source: libcfa/src/concurrency/preemption.cfa@ fe97de26

ADT arm-eh ast-experimental enum forall-pointer-decay jacob/cs343-translation new-ast-unique-expr pthread-emulation qualifiedEnum
Last change on this file since fe97de26 was 297cf18, checked in by Thierry Delisle <tdelisle@…>, 5 years ago

Merge branch 'master' of plg.uwaterloo.ca:software/cfa/cfa-cc
  • Property mode set to 100644
File size: 25.3 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 : Fri Nov 6 07:42:13 2020
13// Update Count : 54
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#include "kernel_private.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 * this );
41
42// FwdDeclarations : Signal handlers
43static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ );
44static void sigHandler_alarm ( __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__ )
59#define CFA_REG_IP arm_pc
60#elif defined( __aarch64__ )
61#define CFA_REG_IP pc
62#else
63#error unsupported hardware architecture
64#endif
65
66KERNEL_STORAGE(event_kernel_t, event_kernel); // private storage for event kernel
67event_kernel_t * event_kernel; // kernel public handle to even kernel
68static pthread_t alarm_thread; // pthread handle to alarm thread
69static void * alarm_stack; // pthread stack for alarm thread
70
71static void ?{}(event_kernel_t & this) with( this ) {
72 alarms{};
73 lock{};
74}
75
76enum {
77 PREEMPT_NORMAL = 0,
78 PREEMPT_TERMINATE = 1,
79};
80
81//=============================================================================================
82// Kernel Preemption logic
83//=============================================================================================
84
85// Get next expired node
86static inline alarm_node_t * get_expired( alarm_list_t * alarms, Time currtime ) {
87 if( ! & (*alarms)`first ) return 0p; // If no alarms return null
88 if( (*alarms)`first.alarm >= currtime ) return 0p; // If alarms head not expired return null
89 return pop(alarms); // Otherwise just pop head
90}
91
92// Tick one frame of the Discrete Event Simulation for alarms
93static void tick_preemption(void) {
94 alarm_node_t * node = 0p; // Used in the while loop but cannot be declared in the while condition
95 alarm_list_t * alarms = &event_kernel->alarms; // Local copy for ease of reading
96 Time currtime = __kernel_get_time(); // Check current time once so everything "happens at once"
97
98 //Loop throught every thing expired
99 while( node = get_expired( alarms, currtime ) ) {
100 // __cfaabi_dbg_print_buffer_decl( " KERNEL: preemption tick.\n" );
101 Duration period = node->period;
102 if( period == 0) {
103 node->set = false; // Node is one-shot, just mark it as not pending
104 }
105
106 // Check if this is a kernel
107 if( node->type == Kernel ) {
108 preempt( node->proc );
109 }
110 else if( node->type == User ) {
111 timeout( node->thrd );
112 }
113 else {
114 node->callback(*node);
115 }
116
117 // Check if this is a periodic alarm
118 if( period > 0 ) {
119 // __cfaabi_dbg_print_buffer_local( " KERNEL: alarm period is %lu.\n", period.tv );
120 node->alarm = currtime + period; // Alarm is periodic, add currtime to it (used cached current time)
121 insert( alarms, node ); // Reinsert the node for the next time it triggers
122 }
123 }
124
125 // If there are still alarms pending, reset the timer
126 if( & (*alarms)`first ) {
127 __cfadbg_print_buffer_decl(preemption, " KERNEL: @%ju(%ju) resetting alarm to %ju.\n", currtime.tv, __kernel_get_time().tv, (alarms->head->alarm - currtime).tv);
128 Duration delta = (*alarms)`first.alarm - currtime;
129 Duration capped = max(delta, 50`us);
130 // itimerval tim = { caped };
131 // __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);
132
133 __kernel_set_timer( capped );
134 }
135}
136
137// Update the preemption of a processor and notify interested parties
138void update_preemption( processor * this, Duration duration ) {
139 alarm_node_t * alarm = this->preemption_alarm;
140
141 // Alarms need to be enabled
142 if ( duration > 0 && ! alarm->set ) {
143 alarm->alarm = __kernel_get_time() + duration;
144 alarm->period = duration;
145 register_self( alarm );
146 }
147 // Zero duration but alarm is set
148 else if ( duration == 0 && alarm->set ) {
149 unregister_self( alarm );
150 alarm->alarm = 0;
151 alarm->period = 0;
152 }
153 // If alarm is different from previous, change it
154 else if ( duration > 0 && alarm->period != duration ) {
155 unregister_self( alarm );
156 alarm->alarm = __kernel_get_time() + duration;
157 alarm->period = duration;
158 register_self( alarm );
159 }
160}
161
162//=============================================================================================
163// Kernel Signal Tools
164//=============================================================================================
165// In a user-level threading system, there are handful of thread-local variables where this problem occurs on the ARM.
