source: libcfa/src/concurrency/preemption.cfa@ 67a1c67

ADT ast-experimental pthread-emulation
Last change on this file since 67a1c67 was 1bcbf02, checked in by Thierry Delisle <tdelisle@…>, 3 years ago

Changed declarations using _Thread_local to use thread.
I'm fairly sure they do exactly the same, but thread is:

  • more consistent with uC++.
  • Shorter.
  • Better documented.
  • Property mode set to 100644
File size: 27.4 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 Feb 17 11:18:57 2022
13// Update Count : 59
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() libcfa_public {
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
99//=============================================================================================
100// Kernel Preemption logic
101//=============================================================================================
102
103// Get next expired node
104static inline alarm_node_t * get_expired( alarm_list_t * alarms, Time currtime ) {
105 if( ! & (*alarms)`first ) return 0p; // If no alarms return null
106 if( (*alarms)`first.timeval >= currtime ) return 0p; // If alarms head not expired return null
107 return pop(alarms); // Otherwise just pop head
108}
109
110// Tick one frame of the Discrete Event Simulation for alarms
111static void tick_preemption(void) {
112 alarm_node_t * node = 0p; // Used in the while loop but cannot be declared in the while condition
113 alarm_list_t * alarms = &event_kernel->alarms; // Local copy for ease of reading
114 Time currtime = __kernel_get_time(); // Check current time once so everything "happens at once"
115
116 //Loop throught every thing expired
117 while( node = get_expired( alarms, currtime ) ) {
118 __cfadbg_print_buffer_decl( preemption, " KERNEL: preemption tick %lu\n", currtime.tn);
119 Duration period = node->period;
120 if( period == 0) {
121 node->set = false; // Node is one-shot, just mark it as not pending
122 }
123
124 __cfadbg_print_buffer_local( preemption, " KERNEL: alarm ticking node %p.\n", node );
125
126
127 // Check if this is a kernel
128 if( node->type == Kernel ) {
129 preempt( node->proc );
130 }
131 else if( node->type == User ) {
132 __cfadbg_print_buffer_local( preemption, " KERNEL: alarm unparking %p.\n", node->thrd );
133 timeout( node->thrd );
134 }
135 else {
136 node->callback(*node);
137 }
138
139 // Check if this is a periodic alarm
140 if( period > 0 ) {
141 __cfadbg_print_buffer_local( preemption, " KERNEL: alarm period is %lu.\n", period`ns );
142 node->timeval = currtime + period; // Alarm is periodic, add currtime to it (used cached current time)
143 insert( alarms, node ); // Reinsert the node for the next time it triggers
144 }
145 }
146
147 // If there are still alarms pending, reset the timer
148 if( & (*alarms)`first ) {
149 Duration delta = (*alarms)`first.timeval - currtime;
150 __kernel_set_timer( delta );
151 }
152}
153
154// Update the preemption of a processor and notify interested parties
155void update_preemption( processor * this, Duration duration ) {
156 alarm_node_t * alarm = this->preemption_alarm;
157
158 // Alarms need to be enabled
159 if ( duration > 0 && ! alarm->set ) {
160 alarm->initial = duration;
161 alarm->period = duration;
162 register_self( alarm );
163 }
164 // Zero duration but alarm is set
165 else if ( duration == 0 && alarm->set ) {
166 unregister_self( alarm );
167 alarm->initial = 0;
168 alarm->period = 0;
169 }
170 // If alarm is different from previous, change it
171 else if ( duration > 0 && alarm->period != duration ) {
172 unregister_self( alarm );
173 alarm->initial = duration;
174 alarm->period = duration;
175 register_self( alarm );
176 }
177}
178
179//=============================================================================================
180// Kernel Signal Tools
181//=============================================================================================
182// In a user-level threading system, there are handful of thread-local variables where this problem occurs on the ARM.
183//
184// For each kernel thread running user-level threads, there is a flag variable to indicate if interrupts are
185// enabled/disabled for that kernel thread. Therefore, this variable is made thread local.
186//
187// For example, this code fragment sets the state of the "interrupt" variable in thread-local memory.
