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preemption.cfa @ aec68b6

ADTarm-ehast-experimentalenumforall-pointer-decayjacob/cs343-translationnew-ast-unique-exprpthread-emulationqualifiedEnum

Last change on this file since aec68b6 was a3821fa, checked in by Thierry Delisle <tdelisle@…>, 3 years ago

Changed enable interrupts:

no longer save the caller for debugging
now polls based on parameter passed in

Property mode set to 100644

File size: 25.6 KB

Line
1	//
2	// Cforall Version 1.0.0 Copyright (C) 2016 University of Waterloo
3	//
4	// The contents of this file are covered under the licence agreement in the
5	// file "LICENCE" distributed with Cforall.
6	//
7	// signal.c --
8	//
9	// Author : Thierry Delisle
10	// Created On : Mon Jun 5 14:20:42 2017
11	// Last Modified By : Peter A. Buhr
12	// Last Modified On : Fri Nov 6 07:42:13 2020
13	// Update Count : 54
14	//
15
16	#define __cforall_thread__
17	// #define __CFA_DEBUG_PRINT_PREEMPTION__
18
19	#include "preemption.hfa"
20	#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
58	static void preempt( processor * this );
59	static void timeout( $thread * this );
60
61	// FwdDeclarations : Signal handlers
62	static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ );
63	static void sigHandler_alarm ( __CFA_SIGPARMS__ );
64	static void sigHandler_segv ( __CFA_SIGPARMS__ );
65	static void sigHandler_ill ( __CFA_SIGPARMS__ );
66	static void sigHandler_fpe ( __CFA_SIGPARMS__ );
67	static void sigHandler_abort ( __CFA_SIGPARMS__ );
68
69	// FwdDeclarations : alarm thread main
70	static 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
85	KERNEL_STORAGE(event_kernel_t, event_kernel); // private storage for event kernel
86	event_kernel_t * event_kernel; // kernel public handle to even kernel
87	static pthread_t alarm_thread; // pthread handle to alarm thread
88	static void * alarm_stack; // pthread stack for alarm thread
89
90	static void ?{}(event_kernel_t & this) with( this ) {
91	alarms{};
92	lock{};
93	}
94
95	enum {
96	PREEMPT_NORMAL = 0,
97	PREEMPT_TERMINATE = 1,
98	};
99
100	//=============================================================================================
101	// Kernel Preemption logic
102	//=============================================================================================
103
104	// Get next expired node
105	static 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
112	static 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	__cfadbg_print_buffer_decl( preemption, " KERNEL: preemption tick %lu\n", currtime.tn);
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	__cfadbg_print_buffer_local( preemption, " KERNEL: alarm ticking node %p.\n", node );
126
127
128	// Check if this is a kernel
129	if( node->type == Kernel ) {
130	preempt( node->proc );
131	}
132	else if( node->type == User ) {
133	__cfadbg_print_buffer_local( preemption, " KERNEL: alarm unparking %p.\n", node->thrd );
134	timeout( node->thrd );
135	}
136	else {
137	node->callback(*node);
138	}
139
140	// Check if this is a periodic alarm
141	if( period > 0 ) {
142	__cfadbg_print_buffer_local( preemption, " KERNEL: alarm period is %lu.\n", period`ns );
143	node->alarm = currtime + period; // Alarm is periodic, add currtime to it (used cached current time)
144	insert( alarms, node ); // Reinsert the node for the next time it triggers
145	}
146	}
147
148	// If there are still alarms pending, reset the timer
149	if( & (*alarms)`first ) {
150	Duration delta = (*alarms)`first.alarm - currtime;
151	Duration capped = max(delta, 50`us);
152	__kernel_set_timer( capped );
153	}
154	}
155
156	// Update the preemption of a processor and notify interested parties
157	void update_preemption( processor * this, Duration duration ) {
158	alarm_node_t * alarm = this->preemption_alarm;
159
160	// Alarms need to be enabled
161	if ( duration > 0 && ! alarm->set ) {
162	alarm->alarm = __kernel_get_time() + duration;
163	alarm->period = duration;
164	register_self( alarm );
165	}
166	// Zero duration but alarm is set
167	else if ( duration == 0 && alarm->set ) {
168	unregister_self( alarm );
169	alarm->alarm = 0;
170	alarm->period = 0;
171	}
172	// If alarm is different from previous, change it
173	else if ( duration > 0 && alarm->period != duration ) {
174	unregister_self( alarm );
175	alarm->alarm = __kernel_get_time() + duration;
176	alarm->period = duration;
177	register_self( alarm );
178	}
179	}
180
181	//=============================================================================================
182	// Kernel Signal Tools
183	//=============================================================================================
184	// In a user-level threading system, there are handful of thread-local variables where this problem occurs on the ARM.
