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preemption.cfa@ f815c46

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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 f815c46 was 6047b00, checked in by Thierry Delisle <tdelisle@…>, 5 years ago
Removed SA_RESTART from preemption since it seems to cause more problems than anything else.
Property mode set to `100644`
File size: 26.6 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
18	#include "preemption.hfa"
19	#include <assert.h>
20
21	#include <errno.h>
22	#include <stdio.h>
23	#include <string.h>
24	#include <unistd.h>
25	#include <limits.h> // PTHREAD_STACK_MIN
26
27	#include "bits/signal.hfa"
28	#include "kernel_private.hfa"
29
30	#if !defined(__CFA_DEFAULT_PREEMPTION__)
31	#define __CFA_DEFAULT_PREEMPTION__ 10`ms
32	#endif
33
34	Duration default_preemption() __attribute__((weak)) {
35	return __CFA_DEFAULT_PREEMPTION__;
36	}
37
38	// FwdDeclarations : timeout handlers
39	static void preempt( processor * this );
40	static void timeout( $thread * this );
41
42	// FwdDeclarations : Signal handlers
43	static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ );
44	static void sigHandler_alarm ( __CFA_SIGPARMS__ );
45	static void sigHandler_segv ( __CFA_SIGPARMS__ );
46	static void sigHandler_ill ( __CFA_SIGPARMS__ );
47	static void sigHandler_fpe ( __CFA_SIGPARMS__ );
48	static void sigHandler_abort ( __CFA_SIGPARMS__ );
49
50	// FwdDeclarations : alarm thread main
51	static void * alarm_loop( __attribute__((unused)) void * args );
52
53	// Machine specific register name
54	#if defined( __i386 )
55	#define CFA_REG_IP gregs[REG_EIP]
56	#elif defined( __x86_64 )
57	#define CFA_REG_IP gregs[REG_RIP]
58	#elif defined( __arm__ )
59	#define CFA_REG_IP arm_pc
60	#elif defined( __aarch64__ )
61	#define CFA_REG_IP pc
62	#else
63	#error unsupported hardware architecture
64	#endif
65
66	KERNEL_STORAGE(event_kernel_t, event_kernel); // private storage for event kernel
67	event_kernel_t * event_kernel; // kernel public handle to even kernel
68	static pthread_t alarm_thread; // pthread handle to alarm thread
69	static void * alarm_stack; // pthread stack for alarm thread
70
71	static void ?{}(event_kernel_t & this) with( this ) {
72	alarms{};
73	lock{};
74	}
75
76	enum {
77	PREEMPT_NORMAL = 0,
78	PREEMPT_TERMINATE = 1,
79	};
80
81	//=============================================================================================
82	// Kernel Preemption logic
83	//=============================================================================================
84
85	// Get next expired node
86	static inline alarm_node_t * get_expired( alarm_list_t * alarms, Time currtime ) {
87	if( ! & (*alarms)`first ) return 0p; // If no alarms return null
88	if( (*alarms)`first.alarm >= currtime ) return 0p; // If alarms head not expired return null
89	return pop(alarms); // Otherwise just pop head
90	}
91
92	// Tick one frame of the Discrete Event Simulation for alarms
93	static void tick_preemption(void) {
94	alarm_node_t * node = 0p; // Used in the while loop but cannot be declared in the while condition
95	alarm_list_t * alarms = &event_kernel->alarms; // Local copy for ease of reading
96	Time currtime = __kernel_get_time(); // Check current time once so everything "happens at once"
97
98	//Loop throught every thing expired
99	while( node = get_expired( alarms, currtime ) ) {
100	// __cfaabi_dbg_print_buffer_decl( " KERNEL: preemption tick.\n" );
101	Duration period = node->period;
102	if( period == 0) {
103	node->set = false; // Node is one-shot, just mark it as not pending
104	}
105
106	// Check if this is a kernel
107	if( node->type == Kernel ) {
108	preempt( node->proc );
109	}
110	else if( node->type == User ) {
111	timeout( node->thrd );
112	}
113	else {
114	node->callback(*node);
115	}
116
117	// Check if this is a periodic alarm
118	if( period > 0 ) {
119	// __cfaabi_dbg_print_buffer_local( " KERNEL: alarm period is %lu.\n", period.tv );
120	node->alarm = currtime + period; // Alarm is periodic, add currtime to it (used cached current time)
121	insert( alarms, node ); // Reinsert the node for the next time it triggers
122	}
123	}
124
125	// If there are still alarms pending, reset the timer
126	if( & (*alarms)`first ) {
127	__cfadbg_print_buffer_decl(preemption, " KERNEL: @%ju(%ju) resetting alarm to %ju.\n", currtime.tv, __kernel_get_time().tv, (alarms->head->alarm - currtime).tv);
