source: libcfa/src/concurrency/preemption.cfa@ c7c178b

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 c7c178b was 357fae8, checked in by Thierry Delisle <tdelisle@…>, 4 years ago

Fixed bad copy paste
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File size: 26.9 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 __CFA_DEBUG_PRINT_PREEMPTION__
18
19#include "preemption.hfa"
20#include <assert.h>
21
22#include <errno.h>
23#include <stdio.h>
24#include <string.h>
25#include <unistd.h>
26#include <limits.h> // PTHREAD_STACK_MIN
27
28#include "bits/signal.hfa"
29#include "kernel_private.hfa"
30
31
32#if !defined(__CFA_DEFAULT_PREEMPTION__)
33#define __CFA_DEFAULT_PREEMPTION__ 10`ms
34#endif
35
36__attribute__((weak)) Duration default_preemption() {
37 const char * preempt_rate_s = getenv("CFA_DEFAULT_PREEMPTION");
38 if(!preempt_rate_s) {
39 __cfadbg_print_safe(preemption, "No CFA_DEFAULT_PREEMPTION in ENV\n");
40 return __CFA_DEFAULT_PREEMPTION__;
41 }
42
43 char * endptr = 0p;
44 long int preempt_rate_l = strtol(preempt_rate_s, &endptr, 10);
45 if(preempt_rate_l < 0 || preempt_rate_l > 65535) {
46 __cfadbg_print_safe(preemption, "CFA_DEFAULT_PREEMPTION out of range : %ld\n", preempt_rate_l);
47 return __CFA_DEFAULT_PREEMPTION__;
48 }
49 if('\0' != *endptr) {
50 __cfadbg_print_safe(preemption, "CFA_DEFAULT_PREEMPTION not a decimal number : %s\n", preempt_rate_s);
51 return __CFA_DEFAULT_PREEMPTION__;
52 }
53
54 return preempt_rate_l`ms;
55}
56
57// FwdDeclarations : timeout handlers
58static void preempt( processor * this );
59static void timeout( $thread * this );
60
61// FwdDeclarations : Signal handlers
62static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ );
63static void sigHandler_alarm ( __CFA_SIGPARMS__ );
64static void sigHandler_segv ( __CFA_SIGPARMS__ );
65static void sigHandler_ill ( __CFA_SIGPARMS__ );
66static void sigHandler_fpe ( __CFA_SIGPARMS__ );
67static void sigHandler_abort ( __CFA_SIGPARMS__ );
68
69// FwdDeclarations : alarm thread main
70static void * alarm_loop( __attribute__((unused)) void * args );
71
72// Machine specific register name
73#if defined( __i386 )
74#define CFA_REG_IP gregs[REG_EIP]
75#elif defined( __x86_64 )
76#define CFA_REG_IP gregs[REG_RIP]
77#elif defined( __arm__ )
78#define CFA_REG_IP arm_pc
79#elif defined( __aarch64__ )
80#define CFA_REG_IP pc
81#else
82#error unsupported hardware architecture
83#endif
84
85KERNEL_STORAGE(event_kernel_t, event_kernel); // private storage for event kernel
86event_kernel_t * event_kernel; // kernel public handle to even kernel
87static pthread_t alarm_thread; // pthread handle to alarm thread
88static void * alarm_stack; // pthread stack for alarm thread
89
90static void ?{}(event_kernel_t & this) with( this ) {
91 alarms{};
92 lock{};
93}
94
95enum {
96 PREEMPT_NORMAL = 0,
97 PREEMPT_TERMINATE = 1,
98};
99
100//=============================================================================================
101// Kernel Preemption logic
102//=============================================================================================
103
104// Get next expired node
105static inline alarm_node_t * get_expired( alarm_list_t * alarms, Time currtime ) {
106 if( ! & (*alarms)`first ) return 0p; // If no alarms return null
107 if( (*alarms)`first.alarm >= currtime ) return 0p; // If alarms head not expired return null
108 return pop(alarms); // Otherwise just pop head
109}
110
111// Tick one frame of the Discrete Event Simulation for alarms
112static void tick_preemption(void) {
113 alarm_node_t * node = 0p; // Used in the while loop but cannot be declared in the while condition
114 alarm_list_t * alarms = &event_kernel->alarms; // Local copy for ease of reading
115 Time currtime = __kernel_get_time(); // Check current time once so everything "happens at once"
116
117 //Loop throught every thing expired
