source: libcfa/src/concurrency/preemption.cfa@ b51e389c

ADT ast-experimental enum forall-pointer-decay jacob/cs343-translation new-ast-unique-expr pthread-emulation qualifiedEnum
Last change on this file since b51e389c was c457dc41, checked in by Thierry Delisle <tdelisle@…>, 4 years ago

Fix sequential handling of timers
  • Property mode set to 100644
File size: 25.8 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// #define __CFA_DEBUG_PRINT_PREEMPTION__
18
19#include "preemption.hfa"
20
21#include <assert.h>
22
23#include <errno.h>
24#include <stdio.h>
25#include <string.h>
26#include <unistd.h>
27#include <limits.h> // PTHREAD_STACK_MIN
28
29#include "bits/debug.hfa"
30#include "bits/signal.hfa"
31#include "kernel_private.hfa"
32
33
34#if !defined(__CFA_DEFAULT_PREEMPTION__)
35#define __CFA_DEFAULT_PREEMPTION__ 10`ms
36#endif
37
38__attribute__((weak)) Duration default_preemption() {
39 const char * preempt_rate_s = getenv("CFA_DEFAULT_PREEMPTION");
40 if(!preempt_rate_s) {
41 __cfadbg_print_safe(preemption, "No CFA_DEFAULT_PREEMPTION in ENV\n");
42 return __CFA_DEFAULT_PREEMPTION__;
43 }
44
45 char * endptr = 0p;
46 long int preempt_rate_l = strtol(preempt_rate_s, &endptr, 10);
47 if(preempt_rate_l < 0 || preempt_rate_l > 65535) {
48 __cfadbg_print_safe(preemption, "CFA_DEFAULT_PREEMPTION out of range : %ld\n", preempt_rate_l);
49 return __CFA_DEFAULT_PREEMPTION__;
50 }
51 if('\0' != *endptr) {
52 __cfadbg_print_safe(preemption, "CFA_DEFAULT_PREEMPTION not a decimal number : %s\n", preempt_rate_s);
53 return __CFA_DEFAULT_PREEMPTION__;
54 }
55
56 return preempt_rate_l`ms;
57}
58
59// FwdDeclarations : timeout handlers
60static void preempt( processor * this );
61static void timeout( $thread * this );
62
63// FwdDeclarations : Signal handlers
64static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ );
65static void sigHandler_alarm ( __CFA_SIGPARMS__ );
66static void sigHandler_segv ( __CFA_SIGPARMS__ );
67static void sigHandler_ill ( __CFA_SIGPARMS__ );
68static void sigHandler_fpe ( __CFA_SIGPARMS__ );
69static void sigHandler_abort ( __CFA_SIGPARMS__ );
70
71// FwdDeclarations : alarm thread main
72static void * alarm_loop( __attribute__((unused)) void * args );
73
74// Machine specific register name
75#if defined( __i386 )
76#define CFA_REG_IP gregs[REG_EIP]
77#elif defined( __x86_64 )
78#define CFA_REG_IP gregs[REG_RIP]
79#elif defined( __arm__ )
80#define CFA_REG_IP arm_pc
81#elif defined( __aarch64__ )
82#define CFA_REG_IP pc
83#else
84#error unsupported hardware architecture
85#endif
86
87KERNEL_STORAGE(event_kernel_t, event_kernel); // private storage for event kernel
88event_kernel_t * event_kernel; // kernel public handle to even kernel
89static pthread_t alarm_thread; // pthread handle to alarm thread
90static void * alarm_stack; // pthread stack for alarm thread
91
92static void ?{}(event_kernel_t & this) with( this ) {
93 alarms{};
94 lock{};
95}
96
97enum {
98 PREEMPT_NORMAL = 0,
99 PREEMPT_TERMINATE = 1,
100};
101
102//=============================================================================================
103// Kernel Preemption logic
104//=============================================================================================
105
106// Get next expired node
107static inline alarm_node_t * get_expired( alarm_list_t * alarms, Time currtime ) {
108 if( ! & (*alarms)`first ) return 0p; // If no alarms return null
109 if( (*alarms)`first.timeval >= currtime ) return 0p; // If alarms head not expired return null
110 return pop(alarms); // Otherwise just pop head
111}
112
113// Tick one frame of the Discrete Event Simulation for alarms
114static void tick_preemption(void) {
115 alarm_node_t * node = 0p; // Used in the while loop but cannot be declared in the while condition
116 alarm_list_t * alarms = &event_kernel->alarms; // Local copy for ease of reading
117 Time currtime = __kernel_get_time(); // Check current time once so everything "happens at once"
118
119 //Loop throught every thing expired
