyset( &mask );
252 sigaddset( &mask, sig );
253
254 if ( pthread_sigmask( SIG_BLOCK, &mask, NULL ) == -1 ) {
255 abort( "internal error, pthread_sigmask" );
256 }
257}
258
259// kill wrapper : signal a processor
260static void preempt( processor * this ) {
261 sigval_t value = { PREEMPT_NORMAL };
262 pthread_sigqueue( this->kernel_thread, SIGUSR1, value );
263}
264
265// kill wrapper : signal a processor
266void terminate(processor * this) {
267 disable_interrupts();
268 __atomic_store_n(&this->do_terminate, true, __ATOMIC_SEQ_CST);
269 wake( this );
270 sigval_t value = { PREEMPT_TERMINATE };
271 enable_interrupts( __cfaabi_dbg_ctx );
272 pthread_sigqueue( this->kernel_thread, SIGUSR1, value );
273}
274
275// reserved for future use
276static void timeout( thread_desc * this ) {
277 //TODO : implement waking threads
278}
279
280// KERNEL ONLY
281// Check if a CtxSwitch signal handler shoud defer
282// If true : preemption is safe
283// If false : preemption is unsafe and marked as pending
284static inline bool preemption_ready() {
285 // Check if preemption is safe
286 bool ready = kernelTLS.preemption_state.enabled && ! kernelTLS.preemption_state.in_progress;
287
288 // Adjust the pending flag accordingly
289 kernelTLS.this_processor->pending_preemption = !ready;
290 return ready;
291}
292
293//=============================================================================================
294// Kernel Signal Startup/Shutdown logic
295//=============================================================================================
296
297// Startup routine to activate preemption
298// Called from kernel_startup
299void kernel_start_preemption() {
300 __cfaabi_dbg_print_safe( "Kernel : Starting preemption\n" );
301
302 // Start with preemption disabled until ready
303 kernelTLS.preemption_state.enabled = false;
304 kernelTLS.preemption_state.disable_count = 1;
305
306 // Initialize the event kernel
307 event_kernel = (event_kernel_t *)&storage_event_kernel;
308 (*event_kernel){};
309
310 // Setup proper signal handlers
311 __cfaabi_sigaction( SIGUSR1, sigHandler_ctxSwitch, SA_SIGINFO | SA_RESTART ); // CtxSwitch handler
312
313 signal_block( SIGALRM );
314
315 pthread_create( &alarm_thread, NULL, alarm_loop, NULL );
316}
317
318// Shutdown routine to deactivate preemption
319// Called from kernel_shutdown
320void kernel_stop_preemption() {
321 __cfaabi_dbg_print_safe( "Kernel : Preemption stopping\n" );
322
323 // Block all signals since we are already shutting down
324 sigset_t mask;
325 sigfillset( &mask );
326 sigprocmask( SIG_BLOCK, &mask, NULL );
327
328 // Notify the alarm thread of the shutdown
329 sigval val = { 1 };
330 pthread_sigqueue( alarm_thread, SIGALRM, val );
331
332 // Wait for the preemption thread to finish
333 pthread_join( alarm_thread, NULL );
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
362void 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 iterrupt
368 // we 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), NULL ) == -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 BlockInternal( kernelTLS.this_thread ); // Do the actual CtxSwitch
401}
402
403// Main of the alarm thread
404// Waits on SIGALRM and send SIGUSR1 to whom ever needs it
405void * alarm_loop( __attribute__((unused)) void * args ) {
406 // Block sigalrms to control when they arrive
407 sigset_t mask;
408 sigfillset(&mask);
409 if ( pthread_sigmask( SIG_BLOCK, &mask, NULL ) == -1 ) {
410 abort( "internal error, pthread_sigmask" );
411 }
412
413 sigemptyset( &mask );
414 sigaddset( &mask, SIGALRM );
415
416 // Main loop
417 while( true ) {
418 // Wait for a sigalrm
419 siginfo_t info;
420 int sig = sigwaitinfo( &mask, &info );
421
422 if( sig < 0 ) {
423 //Error!
424 int err = errno;
425 switch( err ) {
426 case EAGAIN :
427 case EINTR :
428 {__cfaabi_dbg_print_buffer_decl( " KERNEL: Spurious wakeup %d.\n", err );}
429 continue;
430 case EINVAL :
431 abort( "Timeout was invalid." );
432 default:
433 abort( "Unhandled error %d", err);
434 }
435 }
436
437 // If another signal arrived something went wrong
438 assertf(sig == SIGALRM, "Kernel Internal Error, sigwait: Unexpected signal %d (%d : %d)\n", sig, info.si_code, info.si_value.sival_int);
439
440 // __cfaabi_dbg_print_safe( "Kernel : Caught alarm from %d with %d\n", info.si_code, info.si_value.sival_int );
441 // Switch on the code (a.k.a. the sender) to
442 switch( info.si_code )
443 {
444 // Timers can apparently be marked as sent for the kernel
445 // In either case, tick preemption
446 case SI_TIMER:
447 case SI_KERNEL:
448 // __cfaabi_dbg_print_safe( "Kernel : Preemption thread tick\n" );
449 lock( event_kernel->lock __cfaabi_dbg_ctx2 );
450 tick_preemption();
451 unlock( event_kernel->lock );
452 break;
453 // Signal was not sent by the kernel but by an other thread
454 case SI_QUEUE:
455 // For now, other thread only signal the alarm thread to shut it down
456 // If this needs to change use info.si_value and handle the case here
457 goto EXIT;
458 }
459 }
460
461EXIT:
462 __cfaabi_dbg_print_safe( "Kernel : Preemption thread stopping\n" );
463 return NULL;
464}
465
466//=============================================================================================
467// Kernel Signal Debug
468//=============================================================================================
469
470void __cfaabi_check_preemption() {
471 bool ready = kernelTLS.preemption_state.enabled;
472 if(!ready) { abort("Preemption should be ready"); }
473
474 sigset_t oldset;
475 int ret;
476 ret = pthread_sigmask(0, NULL, &oldset);
477 if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
478
479 ret = sigismember(&oldset, SIGUSR1);
480 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
481 if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
482
483 ret = sigismember(&oldset, SIGALRM);
484 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
485 if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
486
487 ret = sigismember(&oldset, SIGTERM);
488 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
489 if(ret == 1) { abort("ERROR SIGTERM is disabled"); }
490}
491
492#ifdef __CFA_WITH_VERIFY__
493bool __cfaabi_dbg_in_kernel() {
494 return !kernelTLS.preemption_state.enabled;
495}
496#endif
497
498// Local Variables: //
499// mode: c //
500// tab-width: 4 //
501// End: //
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