118 while( node = get_expired( alarms, currtime ) ) {
119 // __cfaabi_dbg_print_buffer_decl( " KERNEL: preemption tick.\n" );
120 Duration period = node->period;
121 if( period == 0) {
122 node->set = false; // Node is one-shot, just mark it as not pending
123 }
124
125 // Check if this is a kernel
126 if( node->type == Kernel ) {
127 preempt( node->proc );
128 }
129 else if( node->type == User ) {
130 timeout( node->thrd );
131 }
132 else {
133 node->callback(*node);
134 }
135
136 // Check if this is a periodic alarm
137 if( period > 0 ) {
138 // __cfaabi_dbg_print_buffer_local( " KERNEL: alarm period is %lu.\n", period.tv );
139 node->alarm = currtime + period; // Alarm is periodic, add currtime to it (used cached current time)
140 insert( alarms, node ); // Reinsert the node for the next time it triggers
141 }
142 }
143
144 // If there are still alarms pending, reset the timer
145 if( & (*alarms)`first ) {
146 Duration delta = (*alarms)`first.alarm - currtime;
147 Duration capped = max(delta, 50`us);
148 __kernel_set_timer( capped );
149 }
150}
151
152// Update the preemption of a processor and notify interested parties
153void update_preemption( processor * this, Duration duration ) {
154 alarm_node_t * alarm = this->preemption_alarm;
155
156 // Alarms need to be enabled
157 if ( duration > 0 && ! alarm->set ) {
158 alarm->alarm = __kernel_get_time() + duration;
159 alarm->period = duration;
160 register_self( alarm );
161 }
162 // Zero duration but alarm is set
163 else if ( duration == 0 && alarm->set ) {
164 unregister_self( alarm );
165 alarm->alarm = 0;
166 alarm->period = 0;
167 }
168 // If alarm is different from previous, change it
169 else if ( duration > 0 && alarm->period != duration ) {
170 unregister_self( alarm );
171 alarm->alarm = __kernel_get_time() + duration;
172 alarm->period = duration;
173 register_self( alarm );
174 }
175}
176
177//=============================================================================================
178// Kernel Signal Tools
179//=============================================================================================
180// In a user-level threading system, there are handful of thread-local variables where this problem occurs on the ARM.
181//
182// For each kernel thread running user-level threads, there is a flag variable to indicate if interrupts are
183// enabled/disabled for that kernel thread. Therefore, this variable is made thread local.
184//
185// For example, this code fragment sets the state of the "interrupt" variable in thread-local memory.
186//
187// _Thread_local volatile int interrupts;
188// int main() {
189// interrupts = 0; // disable interrupts }
190//
191// which generates the following code on the ARM
192//
193// (gdb) disassemble main
194// Dump of assembler code for function main:
195// 0x0000000000000610 <+0>: mrs x1, tpidr_el0
196// 0x0000000000000614 <+4>: mov w0, #0x0 // #0
197// 0x0000000000000618 <+8>: add x1, x1, #0x0, lsl #12
198// 0x000000000000061c <+12>: add x1, x1, #0x10
199// 0x0000000000000620 <+16>: str wzr, [x1]
200// 0x0000000000000624 <+20>: ret
201//
202// The mrs moves a pointer from coprocessor register tpidr_el0 into register x1. Register w0 is set to 0. The two adds
203// increase the TLS pointer with the displacement (offset) 0x10, which is the location in the TSL of variable
204// "interrupts". Finally, 0 is stored into "interrupts" through the pointer in register x1 that points into the
205// TSL. Now once x1 has the pointer to the location of the TSL for kernel thread N, it can be be preempted at a
206// user-level and the user thread is put on the user-level ready-queue. When the preempted thread gets to the front of
207// the user-level ready-queue it is run on kernel thread M. It now stores 0 into "interrupts" back on kernel thread N,
208// turning off interrupt on the wrong kernel thread.