188//
189// _Thread_local volatile int interrupts;
190// int main() {
191// interrupts = 0; // disable interrupts }
192//
193// which generates the following code on the ARM
194//
195// (gdb) disassemble main
196// Dump of assembler code for function main:
197// 0x0000000000000610 <+0>: mrs x1, tpidr_el0
198// 0x0000000000000614 <+4>: mov w0, #0x0 // #0
199// 0x0000000000000618 <+8>: add x1, x1, #0x0, lsl #12
200// 0x000000000000061c <+12>: add x1, x1, #0x10
201// 0x0000000000000620 <+16>: str wzr, [x1]
202// 0x0000000000000624 <+20>: ret
203//
204// The mrs moves a pointer from coprocessor register tpidr_el0 into register x1. Register w0 is set to 0. The two adds
205// increase the TLS pointer with the displacement (offset) 0x10, which is the location in the TSL of variable
206// "interrupts". Finally, 0 is stored into "interrupts" through the pointer in register x1 that points into the
207// TSL. Now once x1 has the pointer to the location of the TSL for kernel thread N, it can be be preempted at a
208// user-level and the user thread is put on the user-level ready-queue. When the preempted thread gets to the front of
209// the user-level ready-queue it is run on kernel thread M. It now stores 0 into "interrupts" back on kernel thread N,
210// turning off interrupt on the wrong kernel thread.
211//
212// On the x86, the following code is generated for the same code fragment.
213//
214// (gdb) disassemble main
215// Dump of assembler code for function main:
216// 0x0000000000400420 <+0>: movl $0x0,%fs:0xfffffffffffffffc
217// 0x000000000040042c <+12>: xor %eax,%eax
218// 0x000000000040042e <+14>: retq
219//
220// and there is base-displacement addressing used to atomically reset variable "interrupts" off of the TSL pointer in
221// register "fs".
222//
223// Hence, the ARM has base-displacement address for the general purpose registers, BUT not to the coprocessor
224// registers. As a result, generating the address for the write into variable "interrupts" is no longer atomic.
225//
226// Note this problem does NOT occur when just using multiple kernel threads because the preemption ALWAYS restarts the
227// thread on the same kernel thread.
228//
229// The obvious question is why does ARM use a coprocessor register to store the TSL pointer given that coprocessor
230// registers are second-class registers with respect to the instruction set. One possible answer is that they did not
231// want to dedicate one of the general registers to hold the TLS pointer and there was a free coprocessor register
232// available.
233
234//-----------------------------------------------------------------------------
235// Some assembly required
236#define __cfaasm_label(label, when) when: asm volatile goto(".global __cfaasm_" #label "_" #when "\n" "__cfaasm_" #label "_" #when ":":::"memory":when)
237
238//----------
239// special case for preemption since used often
240__attribute__((optimize("no-reorder-blocks"))) bool __preemption_enabled() libcfa_public {
241 // create a assembler label before
242 // marked as clobber all to avoid movement
243 __cfaasm_label(check, before);
244
245 // access tls as normal
246 bool enabled = __cfaabi_tls.preemption_state.enabled;
247
248 // Check if there is a pending preemption
249 processor * proc = __cfaabi_tls.this_processor;
250 bool pending = proc ? proc->pending_preemption : false;
251 if( enabled && pending ) proc->pending_preemption = false;
252
253 // create a assembler label after
254 // marked as clobber all to avoid movement
255 __cfaasm_label(check, after);
256
257 // If we can preempt and there is a pending one
258 // this is a good time to yield
259 if( enabled && pending ) {
260 force_yield( __POLL_PREEMPTION );
261 }
262 return enabled;
263}
264
265struct asm_region {
266 void * before;
267 void * after;
268};
269
270static inline bool __cfaasm_in( void * ip, struct asm_region & region ) {
271 return ip >= region.before && ip <= region.after;
272}
273
274
275//----------
276// Get data from the TLS block
277// struct asm_region __cfaasm_get;
278uintptr_t __cfatls_get( unsigned long int offset ) __attribute__((__noinline__, visibility("default"))); //no inline to avoid problems
279uintptr_t __cfatls_get( unsigned long int offset ) {
280 // create a assembler label before
281 // marked as clobber all to avoid movement
282 __cfaasm_label(get, before);
283
284 // access tls as normal (except for pointer arithmetic)
285 uintptr_t val = *(uintptr_t*)((uintptr_t)&__cfaabi_tls + offset);
286
287 // create a assembler label after
288 // marked as clobber all to avoid movement
289 __cfaasm_label(get, after);
290
291 // This is used everywhere, to avoid cost, we DO NOT poll pending preemption
292 return val;
293}
294
295extern "C" {
296 // Disable interrupts by incrementing the counter
297 __attribute__((__noinline__, visibility("default"))) void disable_interrupts() libcfa_public {
298 // create a assembler label before
299 // marked as clobber all to avoid movement
300 __cfaasm_label(dsable, before);
301
302 with( __cfaabi_tls.preemption_state ) {
303 #if GCC_VERSION > 50000
304 static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
305 #endif
306
307 // Set enabled flag to false
308 // should be atomic to avoid preemption in the middle of the operation.
