source: libcfa/src/concurrency/preemption.cfa@ b10c39a0

ADT arm-eh ast-experimental cleanup-dtors enum forall-pointer-decay jacob/cs343-translation jenkins-sandbox new-ast new-ast-unique-expr pthread-emulation qualifiedEnum
Last change on this file since b10c39a0 was 73abe95, checked in by Thierry Delisle <tdelisle@…>, 7 years ago

Replace extension-less headers with .hfa
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File size: 16.6 KB
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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.hfa"
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.hfa"
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
41static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ );
42static void sigHandler_segv ( __CFA_SIGPARMS__ );
43static void sigHandler_ill ( __CFA_SIGPARMS__ );
44static void sigHandler_fpe ( __CFA_SIGPARMS__ );
45static void sigHandler_abort ( __CFA_SIGPARMS__ );
46
47// FwdDeclarations : alarm thread main
48static void * 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
65static void ?{}(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
87static void 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// reserved for future use
266static void timeout( thread_desc * this ) {
267 //TODO : implement waking threads
268}
269
270// KERNEL ONLY
271// Check if a CtxSwitch signal handler shoud defer
272// If true : preemption is safe
273// If false : preemption is unsafe and marked as pending
274static inline bool preemption_ready() {
275 // Check if preemption is safe
276 bool ready = kernelTLS.preemption_state.enabled && ! kernelTLS.preemption_state.in_progress;
277
278 // Adjust the pending flag accordingly
279 kernelTLS.this_processor->pending_preemption = !ready;
280 return ready;
281}
282
283//=============================================================================================
284// Kernel Signal Startup/Shutdown logic
285//=============================================================================================
286
287// Startup routine to activate preemption
288// Called from kernel_startup
289void kernel_start_preemption() {
290 __cfaabi_dbg_print_safe( "Kernel : Starting preemption\n" );
291
292 // Start with preemption disabled until ready
293 kernelTLS.preemption_state.enabled = false;
294 kernelTLS.preemption_state.disable_count = 1;
295
296 // Initialize the event kernel
297 event_kernel = (event_kernel_t *)&storage_event_kernel;
298 (*event_kernel){};
299
300 // Setup proper signal handlers
301 __cfaabi_sigaction( SIGUSR1, sigHandler_ctxSwitch, SA_SIGINFO | SA_RESTART ); // CtxSwitch handler
302
303 signal_block( SIGALRM );
304
305 pthread_create( &alarm_thread, NULL, alarm_loop, NULL );
306}
307
308// Shutdown routine to deactivate preemption
309// Called from kernel_shutdown
310void kernel_stop_preemption() {
311 __cfaabi_dbg_print_safe( "Kernel : Preemption stopping\n" );
312
313 // Block all signals since we are already shutting down
314 sigset_t mask;
315 sigfillset( &mask );
316 sigprocmask( SIG_BLOCK, &mask, NULL );
317
318 // Notify the alarm thread of the shutdown
319 sigval val = { 1 };
320 pthread_sigqueue( alarm_thread, SIGALRM, val );
321
322 // Wait for the preemption thread to finish
323 pthread_join( alarm_thread, NULL );
324
325 // Preemption is now fully stopped
326
327 __cfaabi_dbg_print_safe( "Kernel : Preemption stopped\n" );
328}
329
330// Raii ctor/dtor for the preemption_scope
331// Used by thread to control when they want to receive preemption signals
332void ?{}( preemption_scope & this, processor * proc ) {
333 (this.alarm){ proc, (Time){ 0 }, 0`s };
334 this.proc = proc;
335 this.proc->preemption_alarm = &this.alarm;
336
337 update_preemption( this.proc, this.proc->cltr->preemption_rate );
338}
339
340void ^?{}( preemption_scope & this ) {
341 disable_interrupts();
342
343 update_preemption( this.proc, 0`s );
344}
345
346//=============================================================================================
347// Kernel Signal Handlers
348//=============================================================================================
349
350// Context switch signal handler
351// Receives SIGUSR1 signal and causes the current thread to yield
352static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ ) {
353 __cfaabi_dbg_debug_do( last_interrupt = (void *)(cxt->uc_mcontext.CFA_REG_IP); )
354
355 // SKULLDUGGERY: if a thread creates a processor and the immediately deletes it,
356 // the interrupt that is supposed to force the kernel thread to preempt might arrive
357 // before the kernel thread has even started running. When that happens an iterrupt
358 // we a null 'this_processor' will be caught, just ignore it.
