source: libcfa/src/concurrency/preemption.cfa@ 7ef162b2

ADT ast-experimental enum forall-pointer-decay pthread-emulation qualifiedEnum
Last change on this file since 7ef162b2 was e84ab3d, checked in by Thierry Delisle <tdelisle@…>, 4 years ago

Step 1 of changing $thread to thread$
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File size: 25.8 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 : Fri Nov 6 07:42:13 2020
13// Update Count : 54
14//
15
16#define __cforall_thread__
17#define _GNU_SOURCE
18
19// #define __CFA_DEBUG_PRINT_PREEMPTION__
20
21#include "preemption.hfa"
22
23#include <assert.h>
24
25#include <errno.h>
26#include <stdio.h>
27#include <string.h>
28#include <unistd.h>
29#include <limits.h> // PTHREAD_STACK_MIN
30
31#include "bits/debug.hfa"
32#include "bits/signal.hfa"
33#include "kernel_private.hfa"
34
35
36#if !defined(__CFA_DEFAULT_PREEMPTION__)
37#define __CFA_DEFAULT_PREEMPTION__ 10`ms
38#endif
39
40__attribute__((weak)) Duration default_preemption() {
41 const char * preempt_rate_s = getenv("CFA_DEFAULT_PREEMPTION");
42 if(!preempt_rate_s) {
43 __cfadbg_print_safe(preemption, "No CFA_DEFAULT_PREEMPTION in ENV\n");
44 return __CFA_DEFAULT_PREEMPTION__;
45 }
46
47 char * endptr = 0p;
48 long int preempt_rate_l = strtol(preempt_rate_s, &endptr, 10);
49 if(preempt_rate_l < 0 || preempt_rate_l > 65535) {
50 __cfadbg_print_safe(preemption, "CFA_DEFAULT_PREEMPTION out of range : %ld\n", preempt_rate_l);
51 return __CFA_DEFAULT_PREEMPTION__;
52 }
53 if('\0' != *endptr) {
54 __cfadbg_print_safe(preemption, "CFA_DEFAULT_PREEMPTION not a decimal number : %s\n", preempt_rate_s);
55 return __CFA_DEFAULT_PREEMPTION__;
56 }
57
58 return preempt_rate_l`ms;
59}
60
61// FwdDeclarations : timeout handlers
62static void preempt( processor * this );
63static void timeout( thread$ * this );
64
65// FwdDeclarations : Signal handlers
66static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ );
67static void sigHandler_alarm ( __CFA_SIGPARMS__ );
68static void sigHandler_segv ( __CFA_SIGPARMS__ );
69static void sigHandler_ill ( __CFA_SIGPARMS__ );
70static void sigHandler_fpe ( __CFA_SIGPARMS__ );
71static void sigHandler_abort ( __CFA_SIGPARMS__ );
72
73// FwdDeclarations : alarm thread main
74static void * alarm_loop( __attribute__((unused)) void * args );
75
76// Machine specific register name
77#if defined( __i386 )
78#define CFA_REG_IP gregs[REG_EIP]
79#elif defined( __x86_64 )
80#define CFA_REG_IP gregs[REG_RIP]
81#elif defined( __arm__ )
82#define CFA_REG_IP arm_pc
83#elif defined( __aarch64__ )
84#define CFA_REG_IP pc
85#else
86#error unsupported hardware architecture
87#endif
88
89KERNEL_STORAGE(event_kernel_t, event_kernel); // private storage for event kernel
90event_kernel_t * event_kernel; // kernel public handle to even kernel
91static pthread_t alarm_thread; // pthread handle to alarm thread
92static void * alarm_stack; // pthread stack for alarm thread
93
94static void ?{}(event_kernel_t & this) with( this ) {
95 alarms{};
96 lock{};
97}
98
99enum {
100 PREEMPT_NORMAL = 0,
101 PREEMPT_TERMINATE = 1,
102};
103
104//=============================================================================================
105// Kernel Preemption logic
106//=============================================================================================
107
108// Get next expired node
109static inline alarm_node_t * get_expired( alarm_list_t * alarms, Time currtime ) {
110 if( ! & (*alarms)`first ) return 0p; // If no alarms return null
111 if( (*alarms)`first.timeval >= currtime ) return 0p; // If alarms head not expired return null
112 return pop(alarms); // Otherwise just pop head
113}
114
115// Tick one frame of the Discrete Event Simulation for alarms
116static void tick_preemption(void) {
117 alarm_node_t * node = 0p; // Used in the while loop but cannot be declared in the while condition
118 alarm_list_t * alarms = &event_kernel->alarms; // Local copy for ease of reading
119 Time currtime = __kernel_get_time(); // Check current time once so everything "happens at once"
