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preemption.cfa @ 02f4eb8

ADTast-experimentalenumforall-pointer-decayjacob/cs343-translationnew-ast-unique-exprpthread-emulationqualifiedEnum

Last change on this file since 02f4eb8 was 43784ac, checked in by Thierry Delisle <tdelisle@…>, 3 years ago
Changed libcfathread to consistently define _GNU_SOURCE
Property mode set to `100644`
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
62	static void preempt( processor * this );
63	static void timeout( $thread * this );
64
65	// FwdDeclarations : Signal handlers
66	static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ );
67	static void sigHandler_alarm ( __CFA_SIGPARMS__ );
68	static void sigHandler_segv ( __CFA_SIGPARMS__ );
69	static void sigHandler_ill ( __CFA_SIGPARMS__ );
70	static void sigHandler_fpe ( __CFA_SIGPARMS__ );
71	static void sigHandler_abort ( __CFA_SIGPARMS__ );
72
73	// FwdDeclarations : alarm thread main
74	static 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
89	KERNEL_STORAGE(event_kernel_t, event_kernel); // private storage for event kernel
90	event_kernel_t * event_kernel; // kernel public handle to even kernel
91	static pthread_t alarm_thread; // pthread handle to alarm thread
92	static void * alarm_stack; // pthread stack for alarm thread
93
94	static void ?{}(event_kernel_t & this) with( this ) {
95	alarms{};
96	lock{};
97	}
98
99	enum {
100	PREEMPT_NORMAL = 0,
101	PREEMPT_TERMINATE = 1,
102	};
103
104	//=============================================================================================
105	// Kernel Preemption logic
106	//=============================================================================================
107
108	// Get next expired node
109	static 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
116	static 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
160	void 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
245	bool __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
259	struct asm_region {
260	void * before;
261	void * after;
262	};
263
264	static 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;
272	uintptr_t __cfatls_get( unsigned long int offset ) __attribute__((__noinline__)); //no inline to avoid problems
273	uintptr_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
287	extern "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
356	void __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__
383	bool __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
394	static 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
405	static 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
416	static 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
422	static void timeout( $thread * this ) {
423	unpark( this );
424	}
425
426	void __disable_interrupts_hard() {
427	sigset_t oldset;
428	int ret;
429	ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset); // workaround trac#208: cast should be unnecessary
430	if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
431
432	ret = sigismember(&oldset, SIGUSR1);
433	if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
434	if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
435
436	ret = sigismember(&oldset, SIGALRM);
437	if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
438	if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
439
440	signal_block( SIGUSR1 );
441	}
442
443	void __enable_interrupts_hard() {
444	signal_unblock( SIGUSR1 );
445
446	sigset_t oldset;
447	int ret;
448	ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset); // workaround trac#208: cast should be unnecessary
449	if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
450
451	ret = sigismember(&oldset, SIGUSR1);
452	if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
453	if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
454
455	ret = sigismember(&oldset, SIGALRM);
456	if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
457	if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
458	}
459
460	//-----------------------------------------------------------------------------
461	// Some assembly required
462	#if defined( __i386 )
463	#ifdef __PIC__
464	#define RELOC_PRELUDE( label ) \
465	"calll .Lcfaasm_prelude_" #label "$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
545	static 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
561	EXIT:
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
573	void __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
595	void __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
618	void __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
624	void ?{}( 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
632	void ^?{}( 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
645	static 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
686	static 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
692	static 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
759	EXIT:
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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