120 while( node = get_expired( alarms, currtime ) ) {
121 __cfadbg_print_buffer_decl( preemption, " KERNEL: preemption tick %lu\n", currtime.tn);
122 Duration period = node->period;
123 if( period == 0) {
124 node->set = false; // Node is one-shot, just mark it as not pending
125 }
126
127 __cfadbg_print_buffer_local( preemption, " KERNEL: alarm ticking node %p.\n", node );
128
129
130 // Check if this is a kernel
131 if( node->type == Kernel ) {
132 preempt( node->proc );
133 }
134 else if( node->type == User ) {
135 __cfadbg_print_buffer_local( preemption, " KERNEL: alarm unparking %p.\n", node->thrd );
136 timeout( node->thrd );
137 }
138 else {
139 node->callback(*node);
140 }
141
142 // Check if this is a periodic alarm
143 if( period > 0 ) {
144 __cfadbg_print_buffer_local( preemption, " KERNEL: alarm period is %lu.\n", period`ns );
145 node->timeval = currtime + period; // Alarm is periodic, add currtime to it (used cached current time)
146 insert( alarms, node ); // Reinsert the node for the next time it triggers
147 }
148 }
149
150 // If there are still alarms pending, reset the timer
151 if( & (*alarms)`first ) {
152 Duration delta = (*alarms)`first.timeval - currtime;
153 __kernel_set_timer( delta );
154 }
155}
156
157// Update the preemption of a processor and notify interested parties
158void update_preemption( processor * this, Duration duration ) {
159 alarm_node_t * alarm = this->preemption_alarm;
160
161 // Alarms need to be enabled
162 if ( duration > 0 && ! alarm->set ) {
163 alarm->initial = duration;
164 alarm->period = duration;
165 register_self( alarm );
166 }
167 // Zero duration but alarm is set
168 else if ( duration == 0 && alarm->set ) {
169 unregister_self( alarm );
170 alarm->initial = 0;
171 alarm->period = 0;
172 }
173 // If alarm is different from previous, change it
174 else if ( duration > 0 && alarm->period != duration ) {
175 unregister_self( alarm );
176 alarm->initial = duration;
177 alarm->period = duration;
178 register_self( alarm );
179 }
180}
181
182//=============================================================================================
183// Kernel Signal Tools
184//=============================================================================================
185// In a user-level threading system, there are handful of thread-local variables where this problem occurs on the ARM.
186//
187// For each kernel thread running user-level threads, there is a flag variable to indicate if interrupts are
188// enabled/disabled for that kernel thread. Therefore, this variable is made thread local.
189//
190// For example, this code fragment sets the state of the "interrupt" variable in thread-local memory.
191//
192// _Thread_local volatile int interrupts;
193// int main() {
194// interrupts = 0; // disable interrupts }
195//
196// which generates the following code on the ARM
197//
198// (gdb) disassemble main
199// Dump of assembler code for function main:
200// 0x0000000000000610 <+0>: mrs x1, tpidr_el0
201// 0x0000000000000614 <+4>: mov w0, #0x0 // #0
202// 0x0000000000000618 <+8>: add x1, x1, #0x0, lsl #12
203// 0x000000000000061c <+12>: add x1, x1, #0x10
204// 0x0000000000000620 <+16>: str wzr, [x1]
205// 0x0000000000000624 <+20>: ret
206//
207// The mrs moves a pointer from coprocessor register tpidr_el0 into register x1. Register w0 is set to 0. The two adds
208// increase the TLS pointer with the displacement (offset) 0x10, which is the location in the TSL of variable
209// "interrupts". Finally, 0 is stored into "interrupts" through the pointer in register x1 that points into the
210// TSL. Now once x1 has the pointer to the location of the TSL for kernel thread N, it can be be preempted at a
211// user-level and the user thread is put on the user-level ready-queue. When the preempted thread gets to the front of
212// the user-level ready-queue it is run on kernel thread M. It now stores 0 into "interrupts" back on kernel thread N,
213// turning off interrupt on the wrong kernel thread.