166//
167// For each kernel thread running user-level threads, there is a flag variable to indicate if interrupts are
168// enabled/disabled for that kernel thread. Therefore, this variable is made thread local.
169//
170// For example, this code fragment sets the state of the "interrupt" variable in thread-local memory.
171//
172// _Thread_local volatile int interrupts;
173// int main() {
174// interrupts = 0; // disable interrupts }
175//
176// which generates the following code on the ARM
177//
178// (gdb) disassemble main
179// Dump of assembler code for function main:
180// 0x0000000000000610 <+0>: mrs x1, tpidr_el0
181// 0x0000000000000614 <+4>: mov w0, #0x0 // #0
182// 0x0000000000000618 <+8>: add x1, x1, #0x0, lsl #12
183// 0x000000000000061c <+12>: add x1, x1, #0x10
184// 0x0000000000000620 <+16>: str wzr, [x1]
185// 0x0000000000000624 <+20>: ret
186//
187// The mrs moves a pointer from coprocessor register tpidr_el0 into register x1. Register w0 is set to 0. The two adds
188// increase the TLS pointer with the displacement (offset) 0x10, which is the location in the TSL of variable
189// "interrupts". Finally, 0 is stored into "interrupts" through the pointer in register x1 that points into the
190// TSL. Now once x1 has the pointer to the location of the TSL for kernel thread N, it can be be preempted at a
191// user-level and the user thread is put on the user-level ready-queue. When the preempted thread gets to the front of
192// the user-level ready-queue it is run on kernel thread M. It now stores 0 into "interrupts" back on kernel thread N,
193// turning off interrupt on the wrong kernel thread.
194//
195// On the x86, the following code is generated for the same code fragment.
196//
197// (gdb) disassemble main
198// Dump of assembler code for function main:
199// 0x0000000000400420 <+0>: movl $0x0,%fs:0xfffffffffffffffc
200// 0x000000000040042c <+12>: xor %eax,%eax
201// 0x000000000040042e <+14>: retq
202//
203// and there is base-displacement addressing used to atomically reset variable "interrupts" off of the TSL pointer in
204// register "fs".
205//
206// Hence, the ARM has base-displacement address for the general purpose registers, BUT not to the coprocessor
207// registers. As a result, generating the address for the write into variable "interrupts" is no longer atomic.
208//
209// Note this problem does NOT occur when just using multiple kernel threads because the preemption ALWAYS restarts the
210// thread on the same kernel thread.
211//
212// The obvious question is why does ARM use a coprocessor register to store the TSL pointer given that coprocessor
213// registers are second-class registers with respect to the instruction set. One possible answer is that they did not
214// want to dedicate one of the general registers to hold the TLS pointer and there was a free coprocessor register
215// available.