185	//
186	// For each kernel thread running user-level threads, there is a flag variable to indicate if interrupts are
187	// enabled/disabled for that kernel thread. Therefore, this variable is made thread local.
188	//
189	// For example, this code fragment sets the state of the "interrupt" variable in thread-local memory.
190	//
191	// _Thread_local volatile int interrupts;
192	// int main() {
193	// interrupts = 0; // disable interrupts }
194	//
195	// which generates the following code on the ARM
196	//
197	// (gdb) disassemble main
198	// Dump of assembler code for function main:
199	// 0x0000000000000610 <+0>: mrs x1, tpidr_el0
200	// 0x0000000000000614 <+4>: mov w0, #0x0 // #0
201	// 0x0000000000000618 <+8>: add x1, x1, #0x0, lsl #12
202	// 0x000000000000061c <+12>: add x1, x1, #0x10
203	// 0x0000000000000620 <+16>: str wzr, [x1]
204	// 0x0000000000000624 <+20>: ret
205	//
206	// The mrs moves a pointer from coprocessor register tpidr_el0 into register x1. Register w0 is set to 0. The two adds
207	// increase the TLS pointer with the displacement (offset) 0x10, which is the location in the TSL of variable
208	// "interrupts". Finally, 0 is stored into "interrupts" through the pointer in register x1 that points into the
209	// TSL. Now once x1 has the pointer to the location of the TSL for kernel thread N, it can be be preempted at a
210	// user-level and the user thread is put on the user-level ready-queue. When the preempted thread gets to the front of
211	// the user-level ready-queue it is run on kernel thread M. It now stores 0 into "interrupts" back on kernel thread N,
212	// turning off interrupt on the wrong kernel thread.
213	//
214	// On the x86, the following code is generated for the same code fragment.
215	//
216	// (gdb) disassemble main
217	// Dump of assembler code for function main:
218	// 0x0000000000400420 <+0>: movl $0x0,%fs:0xfffffffffffffffc
219	// 0x000000000040042c <+12>: xor %eax,%eax
220	// 0x000000000040042e <+14>: retq
221	//
222	// and there is base-displacement addressing used to atomically reset variable "interrupts" off of the TSL pointer in
223	// register "fs".
224	//
225	// Hence, the ARM has base-displacement address for the general purpose registers, BUT not to the coprocessor
226	// registers. As a result, generating the address for the write into variable "interrupts" is no longer atomic.
227	//
228	// Note this problem does NOT occur when just using multiple kernel threads because the preemption ALWAYS restarts the
229	// thread on the same kernel thread.
230	//
231	// The obvious question is why does ARM use a coprocessor register to store the TSL pointer given that coprocessor
232	// registers are second-class registers with respect to the instruction set. One possible answer is that they did not
233	// want to dedicate one of the general registers to hold the TLS pointer and there was a free coprocessor register
234	// available.