128	Duration delta = (*alarms)`first.alarm - currtime;
129	Duration capped = max(delta, 50`us);
130	// itimerval tim = { caped };
131	// __cfaabi_dbg_print_buffer_local( " Values are %lu, %lu, %lu %lu.\n", delta.tv, caped.tv, tim.it_value.tv_sec, tim.it_value.tv_usec);
132
133	__kernel_set_timer( capped );
134	}
135	}
136
137	// Update the preemption of a processor and notify interested parties
138	void update_preemption( processor * this, Duration duration ) {
139	alarm_node_t * alarm = this->preemption_alarm;
140
141	// Alarms need to be enabled
142	if ( duration > 0 && ! alarm->set ) {
143	alarm->alarm = __kernel_get_time() + duration;
144	alarm->period = duration;
145	register_self( alarm );
146	}
147	// Zero duration but alarm is set
148	else if ( duration == 0 && alarm->set ) {
149	unregister_self( alarm );
150	alarm->alarm = 0;
151	alarm->period = 0;
152	}
153	// If alarm is different from previous, change it
154	else if ( duration > 0 && alarm->period != duration ) {
155	unregister_self( alarm );
156	alarm->alarm = __kernel_get_time() + duration;
157	alarm->period = duration;
158	register_self( alarm );
159	}
160	}
161
162	//=============================================================================================
163	// Kernel Signal Tools
164	//=============================================================================================
165	// In a user-level threading system, there are handful of thread-local variables where this problem occurs on the ARM.
166	//
167	// For each kernel thread running user-level threads, there is a flag variable to indicate if interrupts are
168	// enabled/disabled for that kernel thread. Therefore, this variable is made thread local.
169	//
170	// For example, this code fragment sets the state of the "interrupt" variable in thread-local memory.
171	//
172	// _Thread_local volatile int interrupts;
173	// int main() {
174	// interrupts = 0; // disable interrupts }
175	//
176	// which generates the following code on the ARM
177	//
178	// (gdb) disassemble main
179	// Dump of assembler code for function main:
180	// 0x0000000000000610 <+0>: mrs x1, tpidr_el0
181	// 0x0000000000000614 <+4>: mov w0, #0x0 // #0
182	// 0x0000000000000618 <+8>: add x1, x1, #0x0, lsl #12
183	// 0x000000000000061c <+12>: add x1, x1, #0x10
184	// 0x0000000000000620 <+16>: str wzr, [x1]
185	// 0x0000000000000624 <+20>: ret
186	//
187	// The mrs moves a pointer from coprocessor register tpidr_el0 into register x1. Register w0 is set to 0. The two adds
188	// increase the TLS pointer with the displacement (offset) 0x10, which is the location in the TSL of variable
189	// "interrupts". Finally, 0 is stored into "interrupts" through the pointer in register x1 that points into the
190	// TSL. Now once x1 has the pointer to the location of the TSL for kernel thread N, it can be be preempted at a
191	// user-level and the user thread is put on the user-level ready-queue. When the preempted thread gets to the front of
192	// the user-level ready-queue it is run on kernel thread M. It now stores 0 into "interrupts" back on kernel thread N,
193	// turning off interrupt on the wrong kernel thread.
194	//
195	// On the x86, the following code is generated for the same code fragment.
196	//
197	// (gdb) disassemble main
198	// Dump of assembler code for function main:
199	// 0x0000000000400420 <+0>: movl $0x0,%fs:0xfffffffffffffffc
200	// 0x000000000040042c <+12>: xor %eax,%eax
201	// 0x000000000040042e <+14>: retq
202	//
203	// and there is base-displacement addressing used to atomically reset variable "interrupts" off of the TSL pointer in
204	// register "fs".
205	//
206	// Hence, the ARM has base-displacement address for the general purpose registers, BUT not to the coprocessor
207	// registers. As a result, generating the address for the write into variable "interrupts" is no longer atomic.
208	//
209	// Note this problem does NOT occur when just using multiple kernel threads because the preemption ALWAYS restarts the
210	// thread on the same kernel thread.
211	//
212	// The obvious question is why does ARM use a coprocessor register to store the TSL pointer given that coprocessor
213	// registers are second-class registers with respect to the instruction set. One possible answer is that they did not
214	// want to dedicate one of the general registers to hold the TLS pointer and there was a free coprocessor register
215	// available.