309 // use memory order RELAXED since there is no inter-thread on this variable requirements
310 __atomic_store_n(&enabled, false, __ATOMIC_RELAXED);
311
312 // Signal the compiler that a fence is needed but only for signal handlers
313 __atomic_signal_fence(__ATOMIC_ACQUIRE);
314
315 __attribute__((unused)) unsigned short new_val = disable_count + 1;
316 disable_count = new_val;
317 verify( new_val < 65_000u ); // If this triggers someone is disabling interrupts without enabling them
318 }
319
320 // create a assembler label after
321 // marked as clobber all to avoid movement
322 __cfaasm_label(dsable, after);
323
324 }
325
326 // Enable interrupts by decrementing the counter
327 // If counter reaches 0, execute any pending __cfactx_switch
328 void enable_interrupts( bool poll ) libcfa_public {
329 // Cache the processor now since interrupts can start happening after the atomic store
330 processor * proc = __cfaabi_tls.this_processor;
331 /* paranoid */ verify( !poll || proc );
332
333 with( __cfaabi_tls.preemption_state ){
334 unsigned short prev = disable_count;
335 disable_count -= 1;
336
337 // If this triggers someone is enabled already enabled interruptsverify( prev != 0u );
338 /* paranoid */ verify( prev != 0u );
339
340 // Check if we need to prempt the thread because an interrupt was missed
341 if( prev == 1 ) {
342 #if GCC_VERSION > 50000
343 static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
344 #endif
345
346 // Set enabled flag to true
347 // should be atomic to avoid preemption in the middle of the operation.
348 // use memory order RELAXED since there is no inter-thread on this variable requirements
349 __atomic_store_n(&enabled, true, __ATOMIC_RELAXED);
350
351 // Signal the compiler that a fence is needed but only for signal handlers
352 __atomic_signal_fence(__ATOMIC_RELEASE);
353 if( poll && proc->pending_preemption ) {
354 proc->pending_preemption = false;
355 force_yield( __POLL_PREEMPTION );
356 }
357 }
358 }
359 }
360
361 // Check whether or not there is pending preemption
362 // force_yield( __POLL_PREEMPTION ) if appropriate
363 // return true if the thread was in an interruptable state
364 // i.e. on a real processor and not in the kernel
365 // (can return true even if no preemption was pending)
366 bool poll_interrupts() libcfa_public {
367 // Cache the processor now since interrupts can start happening after the atomic store
368 processor * proc = publicTLS_get( this_processor );
369 if ( ! proc ) return false;
370 if ( ! __preemption_enabled() ) return false;
371
372 with( __cfaabi_tls.preemption_state ){
373 // Signal the compiler that a fence is needed but only for signal handlers
374 __atomic_signal_fence(__ATOMIC_RELEASE);
375 if( proc->pending_preemption ) {
376 proc->pending_preemption = false;
377 force_yield( __POLL_PREEMPTION );
378 }
379 }
380
381 return true;
382 }
383}
384
385//-----------------------------------------------------------------------------
386// Kernel Signal Debug
387void __cfaabi_check_preemption() libcfa_public {
388 bool ready = __preemption_enabled();
389 if(!ready) { abort("Preemption should be ready"); }
390
391 sigset_t oldset;
392 int ret;
393 ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset); // workaround trac#208: cast should be unnecessary
394 if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
395
396 ret = sigismember(&oldset, SIGUSR1);
397 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
398 if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
399
400 ret = sigismember(&oldset, SIGALRM);