235
236	//-----------------------------------------------------------------------------
237	// Some assembly required
238	#define __cfaasm_label(label, when) when: asm volatile goto(".global __cfaasm_" #label "_" #when "\n" "__cfaasm_" #label "_" #when ":":::"memory":when)
239
240	//----------
241	// special case for preemption since used often
242	bool __preemption_enabled() {
243	// create a assembler label before
244	// marked as clobber all to avoid movement
245	__cfaasm_label(check, before);
246
247	// access tls as normal
248	bool enabled = __cfaabi_tls.preemption_state.enabled;
249
250	// create a assembler label after
251	// marked as clobber all to avoid movement
252	__cfaasm_label(check, after);
253	return enabled;
254	}
255
256	struct asm_region {
257	void * before;
258	void * after;
259	};
260
261	static inline bool __cfaasm_in( void * ip, struct asm_region & region ) {
262	return ip >= region.before && ip <= region.after;
263	}
264
265
266	//----------
267	// Get data from the TLS block
268	// struct asm_region __cfaasm_get;
269	uintptr_t __cfatls_get( unsigned long int offset ) __attribute__((__noinline__)); //no inline to avoid problems
270	uintptr_t __cfatls_get( unsigned long int offset ) {
271	// create a assembler label before
272	// marked as clobber all to avoid movement
273	__cfaasm_label(get, before);
274
275	// access tls as normal (except for pointer arithmetic)
276	uintptr_t val = (uintptr_t)((uintptr_t)&__cfaabi_tls + offset);
277
278	// create a assembler label after
279	// marked as clobber all to avoid movement
280	__cfaasm_label(get, after);
281	return val;
282	}
283
284	extern "C" {
285	// Disable interrupts by incrementing the counter
286	void disable_interrupts() {
287	// create a assembler label before
288	// marked as clobber all to avoid movement
289	__cfaasm_label(dsable, before);
290
291	with( __cfaabi_tls.preemption_state ) {
292	#if GCC_VERSION > 50000
293	static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
294	#endif
295
296	// Set enabled flag to false
297	// should be atomic to avoid preemption in the middle of the operation.
298	// use memory order RELAXED since there is no inter-thread on this variable requirements
299	__atomic_store_n(&enabled, false, __ATOMIC_RELAXED);
300
301	// Signal the compiler that a fence is needed but only for signal handlers
302	__atomic_signal_fence(__ATOMIC_ACQUIRE);
303
304	__attribute__((unused)) unsigned short new_val = disable_count + 1;
305	disable_count = new_val;
306	verify( new_val < 65_000u ); // If this triggers someone is disabling interrupts without enabling them
307	}
308
309	// create a assembler label after
310	// marked as clobber all to avoid movement
311	__cfaasm_label(dsable, after);
312
313	}
314
315	// Enable interrupts by decrementing the counter
316	// If counter reaches 0, execute any pending __cfactx_switch
317	void enable_interrupts( bool poll ) {
318	// Cache the processor now since interrupts can start happening after the atomic store
319	processor * proc = __cfaabi_tls.this_processor;
320	/* paranoid */ verify( !poll \|\| proc );
321
322	with( __cfaabi_tls.preemption_state ){
323	unsigned short prev = disable_count;
324	disable_count -= 1;
325
326	// If this triggers someone is enabled already enabled interruptsverify( prev != 0u );
327	/* paranoid */ verify( prev != 0u );
328
329	// Check if we need to prempt the thread because an interrupt was missed
330	if( prev == 1 ) {
331	#if GCC_VERSION > 50000
332	static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
333	#endif
334
335	// Set enabled flag to true
336	// should be atomic to avoid preemption in the middle of the operation.