216
217	//-----------------------------------------------------------------------------
218	// Some assembly required
219	#define __cfaasm_label(label, when) when: asm volatile goto(".global __cfaasm_" #label "_" #when "\n" "__cfaasm_" #label "_" #when ":":::"memory":when)
220
221	//----------
222	// special case for preemption since used often
223	bool __preemption_enabled() {
224	// create a assembler label before
225	// marked as clobber all to avoid movement
226	__cfaasm_label(check, before);
227
228	// access tls as normal
229	bool enabled = __cfaabi_tls.preemption_state.enabled;
230
231	// create a assembler label after
232	// marked as clobber all to avoid movement
233	__cfaasm_label(check, after);
234	return enabled;
235	}
236
237	struct asm_region {
238	void * before;
239	void * after;
240	};
241
242	static inline bool __cfaasm_in( void * ip, struct asm_region & region ) {
243	return ip >= region.before && ip <= region.after;
244	}
245
246
247	//----------
248	// Get data from the TLS block
249	// struct asm_region __cfaasm_get;
250	uintptr_t __cfatls_get( unsigned long int offset ) __attribute__((__noinline__)); //no inline to avoid problems
251	uintptr_t __cfatls_get( unsigned long int offset ) {
252	// create a assembler label before
253	// marked as clobber all to avoid movement
254	__cfaasm_label(get, before);
255
256	// access tls as normal (except for pointer arithmetic)
257	uintptr_t val = (uintptr_t)((uintptr_t)&__cfaabi_tls + offset);
258
259	// create a assembler label after
260	// marked as clobber all to avoid movement
261	__cfaasm_label(get, after);
262	return val;
263	}
264
265	extern "C" {
266	// Disable interrupts by incrementing the counter
267	void disable_interrupts() {
268	// create a assembler label before
269	// marked as clobber all to avoid movement
270	__cfaasm_label(dsable, before);
271
272	with( __cfaabi_tls.preemption_state ) {
273	#if GCC_VERSION > 50000
274	static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
275	#endif
276
277	// Set enabled flag to false
278	// should be atomic to avoid preemption in the middle of the operation.
279	// use memory order RELAXED since there is no inter-thread on this variable requirements
280	__atomic_store_n(&enabled, false, __ATOMIC_RELAXED);
281
282	// Signal the compiler that a fence is needed but only for signal handlers
283	__atomic_signal_fence(__ATOMIC_ACQUIRE);
284
285	__attribute__((unused)) unsigned short new_val = disable_count + 1;
286	disable_count = new_val;
287	verify( new_val < 65_000u ); // If this triggers someone is disabling interrupts without enabling them
288	}
289
290	// create a assembler label after
291	// marked as clobber all to avoid movement
292	__cfaasm_label(dsable, after);
293
294	}
295
296	// Enable interrupts by decrementing the counter
297	// If counter reaches 0, execute any pending __cfactx_switch
298	void enable_interrupts( __cfaabi_dbg_ctx_param ) {
299	// Cache the processor now since interrupts can start happening after the atomic store
300	processor * proc = __cfaabi_tls.this_processor;
301	/* paranoid */ verify( proc );
302
303	with( __cfaabi_tls.preemption_state ){
304	unsigned short prev = disable_count;
305	disable_count -= 1;
306
307	// If this triggers someone is enabled already enabled interruptsverify( prev != 0u );
308	/* paranoid */ verify( prev != 0u );
309
310	// Check if we need to prempt the thread because an interrupt was missed
311	if( prev == 1 ) {
312	#if GCC_VERSION > 50000
313	static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
314	#endif
315
316	// Set enabled flag to true
317	// should be atomic to avoid preemption in the middle of the operation.
318	// use memory order RELAXED since there is no inter-thread on this variable requirements
319	__atomic_store_n(&enabled, true, __ATOMIC_RELAXED);
320
321	// Signal the compiler that a fence is needed but only for signal handlers
322	__atomic_signal_fence(__ATOMIC_RELEASE);
323	if( proc->pending_preemption ) {
324	proc->pending_preemption = false;
325	force_yield( __POLL_PREEMPTION );
326	}
327	}
328	}
329
330	// For debugging purposes : keep track of the last person to enable the interrupts
331	__cfaabi_dbg_debug_do( proc->last_enable = caller; )
332	}
333
334	// Disable interrupts by incrementint the counter
335	// Don't execute any pending __cfactx_switch even if counter reaches 0
336	void enable_interrupts_noPoll() {
337	unsigned short prev = __cfaabi_tls.preemption_state.disable_count;
338	__cfaabi_tls.preemption_state.disable_count -= 1;
339	// If this triggers someone is enabled already enabled interrupts
340	/* paranoid */ verifyf( prev != 0u, "Incremented from %u\n", prev );
341	if( prev == 1 ) {
342	#if GCC_VERSION > 50000
343	static_assert(__atomic_always_lock_free(sizeof(__cfaabi_tls.preemption_state.enabled), &__cfaabi_tls.preemption_state.enabled), "Must be lock-free");
344	#endif
345	// Set enabled flag to true
346	// should be atomic to avoid preemption in the middle of the operation.