214//
215// On the x86, the following code is generated for the same code fragment.
216//
217// (gdb) disassemble main
218// Dump of assembler code for function main:
219// 0x0000000000400420 <+0>: movl $0x0,%fs:0xfffffffffffffffc
220// 0x000000000040042c <+12>: xor %eax,%eax
221// 0x000000000040042e <+14>: retq
222//
223// and there is base-displacement addressing used to atomically reset variable "interrupts" off of the TSL pointer in
224// register "fs".
225//
226// Hence, the ARM has base-displacement address for the general purpose registers, BUT not to the coprocessor
227// registers. As a result, generating the address for the write into variable "interrupts" is no longer atomic.
228//
229// Note this problem does NOT occur when just using multiple kernel threads because the preemption ALWAYS restarts the
230// thread on the same kernel thread.
231//
232// The obvious question is why does ARM use a coprocessor register to store the TSL pointer given that coprocessor
233// registers are second-class registers with respect to the instruction set. One possible answer is that they did not
234// want to dedicate one of the general registers to hold the TLS pointer and there was a free coprocessor register
235// available.
236
237//-----------------------------------------------------------------------------
238// Some assembly required
239#define __cfaasm_label(label, when) when: asm volatile goto(".global __cfaasm_" #label "_" #when "\n" "__cfaasm_" #label "_" #when ":":::"memory":when)
240
241//----------
242// special case for preemption since used often
243bool __preemption_enabled() {
244 // create a assembler label before
245 // marked as clobber all to avoid movement
246 __cfaasm_label(check, before);
247
248 // access tls as normal
249 bool enabled = __cfaabi_tls.preemption_state.enabled;
250
251 // create a assembler label after
252 // marked as clobber all to avoid movement
253 __cfaasm_label(check, after);
254 return enabled;
255}
256
257struct asm_region {
258 void * before;
259 void * after;
260};
261
262static inline bool __cfaasm_in( void * ip, struct asm_region & region ) {
263 return ip >= region.before && ip <= region.after;
264}
265
266
267//----------
268// Get data from the TLS block
269// struct asm_region __cfaasm_get;
270uintptr_t __cfatls_get( unsigned long int offset ) __attribute__((__noinline__)); //no inline to avoid problems
271uintptr_t __cfatls_get( unsigned long int offset ) {
272 // create a assembler label before
273 // marked as clobber all to avoid movement
274 __cfaasm_label(get, before);
275
276 // access tls as normal (except for pointer arithmetic)
277 uintptr_t val = *(uintptr_t*)((uintptr_t)&__cfaabi_tls + offset);
278
279 // create a assembler label after
280 // marked as clobber all to avoid movement
281 __cfaasm_label(get, after);
282 return val;
283}
284
285extern "C" {
286 // Disable interrupts by incrementing the counter
287 void disable_interrupts() {
288 // create a assembler label before
289 // marked as clobber all to avoid movement
290 __cfaasm_label(dsable, before);
291
292 with( __cfaabi_tls.preemption_state ) {
293 #if GCC_VERSION > 50000
294 static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
295 #endif
296
297 // Set enabled flag to false
298 // should be atomic to avoid preemption in the middle of the operation.
299 // use memory order RELAXED since there is no inter-thread on this variable requirements
300 __atomic_store_n(&enabled, false, __ATOMIC_RELAXED);
301
302 // Signal the compiler that a fence is needed but only for signal handlers
303 __atomic_signal_fence(__ATOMIC_ACQUIRE);
304
305 __attribute__((unused)) unsigned short new_val = disable_count + 1;
306 disable_count = new_val;
307 verify( new_val < 65_000u ); // If this triggers someone is disabling interrupts without enabling them
308 }
309
310 // create a assembler label after
311 // marked as clobber all to avoid movement
312 __cfaasm_label(dsable, after);
313
314 }
315
316 // Enable interrupts by decrementing the counter
317 // If counter reaches 0, execute any pending __cfactx_switch
318 void enable_interrupts( bool poll ) {
319 // Cache the processor now since interrupts can start happening after the atomic store
320 processor * proc = __cfaabi_tls.this_processor;
321 /* paranoid */ verify( !poll || proc );
322
323 with( __cfaabi_tls.preemption_state ){
324 unsigned short prev = disable_count;
325 disable_count -= 1;
326
327 // If this triggers someone is enabled already enabled interruptsverify( prev != 0u );
328 /* paranoid */ verify( prev != 0u );
329
330 // Check if we need to prempt the thread because an interrupt was missed
331 if( prev == 1 ) {
332 #if GCC_VERSION > 50000
333 static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
334 #endif
335
336 // Set enabled flag to true
337 // should be atomic to avoid preemption in the middle of the operation.