401 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
402 if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
403
404 ret = sigismember(&oldset, SIGTERM);
405 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
406 if(ret == 1) { abort("ERROR SIGTERM is disabled"); }
407}
408
409#ifdef __CFA_WITH_VERIFY__
410bool __cfaabi_dbg_in_kernel() {
411 return !__preemption_enabled();
412}
413#endif
414
415#undef __cfaasm_label
416
417//-----------------------------------------------------------------------------
418// Signal handling
419
420// sigprocmask wrapper : unblock a single signal
421static inline void signal_unblock( int sig ) {
422 sigset_t mask;
423 sigemptyset( &mask );
424 sigaddset( &mask, sig );
425
426 if ( pthread_sigmask( SIG_UNBLOCK, &mask, 0p ) == -1 ) {
427 abort( "internal error, pthread_sigmask" );
428 }
429}
430
431// sigprocmask wrapper : block a single signal
432static inline void signal_block( int sig ) {
433 sigset_t mask;
434 sigemptyset( &mask );
435 sigaddset( &mask, sig );
436
437 if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
438 abort( "internal error, pthread_sigmask" );
439 }
440}
441
442// kill wrapper : signal a processor
443static void preempt( processor * this ) {
444 sigval_t value = { PREEMPT_NORMAL };
445 pthread_sigqueue( this->kernel_thread, SIGUSR1, value );
446}
447
448// reserved for future use
449static void timeout( thread$ * this ) {
450 unpark( this );
451}
452
453void __disable_interrupts_hard() {
454 sigset_t oldset;
455 int ret;
456 ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset); // workaround trac#208: cast should be unnecessary
457 if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
458
459 ret = sigismember(&oldset, SIGUSR1);
460 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
461 if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
462
463 ret = sigismember(&oldset, SIGALRM);
464 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
465 if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
466
467 signal_block( SIGUSR1 );
468}
469
470void __enable_interrupts_hard() {
471 signal_unblock( SIGUSR1 );
472
473 sigset_t oldset;
474 int ret;
475 ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset); // workaround trac#208: cast should be unnecessary
476 if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
477
478 ret = sigismember(&oldset, SIGUSR1);
479 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
480 if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
481
482 ret = sigismember(&oldset, SIGALRM);
483 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
484 if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
485}
486
487//-----------------------------------------------------------------------------
488// Some assembly required
489#if defined( __i386 )
490 #ifdef __PIC__
491 #define RELOC_PRELUDE( label ) \
492 "calll .Lcfaasm_prelude_" #label "$pb\n\t" \
493 ".Lcfaasm_prelude_" #label "$pb:\n\t" \
494 "popl %%eax\n\t" \
495 ".Lcfaasm_prelude_" #label "_end:\n\t" \
496 "addl $_GLOBAL_OFFSET_TABLE_+(.Lcfaasm_prelude_" #label "_end-.Lcfaasm_prelude_" #label "$pb), %%eax\n\t"
497 #define RELOC_PREFIX ""
498 #define RELOC_SUFFIX "@GOT(%%eax)"
499 #else
500 #define RELOC_PREFIX "$"
501 #define RELOC_SUFFIX ""
502 #endif
503 #define __cfaasm_label( label ) struct asm_region label = \
504 ({ \
505 struct asm_region region; \
506 asm( \
507 RELOC_PRELUDE( label ) \
508 "movl " RELOC_PREFIX "__cfaasm_" #label "_before" RELOC_SUFFIX ", %[vb]\n\t" \