216
217//-----------------------------------------------------------------------------
218// Some assembly required
219#define __cfaasm_label(label, when) when: asm volatile goto(".global __cfaasm_" #label "_" #when "\n" "__cfaasm_" #label "_" #when ":":::"memory":when)
220
221//----------
222// special case for preemption since used often
223bool __preemption_enabled() {
224 // create a assembler label before
225 // marked as clobber all to avoid movement
226 __cfaasm_label(check, before);
227
228 // access tls as normal
229 bool enabled = __cfaabi_tls.preemption_state.enabled;
230
231 // create a assembler label after
232 // marked as clobber all to avoid movement
233 __cfaasm_label(check, after);
234 return enabled;
235}
236
237struct asm_region {
238 void * before;
239 void * after;
240};
241
242static inline bool __cfaasm_in( void * ip, struct asm_region & region ) {
243 return ip >= region.before && ip <= region.after;
244}
245
246
247//----------
248// Get data from the TLS block
249// struct asm_region __cfaasm_get;
250uintptr_t __cfatls_get( unsigned long int offset ) __attribute__((__noinline__)); //no inline to avoid problems
251uintptr_t __cfatls_get( unsigned long int offset ) {
252 // create a assembler label before
253 // marked as clobber all to avoid movement
254 __cfaasm_label(get, before);
255
256 // access tls as normal (except for pointer arithmetic)
257 uintptr_t val = *(uintptr_t*)((uintptr_t)&__cfaabi_tls + offset);
258
259 // create a assembler label after
260 // marked as clobber all to avoid movement
261 __cfaasm_label(get, after);
262 return val;
263}
264
265extern "C" {
266 // Disable interrupts by incrementing the counter
267 void disable_interrupts() {
268 // create a assembler label before
269 // marked as clobber all to avoid movement
270 __cfaasm_label(dsable, before);
271
272 with( __cfaabi_tls.preemption_state ) {
273 #if GCC_VERSION > 50000
274 static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
275 #endif
276
277 // Set enabled flag to false
278 // should be atomic to avoid preemption in the middle of the operation.
279 // use memory order RELAXED since there is no inter-thread on this variable requirements
280 __atomic_store_n(&enabled, false, __ATOMIC_RELAXED);
281
282 // Signal the compiler that a fence is needed but only for signal handlers
283 __atomic_signal_fence(__ATOMIC_ACQUIRE);
284
285 __attribute__((unused)) unsigned short new_val = disable_count + 1;
286 disable_count = new_val;
287 verify( new_val < 65_000u ); // If this triggers someone is disabling interrupts without enabling them
288 }
289
290 // create a assembler label after
291 // marked as clobber all to avoid movement
292 __cfaasm_label(dsable, after);
293
294 }
295
296 // Enable interrupts by decrementing the counter
297 // If counter reaches 0, execute any pending __cfactx_switch
298 void enable_interrupts( __cfaabi_dbg_ctx_param ) {
299 // Cache the processor now since interrupts can start happening after the atomic store
300 processor * proc = __cfaabi_tls.this_processor;
301 /* paranoid */ verify( proc );
302
303 with( __cfaabi_tls.preemption_state ){
304 unsigned short prev = disable_count;
305 disable_count -= 1;
306
307 // If this triggers someone is enabled already enabled interruptsverify( prev != 0u );
308 /* paranoid */ verify( prev != 0u );
309
310 // Check if we need to prempt the thread because an interrupt was missed
311 if( prev == 1 ) {
312 #if GCC_VERSION > 50000
313 static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
314 #endif
315
316 // Set enabled flag to true
317 // should be atomic to avoid preemption in the middle of the operation.
318 // use memory order RELAXED since there is no inter-thread on this variable requirements
319 __atomic_store_n(&enabled, true, __ATOMIC_RELAXED);
320
321 // Signal the compiler that a fence is needed but only for signal handlers
322 __atomic_signal_fence(__ATOMIC_RELEASE);
323 if( proc->pending_preemption ) {
324 proc->pending_preemption = false;
325 force_yield( __POLL_PREEMPTION );
326 }
327 }
328 }
329
330 // For debugging purposes : keep track of the last person to enable the interrupts
331 __cfaabi_dbg_debug_do( proc->last_enable = caller; )
332 }
333
334 // Disable interrupts by incrementint the counter
335 // Don't execute any pending __cfactx_switch even if counter reaches 0
336 void enable_interrupts_noPoll() {
337 unsigned short prev = __cfaabi_tls.preemption_state.disable_count;
338 __cfaabi_tls.preemption_state.disable_count -= 1;
339 // If this triggers someone is enabled already enabled interrupts
340 /* paranoid */ verifyf( prev != 0u, "Incremented from %u\n", prev );
341 if( prev == 1 ) {
342 #if GCC_VERSION > 50000
343 static_assert(__atomic_always_lock_free(sizeof(__cfaabi_tls.preemption_state.enabled), &__cfaabi_tls.preemption_state.enabled), "Must be lock-free");
344 #endif
345 // Set enabled flag to true
346 // should be atomic to avoid preemption in the middle of the operation.