209//
210// On the x86, the following code is generated for the same code fragment.
211//
212// (gdb) disassemble main
213// Dump of assembler code for function main:
214// 0x0000000000400420 <+0>: movl $0x0,%fs:0xfffffffffffffffc
215// 0x000000000040042c <+12>: xor %eax,%eax
216// 0x000000000040042e <+14>: retq
217//
218// and there is base-displacement addressing used to atomically reset variable "interrupts" off of the TSL pointer in
219// register "fs".
220//
221// Hence, the ARM has base-displacement address for the general purpose registers, BUT not to the coprocessor
222// registers. As a result, generating the address for the write into variable "interrupts" is no longer atomic.
223//
224// Note this problem does NOT occur when just using multiple kernel threads because the preemption ALWAYS restarts the
225// thread on the same kernel thread.
226//
227// The obvious question is why does ARM use a coprocessor register to store the TSL pointer given that coprocessor
228// registers are second-class registers with respect to the instruction set. One possible answer is that they did not
229// want to dedicate one of the general registers to hold the TLS pointer and there was a free coprocessor register
230// available.
231
232//-----------------------------------------------------------------------------
233// Some assembly required
234#define __cfaasm_label(label, when) when: asm volatile goto(".global __cfaasm_" #label "_" #when "\n" "__cfaasm_" #label "_" #when ":":::"memory":when)
235
236//----------
237// special case for preemption since used often
238bool __preemption_enabled() {
239 // create a assembler label before
240 // marked as clobber all to avoid movement
241 __cfaasm_label(check, before);
242
243 // access tls as normal
244 bool enabled = __cfaabi_tls.preemption_state.enabled;
245
246 // create a assembler label after
247 // marked as clobber all to avoid movement
248 __cfaasm_label(check, after);
249 return enabled;
250}
251
252struct asm_region {
253 void * before;
254 void * after;
255};
256
257static inline bool __cfaasm_in( void * ip, struct asm_region & region ) {
258 return ip >= region.before && ip <= region.after;
259}
260
261
262//----------
263// Get data from the TLS block
264// struct asm_region __cfaasm_get;
265uintptr_t __cfatls_get( unsigned long int offset ) __attribute__((__noinline__)); //no inline to avoid problems
266uintptr_t __cfatls_get( unsigned long int offset ) {
267 // create a assembler label before
268 // marked as clobber all to avoid movement
269 __cfaasm_label(get, before);
270
271 // access tls as normal (except for pointer arithmetic)
272 uintptr_t val = *(uintptr_t*)((uintptr_t)&__cfaabi_tls + offset);
273
274 // create a assembler label after
275 // marked as clobber all to avoid movement
276 __cfaasm_label(get, after);
277 return val;
278}
279
280extern "C" {
281 // Disable interrupts by incrementing the counter
282 void disable_interrupts() {
283 // create a assembler label before
284 // marked as clobber all to avoid movement
285 __cfaasm_label(dsable, before);
286
287 with( __cfaabi_tls.preemption_state ) {
288 #if GCC_VERSION > 50000
289 static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
290 #endif
291
292 // Set enabled flag to false
293 // should be atomic to avoid preemption in the middle of the operation.