338 // use memory order RELAXED since there is no inter-thread on this variable requirements
339 __atomic_store_n(&enabled, true, __ATOMIC_RELAXED);
340
341 // Signal the compiler that a fence is needed but only for signal handlers
342 __atomic_signal_fence(__ATOMIC_RELEASE);
343 if( poll && proc->pending_preemption ) {
344 proc->pending_preemption = false;
345 force_yield( __POLL_PREEMPTION );
346 }
347 }
348 }
349 }
350}
351
352//-----------------------------------------------------------------------------
353// Kernel Signal Debug
354void __cfaabi_check_preemption() {
355 bool ready = __preemption_enabled();
356 if(!ready) { abort("Preemption should be ready"); }
357
358 __cfaasm_label(debug, before);
359
360 sigset_t oldset;
361 int ret;
362 ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset); // workaround trac#208: cast should be unnecessary
363 if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
364
365 ret = sigismember(&oldset, SIGUSR1);
366 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
367 if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
368
369 ret = sigismember(&oldset, SIGALRM);
370 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
371 if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
372
373 ret = sigismember(&oldset, SIGTERM);
374 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
375 if(ret == 1) { abort("ERROR SIGTERM is disabled"); }
376
377 __cfaasm_label(debug, after);
378}
379
380#ifdef __CFA_WITH_VERIFY__
381bool __cfaabi_dbg_in_kernel() {
382 return !__preemption_enabled();
383}
384#endif
385
386#undef __cfaasm_label
387
388//-----------------------------------------------------------------------------
389// Signal handling
390
391// sigprocmask wrapper : unblock a single signal
392static inline void signal_unblock( int sig ) {
393 sigset_t mask;
394 sigemptyset( &mask );
395 sigaddset( &mask, sig );
396
397 if ( pthread_sigmask( SIG_UNBLOCK, &mask, 0p ) == -1 ) {
398 abort( "internal error, pthread_sigmask" );
399 }
400}
401
402// sigprocmask wrapper : block a single signal
403static inline void signal_block( int sig ) {
404 sigset_t mask;
405 sigemptyset( &mask );
406 sigaddset( &mask, sig );
407
408 if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
409 abort( "internal error, pthread_sigmask" );
410 }
411}
412
413// kill wrapper : signal a processor
414static void preempt( processor * this ) {
415 sigval_t value = { PREEMPT_NORMAL };
416 pthread_sigqueue( this->kernel_thread, SIGUSR1, value );
417}
418
419// reserved for future use
420static void timeout( $thread * this ) {
421 unpark( this );
422}
423
424void __disable_interrupts_hard() {
425 sigset_t oldset;
426 int ret;
427 ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset); // workaround trac#208: cast should be unnecessary
428 if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
429
430 ret = sigismember(&oldset, SIGUSR1);
431 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
432 if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
433
434 ret = sigismember(&oldset, SIGALRM);
435 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
436 if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
437
438 signal_block( SIGUSR1 );
439}
440
441void __enable_interrupts_hard() {
442 signal_unblock( SIGUSR1 );
443
444 sigset_t oldset;
445 int ret;
446 ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset); // workaround trac#208: cast should be unnecessary
447 if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
448
449 ret = sigismember(&oldset, SIGUSR1);
450 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