347 // use memory order RELAXED since there is no inter-thread on this variable requirements
348 __atomic_store_n(&__cfaabi_tls.preemption_state.enabled, true, __ATOMIC_RELAXED);
349
350 // Signal the compiler that a fence is needed but only for signal handlers
351 __atomic_signal_fence(__ATOMIC_RELEASE);
352 }
353 }
354}
355
356//-----------------------------------------------------------------------------
357// Kernel Signal Debug
358void __cfaabi_check_preemption() {
359 bool ready = __preemption_enabled();
360 if(!ready) { abort("Preemption should be ready"); }
361
362 __cfaasm_label(debug, before);
363
364 sigset_t oldset;
365 int ret;
366 ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset); // workaround trac#208: cast should be unnecessary
367 if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
368
369 ret = sigismember(&oldset, SIGUSR1);
370 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
371 if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
372
373 ret = sigismember(&oldset, SIGALRM);
374 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
375 if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
376
377 ret = sigismember(&oldset, SIGTERM);
378 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
379 if(ret == 1) { abort("ERROR SIGTERM is disabled"); }
380
381 __cfaasm_label(debug, after);
382}
383
384#ifdef __CFA_WITH_VERIFY__
385bool __cfaabi_dbg_in_kernel() {
386 return !__preemption_enabled();
387}
388#endif
389
390#undef __cfaasm_label
391
392//-----------------------------------------------------------------------------
393// Signal handling
394
395// sigprocmask wrapper : unblock a single signal
396static inline void signal_unblock( int sig ) {
397 sigset_t mask;
398 sigemptyset( &mask );
399 sigaddset( &mask, sig );
400
401 if ( pthread_sigmask( SIG_UNBLOCK, &mask, 0p ) == -1 ) {
402 abort( "internal error, pthread_sigmask" );
403 }
404}
405
406// sigprocmask wrapper : block a single signal
407static inline void signal_block( int sig ) {
408 sigset_t mask;
409 sigemptyset( &mask );
410 sigaddset( &mask, sig );
411
412 if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
413 abort( "internal error, pthread_sigmask" );
414 }
415}
416
417// kill wrapper : signal a processor
418static void preempt( processor * this ) {
419 sigval_t value = { PREEMPT_NORMAL };
420 pthread_sigqueue( this->kernel_thread, SIGUSR1, value );
421}
422
423// reserved for future use
424static void timeout( $thread * this ) {
425 unpark( this );
426}
427
428//-----------------------------------------------------------------------------
429// Some assembly required
430#if defined( __i386 )
431 #ifdef __PIC__
432 #define RELOC_PRELUDE( label ) \
433 "calll .Lcfaasm_prelude_" #label "$pb\n\t" \
434 ".Lcfaasm_prelude_" #label "$pb:\n\t" \
435 "popl %%eax\n\t" \
436 ".Lcfaasm_prelude_" #label "_end:\n\t" \
437 "addl $_GLOBAL_OFFSET_TABLE_+(.Lcfaasm_prelude_" #label "_end-.Lcfaasm_prelude_" #label "$pb), %%eax\n\t"
438 #define RELOC_PREFIX ""
439 #define RELOC_SUFFIX "@GOT(%%eax)"
440 #else
441 #define RELOC_PREFIX "$"
442 #define RELOC_SUFFIX ""
443 #endif
444 #define __cfaasm_label( label ) struct asm_region label = \
445 ({ \
446 struct asm_region region; \
447 asm( \
448 RELOC_PRELUDE( label ) \
449 "movl " RELOC_PREFIX "__cfaasm_" #label "_before" RELOC_SUFFIX ", %[vb]\n\t" \
450 "movl " RELOC_PREFIX "__cfaasm_" #label "_after" RELOC_SUFFIX ", %[va]\n\t" \