294 // use memory order RELAXED since there is no inter-thread on this variable requirements
295 __atomic_store_n(&enabled, false, __ATOMIC_RELAXED);
296
297 // Signal the compiler that a fence is needed but only for signal handlers
298 __atomic_signal_fence(__ATOMIC_ACQUIRE);
299
300 __attribute__((unused)) unsigned short new_val = disable_count + 1;
301 disable_count = new_val;
302 verify( new_val < 65_000u ); // If this triggers someone is disabling interrupts without enabling them
303 }
304
305 // create a assembler label after
306 // marked as clobber all to avoid movement
307 __cfaasm_label(dsable, after);
308
309 }
310
311 // Enable interrupts by decrementing the counter
312 // If counter reaches 0, execute any pending __cfactx_switch
313 void enable_interrupts( __cfaabi_dbg_ctx_param ) {
314 // Cache the processor now since interrupts can start happening after the atomic store
315 processor * proc = __cfaabi_tls.this_processor;
316 /* paranoid */ verify( proc );
317
318 with( __cfaabi_tls.preemption_state ){
319 unsigned short prev = disable_count;
320 disable_count -= 1;
321
322 // If this triggers someone is enabled already enabled interruptsverify( prev != 0u );
323 /* paranoid */ verify( prev != 0u );
324
325 // Check if we need to prempt the thread because an interrupt was missed
326 if( prev == 1 ) {
327 #if GCC_VERSION > 50000
328 static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
329 #endif
330
331 // Set enabled flag to true
332 // should be atomic to avoid preemption in the middle of the operation.
333 // use memory order RELAXED since there is no inter-thread on this variable requirements
334 __atomic_store_n(&enabled, true, __ATOMIC_RELAXED);
335
336 // Signal the compiler that a fence is needed but only for signal handlers
337 __atomic_signal_fence(__ATOMIC_RELEASE);
338 if( proc->pending_preemption ) {
339 proc->pending_preemption = false;
340 force_yield( __POLL_PREEMPTION );
341 }
342 }
343 }
344
345 // For debugging purposes : keep track of the last person to enable the interrupts
346 __cfaabi_dbg_debug_do( proc->last_enable = caller; )
347 }
348
349 // Disable interrupts by incrementint the counter
350 // Don't execute any pending __cfactx_switch even if counter reaches 0
351 void enable_interrupts_noPoll() {
352 unsigned short prev = __cfaabi_tls.preemption_state.disable_count;
353 __cfaabi_tls.preemption_state.disable_count -= 1;
354 // If this triggers someone is enabled already enabled interrupts
355 /* paranoid */ verifyf( prev != 0u, "Incremented from %u\n", prev );
356 if( prev == 1 ) {
357 #if GCC_VERSION > 50000
358 static_assert(__atomic_always_lock_free(sizeof(__cfaabi_tls.preemption_state.enabled), &__cfaabi_tls.preemption_state.enabled), "Must be lock-free");
359 #endif
360 // Set enabled flag to true
361 // should be atomic to avoid preemption in the middle of the operation.