451 if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
452
453 ret = sigismember(&oldset, SIGALRM);
454 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
455 if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
456}
457
458//-----------------------------------------------------------------------------
459// Some assembly required
460#if defined( __i386 )
461 #ifdef __PIC__
462 #define RELOC_PRELUDE( label ) \
463 "calll .Lcfaasm_prelude_" #label "$pb\n\t" \
464 ".Lcfaasm_prelude_" #label "$pb:\n\t" \
465 "popl %%eax\n\t" \
466 ".Lcfaasm_prelude_" #label "_end:\n\t" \
467 "addl $_GLOBAL_OFFSET_TABLE_+(.Lcfaasm_prelude_" #label "_end-.Lcfaasm_prelude_" #label "$pb), %%eax\n\t"
468 #define RELOC_PREFIX ""
469 #define RELOC_SUFFIX "@GOT(%%eax)"
470 #else
471 #define RELOC_PREFIX "$"
472 #define RELOC_SUFFIX ""
473 #endif
474 #define __cfaasm_label( label ) struct asm_region label = \
475 ({ \
476 struct asm_region region; \
477 asm( \
478 RELOC_PRELUDE( label ) \
479 "movl " RELOC_PREFIX "__cfaasm_" #label "_before" RELOC_SUFFIX ", %[vb]\n\t" \
480 "movl " RELOC_PREFIX "__cfaasm_" #label "_after" RELOC_SUFFIX ", %[va]\n\t" \
481 : [vb]"=r"(region.before), [va]"=r"(region.after) \
482 ); \
483 region; \
484 });
485#elif defined( __x86_64 )
486 #ifdef __PIC__
487 #define RELOC_PREFIX ""
488 #define RELOC_SUFFIX "@GOTPCREL(%%rip)"
489 #else
490 #define RELOC_PREFIX "$"
491 #define RELOC_SUFFIX ""
492 #endif
493 #define __cfaasm_label( label ) struct asm_region label = \
494 ({ \
495 struct asm_region region; \
496 asm( \
497 "movq " RELOC_PREFIX "__cfaasm_" #label "_before" RELOC_SUFFIX ", %[vb]\n\t" \
498 "movq " RELOC_PREFIX "__cfaasm_" #label "_after" RELOC_SUFFIX ", %[va]\n\t" \
499 : [vb]"=r"(region.before), [va]"=r"(region.after) \
500 ); \
501 region; \
502 });
503#elif defined( __aarch64__ )
504 #ifdef __PIC__
505 // Note that this works only for gcc
506 #define __cfaasm_label( label ) struct asm_region label = \
507 ({ \
508 struct asm_region region; \
509 asm( \
510 "adrp %[vb], _GLOBAL_OFFSET_TABLE_" "\n\t" \
511 "ldr %[vb], [%[vb], #:gotpage_lo15:__cfaasm_" #label "_before]" "\n\t" \
512 "adrp %[va], _GLOBAL_OFFSET_TABLE_" "\n\t" \
513 "ldr %[va], [%[va], #:gotpage_lo15:__cfaasm_" #label "_after]" "\n\t" \
514 : [vb]"=r"(region.before), [va]"=r"(region.after) \
515 ); \
516 region; \
517 });
518 #else
519 #error this is not the right thing to do
520 /*
521 #define __cfaasm_label( label ) struct asm_region label = \
522 ({ \
523 struct asm_region region; \
524 asm( \
525 "adrp %[vb], __cfaasm_" #label "_before" "\n\t" \
526 "add %[vb], %[vb], :lo12:__cfaasm_" #label "_before" "\n\t" \
527 "adrp %[va], :got:__cfaasm_" #label "_after" "\n\t" \
528 "add %[va], %[va], :lo12:__cfaasm_" #label "_after" "\n\t" \
529 : [vb]"=r"(region.before), [va]"=r"(region.after) \
530 ); \
531 region; \
532 });
533 */
534 #endif
535#else
536 #error unknown hardware architecture
537#endif
538
539// KERNEL ONLY
540// Check if a __cfactx_switch signal handler shoud defer
541// If true : preemption is safe
542// If false : preemption is unsafe and marked as pending
543static inline bool preemption_ready( void * ip ) {
544 // Get all the region for which it is not safe to preempt
545 __cfaasm_label( get );
546 __cfaasm_label( check );
547 __cfaasm_label( dsable );
548 __cfaasm_label( debug );
549
550 // Check if preemption is safe
551 bool ready = true;
552 if( __cfaasm_in( ip, get ) ) { ready = false; goto EXIT; };
553 if( __cfaasm_in( ip, check ) ) { ready = false; goto EXIT; };
554 if( __cfaasm_in( ip, dsable ) ) { ready = false; goto EXIT; };
555 if( __cfaasm_in( ip, debug ) ) { ready = false; goto EXIT; };