120
121 //Loop throught every thing expired
122 while( node = get_expired( alarms, currtime ) ) {
123 __cfadbg_print_buffer_decl( preemption, " KERNEL: preemption tick %lu\n", currtime.tn);
124 Duration period = node->period;
125 if( period == 0) {
126 node->set = false; // Node is one-shot, just mark it as not pending
127 }
128
129 __cfadbg_print_buffer_local( preemption, " KERNEL: alarm ticking node %p.\n", node );
130
131
132 // Check if this is a kernel
133 if( node->type == Kernel ) {
134 preempt( node->proc );
135 }
136 else if( node->type == User ) {
137 __cfadbg_print_buffer_local( preemption, " KERNEL: alarm unparking %p.\n", node->thrd );
138 timeout( node->thrd );
139 }
140 else {
141 node->callback(*node);
142 }
143
144 // Check if this is a periodic alarm
145 if( period > 0 ) {
146 __cfadbg_print_buffer_local( preemption, " KERNEL: alarm period is %lu.\n", period`ns );
147 node->timeval = currtime + period; // Alarm is periodic, add currtime to it (used cached current time)
148 insert( alarms, node ); // Reinsert the node for the next time it triggers
149 }
150 }
151
152 // If there are still alarms pending, reset the timer
153 if( & (*alarms)`first ) {
154 Duration delta = (*alarms)`first.timeval - currtime;
155 __kernel_set_timer( delta );
156 }
157}
158
159// Update the preemption of a processor and notify interested parties
160void update_preemption( processor * this, Duration duration ) {
161 alarm_node_t * alarm = this->preemption_alarm;
162
163 // Alarms need to be enabled
164 if ( duration > 0 && ! alarm->set ) {
165 alarm->initial = duration;
166 alarm->period = duration;
167 register_self( alarm );
168 }
169 // Zero duration but alarm is set
170 else if ( duration == 0 && alarm->set ) {
171 unregister_self( alarm );
172 alarm->initial = 0;
173 alarm->period = 0;
174 }
175 // If alarm is different from previous, change it
176 else if ( duration > 0 && alarm->period != duration ) {
177 unregister_self( alarm );
178 alarm->initial = duration;
179 alarm->period = duration;
180 register_self( alarm );
181 }
182}
183
184//=============================================================================================
185// Kernel Signal Tools
186//=============================================================================================
187// In a user-level threading system, there are handful of thread-local variables where this problem occurs on the ARM.
188//
189// For each kernel thread running user-level threads, there is a flag variable to indicate if interrupts are
190// enabled/disabled for that kernel thread. Therefore, this variable is made thread local.
191//
192// For example, this code fragment sets the state of the "interrupt" variable in thread-local memory.
193//
194// _Thread_local volatile int interrupts;
195// int main() {
196// interrupts = 0; // disable interrupts }
197//
198// which generates the following code on the ARM
199//
200// (gdb) disassemble main
201// Dump of assembler code for function main:
202// 0x0000000000000610 <+0>: mrs x1, tpidr_el0
203// 0x0000000000000614 <+4>: mov w0, #0x0 // #0
204// 0x0000000000000618 <+8>: add x1, x1, #0x0, lsl #12
205// 0x000000000000061c <+12>: add x1, x1, #0x10
206// 0x0000000000000620 <+16>: str wzr, [x1]
207// 0x0000000000000624 <+20>: ret
208//
209// The mrs moves a pointer from coprocessor register tpidr_el0 into register x1. Register w0 is set to 0. The two adds
210// increase the TLS pointer with the displacement (offset) 0x10, which is the location in the TSL of variable
211// "interrupts". Finally, 0 is stored into "interrupts" through the pointer in register x1 that points into the
212// TSL. Now once x1 has the pointer to the location of the TSL for kernel thread N, it can be be preempted at a
213// user-level and the user thread is put on the user-level ready-queue. When the preempted thread gets to the front of
214// the user-level ready-queue it is run on kernel thread M. It now stores 0 into "interrupts" back on kernel thread N,
215// turning off interrupt on the wrong kernel thread.