362 // use memory order RELAXED since there is no inter-thread on this variable requirements
363 __atomic_store_n(&__cfaabi_tls.preemption_state.enabled, true, __ATOMIC_RELAXED);
364
365 // Signal the compiler that a fence is needed but only for signal handlers
366 __atomic_signal_fence(__ATOMIC_RELEASE);
367 }
368 }
369}
370
371//-----------------------------------------------------------------------------
372// Kernel Signal Debug
373void __cfaabi_check_preemption() {
374 bool ready = __preemption_enabled();
375 if(!ready) { abort("Preemption should be ready"); }
376
377 __cfaasm_label(debug, before);
378
379 sigset_t oldset;
380 int ret;
381 ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset); // workaround trac#208: cast should be unnecessary
382 if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
383
384 ret = sigismember(&oldset, SIGUSR1);
385 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
386 if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
387
388 ret = sigismember(&oldset, SIGALRM);
389 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
390 if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
391
392 ret = sigismember(&oldset, SIGTERM);
393 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
394 if(ret == 1) { abort("ERROR SIGTERM is disabled"); }
395
396 __cfaasm_label(debug, after);
397}
398
399#ifdef __CFA_WITH_VERIFY__
400bool __cfaabi_dbg_in_kernel() {
401 return !__preemption_enabled();
402}
403#endif
404
405#undef __cfaasm_label
406
407//-----------------------------------------------------------------------------
408// Signal handling
409
410// sigprocmask wrapper : unblock a single signal
411static inline void signal_unblock( int sig ) {
412 sigset_t mask;
413 sigemptyset( &mask );
414 sigaddset( &mask, sig );
415
416 if ( pthread_sigmask( SIG_UNBLOCK, &mask, 0p ) == -1 ) {
417 abort( "internal error, pthread_sigmask" );
418 }
419}
420
421// sigprocmask wrapper : block a single signal
422static inline void signal_block( int sig ) {
423 sigset_t mask;
424 sigemptyset( &mask );
425 sigaddset( &mask, sig );
426
427 if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
428 abort( "internal error, pthread_sigmask" );
429 }
430}
431
432// kill wrapper : signal a processor
433static void preempt( processor * this ) {
434 sigval_t value = { PREEMPT_NORMAL };
435 pthread_sigqueue( this->kernel_thread, SIGUSR1, value );
436}
437
438// reserved for future use
439static void timeout( $thread * this ) {
440 unpark( this );
441}
442
443void __disable_interrupts_hard() {
444 sigset_t oldset;
445 int ret;
446 ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset); // workaround trac#208: cast should be unnecessary
447 if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
448
449 ret = sigismember(&oldset, SIGUSR1);
450 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
451 if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
452
453 ret = sigismember(&oldset, SIGALRM);
454 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
455 if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
456
457 signal_block( SIGUSR1 );
458}
459
460void __enable_interrupts_hard() {
461 signal_unblock( SIGUSR1 );
462
463 sigset_t oldset;
464 int ret;
465 ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset); // workaround trac#208: cast should be unnecessary
466 if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
467
468 ret = sigismember(&oldset, SIGUSR1);
469 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
470 if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
471
472 ret = sigismember(&oldset, SIGALRM);
473 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
474 if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
475}
476
477//-----------------------------------------------------------------------------