556 if( !__cfaabi_tls.preemption_state.enabled) { ready = false; goto EXIT; };
557 if( __cfaabi_tls.preemption_state.in_progress ) { ready = false; goto EXIT; };
558
559EXIT:
560 // Adjust the pending flag accordingly
561 __cfaabi_tls.this_processor->pending_preemption = !ready;
562 return ready;
563}
564
565//=============================================================================================
566// Kernel Signal Startup/Shutdown logic
567//=============================================================================================
568
569// Startup routine to activate preemption
570// Called from kernel_startup
571void __kernel_alarm_startup() {
572 __cfaabi_dbg_print_safe( "Kernel : Starting preemption\n" );
573
574 // Start with preemption disabled until ready
575 __cfaabi_tls.preemption_state.enabled = false;
576 __cfaabi_tls.preemption_state.disable_count = 1;
577
578 // Initialize the event kernel
579 event_kernel = (event_kernel_t *)&storage_event_kernel;
580 (*event_kernel){};
581
582 // Setup proper signal handlers
583 __cfaabi_sigaction( SIGUSR1, sigHandler_ctxSwitch, SA_SIGINFO ); // __cfactx_switch handler
584 __cfaabi_sigaction( SIGALRM, sigHandler_alarm , SA_SIGINFO ); // debug handler
585
586 signal_block( SIGALRM );
587
588 alarm_stack = __create_pthread( &alarm_thread, alarm_loop, 0p );
589}
590
591// Shutdown routine to deactivate preemption
592// Called from kernel_shutdown
593void __kernel_alarm_shutdown() {
594 __cfaabi_dbg_print_safe( "Kernel : Preemption stopping\n" );
595
596 // Block all signals since we are already shutting down
597 sigset_t mask;
598 sigfillset( &mask );
599 sigprocmask( SIG_BLOCK, &mask, 0p );
600
601 // Notify the alarm thread of the shutdown
602 sigval val;
603 val.sival_int = 0;
604 pthread_sigqueue( alarm_thread, SIGALRM, val );
605
606 // Wait for the preemption thread to finish
607
608 __destroy_pthread( alarm_thread, alarm_stack, 0p );
609
610 // Preemption is now fully stopped
611
612 __cfaabi_dbg_print_safe( "Kernel : Preemption stopped\n" );
613}
614
615// Prevent preemption since we are about to start terminating things
616void __kernel_abort_lock(void) {
617 signal_block( SIGUSR1 );
618}
619
620// Raii ctor/dtor for the preemption_scope
621// Used by thread to control when they want to receive preemption signals
622void ?{}( preemption_scope & this, processor * proc ) {
623 (this.alarm){ proc, 0`s, 0`s };
624 this.proc = proc;
625 this.proc->preemption_alarm = &this.alarm;
626
627 update_preemption( this.proc, this.proc->cltr->preemption_rate );
628}
629
630void ^?{}( preemption_scope & this ) {
631 disable_interrupts();
632
633 update_preemption( this.proc, 0`s );
634}
635
636//=============================================================================================
637// Kernel Signal Handlers
638//=============================================================================================
639__cfaabi_dbg_debug_do( static thread_local void * last_interrupt = 0; )
640
641// Context switch signal handler
642// Receives SIGUSR1 signal and causes the current thread to yield
643static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ ) {
644 void * ip = (void *)(cxt->uc_mcontext.CFA_REG_IP);
645 __cfaabi_dbg_debug_do( last_interrupt = ip; )
646
647 // SKULLDUGGERY: if a thread creates a processor and the immediately deletes it,
648 // the interrupt that is supposed to force the kernel thread to preempt might arrive
649 // before the kernel thread has even started running. When that happens, an interrupt
650 // with a null 'this_processor' will be caught, just ignore it.