216//
217// On the x86, the following code is generated for the same code fragment.
218//
219// (gdb) disassemble main
220// Dump of assembler code for function main:
221// 0x0000000000400420 <+0>: movl $0x0,%fs:0xfffffffffffffffc
222// 0x000000000040042c <+12>: xor %eax,%eax
223// 0x000000000040042e <+14>: retq
224//
225// and there is base-displacement addressing used to atomically reset variable "interrupts" off of the TSL pointer in
226// register "fs".
227//
228// Hence, the ARM has base-displacement address for the general purpose registers, BUT not to the coprocessor
229// registers. As a result, generating the address for the write into variable "interrupts" is no longer atomic.
230//
231// Note this problem does NOT occur when just using multiple kernel threads because the preemption ALWAYS restarts the
232// thread on the same kernel thread.
233//
234// The obvious question is why does ARM use a coprocessor register to store the TSL pointer given that coprocessor
235// registers are second-class registers with respect to the instruction set. One possible answer is that they did not
236// want to dedicate one of the general registers to hold the TLS pointer and there was a free coprocessor register
237// available.
238
239//-----------------------------------------------------------------------------
240// Some assembly required
241#define __cfaasm_label(label, when) when: asm volatile goto(".global __cfaasm_" #label "_" #when "\n" "__cfaasm_" #label "_" #when ":":::"memory":when)
242
243//----------
244// special case for preemption since used often
245bool __preemption_enabled() {
246 // create a assembler label before
247 // marked as clobber all to avoid movement
248 __cfaasm_label(check, before);
249
250 // access tls as normal
251 bool enabled = __cfaabi_tls.preemption_state.enabled;
252
253 // create a assembler label after
254 // marked as clobber all to avoid movement
255 __cfaasm_label(check, after);
256 return enabled;
257}
258
259struct asm_region {
260 void * before;
261 void * after;
262};
263
264static inline bool __cfaasm_in( void * ip, struct asm_region & region ) {
265 return ip >= region.before && ip <= region.after;
266}
267
268
269//----------
270// Get data from the TLS block
271// struct asm_region __cfaasm_get;
272uintptr_t __cfatls_get( unsigned long int offset ) __attribute__((__noinline__)); //no inline to avoid problems
273uintptr_t __cfatls_get( unsigned long int offset ) {
274 // create a assembler label before
275 // marked as clobber all to avoid movement
276 __cfaasm_label(get, before);
277
278 // access tls as normal (except for pointer arithmetic)
279 uintptr_t val = *(uintptr_t*)((uintptr_t)&__cfaabi_tls + offset);
280
281 // create a assembler label after
282 // marked as clobber all to avoid movement
283 __cfaasm_label(get, after);
284 return val;
285}
286
287extern "C" {
288 // Disable interrupts by incrementing the counter
289 void disable_interrupts() {
290 // create a assembler label before
291 // marked as clobber all to avoid movement
292 __cfaasm_label(dsable, before);
293
294 with( __cfaabi_tls.preemption_state ) {
295 #if GCC_VERSION > 50000
296 static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
297 #endif
298
299 // Set enabled flag to false
300 // should be atomic to avoid preemption in the middle of the operation.
301 // use memory order RELAXED since there is no inter-thread on this variable requirements
302 __atomic_store_n(&enabled, false, __ATOMIC_RELAXED);
303
304 // Signal the compiler that a fence is needed but only for signal handlers
305 __atomic_signal_fence(__ATOMIC_ACQUIRE);
306
307 __attribute__((unused)) unsigned short new_val = disable_count + 1;
308 disable_count = new_val;
309 verify( new_val < 65_000u ); // If this triggers someone is disabling interrupts without enabling them
310 }
311
312 // create a assembler label after
313 // marked as clobber all to avoid movement
314 __cfaasm_label(dsable, after);
315
316 }
317
318 // Enable interrupts by decrementing the counter
319 // If counter reaches 0, execute any pending __cfactx_switch
320 void enable_interrupts( bool poll ) {
321 // Cache the processor now since interrupts can start happening after the atomic store
322 processor * proc = __cfaabi_tls.this_processor;
323 /* paranoid */ verify( !poll || proc );
324
325 with( __cfaabi_tls.preemption_state ){
326 unsigned short prev = disable_count;
327 disable_count -= 1;
328
329 // If this triggers someone is enabled already enabled interruptsverify( prev != 0u );
330 /* paranoid */ verify( prev != 0u );
331
332 // Check if we need to prempt the thread because an interrupt was missed
333 if( prev == 1 ) {
334 #if GCC_VERSION > 50000
335 static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
336 #endif
337
338 // Set enabled flag to true
339 // should be atomic to avoid preemption in the middle of the operation.