337	// use memory order RELAXED since there is no inter-thread on this variable requirements
338	__atomic_store_n(&enabled, true, __ATOMIC_RELAXED);
339
340	// Signal the compiler that a fence is needed but only for signal handlers
341	__atomic_signal_fence(__ATOMIC_RELEASE);
342	if( poll && proc->pending_preemption ) {
343	proc->pending_preemption = false;
344	force_yield( __POLL_PREEMPTION );
345	}
346	}
347	}
348	}
349	}
350
351	//-----------------------------------------------------------------------------
352	// Kernel Signal Debug
353	void __cfaabi_check_preemption() {
354	bool ready = __preemption_enabled();
355	if(!ready) { abort("Preemption should be ready"); }
356
357	__cfaasm_label(debug, before);
358
359	sigset_t oldset;
360	int ret;
361	ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset); // workaround trac#208: cast should be unnecessary
362	if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
363
364	ret = sigismember(&oldset, SIGUSR1);
365	if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
366	if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
367
368	ret = sigismember(&oldset, SIGALRM);
369	if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
370	if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
371
372	ret = sigismember(&oldset, SIGTERM);
373	if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
374	if(ret == 1) { abort("ERROR SIGTERM is disabled"); }
375
376	__cfaasm_label(debug, after);
377	}
378
379	#ifdef __CFA_WITH_VERIFY__
380	bool __cfaabi_dbg_in_kernel() {
381	return !__preemption_enabled();
382	}
383	#endif
384
385	#undef __cfaasm_label
386
387	//-----------------------------------------------------------------------------
388	// Signal handling
389
390	// sigprocmask wrapper : unblock a single signal
391	static inline void signal_unblock( int sig ) {
392	sigset_t mask;
393	sigemptyset( &mask );
394	sigaddset( &mask, sig );
395
396	if ( pthread_sigmask( SIG_UNBLOCK, &mask, 0p ) == -1 ) {
397	abort( "internal error, pthread_sigmask" );
398	}
399	}
400
401	// sigprocmask wrapper : block a single signal
402	static inline void signal_block( int sig ) {
403	sigset_t mask;
404	sigemptyset( &mask );
405	sigaddset( &mask, sig );
406
407	if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
408	abort( "internal error, pthread_sigmask" );
409	}
410	}
411
412	// kill wrapper : signal a processor
413	static void preempt( processor * this ) {
414	sigval_t value = { PREEMPT_NORMAL };
415	pthread_sigqueue( this->kernel_thread, SIGUSR1, value );
416	}
417
418	// reserved for future use
419	static void timeout( $thread * this ) {
420	unpark( this );
421	}
422
423	void __disable_interrupts_hard() {
424	sigset_t oldset;
425	int ret;
426	ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset); // workaround trac#208: cast should be unnecessary
427	if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
428
429	ret = sigismember(&oldset, SIGUSR1);
430	if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
431	if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
432
433	ret = sigismember(&oldset, SIGALRM);
434	if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
435	if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
436
437	signal_block( SIGUSR1 );
438	}
439
440	void __enable_interrupts_hard() {
441	signal_unblock( SIGUSR1 );
442
443	sigset_t oldset;
444	int ret;
445	ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset); // workaround trac#208: cast should be unnecessary
446	if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
447
448	ret = sigismember(&oldset, SIGUSR1);
449	if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