651 if(! __cfaabi_tls.this_processor ) return;
652
653 choose(sfp->si_value.sival_int) {
654 case PREEMPT_NORMAL : ;// Normal case, nothing to do here
655 case PREEMPT_TERMINATE: verify( __atomic_load_n( &__cfaabi_tls.this_processor->do_terminate, __ATOMIC_SEQ_CST ) );
656 default:
657 abort( "internal error, signal value is %d", sfp->si_value.sival_int );
658 }
659
660 // Check if it is safe to preempt here
661 if( !preemption_ready( ip ) ) { return; }
662
663 __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) );
664
665 // Sync flag : prevent recursive calls to the signal handler
666 __cfaabi_tls.preemption_state.in_progress = true;
667
668 // Clear sighandler mask before context switching.
669 #if GCC_VERSION > 50000
670 static_assert( sizeof( sigset_t ) == sizeof( cxt->uc_sigmask ), "Expected cxt->uc_sigmask to be of sigset_t" );
671 #endif
672 if ( pthread_sigmask( SIG_SETMASK, (sigset_t *)&(cxt->uc_sigmask), 0p ) == -1 ) {
673 abort( "internal error, sigprocmask" );
674 }
675
676 // Clear the in progress flag
677 __cfaabi_tls.preemption_state.in_progress = false;
678
679 // Preemption can occur here
680
681 force_yield( __ALARM_PREEMPTION ); // Do the actual __cfactx_switch
682}
683
684static void sigHandler_alarm( __CFA_SIGPARMS__ ) {
685 abort("SIGALRM should never reach the signal handler");
686}
687
688// Main of the alarm thread
689// Waits on SIGALRM and send SIGUSR1 to whom ever needs it
690static void * alarm_loop( __attribute__((unused)) void * args ) {
691 unsigned id = register_proc_id();
692
693 // Block sigalrms to control when they arrive
694 sigset_t mask;
695 sigfillset(&mask);
696 if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
697 abort( "internal error, pthread_sigmask" );
698 }
699
700 sigemptyset( &mask );
701 sigaddset( &mask, SIGALRM );
702
703 // Main loop
704 while( true ) {
705 // Wait for a sigalrm
706 siginfo_t info;
707 int sig = sigwaitinfo( &mask, &info );
708
709 __cfadbg_print_buffer_decl ( preemption, " KERNEL: sigwaitinfo returned %d, c: %d, v: %d\n", sig, info.si_code, info.si_value.sival_int );
710 __cfadbg_print_buffer_local( preemption, " KERNEL: SI_QUEUE %d, SI_TIMER %d, SI_KERNEL %d\n", SI_QUEUE, SI_TIMER, SI_KERNEL );
711
712 if( sig < 0 ) {
713 //Error!
714 int err = errno;
715 switch( err ) {
716 case EAGAIN :
717 case EINTR :
718 {__cfadbg_print_buffer_local( preemption, " KERNEL: Spurious wakeup %d.\n", err );}
719 continue;
720 case EINVAL :
721 abort( "Timeout was invalid." );
722 default:
723 abort( "Unhandled error %d", err);
724 }
725 }
726
727 // If another signal arrived something went wrong
728 assertf(sig == SIGALRM, "Kernel Internal Error, sigwait: Unexpected signal %d (%d : %d)\n", sig, info.si_code, info.si_value.sival_int);
729
730 // Switch on the code (a.k.a. the sender) to
731 switch( info.si_code )
732 {
733 // Signal was not sent by the kernel but by an other thread
734 case SI_QUEUE:
735 // other threads may signal the alarm thread to shut it down
736 // or to manual cause the preemption tick
737 // use info.si_value and handle the case here
738 switch( info.si_value.sival_int ) {
739 case 0:
740 goto EXIT;
741 default:
742 abort( "SI_QUEUE with val %d", info.si_value.sival_int);
743 }
744 // fallthrough
745 // Timers can apparently be marked as sent for the kernel
746 // In either case, tick preemption
747 case SI_TIMER:
748 case SI_KERNEL:
749 // __cfaabi_dbg_print_safe( "Kernel : Preemption thread tick\n" );
750 lock( event_kernel->lock __cfaabi_dbg_ctx2 );
751 tick_preemption();
752 unlock( event_kernel->lock );
753 break;
754 }
755 }
756
757EXIT:
758 __cfaabi_dbg_print_safe( "Kernel : Preemption thread stopping\n" );
759 unregister_proc_id(id);
760
761 return 0p;
762}
763
764// Local Variables: //
765// mode: c //
766// tab-width: 4 //
767// End: //
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