source: libcfa/src/concurrency/preemption.cfa@ 76e2113

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 76e2113 was 2d8f7b0, checked in by Thierry Delisle <tdelisle@…>, 5 years ago

Implemented basic non-blocking io
  • 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 : Thu Dec 5 16:34:05 2019
13// Update Count : 43
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#include <limits.h> // PTHREAD_STACK_MIN
27}
28
29#include "bits/signal.hfa"
30
31#if !defined(__CFA_DEFAULT_PREEMPTION__)
32#define __CFA_DEFAULT_PREEMPTION__ 10`ms
33#endif
34
35Duration default_preemption() __attribute__((weak)) {
36 return __CFA_DEFAULT_PREEMPTION__;
37}
38
39// FwdDeclarations : timeout handlers
40static void preempt( processor * this );
41static void timeout( $thread * this );
42
43// FwdDeclarations : Signal handlers
44static void sigHandler_ctxSwitch( __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 arm_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->head ) return 0p; // If no alarms return null
86 if( alarms->head->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() {
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
100 // Check if this is a kernel
101 if( node->kernel_alarm ) {
102 preempt( node->proc );
103 }
104 else {
105 timeout( node->thrd );
106 }
107
108 // Check if this is a periodic alarm
109 Duration period = node->period;
110 if( period > 0 ) {
111 // __cfaabi_dbg_print_buffer_local( " KERNEL: alarm period is %lu.\n", period.tv );
112 node->alarm = currtime + period; // Alarm is periodic, add currtime to it (used cached current time)
113 insert( alarms, node ); // Reinsert the node for the next time it triggers
114 }
115 else {
116 node->set = false; // Node is one-shot, just mark it as not pending
117 }
118 }
119
120 // If there are still alarms pending, reset the timer
121 if( alarms->head ) {
122 __cfaabi_dbg_print_buffer_decl( " KERNEL: @%ju(%ju) resetting alarm to %ju.\n", currtime.tv, __kernel_get_time().tv, (alarms->head->alarm - currtime).tv);
123 Duration delta = alarms->head->alarm - currtime;
124 Duration caped = 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( caped );
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
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( $thread * this ) {
270 __unpark( this __cfaabi_dbg_ctx2 );
271}
272
273// KERNEL ONLY
274// Check if a __cfactx_switch signal handler shoud defer
275// If true : preemption is safe
276// If false : preemption is unsafe and marked as pending
277static inline bool preemption_ready() {
278 // Check if preemption is safe
279 bool ready = kernelTLS.preemption_state.enabled && ! kernelTLS.preemption_state.in_progress;
280
281 // Adjust the pending flag accordingly
282 kernelTLS.this_processor->pending_preemption = !ready;
283 return ready;
284}
285
286//=============================================================================================
287// Kernel Signal Startup/Shutdown logic
288//=============================================================================================
289
290// Startup routine to activate preemption
291// Called from kernel_startup
292void kernel_start_preemption() {
293 __cfaabi_dbg_print_safe( "Kernel : Starting preemption\n" );
294
295 // Start with preemption disabled until ready
296 kernelTLS.preemption_state.enabled = false;
297 kernelTLS.preemption_state.disable_count = 1;
298
299 // Initialize the event kernel
300 event_kernel = (event_kernel_t *)&storage_event_kernel;
301 (*event_kernel){};
302
303 // Setup proper signal handlers
304 __cfaabi_sigaction( SIGUSR1, sigHandler_ctxSwitch, SA_SIGINFO | SA_RESTART ); // __cfactx_switch handler
305
306 signal_block( SIGALRM );
307
308 alarm_stack = __create_pthread( &alarm_thread, alarm_loop, 0p );
309}
310
311// Shutdown routine to deactivate preemption
312// Called from kernel_shutdown
313void kernel_stop_preemption() {
314 __cfaabi_dbg_print_safe( "Kernel : Preemption stopping\n" );
315
316 // Block all signals since we are already shutting down
317 sigset_t mask;
318 sigfillset( &mask );
319 sigprocmask( SIG_BLOCK, &mask, 0p );
320
321 // Notify the alarm thread of the shutdown
322 sigval val = { 1 };
323 pthread_sigqueue( alarm_thread, SIGALRM, val );
324
325 // Wait for the preemption thread to finish
326
327 pthread_join( alarm_thread, 0p );
328 free( alarm_stack );
329
330 // Preemption is now fully stopped
331
332 __cfaabi_dbg_print_safe( "Kernel : Preemption stopped\n" );
333}
334
335// Raii ctor/dtor for the preemption_scope
336// Used by thread to control when they want to receive preemption signals
337void ?{}( preemption_scope & this, processor * proc ) {
338 (this.alarm){ proc, (Time){ 0 }, 0`s };
339 this.proc = proc;
340 this.proc->preemption_alarm = &this.alarm;
341
342 update_preemption( this.proc, this.proc->cltr->preemption_rate );
343}
344
345void ^?{}( preemption_scope & this ) {
346 disable_interrupts();
347
348 update_preemption( this.proc, 0`s );
349}
350
351//=============================================================================================
352// Kernel Signal Handlers
353//=============================================================================================
354
355// Context switch signal handler
356// Receives SIGUSR1 signal and causes the current thread to yield
357static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ ) {
358 __cfaabi_dbg_debug_do( last_interrupt = (void *)(cxt->uc_mcontext.CFA_REG_IP); )
359
360 // SKULLDUGGERY: if a thread creates a processor and the immediately deletes it,
361 // the interrupt that is supposed to force the kernel thread to preempt might arrive
362 // before the kernel thread has even started running. When that happens an iterrupt
363 // we a null 'this_processor' will be caught, just ignore it.