340 // use memory order RELAXED since there is no inter-thread on this variable requirements
341 __atomic_store_n(&enabled, true, __ATOMIC_RELAXED);
342
343 // Signal the compiler that a fence is needed but only for signal handlers
344 __atomic_signal_fence(__ATOMIC_RELEASE);
345 if( poll && proc->pending_preemption ) {
346 proc->pending_preemption = false;
347 force_yield( __POLL_PREEMPTION );
348 }
349 }
350 }
351 }
352}
353
354//-----------------------------------------------------------------------------
355// Kernel Signal Debug
356void __cfaabi_check_preemption() {
357 bool ready = __preemption_enabled();
358 if(!ready) { abort("Preemption should be ready"); }
359
360 __cfaasm_label(debug, before);
361
362 sigset_t oldset;
363 int ret;
364 ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset); // workaround trac#208: cast should be unnecessary
365 if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
366
367 ret = sigismember(&oldset, SIGUSR1);
368 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
369 if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
370
371 ret = sigismember(&oldset, SIGALRM);
372 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
373 if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
374
375 ret = sigismember(&oldset, SIGTERM);
376 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
377 if(ret == 1) { abort("ERROR SIGTERM is disabled"); }
378
379 __cfaasm_label(debug, after);
380}
381
382#ifdef __CFA_WITH_VERIFY__
383bool __cfaabi_dbg_in_kernel() {
384 return !__preemption_enabled();
385}
386#endif
387
388#undef __cfaasm_label
389
390//-----------------------------------------------------------------------------
391// Signal handling
392
393// sigprocmask wrapper : unblock a single signal
394static inline void signal_unblock( int sig ) {
395 sigset_t mask;
396 sigemptyset( &mask );
397 sigaddset( &mask, sig );
398
399 if ( pthread_sigmask( SIG_UNBLOCK, &mask, 0p ) == -1 ) {
400 abort( "internal error, pthread_sigmask" );
401 }
402}
403
404// sigprocmask wrapper : block a single signal
405static inline void signal_block( int sig ) {
406 sigset_t mask;
407 sigemptyset( &mask );
408 sigaddset( &mask, sig );
409
410 if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
411 abort( "internal error, pthread_sigmask" );
412 }
413}
414
415// kill wrapper : signal a processor
416static void preempt( processor * this ) {
417 sigval_t value = { PREEMPT_NORMAL };
418 pthread_sigqueue( this->kernel_thread, SIGUSR1, value );
419}
420
421// reserved for future use
422static void timeout( thread$ * this ) {
423 unpark( this );
424}
425
426void __disable_interrupts_hard() {
427 sigset_t oldset;
428 int ret;
429 ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset); // workaround trac#208: cast should be unnecessary
430 if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
431
432 ret = sigismember(&oldset, SIGUSR1);
433 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
434 if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
435
436 ret = sigismember(&oldset, SIGALRM);
437 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
438 if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
439
440 signal_block( SIGUSR1 );
441}
442
443void __enable_interrupts_hard() {
444 signal_unblock( SIGUSR1 );
445
446 sigset_t oldset;
447 int ret;
448 ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset); // workaround trac#208: cast should be unnecessary
449 if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
450
451 ret = sigismember(&oldset, SIGUSR1);
452 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