450	if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
451
452	ret = sigismember(&oldset, SIGALRM);
453	if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
454	if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
455	}
456
457	//-----------------------------------------------------------------------------
458	// Some assembly required
459	#if defined( __i386 )
460	#ifdef __PIC__
461	#define RELOC_PRELUDE( label ) \
462	"calll .Lcfaasm_prelude_" #label "$pb\n\t" \
463	".Lcfaasm_prelude_" #label "$pb:\n\t" \
464	"popl %%eax\n\t" \
465	".Lcfaasm_prelude_" #label "_end:\n\t" \
466	"addl $_GLOBAL_OFFSET_TABLE_+(.Lcfaasm_prelude_" #label "_end-.Lcfaasm_prelude_" #label "$pb), %%eax\n\t"
467	#define RELOC_PREFIX ""
468	#define RELOC_SUFFIX "@GOT(%%eax)"
469	#else
470	#define RELOC_PREFIX "$"
471	#define RELOC_SUFFIX ""
472	#endif
473	#define __cfaasm_label( label ) struct asm_region label = \
474	({ \
475	struct asm_region region; \
476	asm( \
477	RELOC_PRELUDE( label ) \
478	"movl " RELOC_PREFIX "__cfaasm_" #label "_before" RELOC_SUFFIX ", %[vb]\n\t" \
479	"movl " RELOC_PREFIX "__cfaasm_" #label "_after" RELOC_SUFFIX ", %[va]\n\t" \
480	: [vb]"=r"(region.before), [va]"=r"(region.after) \
481	); \
482	region; \
483	});
484	#elif defined( __x86_64 )
485	#ifdef __PIC__
486	#define RELOC_PREFIX ""
487	#define RELOC_SUFFIX "@GOTPCREL(%%rip)"
488	#else
489	#define RELOC_PREFIX "$"
490	#define RELOC_SUFFIX ""
491	#endif
492	#define __cfaasm_label( label ) struct asm_region label = \
493	({ \
494	struct asm_region region; \
495	asm( \
496	"movq " RELOC_PREFIX "__cfaasm_" #label "_before" RELOC_SUFFIX ", %[vb]\n\t" \
497	"movq " RELOC_PREFIX "__cfaasm_" #label "_after" RELOC_SUFFIX ", %[va]\n\t" \
498	: [vb]"=r"(region.before), [va]"=r"(region.after) \
499	); \
500	region; \
501	});
502	#elif defined( __aarch64__ )
503	#ifdef __PIC__
504	// Note that this works only for gcc
505	#define __cfaasm_label( label ) struct asm_region label = \
506	({ \
507	struct asm_region region; \
508	asm( \
509	"adrp %[vb], _GLOBAL_OFFSET_TABLE_" "\n\t" \
510	"ldr %[vb], [%[vb], #:gotpage_lo15:__cfaasm_" #label "_before]" "\n\t" \
511	"adrp %[va], _GLOBAL_OFFSET_TABLE_" "\n\t" \
512	"ldr %[va], [%[va], #:gotpage_lo15:__cfaasm_" #label "_after]" "\n\t" \
513	: [vb]"=r"(region.before), [va]"=r"(region.after) \
514	); \
515	region; \
516	});
517	#else
518	#error this is not the right thing to do
519	/*
520	#define __cfaasm_label( label ) struct asm_region label = \
521	({ \
522	struct asm_region region; \
523	asm( \
524	"adrp %[vb], __cfaasm_" #label "_before" "\n\t" \
525	"add %[vb], %[vb], :lo12:__cfaasm_" #label "_before" "\n\t" \
526	"adrp %[va], :got:__cfaasm_" #label "_after" "\n\t" \
527	"add %[va], %[va], :lo12:__cfaasm_" #label "_after" "\n\t" \
528	: [vb]"=r"(region.before), [va]"=r"(region.after) \
529	); \
530	region; \
531	});
532	*/
533	#endif
534	#else
535	#error unknown hardware architecture
536	#endif
537
538	// KERNEL ONLY
539	// Check if a __cfactx_switch signal handler shoud defer
540	// If true : preemption is safe
541	// If false : preemption is unsafe and marked as pending
542	static inline bool preemption_ready( void * ip ) {
543	// Get all the region for which it is not safe to preempt
544	__cfaasm_label( get );
545	__cfaasm_label( check );
546	__cfaasm_label( dsable );
547	__cfaasm_label( debug );
548
549	// Check if preemption is safe
550	bool ready = true;
551	if( __cfaasm_in( ip, get ) ) { ready = false; goto EXIT; };
552	if( __cfaasm_in( ip, check ) ) { ready = false; goto EXIT; };
553	if( __cfaasm_in( ip, dsable ) ) { ready = false; goto EXIT; };
554	if( __cfaasm_in( ip, debug ) ) { ready = false; goto EXIT; };