478// Some assembly required
479#if defined( __i386 )
480 #ifdef __PIC__
481 #define RELOC_PRELUDE( label ) \
482 "calll .Lcfaasm_prelude_" #label "$pb\n\t" \
483 ".Lcfaasm_prelude_" #label "$pb:\n\t" \
484 "popl %%eax\n\t" \
485 ".Lcfaasm_prelude_" #label "_end:\n\t" \
486 "addl $_GLOBAL_OFFSET_TABLE_+(.Lcfaasm_prelude_" #label "_end-.Lcfaasm_prelude_" #label "$pb), %%eax\n\t"
487 #define RELOC_PREFIX ""
488 #define RELOC_SUFFIX "@GOT(%%eax)"
489 #else
490 #define RELOC_PREFIX "$"
491 #define RELOC_SUFFIX ""
492 #endif
493 #define __cfaasm_label( label ) struct asm_region label = \
494 ({ \
495 struct asm_region region; \
496 asm( \
497 RELOC_PRELUDE( label ) \
498 "movl " RELOC_PREFIX "__cfaasm_" #label "_before" RELOC_SUFFIX ", %[vb]\n\t" \
499 "movl " RELOC_PREFIX "__cfaasm_" #label "_after" RELOC_SUFFIX ", %[va]\n\t" \
500 : [vb]"=r"(region.before), [va]"=r"(region.after) \
501 ); \
502 region; \
503 });
504#elif defined( __x86_64 )
505 #ifdef __PIC__
506 #define RELOC_PREFIX ""
507 #define RELOC_SUFFIX "@GOTPCREL(%%rip)"
508 #else
509 #define RELOC_PREFIX "$"
510 #define RELOC_SUFFIX ""
511 #endif
512 #define __cfaasm_label( label ) struct asm_region label = \
513 ({ \
514 struct asm_region region; \
515 asm( \
516 "movq " RELOC_PREFIX "__cfaasm_" #label "_before" RELOC_SUFFIX ", %[vb]\n\t" \
517 "movq " RELOC_PREFIX "__cfaasm_" #label "_after" RELOC_SUFFIX ", %[va]\n\t" \
518 : [vb]"=r"(region.before), [va]"=r"(region.after) \
519 ); \
520 region; \
521 });
522#elif defined( __aarch64__ )
523 #ifdef __PIC__
524 // Note that this works only for gcc
525 #define __cfaasm_label( label ) struct asm_region label = \
526 ({ \
527 struct asm_region region; \
528 asm( \
529 "adrp %[vb], _GLOBAL_OFFSET_TABLE_" "\n\t" \
530 "ldr %[vb], [%[vb], #:gotpage_lo15:__cfaasm_" #label "_before]" "\n\t" \
531 "adrp %[va], _GLOBAL_OFFSET_TABLE_" "\n\t" \
532 "ldr %[va], [%[va], #:gotpage_lo15:__cfaasm_" #label "_after]" "\n\t" \
533 : [vb]"=r"(region.before), [va]"=r"(region.after) \
534 ); \
535 region; \
536 });
537 #else
538 #error this is not the right thing to do
539 /*
540 #define __cfaasm_label( label ) struct asm_region label = \
541 ({ \
542 struct asm_region region; \
543 asm( \
544 "adrp %[vb], __cfaasm_" #label "_before" "\n\t" \
545 "add %[vb], %[vb], :lo12:__cfaasm_" #label "_before" "\n\t" \
546 "adrp %[va], :got:__cfaasm_" #label "_after" "\n\t" \
547 "add %[va], %[va], :lo12:__cfaasm_" #label "_after" "\n\t" \
548 : [vb]"=r"(region.before), [va]"=r"(region.after) \
549 ); \
550 region; \
551 });
552 */
553 #endif
554#else
555 #error unknown hardware architecture
556#endif
557
558// KERNEL ONLY
559// Check if a __cfactx_switch signal handler shoud defer
560// If true : preemption is safe
561// If false : preemption is unsafe and marked as pending
562static inline bool preemption_ready( void * ip ) {
563 // Get all the region for which it is not safe to preempt
564 __cfaasm_label( get );
565 __cfaasm_label( check );
566 __cfaasm_label( dsable );
567 __cfaasm_label( debug );
568
569 // Check if preemption is safe
570 bool ready = true;
571 if( __cfaasm_in( ip, get ) ) { ready = false; goto EXIT; };
572 if( __cfaasm_in( ip, check ) ) { ready = false; goto EXIT; };
573 if( __cfaasm_in( ip, dsable ) ) { ready = false; goto EXIT; };
574 if( __cfaasm_in( ip, debug ) ) { ready = false; goto EXIT; };
575 if( !__cfaabi_tls.preemption_state.enabled) { ready = false; goto EXIT; };
576 if( __cfaabi_tls.preemption_state.in_progress ) { ready = false; goto EXIT; };
577
578EXIT:
579 // Adjust the pending flag accordingly
580 __cfaabi_tls.this_processor->pending_preemption = !ready;
581 return ready;
582}
583
584//=============================================================================================
585// Kernel Signal Startup/Shutdown logic