364 if(! kernelTLS.this_processor ) return;
365
366 choose(sfp->si_value.sival_int) {
367 case PREEMPT_NORMAL : ;// Normal case, nothing to do here
368 case PREEMPT_TERMINATE: verify( __atomic_load_n( &kernelTLS.this_processor->do_terminate, __ATOMIC_SEQ_CST ) );
369 default:
370 abort( "internal error, signal value is %d", sfp->si_value.sival_int );
371 }
372
373 // Check if it is safe to preempt here
374 if( !preemption_ready() ) { return; }
375
376 __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) );
377
378 // Sync flag : prevent recursive calls to the signal handler
379 kernelTLS.preemption_state.in_progress = true;
380
381 // Clear sighandler mask before context switching.
382 #if GCC_VERSION > 50000
383 static_assert( sizeof( sigset_t ) == sizeof( cxt->uc_sigmask ), "Expected cxt->uc_sigmask to be of sigset_t" );
384 #endif
385 if ( pthread_sigmask( SIG_SETMASK, (sigset_t *)&(cxt->uc_sigmask), 0p ) == -1 ) {
386 abort( "internal error, sigprocmask" );
387 }
388
389 // TODO: this should go in finish action
390 // Clear the in progress flag
391 kernelTLS.preemption_state.in_progress = false;
392
393 // Preemption can occur here
394
395 force_yield( __ALARM_PREEMPTION ); // Do the actual __cfactx_switch
396}
397
398// Main of the alarm thread
399// Waits on SIGALRM and send SIGUSR1 to whom ever needs it
400static void * alarm_loop( __attribute__((unused)) void * args ) {
401 // Block sigalrms to control when they arrive
402 sigset_t mask;
403 sigfillset(&mask);
404 if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
405 abort( "internal error, pthread_sigmask" );
406 }
407
408 sigemptyset( &mask );
409 sigaddset( &mask, SIGALRM );
410
411 // Main loop
412 while( true ) {
413 // Wait for a sigalrm
414 siginfo_t info;
415 int sig = sigwaitinfo( &mask, &info );
416
417 if( sig < 0 ) {
418 //Error!
419 int err = errno;
420 switch( err ) {
421 case EAGAIN :
422 case EINTR :
423 {__cfaabi_dbg_print_buffer_decl( " KERNEL: Spurious wakeup %d.\n", err );}
424 continue;
425 case EINVAL :
426 abort( "Timeout was invalid." );
427 default:
428 abort( "Unhandled error %d", err);
429 }
430 }
431
432 // If another signal arrived something went wrong
433 assertf(sig == SIGALRM, "Kernel Internal Error, sigwait: Unexpected signal %d (%d : %d)\n", sig, info.si_code, info.si_value.sival_int);
434
435 // __cfaabi_dbg_print_safe( "Kernel : Caught alarm from %d with %d\n", info.si_code, info.si_value.sival_int );
436 // Switch on the code (a.k.a. the sender) to
437 switch( info.si_code )
438 {
439 // Timers can apparently be marked as sent for the kernel
440 // In either case, tick preemption
441 case SI_TIMER:
442 case SI_KERNEL:
443 // __cfaabi_dbg_print_safe( "Kernel : Preemption thread tick\n" );
444 lock( event_kernel->lock __cfaabi_dbg_ctx2 );
445 tick_preemption();
446 unlock( event_kernel->lock );
447 break;
448 // Signal was not sent by the kernel but by an other thread
449 case SI_QUEUE:
450 // For now, other thread only signal the alarm thread to shut it down
451 // If this needs to change use info.si_value and handle the case here
452 goto EXIT;
453 }
454 }
455
456EXIT:
457 __cfaabi_dbg_print_safe( "Kernel : Preemption thread stopping\n" );
458 return 0p;
459}
460
461//=============================================================================================
462// Kernel Signal Debug
463//=============================================================================================
464
465void __cfaabi_check_preemption() {
466 bool ready = kernelTLS.preemption_state.enabled;
467 if(!ready) { abort("Preemption should be ready"); }
468
469 sigset_t oldset;
470 int ret;
471 ret = pthread_sigmask(0, 0p, &oldset);
472 if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
473
474 ret = sigismember(&oldset, SIGUSR1);
475 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
476 if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
477
478 ret = sigismember(&oldset, SIGALRM);
479 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
480 if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
481
482 ret = sigismember(&oldset, SIGTERM);
483 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
484 if(ret == 1) { abort("ERROR SIGTERM is disabled"); }
485}
486
487#ifdef __CFA_WITH_VERIFY__
488bool __cfaabi_dbg_in_kernel() {
489 return !kernelTLS.preemption_state.enabled;
490}
491#endif
492
493// Local Variables: //
494// mode: c //
495// tab-width: 4 //
496// End: //
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