453 if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
454
455 ret = sigismember(&oldset, SIGALRM);
456 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
457 if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
458}
459
460//-----------------------------------------------------------------------------
461// Some assembly required
462#if defined( __i386 )
463 #ifdef __PIC__
464 #define RELOC_PRELUDE( label ) \
465 "calll .Lcfaasm_prelude_" #label "$pb\n\t" \
466 ".Lcfaasm_prelude_" #label "$pb:\n\t" \
467 "popl %%eax\n\t" \
468 ".Lcfaasm_prelude_" #label "_end:\n\t" \
469 "addl $_GLOBAL_OFFSET_TABLE_+(.Lcfaasm_prelude_" #label "_end-.Lcfaasm_prelude_" #label "$pb), %%eax\n\t"
470 #define RELOC_PREFIX ""
471 #define RELOC_SUFFIX "@GOT(%%eax)"
472 #else
473 #define RELOC_PREFIX "$"
474 #define RELOC_SUFFIX ""
475 #endif
476 #define __cfaasm_label( label ) struct asm_region label = \
477 ({ \
478 struct asm_region region; \
479 asm( \
480 RELOC_PRELUDE( label ) \
481 "movl " RELOC_PREFIX "__cfaasm_" #label "_before" RELOC_SUFFIX ", %[vb]\n\t" \
482 "movl " RELOC_PREFIX "__cfaasm_" #label "_after" RELOC_SUFFIX ", %[va]\n\t" \
483 : [vb]"=r"(region.before), [va]"=r"(region.after) \
484 ); \
485 region; \
486 });
487#elif defined( __x86_64 )
488 #ifdef __PIC__
489 #define RELOC_PREFIX ""
490 #define RELOC_SUFFIX "@GOTPCREL(%%rip)"
491 #else
492 #define RELOC_PREFIX "$"
493 #define RELOC_SUFFIX ""
494 #endif
495 #define __cfaasm_label( label ) struct asm_region label = \
496 ({ \
497 struct asm_region region; \
498 asm( \
499 "movq " RELOC_PREFIX "__cfaasm_" #label "_before" RELOC_SUFFIX ", %[vb]\n\t" \
500 "movq " RELOC_PREFIX "__cfaasm_" #label "_after" RELOC_SUFFIX ", %[va]\n\t" \
501 : [vb]"=r"(region.before), [va]"=r"(region.after) \
502 ); \
503 region; \
504 });
505#elif defined( __aarch64__ )
506 #ifdef __PIC__
507 // Note that this works only for gcc
508 #define __cfaasm_label( label ) struct asm_region label = \
509 ({ \
510 struct asm_region region; \
511 asm( \
512 "adrp %[vb], _GLOBAL_OFFSET_TABLE_" "\n\t" \
513 "ldr %[vb], [%[vb], #:gotpage_lo15:__cfaasm_" #label "_before]" "\n\t" \
514 "adrp %[va], _GLOBAL_OFFSET_TABLE_" "\n\t" \
515 "ldr %[va], [%[va], #:gotpage_lo15:__cfaasm_" #label "_after]" "\n\t" \
516 : [vb]"=r"(region.before), [va]"=r"(region.after) \
517 ); \
518 region; \
519 });
520 #else
521 #error this is not the right thing to do
522 /*
523 #define __cfaasm_label( label ) struct asm_region label = \
524 ({ \
525 struct asm_region region; \
526 asm( \
527 "adrp %[vb], __cfaasm_" #label "_before" "\n\t" \
528 "add %[vb], %[vb], :lo12:__cfaasm_" #label "_before" "\n\t" \
529 "adrp %[va], :got:__cfaasm_" #label "_after" "\n\t" \
530 "add %[va], %[va], :lo12:__cfaasm_" #label "_after" "\n\t" \
531 : [vb]"=r"(region.before), [va]"=r"(region.after) \
532 ); \
533 region; \
534 });
535 */
536 #endif
537#else
538 #error unknown hardware architecture
539#endif
540
541// KERNEL ONLY
542// Check if a __cfactx_switch signal handler shoud defer
543// If true : preemption is safe
544// If false : preemption is unsafe and marked as pending
545static inline bool preemption_ready( void * ip ) {
546 // Get all the region for which it is not safe to preempt
547 __cfaasm_label( get );
548 __cfaasm_label( check );
549 __cfaasm_label( dsable );
550 __cfaasm_label( debug );
551
552 // Check if preemption is safe
553 bool ready = true;
554 if( __cfaasm_in( ip, get ) ) { ready = false; goto EXIT; };
555 if( __cfaasm_in( ip, check ) ) { ready = false; goto EXIT; };
556 if( __cfaasm_in( ip, dsable ) ) { ready = false; goto EXIT; };
557 if( __cfaasm_in( ip, debug ) ) { ready = false; goto EXIT; };