586//=============================================================================================
587
588// Startup routine to activate preemption
589// Called from kernel_startup
590void __kernel_alarm_startup() {
591 __cfaabi_dbg_print_safe( "Kernel : Starting preemption\n" );
592
593 // Start with preemption disabled until ready
594 __cfaabi_tls.preemption_state.enabled = false;
595 __cfaabi_tls.preemption_state.disable_count = 1;
596
597 // Initialize the event kernel
598 event_kernel = (event_kernel_t *)&storage_event_kernel;
599 (*event_kernel){};
600
601 // Setup proper signal handlers
602 __cfaabi_sigaction( SIGUSR1, sigHandler_ctxSwitch, SA_SIGINFO ); // __cfactx_switch handler
603 __cfaabi_sigaction( SIGALRM, sigHandler_alarm , SA_SIGINFO ); // debug handler
604
605 signal_block( SIGALRM );
606
607 alarm_stack = __create_pthread( &alarm_thread, alarm_loop, 0p );
608}
609
610// Shutdown routine to deactivate preemption
611// Called from kernel_shutdown
612void __kernel_alarm_shutdown() {
613 __cfaabi_dbg_print_safe( "Kernel : Preemption stopping\n" );
614
615 // Block all signals since we are already shutting down
616 sigset_t mask;
617 sigfillset( &mask );
618 sigprocmask( SIG_BLOCK, &mask, 0p );
619
620 // Notify the alarm thread of the shutdown
621 sigval val = { 1 };
622 pthread_sigqueue( alarm_thread, SIGALRM, val );
623
624 // Wait for the preemption thread to finish
625
626 __destroy_pthread( alarm_thread, alarm_stack, 0p );
627
628 // Preemption is now fully stopped
629
630 __cfaabi_dbg_print_safe( "Kernel : Preemption stopped\n" );
631}
632
633// Prevent preemption since we are about to start terminating things
634void __kernel_abort_lock(void) {
635 signal_block( SIGUSR1 );
636}
637
638// Raii ctor/dtor for the preemption_scope
639// Used by thread to control when they want to receive preemption signals
640void ?{}( preemption_scope & this, processor * proc ) {
641 (this.alarm){ proc, (Time){ 0 }, 0`s };
642 this.proc = proc;
643 this.proc->preemption_alarm = &this.alarm;
644
645 update_preemption( this.proc, this.proc->cltr->preemption_rate );
646}
647
648void ^?{}( preemption_scope & this ) {
649 disable_interrupts();
650
651 update_preemption( this.proc, 0`s );
652}
653
654//=============================================================================================
655// Kernel Signal Handlers
656//=============================================================================================
657__cfaabi_dbg_debug_do( static thread_local void * last_interrupt = 0; )
658
659// Context switch signal handler
660// Receives SIGUSR1 signal and causes the current thread to yield
661static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ ) {
662 void * ip = (void *)(cxt->uc_mcontext.CFA_REG_IP);
663 __cfaabi_dbg_debug_do( last_interrupt = ip; )
664
665 // SKULLDUGGERY: if a thread creates a processor and the immediately deletes it,
666 // the interrupt that is supposed to force the kernel thread to preempt might arrive
667 // before the kernel thread has even started running. When that happens, an interrupt
668 // with a null 'this_processor' will be caught, just ignore it.
669 if(! __cfaabi_tls.this_processor ) return;
670
671 choose(sfp->si_value.sival_int) {
672 case PREEMPT_NORMAL : ;// Normal case, nothing to do here
673 case PREEMPT_TERMINATE: verify( __atomic_load_n( &__cfaabi_tls.this_processor->do_terminate, __ATOMIC_SEQ_CST ) );
674 default:
675 abort( "internal error, signal value is %d", sfp->si_value.sival_int );
676 }
677
678 // Check if it is safe to preempt here
679 if( !preemption_ready( ip ) ) { return; }
680
681 __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) );
682
683 // Sync flag : prevent recursive calls to the signal handler
684 __cfaabi_tls.preemption_state.in_progress = true;
685
686 // Clear sighandler mask before context switching.