451 : [vb]"=r"(region.before), [va]"=r"(region.after) \
452 ); \
453 region; \
454 });
455#elif defined( __x86_64 )
456 #ifdef __PIC__
457 #define RELOC_PREFIX ""
458 #define RELOC_SUFFIX "@GOTPCREL(%%rip)"
459 #else
460 #define RELOC_PREFIX "$"
461 #define RELOC_SUFFIX ""
462 #endif
463 #define __cfaasm_label( label ) struct asm_region label = \
464 ({ \
465 struct asm_region region; \
466 asm( \
467 "movq " RELOC_PREFIX "__cfaasm_" #label "_before" RELOC_SUFFIX ", %[vb]\n\t" \
468 "movq " RELOC_PREFIX "__cfaasm_" #label "_after" RELOC_SUFFIX ", %[va]\n\t" \
469 : [vb]"=r"(region.before), [va]"=r"(region.after) \
470 ); \
471 region; \
472 });
473#elif defined( __aarch64__ )
474 #ifdef __PIC__
475 // Note that this works only for gcc
476 #define __cfaasm_label( label ) struct asm_region label = \
477 ({ \
478 struct asm_region region; \
479 asm( \
480 "adrp %[vb], _GLOBAL_OFFSET_TABLE_" "\n\t" \
481 "ldr %[vb], [%[vb], #:gotpage_lo15:__cfaasm_" #label "_before]" "\n\t" \
482 "adrp %[va], _GLOBAL_OFFSET_TABLE_" "\n\t" \
483 "ldr %[va], [%[va], #:gotpage_lo15:__cfaasm_" #label "_after]" "\n\t" \
484 : [vb]"=r"(region.before), [va]"=r"(region.after) \
485 ); \
486 region; \
487 });
488 #else
489 #error this is not the right thing to do
490 /*
491 #define __cfaasm_label( label ) struct asm_region label = \
492 ({ \
493 struct asm_region region; \
494 asm( \
495 "adrp %[vb], __cfaasm_" #label "_before" "\n\t" \
496 "add %[vb], %[vb], :lo12:__cfaasm_" #label "_before" "\n\t" \
497 "adrp %[va], :got:__cfaasm_" #label "_after" "\n\t" \
498 "add %[va], %[va], :lo12:__cfaasm_" #label "_after" "\n\t" \
499 : [vb]"=r"(region.before), [va]"=r"(region.after) \
500 ); \
501 region; \
502 });
503 */
504 #endif
505#else
506 #error unknown hardware architecture
507#endif
508
509// KERNEL ONLY
510// Check if a __cfactx_switch signal handler shoud defer
511// If true : preemption is safe
512// If false : preemption is unsafe and marked as pending
513static inline bool preemption_ready( void * ip ) {
514 // Get all the region for which it is not safe to preempt
515 __cfaasm_label( get );
516 __cfaasm_label( check );
517 __cfaasm_label( dsable );
518 __cfaasm_label( debug );
519
520 // Check if preemption is safe
521 bool ready = true;
522 if( __cfaasm_in( ip, get ) ) { ready = false; goto EXIT; };
523 if( __cfaasm_in( ip, check ) ) { ready = false; goto EXIT; };
524 if( __cfaasm_in( ip, dsable ) ) { ready = false; goto EXIT; };
525 if( __cfaasm_in( ip, debug ) ) { ready = false; goto EXIT; };
526 if( !__cfaabi_tls.preemption_state.enabled) { ready = false; goto EXIT; };
527 if( __cfaabi_tls.preemption_state.in_progress ) { ready = false; goto EXIT; };
528
529EXIT:
530 // Adjust the pending flag accordingly
531 __cfaabi_tls.this_processor->pending_preemption = !ready;
532 return ready;
533}
534
535//=============================================================================================
536// Kernel Signal Startup/Shutdown logic
537//=============================================================================================
538
539// Startup routine to activate preemption
540// Called from kernel_startup
541void __kernel_alarm_startup() {
542 __cfaabi_dbg_print_safe( "Kernel : Starting preemption\n" );
543
544 // Start with preemption disabled until ready
545 __cfaabi_tls.preemption_state.enabled = false;
546 __cfaabi_tls.preemption_state.disable_count = 1;