558 if( !__cfaabi_tls.preemption_state.enabled) { ready = false; goto EXIT; };
559 if( __cfaabi_tls.preemption_state.in_progress ) { ready = false; goto EXIT; };
560
561EXIT:
562 // Adjust the pending flag accordingly
563 __cfaabi_tls.this_processor->pending_preemption = !ready;
564 return ready;
565}
566
567//=============================================================================================
568// Kernel Signal Startup/Shutdown logic
569//=============================================================================================
570
571// Startup routine to activate preemption
572// Called from kernel_startup
573void __kernel_alarm_startup() {
574 __cfaabi_dbg_print_safe( "Kernel : Starting preemption\n" );
575
576 // Start with preemption disabled until ready
577 __cfaabi_tls.preemption_state.enabled = false;
578 __cfaabi_tls.preemption_state.disable_count = 1;
579
580 // Initialize the event kernel
581 event_kernel = (event_kernel_t *)&storage_event_kernel;
582 (*event_kernel){};
583
584 // Setup proper signal handlers
585 __cfaabi_sigaction( SIGUSR1, sigHandler_ctxSwitch, SA_SIGINFO ); // __cfactx_switch handler
586 __cfaabi_sigaction( SIGALRM, sigHandler_alarm , SA_SIGINFO ); // debug handler
587
588 signal_block( SIGALRM );
589
590 alarm_stack = __create_pthread( &alarm_thread, alarm_loop, 0p );
591}
592
593// Shutdown routine to deactivate preemption
594// Called from kernel_shutdown
595void __kernel_alarm_shutdown() {
596 __cfaabi_dbg_print_safe( "Kernel : Preemption stopping\n" );
597
598 // Block all signals since we are already shutting down
599 sigset_t mask;
600 sigfillset( &mask );
601 sigprocmask( SIG_BLOCK, &mask, 0p );
602
603 // Notify the alarm thread of the shutdown
604 sigval val;
605 val.sival_int = 0;
606 pthread_sigqueue( alarm_thread, SIGALRM, val );
607
608 // Wait for the preemption thread to finish
609
610 __destroy_pthread( alarm_thread, alarm_stack, 0p );
611
612 // Preemption is now fully stopped
613
614 __cfaabi_dbg_print_safe( "Kernel : Preemption stopped\n" );
615}
616
617// Prevent preemption since we are about to start terminating things
618void __kernel_abort_lock(void) {
619 signal_block( SIGUSR1 );
620}
621
622// Raii ctor/dtor for the preemption_scope
623// Used by thread to control when they want to receive preemption signals
624void ?{}( preemption_scope & this, processor * proc ) {
625 (this.alarm){ proc, 0`s, 0`s };
626 this.proc = proc;
627 this.proc->preemption_alarm = &this.alarm;
628
629 update_preemption( this.proc, this.proc->cltr->preemption_rate );
630}
631
632void ^?{}( preemption_scope & this ) {
633 disable_interrupts();
634
635 update_preemption( this.proc, 0`s );
636}
637
638//=============================================================================================
639// Kernel Signal Handlers
640//=============================================================================================
641__cfaabi_dbg_debug_do( static thread_local void * last_interrupt = 0; )
642
643// Context switch signal handler
644// Receives SIGUSR1 signal and causes the current thread to yield
645static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ ) {
646 void * ip = (void *)(cxt->uc_mcontext.CFA_REG_IP);
647 __cfaabi_dbg_debug_do( last_interrupt = ip; )
648
649 // SKULLDUGGERY: if a thread creates a processor and the immediately deletes it,
650 // the interrupt that is supposed to force the kernel thread to preempt might arrive
651 // before the kernel thread has even started running. When that happens, an interrupt
652 // with a null 'this_processor' will be caught, just ignore it.