509 "movl " RELOC_PREFIX "__cfaasm_" #label "_after" RELOC_SUFFIX ", %[va]\n\t" \
510 : [vb]"=r"(region.before), [va]"=r"(region.after) \
511 ); \
512 region; \
513 });
514#elif defined( __x86_64 )
515 #ifdef __PIC__
516 #define RELOC_PREFIX ""
517 #define RELOC_SUFFIX "@GOTPCREL(%%rip)"
518 #else
519 #define RELOC_PREFIX "$"
520 #define RELOC_SUFFIX ""
521 #endif
522 #define __cfaasm_label( label ) struct asm_region label = \
523 ({ \
524 struct asm_region region; \
525 asm( \
526 "movq " RELOC_PREFIX "__cfaasm_" #label "_before" RELOC_SUFFIX ", %[vb]\n\t" \
527 "movq " RELOC_PREFIX "__cfaasm_" #label "_after" RELOC_SUFFIX ", %[va]\n\t" \
528 : [vb]"=r"(region.before), [va]"=r"(region.after) \
529 ); \
530 region; \
531 });
532#elif defined( __aarch64__ )
533 #ifdef __PIC__
534 // Note that this works only for gcc
535 #define __cfaasm_label( label ) struct asm_region label = \
536 ({ \
537 struct asm_region region; \
538 asm( \
539 "adrp %[vb], _GLOBAL_OFFSET_TABLE_" "\n\t" \
540 "ldr %[vb], [%[vb], #:gotpage_lo15:__cfaasm_" #label "_before]" "\n\t" \
541 "adrp %[va], _GLOBAL_OFFSET_TABLE_" "\n\t" \
542 "ldr %[va], [%[va], #:gotpage_lo15:__cfaasm_" #label "_after]" "\n\t" \
543 : [vb]"=r"(region.before), [va]"=r"(region.after) \
544 ); \
545 region; \
546 });
547 #else
548 #error this is not the right thing to do
549 /*
550 #define __cfaasm_label( label ) struct asm_region label = \
551 ({ \
552 struct asm_region region; \
553 asm( \
554 "adrp %[vb], __cfaasm_" #label "_before" "\n\t" \
555 "add %[vb], %[vb], :lo12:__cfaasm_" #label "_before" "\n\t" \
556 "adrp %[va], :got:__cfaasm_" #label "_after" "\n\t" \
557 "add %[va], %[va], :lo12:__cfaasm_" #label "_after" "\n\t" \
558 : [vb]"=r"(region.before), [va]"=r"(region.after) \
559 ); \
560 region; \
561 });
562 */
563 #endif
564#else
565 #error unknown hardware architecture
566#endif
567
568// KERNEL ONLY
569// Check if a __cfactx_switch signal handler shoud defer
570// If true : preemption is safe
571// If false : preemption is unsafe and marked as pending
572static inline bool preemption_ready( void * ip ) {
573 // Get all the region for which it is not safe to preempt
574 __cfaasm_label( get );
575 __cfaasm_label( check );
576 __cfaasm_label( dsable );
577 // __cfaasm_label( debug );
578
579 // Check if preemption is safe
580 bool ready = true;
581 if( __cfaasm_in( ip, get ) ) { ready = false; goto EXIT; };
582 if( __cfaasm_in( ip, check ) ) { ready = false; goto EXIT; };
583 if( __cfaasm_in( ip, dsable ) ) { ready = false; goto EXIT; };
584 // if( __cfaasm_in( ip, debug ) ) { ready = false; goto EXIT; };
585 if( !__cfaabi_tls.preemption_state.enabled) { ready = false; goto EXIT; };
586 if( __cfaabi_tls.preemption_state.in_progress ) { ready = false; goto EXIT; };
587
588EXIT:
589 // Adjust the pending flag accordingly
590 __cfaabi_tls.this_processor->pending_preemption = !ready;
591 return ready;
592}
593
594//=============================================================================================
595// Kernel Signal Startup/Shutdown logic
596//=============================================================================================
597
598// Startup routine to activate preemption
599// Called from kernel_startup
600void __kernel_alarm_startup() {
601 __cfaabi_dbg_print_safe( "Kernel : Starting preemption\n" );
602
603 // Start with preemption disabled until ready
604 __cfaabi_tls.preemption_state.enabled = false;
605 __cfaabi_tls.preemption_state.disable_count = 1;
606
607 // Initialize the event kernel
608 event_kernel = (event_kernel_t *)&storage_event_kernel;