555	if( !__cfaabi_tls.preemption_state.enabled) { ready = false; goto EXIT; };
556	if( __cfaabi_tls.preemption_state.in_progress ) { ready = false; goto EXIT; };
557
558	EXIT:
559	// Adjust the pending flag accordingly
560	__cfaabi_tls.this_processor->pending_preemption = !ready;
561	return ready;
562	}
563
564	//=============================================================================================
565	// Kernel Signal Startup/Shutdown logic
566	//=============================================================================================
567
568	// Startup routine to activate preemption
569	// Called from kernel_startup
570	void __kernel_alarm_startup() {
571	__cfaabi_dbg_print_safe( "Kernel : Starting preemption\n" );
572
573	// Start with preemption disabled until ready
574	__cfaabi_tls.preemption_state.enabled = false;
575	__cfaabi_tls.preemption_state.disable_count = 1;
576
577	// Initialize the event kernel
578	event_kernel = (event_kernel_t *)&storage_event_kernel;
579	(*event_kernel){};
580
581	// Setup proper signal handlers
582	__cfaabi_sigaction( SIGUSR1, sigHandler_ctxSwitch, SA_SIGINFO ); // __cfactx_switch handler
583	__cfaabi_sigaction( SIGALRM, sigHandler_alarm , SA_SIGINFO ); // debug handler
584
585	signal_block( SIGALRM );
586
587	alarm_stack = __create_pthread( &alarm_thread, alarm_loop, 0p );
588	}
589
590	// Shutdown routine to deactivate preemption
591	// Called from kernel_shutdown
592	void __kernel_alarm_shutdown() {
593	__cfaabi_dbg_print_safe( "Kernel : Preemption stopping\n" );
594
595	// Block all signals since we are already shutting down
596	sigset_t mask;
597	sigfillset( &mask );
598	sigprocmask( SIG_BLOCK, &mask, 0p );
599
600	// Notify the alarm thread of the shutdown
601	sigval val = { 1 };
602	pthread_sigqueue( alarm_thread, SIGALRM, val );
603
604	// Wait for the preemption thread to finish
605
606	__destroy_pthread( alarm_thread, alarm_stack, 0p );
607
608	// Preemption is now fully stopped
609
610	__cfaabi_dbg_print_safe( "Kernel : Preemption stopped\n" );
611	}
612
613	// Prevent preemption since we are about to start terminating things
614	void __kernel_abort_lock(void) {
615	signal_block( SIGUSR1 );
616	}
617
618	// Raii ctor/dtor for the preemption_scope
619	// Used by thread to control when they want to receive preemption signals
620	void ?{}( preemption_scope & this, processor * proc ) {
621	(this.alarm){ proc, (Time){ 0 }, 0`s };
622	this.proc = proc;
623	this.proc->preemption_alarm = &this.alarm;
624
625	update_preemption( this.proc, this.proc->cltr->preemption_rate );
626	}
627
628	void ^?{}( preemption_scope & this ) {
629	disable_interrupts();
630
631	update_preemption( this.proc, 0`s );
632	}
633
634	//=============================================================================================
635	// Kernel Signal Handlers
636	//=============================================================================================
637	__cfaabi_dbg_debug_do( static thread_local void * last_interrupt = 0; )
638
639	// Context switch signal handler
640	// Receives SIGUSR1 signal and causes the current thread to yield
641	static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ ) {
642	void * ip = (void *)(cxt->uc_mcontext.CFA_REG_IP);
643	__cfaabi_dbg_debug_do( last_interrupt = ip; )
644
645	// SKULLDUGGERY: if a thread creates a processor and the immediately deletes it,
646	// the interrupt that is supposed to force the kernel thread to preempt might arrive
647	// before the kernel thread has even started running. When that happens, an interrupt
648	// with a null 'this_processor' will be caught, just ignore it.