547
548 // Initialize the event kernel
549 event_kernel = (event_kernel_t *)&storage_event_kernel;
550 (*event_kernel){};
551
552 // Setup proper signal handlers
553 __cfaabi_sigaction( SIGUSR1, sigHandler_ctxSwitch, SA_SIGINFO | SA_RESTART ); // __cfactx_switch handler
554 __cfaabi_sigaction( SIGALRM, sigHandler_alarm , SA_SIGINFO | SA_RESTART ); // debug handler
555
556 signal_block( SIGALRM );
557
558 alarm_stack = __create_pthread( &alarm_thread, alarm_loop, 0p );
559}
560
561// Shutdown routine to deactivate preemption
562// Called from kernel_shutdown
563void __kernel_alarm_shutdown() {
564 __cfaabi_dbg_print_safe( "Kernel : Preemption stopping\n" );
565
566 // Block all signals since we are already shutting down
567 sigset_t mask;
568 sigfillset( &mask );
569 sigprocmask( SIG_BLOCK, &mask, 0p );
570
571 // Notify the alarm thread of the shutdown
572 sigval val = { 1 };
573 pthread_sigqueue( alarm_thread, SIGALRM, val );
574
575 // Wait for the preemption thread to finish
576
577 __destroy_pthread( alarm_thread, alarm_stack, 0p );
578
579 // Preemption is now fully stopped
580
581 __cfaabi_dbg_print_safe( "Kernel : Preemption stopped\n" );
582}
583
584// Raii ctor/dtor for the preemption_scope
585// Used by thread to control when they want to receive preemption signals
586void ?{}( preemption_scope & this, processor * proc ) {
587 (this.alarm){ proc, (Time){ 0 }, 0`s };
588 this.proc = proc;
589 this.proc->preemption_alarm = &this.alarm;
590
591 update_preemption( this.proc, this.proc->cltr->preemption_rate );
592}
593
594void ^?{}( preemption_scope & this ) {
595 disable_interrupts();
596
597 update_preemption( this.proc, 0`s );
598}
599
600//=============================================================================================
601// Kernel Signal Handlers
602//=============================================================================================
603__cfaabi_dbg_debug_do( static thread_local void * last_interrupt = 0; )
604
605// Context switch signal handler
606// Receives SIGUSR1 signal and causes the current thread to yield
607static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ ) {
608 void * ip = (void *)(cxt->uc_mcontext.CFA_REG_IP);
609 __cfaabi_dbg_debug_do( last_interrupt = ip; )
610
611 // SKULLDUGGERY: if a thread creates a processor and the immediately deletes it,
612 // the interrupt that is supposed to force the kernel thread to preempt might arrive
613 // before the kernel thread has even started running. When that happens, an interrupt
614 // with a null 'this_processor' will be caught, just ignore it.
615 if(! __cfaabi_tls.this_processor ) return;
616
617 choose(sfp->si_value.sival_int) {
618 case PREEMPT_NORMAL : ;// Normal case, nothing to do here
619 case PREEMPT_TERMINATE: verify( __atomic_load_n( &__cfaabi_tls.this_processor->do_terminate, __ATOMIC_SEQ_CST ) );
620 default:
621 abort( "internal error, signal value is %d", sfp->si_value.sival_int );
622 }
623
624 // Check if it is safe to preempt here
625 if( !preemption_ready( ip ) ) { return; }
626
627 __cfaabi_dbg_print_buffer_decl( " KERNEL: preempting core %p (%p @ %p).\n", __cfaabi_tls.this_processor, __cfaabi_tls.this_thread, (void *)(cxt->uc_mcontext.CFA_REG_IP) );
628
629 // Sync flag : prevent recursive calls to the signal handler
630 __cfaabi_tls.preemption_state.in_progress = true;
631
632 // Clear sighandler mask before context switching.