609 (*event_kernel){};
610
611 // Setup proper signal handlers
612 __cfaabi_sigaction( SIGUSR1, sigHandler_ctxSwitch, SA_SIGINFO ); // __cfactx_switch handler
613 __cfaabi_sigaction( SIGALRM, sigHandler_alarm , SA_SIGINFO ); // debug handler
614
615 signal_block( SIGALRM );
616
617 alarm_stack = __create_pthread( &alarm_thread, alarm_loop, 0p );
618}
619
620// Shutdown routine to deactivate preemption
621// Called from kernel_shutdown
622void __kernel_alarm_shutdown() {
623 __cfaabi_dbg_print_safe( "Kernel : Preemption stopping\n" );
624
625 // Block all signals since we are already shutting down
626 sigset_t mask;
627 sigfillset( &mask );
628 sigprocmask( SIG_BLOCK, &mask, 0p );
629
630 // Notify the alarm thread of the shutdown
631 sigval val;
632 val.sival_int = 0;
633 pthread_sigqueue( alarm_thread, SIGALRM, val );
634
635 // Wait for the preemption thread to finish
636
637 __destroy_pthread( alarm_thread, alarm_stack, 0p );
638
639 // Preemption is now fully stopped
640
641 __cfaabi_dbg_print_safe( "Kernel : Preemption stopped\n" );
642}
643
644// Prevent preemption since we are about to start terminating things
645void __kernel_abort_lock(void) {
646 signal_block( SIGUSR1 );
647}
648
649// Raii ctor/dtor for the preemption_scope
650// Used by thread to control when they want to receive preemption signals
651void ?{}( preemption_scope & this, processor * proc ) {
652 (this.alarm){ proc, 0`s, 0`s };
653 this.proc = proc;
654 this.proc->preemption_alarm = &this.alarm;
655
656 update_preemption( this.proc, this.proc->cltr->preemption_rate );
657}
658
659void ^?{}( preemption_scope & this ) {
660 disable_interrupts();
661
662 update_preemption( this.proc, 0`s );
663}
664
665//=============================================================================================
666// Kernel Signal Handlers
667//=============================================================================================
668__cfaabi_dbg_debug_do( static __thread void * last_interrupt = 0; )
669
670// Context switch signal handler
671// Receives SIGUSR1 signal and causes the current thread to yield
672static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ ) {
673 void * ip = (void *)(cxt->uc_mcontext.CFA_REG_IP);
674 __cfaabi_dbg_debug_do( last_interrupt = ip; )
675
676 // SKULLDUGGERY: if a thread creates a processor and the immediately deletes it,
677 // the interrupt that is supposed to force the kernel thread to preempt might arrive
678 // before the kernel thread has even started running. When that happens, an interrupt
679 // with a null 'this_processor' will be caught, just ignore it.
680 if(! __cfaabi_tls.this_processor ) return;
681
682 choose(sfp->si_value.sival_int) {
683 case PREEMPT_NORMAL : ;// Normal case, nothing to do here
684 case PREEMPT_IO : ;// I/O asked to stop spinning, nothing to do here
685 case PREEMPT_TERMINATE: verify( __atomic_load_n( &__cfaabi_tls.this_processor->do_terminate, __ATOMIC_SEQ_CST ) );
686 default:
687 abort( "internal error, signal value is %d", sfp->si_value.sival_int );
688 }
689
690 // Check if it is safe to preempt here
691 if( !preemption_ready( ip ) ) {
692 #if !defined(__CFA_NO_STATISTICS__)
693 __cfaabi_tls.this_stats->ready.threads.preempt.rllfwd++;
694 #endif
695 return;
696 }
697
698 __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) );
699
700 // Sync flag : prevent recursive calls to the signal handler
701 __cfaabi_tls.preemption_state.in_progress = true;
702
703 // Clear sighandler mask before context switching.