687 #if GCC_VERSION > 50000
688 static_assert( sizeof( sigset_t ) == sizeof( cxt->uc_sigmask ), "Expected cxt->uc_sigmask to be of sigset_t" );
689 #endif
690 if ( pthread_sigmask( SIG_SETMASK, (sigset_t *)&(cxt->uc_sigmask), 0p ) == -1 ) {
691 abort( "internal error, sigprocmask" );
692 }
693
694 // Clear the in progress flag
695 __cfaabi_tls.preemption_state.in_progress = false;
696
697 // Preemption can occur here
698
699 force_yield( __ALARM_PREEMPTION ); // Do the actual __cfactx_switch
700}
701
702static void sigHandler_alarm( __CFA_SIGPARMS__ ) {
703 abort("SIGALRM should never reach the signal handler");
704}
705
706#if !defined(__CFA_NO_STATISTICS__)
707 int __print_alarm_stats = 0;
708#endif
709
710// Main of the alarm thread
711// Waits on SIGALRM and send SIGUSR1 to whom ever needs it
712static void * alarm_loop( __attribute__((unused)) void * args ) {
713 __processor_id_t id;
714 id.full_proc = false;
715 id.id = doregister(&id);
716 __cfaabi_tls.this_proc_id = &id;
717
718 #if !defined(__CFA_NO_STATISTICS__)
719 struct __stats_t local_stats;
720 __cfaabi_tls.this_stats = &local_stats;
721 __init_stats( &local_stats );
722 #endif
723
724 // Block sigalrms to control when they arrive
725 sigset_t mask;
726 sigfillset(&mask);
727 if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
728 abort( "internal error, pthread_sigmask" );
729 }
730
731 sigemptyset( &mask );
732 sigaddset( &mask, SIGALRM );
733
734 // Main loop
735 while( true ) {
736 // Wait for a sigalrm
737 siginfo_t info;
738 int sig = sigwaitinfo( &mask, &info );
739
740 if( sig < 0 ) {
741 //Error!
742 int err = errno;
743 switch( err ) {
744 case EAGAIN :
745 case EINTR :
746 {__cfaabi_dbg_print_buffer_decl( " KERNEL: Spurious wakeup %d.\n", err );}
747 continue;
748 case EINVAL :
749 abort( "Timeout was invalid." );
750 default:
751 abort( "Unhandled error %d", err);
752 }
753 }
754
755 // If another signal arrived something went wrong
756 assertf(sig == SIGALRM, "Kernel Internal Error, sigwait: Unexpected signal %d (%d : %d)\n", sig, info.si_code, info.si_value.sival_int);
757
758 // __cfaabi_dbg_print_safe( "Kernel : Caught alarm from %d with %d\n", info.si_code, info.si_value.sival_int );
759 // Switch on the code (a.k.a. the sender) to
760 switch( info.si_code )
761 {
762 // Timers can apparently be marked as sent for the kernel
763 // In either case, tick preemption
764 case SI_TIMER:
765 case SI_KERNEL:
766 // __cfaabi_dbg_print_safe( "Kernel : Preemption thread tick\n" );
767 lock( event_kernel->lock __cfaabi_dbg_ctx2 );
768 tick_preemption();
769 unlock( event_kernel->lock );
770 break;
771 // Signal was not sent by the kernel but by an other thread
772 case SI_QUEUE:
773 // For now, other thread only signal the alarm thread to shut it down
774 // If this needs to change use info.si_value and handle the case here
775 goto EXIT;
776 }
777 }
778
779EXIT:
780 __cfaabi_dbg_print_safe( "Kernel : Preemption thread stopping\n" );
781 unregister(&id);
782
783 #if !defined(__CFA_NO_STATISTICS__)
784 if( 0 != __print_alarm_stats ) {
785 __print_stats( &local_stats, __print_alarm_stats, "Alarm", "Thread", 0p );
786 }
787 #endif
788 return 0p;
789}
790
791// Local Variables: //
792// mode: c //
793// tab-width: 4 //
794// End: //
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