359 if(! kernelTLS.this_processor ) return;
360
361 choose(sfp->si_value.sival_int) {
362 case PREEMPT_NORMAL : ;// Normal case, nothing to do here
363 case PREEMPT_TERMINATE: verify( __atomic_load_n( &kernelTLS.this_processor->do_terminate, __ATOMIC_SEQ_CST ) );
364 default:
365 abort( "internal error, signal value is %d", sfp->si_value.sival_int );
366 }
367
368 // Check if it is safe to preempt here
369 if( !preemption_ready() ) { return; }
370
371 __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) );
372
373 // Sync flag : prevent recursive calls to the signal handler
374 kernelTLS.preemption_state.in_progress = true;
375
376 // Clear sighandler mask before context switching.
377 #if GCC_VERSION > 50000
378 static_assert( sizeof( sigset_t ) == sizeof( cxt->uc_sigmask ), "Expected cxt->uc_sigmask to be of sigset_t" );
379 #endif
380 if ( pthread_sigmask( SIG_SETMASK, (sigset_t *)&(cxt->uc_sigmask), NULL ) == -1 ) {
381 abort( "internal error, sigprocmask" );
382 }
383
384 // TODO: this should go in finish action
385 // Clear the in progress flag
386 kernelTLS.preemption_state.in_progress = false;
387
388 // Preemption can occur here
389
390 BlockInternal( kernelTLS.this_thread ); // Do the actual CtxSwitch
391}
392
393// Main of the alarm thread
394// Waits on SIGALRM and send SIGUSR1 to whom ever needs it
395static void * alarm_loop( __attribute__((unused)) void * args ) {
396 // Block sigalrms to control when they arrive
397 sigset_t mask;
398 sigfillset(&mask);
399 if ( pthread_sigmask( SIG_BLOCK, &mask, NULL ) == -1 ) {
400 abort( "internal error, pthread_sigmask" );
401 }
402
403 sigemptyset( &mask );
404 sigaddset( &mask, SIGALRM );
405
406 // Main loop
407 while( true ) {
408 // Wait for a sigalrm
409 siginfo_t info;
410 int sig = sigwaitinfo( &mask, &info );
411
412 if( sig < 0 ) {
413 //Error!
414 int err = errno;
415 switch( err ) {
416 case EAGAIN :
417 case EINTR :
418 {__cfaabi_dbg_print_buffer_decl( " KERNEL: Spurious wakeup %d.\n", err );}
419 continue;
420 case EINVAL :
421 abort( "Timeout was invalid." );
422 default:
423 abort( "Unhandled error %d", err);
424 }
425 }
426
427 // If another signal arrived something went wrong
428 assertf(sig == SIGALRM, "Kernel Internal Error, sigwait: Unexpected signal %d (%d : %d)\n", sig, info.si_code, info.si_value.sival_int);
429
430 // __cfaabi_dbg_print_safe( "Kernel : Caught alarm from %d with %d\n", info.si_code, info.si_value.sival_int );
431 // Switch on the code (a.k.a. the sender) to
432 switch( info.si_code )
433 {
434 // Timers can apparently be marked as sent for the kernel
435 // In either case, tick preemption
436 case SI_TIMER:
437 case SI_KERNEL:
438 // __cfaabi_dbg_print_safe( "Kernel : Preemption thread tick\n" );
439 lock( event_kernel->lock __cfaabi_dbg_ctx2 );
440 tick_preemption();
441 unlock( event_kernel->lock );
442 break;
443 // Signal was not sent by the kernel but by an other thread
444 case SI_QUEUE:
445 // For now, other thread only signal the alarm thread to shut it down
446 // If this needs to change use info.si_value and handle the case here
447 goto EXIT;
448 }
449 }
450
451EXIT:
452 __cfaabi_dbg_print_safe( "Kernel : Preemption thread stopping\n" );
453 return NULL;
454}
455
456//=============================================================================================
457// Kernel Signal Debug
458//=============================================================================================
459
460void __cfaabi_check_preemption() {
461 bool ready = kernelTLS.preemption_state.enabled;
462 if(!ready) { abort("Preemption should be ready"); }
463
464 sigset_t oldset;
465 int ret;
466 ret = pthread_sigmask(0, NULL, &oldset);
467 if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
468
469 ret = sigismember(&oldset, SIGUSR1);
470 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
471 if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
472
473 ret = sigismember(&oldset, SIGALRM);
474 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
475 if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
476
477 ret = sigismember(&oldset, SIGTERM);
478 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
479 if(ret == 1) { abort("ERROR SIGTERM is disabled"); }
480}
481
482#ifdef __CFA_WITH_VERIFY__
483bool __cfaabi_dbg_in_kernel() {
484 return !kernelTLS.preemption_state.enabled;
485}
486#endif
487
488// Local Variables: //
489// mode: c //
490// tab-width: 4 //
491// End: //
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