704 #if GCC_VERSION > 50000
705 static_assert( sizeof( sigset_t ) == sizeof( cxt->uc_sigmask ), "Expected cxt->uc_sigmask to be of sigset_t" );
706 #endif
707 if ( pthread_sigmask( SIG_SETMASK, (sigset_t *)&(cxt->uc_sigmask), 0p ) == -1 ) {
708 abort( "internal error, sigprocmask" );
709 }
710
711 // Clear the in progress flag
712 __cfaabi_tls.preemption_state.in_progress = false;
713
714 // Preemption can occur here
715
716 #if !defined(__CFA_NO_STATISTICS__)
717 __cfaabi_tls.this_stats->ready.threads.preempt.yield++;
718 #endif
719
720 force_yield( __ALARM_PREEMPTION ); // Do the actual __cfactx_switch
721}
722
723static void sigHandler_alarm( __CFA_SIGPARMS__ ) {
724 abort("SIGALRM should never reach the signal handler");
725}
726
727// Main of the alarm thread
728// Waits on SIGALRM and send SIGUSR1 to whom ever needs it
729static void * alarm_loop( __attribute__((unused)) void * args ) {
730 unsigned id = register_proc_id();
731
732 // Block sigalrms to control when they arrive
733 sigset_t mask;
734 sigfillset(&mask);
735 if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
736 abort( "internal error, pthread_sigmask" );
737 }
738
739 sigemptyset( &mask );
740 sigaddset( &mask, SIGALRM );
741
742 // Main loop
743 while( true ) {
744 // Wait for a sigalrm
745 siginfo_t info;
746 int sig = sigwaitinfo( &mask, &info );
747
748 __cfadbg_print_buffer_decl ( preemption, " KERNEL: sigwaitinfo returned %d, c: %d, v: %d\n", sig, info.si_code, info.si_value.sival_int );
749 __cfadbg_print_buffer_local( preemption, " KERNEL: SI_QUEUE %d, SI_TIMER %d, SI_KERNEL %d\n", SI_QUEUE, SI_TIMER, SI_KERNEL );
750
751 if( sig < 0 ) {
752 //Error!
753 int err = errno;
754 switch( err ) {
755 case EAGAIN :
756 case EINTR :
757 {__cfadbg_print_buffer_local( preemption, " KERNEL: Spurious wakeup %d.\n", err );}
758 continue;
759 case EINVAL :
760 abort( "Timeout was invalid." );
761 default:
762 abort( "Unhandled error %d", err);
763 }
764 }
765
766 // If another signal arrived something went wrong
767 assertf(sig == SIGALRM, "Kernel Internal Error, sigwait: Unexpected signal %d (%d : %d)\n", sig, info.si_code, info.si_value.sival_int);
768
769 // Switch on the code (a.k.a. the sender) to
770 switch( info.si_code )
771 {
772 // Signal was not sent by the kernel but by an other thread
773 case SI_QUEUE:
774 // other threads may signal the alarm thread to shut it down
775 // or to manual cause the preemption tick
776 // use info.si_value and handle the case here
777 switch( info.si_value.sival_int ) {
778 case 0:
779 goto EXIT;
780 default:
781 abort( "SI_QUEUE with val %d", info.si_value.sival_int);
782 }
783 // fallthrough
784 // Timers can apparently be marked as sent for the kernel
785 // In either case, tick preemption
786 case SI_TIMER:
787 case SI_KERNEL:
788 // __cfaabi_dbg_print_safe( "Kernel : Preemption thread tick\n" );
789 lock( event_kernel->lock __cfaabi_dbg_ctx2 );
790 tick_preemption();
791 unlock( event_kernel->lock );
792 break;
793 }
794 }
795
796EXIT:
797 __cfaabi_dbg_print_safe( "Kernel : Preemption thread stopping\n" );
798 unregister_proc_id(id);
799
800 return 0p;
801}
802
803// Local Variables: //
804// mode: c //
805// tab-width: 4 //
806// End: //
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