649	if(! __cfaabi_tls.this_processor ) return;
650
651	choose(sfp->si_value.sival_int) {
652	case PREEMPT_NORMAL : ;// Normal case, nothing to do here
653	case PREEMPT_TERMINATE: verify( __atomic_load_n( &__cfaabi_tls.this_processor->do_terminate, __ATOMIC_SEQ_CST ) );
654	default:
655	abort( "internal error, signal value is %d", sfp->si_value.sival_int );
656	}
657
658	// Check if it is safe to preempt here
659	if( !preemption_ready( ip ) ) { return; }
660
661	__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) );
662
663	// Sync flag : prevent recursive calls to the signal handler
664	__cfaabi_tls.preemption_state.in_progress = true;
665
666	// Clear sighandler mask before context switching.
667	#if GCC_VERSION > 50000
668	static_assert( sizeof( sigset_t ) == sizeof( cxt->uc_sigmask ), "Expected cxt->uc_sigmask to be of sigset_t" );
669	#endif
670	if ( pthread_sigmask( SIG_SETMASK, (sigset_t *)&(cxt->uc_sigmask), 0p ) == -1 ) {
671	abort( "internal error, sigprocmask" );
672	}
673
674	// Clear the in progress flag
675	__cfaabi_tls.preemption_state.in_progress = false;
676
677	// Preemption can occur here
678
679	force_yield( __ALARM_PREEMPTION ); // Do the actual __cfactx_switch
680	}
681
682	static void sigHandler_alarm( __CFA_SIGPARMS__ ) {
683	abort("SIGALRM should never reach the signal handler");
684	}
685
686	// Main of the alarm thread
687	// Waits on SIGALRM and send SIGUSR1 to whom ever needs it
688	static void * alarm_loop( __attribute__((unused)) void * args ) {
689	__processor_id_t id;
690	register_proc_id(&id);
691	__cfaabi_tls.this_proc_id = &id;
692
693
694	// Block sigalrms to control when they arrive
695	sigset_t mask;
696	sigfillset(&mask);
697	if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
698	abort( "internal error, pthread_sigmask" );
699	}
700
701	sigemptyset( &mask );
702	sigaddset( &mask, SIGALRM );
703
704	// Main loop
705	while( true ) {
706	// Wait for a sigalrm
707	siginfo_t info;
708	int sig = sigwaitinfo( &mask, &info );
709
710	if( sig < 0 ) {
711	//Error!
712	int err = errno;
713	switch( err ) {
714	case EAGAIN :
715	case EINTR :
716	{__cfaabi_dbg_print_buffer_decl( " KERNEL: Spurious wakeup %d.\n", err );}
717	continue;
718	case EINVAL :
719	abort( "Timeout was invalid." );
720	default:
721	abort( "Unhandled error %d", err);
722	}
723	}
724
725	// If another signal arrived something went wrong
726	assertf(sig == SIGALRM, "Kernel Internal Error, sigwait: Unexpected signal %d (%d : %d)\n", sig, info.si_code, info.si_value.sival_int);
727
728	// __cfaabi_dbg_print_safe( "Kernel : Caught alarm from %d with %d\n", info.si_code, info.si_value.sival_int );
729	// Switch on the code (a.k.a. the sender) to
730	switch( info.si_code )
731	{
732	// Timers can apparently be marked as sent for the kernel
733	// In either case, tick preemption
734	case SI_TIMER:
735	case SI_KERNEL:
736	// __cfaabi_dbg_print_safe( "Kernel : Preemption thread tick\n" );
737	lock( event_kernel->lock __cfaabi_dbg_ctx2 );
738	tick_preemption();
739	unlock( event_kernel->lock );
740	break;
741	// Signal was not sent by the kernel but by an other thread
742	case SI_QUEUE:
743	// For now, other thread only signal the alarm thread to shut it down
744	// If this needs to change use info.si_value and handle the case here
745	goto EXIT;
746	}
747	}
748
749	EXIT:
750	__cfaabi_dbg_print_safe( "Kernel : Preemption thread stopping\n" );
751	register_proc_id(&id);
752
753	return 0p;
754	}
755
756	// Local Variables: //
757	// mode: c //
758	// tab-width: 4 //
759	// End: //

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