633 #if GCC_VERSION > 50000
634 static_assert( sizeof( sigset_t ) == sizeof( cxt->uc_sigmask ), "Expected cxt->uc_sigmask to be of sigset_t" );
635 #endif
636 if ( pthread_sigmask( SIG_SETMASK, (sigset_t *)&(cxt->uc_sigmask), 0p ) == -1 ) {
637 abort( "internal error, sigprocmask" );
638 }
639
640 // Clear the in progress flag
641 __cfaabi_tls.preemption_state.in_progress = false;
642
643 // Preemption can occur here
644
645 force_yield( __ALARM_PREEMPTION ); // Do the actual __cfactx_switch
646}
647
648static void sigHandler_alarm( __CFA_SIGPARMS__ ) {
649 abort("SIGALRM should never reach the signal handler");
650}
651
652#if !defined(__CFA_NO_STATISTICS__)
653 int __print_alarm_stats = 0;
654#endif
655
656// Main of the alarm thread
657// Waits on SIGALRM and send SIGUSR1 to whom ever needs it
658static void * alarm_loop( __attribute__((unused)) void * args ) {
659 __processor_id_t id;
660 id.full_proc = false;
661 id.id = doregister(&id);
662 __cfaabi_tls.this_proc_id = &id;
663
664 #if !defined(__CFA_NO_STATISTICS__)
665 struct __stats_t local_stats;
666 __cfaabi_tls.this_stats = &local_stats;
667 __init_stats( &local_stats );
668 #endif
669
670 // Block sigalrms to control when they arrive
671 sigset_t mask;
672 sigfillset(&mask);
673 if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
674 abort( "internal error, pthread_sigmask" );
675 }
676
677 sigemptyset( &mask );
678 sigaddset( &mask, SIGALRM );
679
680 // Main loop
681 while( true ) {
682 // Wait for a sigalrm
683 siginfo_t info;
684 int sig = sigwaitinfo( &mask, &info );
685
686 if( sig < 0 ) {
687 //Error!
688 int err = errno;
689 switch( err ) {
690 case EAGAIN :
691 case EINTR :
692 {__cfaabi_dbg_print_buffer_decl( " KERNEL: Spurious wakeup %d.\n", err );}
693 continue;
694 case EINVAL :
695 abort( "Timeout was invalid." );
696 default:
697 abort( "Unhandled error %d", err);
698 }
699 }
700
701 // If another signal arrived something went wrong
702 assertf(sig == SIGALRM, "Kernel Internal Error, sigwait: Unexpected signal %d (%d : %d)\n", sig, info.si_code, info.si_value.sival_int);
703
704 // __cfaabi_dbg_print_safe( "Kernel : Caught alarm from %d with %d\n", info.si_code, info.si_value.sival_int );
705 // Switch on the code (a.k.a. the sender) to
706 switch( info.si_code )
707 {
708 // Timers can apparently be marked as sent for the kernel
709 // In either case, tick preemption
710 case SI_TIMER:
711 case SI_KERNEL:
712 // __cfaabi_dbg_print_safe( "Kernel : Preemption thread tick\n" );
713 lock( event_kernel->lock __cfaabi_dbg_ctx2 );
714 tick_preemption();
715 unlock( event_kernel->lock );
716 break;
717 // Signal was not sent by the kernel but by an other thread
718 case SI_QUEUE:
719 // For now, other thread only signal the alarm thread to shut it down
720 // If this needs to change use info.si_value and handle the case here
721 goto EXIT;
722 }
723 }
724
725EXIT:
726 __cfaabi_dbg_print_safe( "Kernel : Preemption thread stopping\n" );
727 unregister(&id);
728
729 #if !defined(__CFA_NO_STATISTICS__)
730 if( 0 != __print_alarm_stats ) {
731 __print_stats( &local_stats, __print_alarm_stats, "Alarm", "Thread", 0p );
732 }
733 #endif
734 return 0p;
735}
736
737// Local Variables: //
738// mode: c //
739// tab-width: 4 //
740// End: //
Note: See TracBrowser for help on using the repository browser.