653 if(! __cfaabi_tls.this_processor ) return;
654
655 choose(sfp->si_value.sival_int) {
656 case PREEMPT_NORMAL : ;// Normal case, nothing to do here
657 case PREEMPT_TERMINATE: verify( __atomic_load_n( &__cfaabi_tls.this_processor->do_terminate, __ATOMIC_SEQ_CST ) );
658 default:
659 abort( "internal error, signal value is %d", sfp->si_value.sival_int );
660 }
661
662 // Check if it is safe to preempt here
663 if( !preemption_ready( ip ) ) { return; }
664
665 __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) );
666
667 // Sync flag : prevent recursive calls to the signal handler
668 __cfaabi_tls.preemption_state.in_progress = true;
669
670 // Clear sighandler mask before context switching.
671 #if GCC_VERSION > 50000
672 static_assert( sizeof( sigset_t ) == sizeof( cxt->uc_sigmask ), "Expected cxt->uc_sigmask to be of sigset_t" );
673 #endif
674 if ( pthread_sigmask( SIG_SETMASK, (sigset_t *)&(cxt->uc_sigmask), 0p ) == -1 ) {
675 abort( "internal error, sigprocmask" );
676 }
677
678 // Clear the in progress flag
679 __cfaabi_tls.preemption_state.in_progress = false;
680
681 // Preemption can occur here
682
683 force_yield( __ALARM_PREEMPTION ); // Do the actual __cfactx_switch
684}
685
686static void sigHandler_alarm( __CFA_SIGPARMS__ ) {
687 abort("SIGALRM should never reach the signal handler");
688}
689
690// Main of the alarm thread
691// Waits on SIGALRM and send SIGUSR1 to whom ever needs it
692static void * alarm_loop( __attribute__((unused)) void * args ) {
693 unsigned id = register_proc_id();
694
695 // Block sigalrms to control when they arrive
696 sigset_t mask;
697 sigfillset(&mask);
698 if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
699 abort( "internal error, pthread_sigmask" );
700 }
701
702 sigemptyset( &mask );
703 sigaddset( &mask, SIGALRM );
704
705 // Main loop
706 while( true ) {
707 // Wait for a sigalrm
708 siginfo_t info;
709 int sig = sigwaitinfo( &mask, &info );
710
711 __cfadbg_print_buffer_decl ( preemption, " KERNEL: sigwaitinfo returned %d, c: %d, v: %d\n", sig, info.si_code, info.si_value.sival_int );
712 __cfadbg_print_buffer_local( preemption, " KERNEL: SI_QUEUE %d, SI_TIMER %d, SI_KERNEL %d\n", SI_QUEUE, SI_TIMER, SI_KERNEL );
713
714 if( sig < 0 ) {
715 //Error!
716 int err = errno;
717 switch( err ) {
718 case EAGAIN :
719 case EINTR :
720 {__cfadbg_print_buffer_local( preemption, " KERNEL: Spurious wakeup %d.\n", err );}
721 continue;
722 case EINVAL :
723 abort( "Timeout was invalid." );
724 default:
725 abort( "Unhandled error %d", err);
726 }
727 }
728
729 // If another signal arrived something went wrong
730 assertf(sig == SIGALRM, "Kernel Internal Error, sigwait: Unexpected signal %d (%d : %d)\n", sig, info.si_code, info.si_value.sival_int);
731
732 // Switch on the code (a.k.a. the sender) to
733 switch( info.si_code )
734 {
735 // Signal was not sent by the kernel but by an other thread
736 case SI_QUEUE:
737 // other threads may signal the alarm thread to shut it down
738 // or to manual cause the preemption tick
739 // use info.si_value and handle the case here
740 switch( info.si_value.sival_int ) {
741 case 0:
742 goto EXIT;
743 default:
744 abort( "SI_QUEUE with val %d", info.si_value.sival_int);
745 }
746 // fallthrough
747 // Timers can apparently be marked as sent for the kernel
748 // In either case, tick preemption
749 case SI_TIMER:
750 case SI_KERNEL:
751 // __cfaabi_dbg_print_safe( "Kernel : Preemption thread tick\n" );
752 lock( event_kernel->lock __cfaabi_dbg_ctx2 );
753 tick_preemption();
754 unlock( event_kernel->lock );
755 break;
756 }
757 }
758
759EXIT:
760 __cfaabi_dbg_print_safe( "Kernel : Preemption thread stopping\n" );
761 unregister_proc_id(id);
762
763 return 0p;
764}
765
766// Local Variables: //
767// mode: c //
768// tab-width: 4 //
769// End: //
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