347	// use memory order RELAXED since there is no inter-thread on this variable requirements
348	__atomic_store_n(&__cfaabi_tls.preemption_state.enabled, true, __ATOMIC_RELAXED);
349
350	// Signal the compiler that a fence is needed but only for signal handlers
351	__atomic_signal_fence(__ATOMIC_RELEASE);
352	}
353	}
354	}
355
356	//-----------------------------------------------------------------------------
357	// Kernel Signal Debug
358	void __cfaabi_check_preemption() {
359	bool ready = __preemption_enabled();
360	if(!ready) { abort("Preemption should be ready"); }
361
362	__cfaasm_label(debug, before);
363
364	sigset_t oldset;
365	int ret;
366	ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset); // workaround trac#208: cast should be unnecessary
367	if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
368
369	ret = sigismember(&oldset, SIGUSR1);
370	if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
371	if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
372
373	ret = sigismember(&oldset, SIGALRM);
374	if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
375	if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
376
377	ret = sigismember(&oldset, SIGTERM);
378	if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
379	if(ret == 1) { abort("ERROR SIGTERM is disabled"); }
380
381	__cfaasm_label(debug, after);
382	}
383
384	#ifdef __CFA_WITH_VERIFY__
385	bool __cfaabi_dbg_in_kernel() {
386	return !__preemption_enabled();
387	}
388	#endif
389
390	#undef __cfaasm_label
391
392	//-----------------------------------------------------------------------------
393	// Signal handling
394
395	// sigprocmask wrapper : unblock a single signal
396	static inline void signal_unblock( int sig ) {
397	sigset_t mask;
398	sigemptyset( &mask );
399	sigaddset( &mask, sig );
400
401	if ( pthread_sigmask( SIG_UNBLOCK, &mask, 0p ) == -1 ) {
402	abort( "internal error, pthread_sigmask" );
403	}
404	}
405
406	// sigprocmask wrapper : block a single signal
407	static inline void signal_block( int sig ) {
408	sigset_t mask;
409	sigemptyset( &mask );
410	sigaddset( &mask, sig );
411
412	if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
413	abort( "internal error, pthread_sigmask" );
414	}
415	}
416
417	// kill wrapper : signal a processor
418	static void preempt( processor * this ) {
419	sigval_t value = { PREEMPT_NORMAL };
420	pthread_sigqueue( this->kernel_thread, SIGUSR1, value );
421	}
422
423	// reserved for future use
424	static void timeout( $thread * this ) {
425	unpark( this );
426	}
427
428	void __disable_interrupts_hard() {
429	sigset_t oldset;
430	int ret;
431	ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset); // workaround trac#208: cast should be unnecessary
432	if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
433
434	ret = sigismember(&oldset, SIGUSR1);
435	if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
436	if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
437
438	ret = sigismember(&oldset, SIGALRM);
439	if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
440	if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
441
442	signal_block( SIGUSR1 );
443	}
444
445	void __enable_interrupts_hard() {
446	signal_unblock( SIGUSR1 );
447
448	sigset_t oldset;
449	int ret;
450	ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset); // workaround trac#208: cast should be unnecessary
451	if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
452
453	ret = sigismember(&oldset, SIGUSR1);
454	if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
455	if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
456
457	ret = sigismember(&oldset, SIGALRM);
458	if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
459	if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
460	}
461
462	//-----------------------------------------------------------------------------
463	// Some assembly required
464	#if defined( __i386 )
465	#ifdef __PIC__
466	#define RELOC_PRELUDE( label ) \
467	"calll .Lcfaasm_prelude_" #label "$pb\n\t" \
468	".Lcfaasm_prelude_" #label "$pb:\n\t" \
469	"popl %%eax\n\t" \
470	".Lcfaasm_prelude_" #label "_end:\n\t" \
471	"addl $_GLOBAL_OFFSET_TABLE_+(.Lcfaasm_prelude_" #label "_end-.Lcfaasm_prelude_" #label "$pb), %%eax\n\t"
472	#define RELOC_PREFIX ""
473	#define RELOC_SUFFIX "@GOT(%%eax)"
474	#else
475	#define RELOC_PREFIX "$"
476	#define RELOC_SUFFIX ""
477	#endif
478	#define __cfaasm_label( label ) struct asm_region label = \
479	({ \
480	struct asm_region region; \
481	asm( \
482	RELOC_PRELUDE( label ) \
483	"movl " RELOC_PREFIX "__cfaasm_" #label "_before" RELOC_SUFFIX ", %[vb]\n\t" \
484	"movl " RELOC_PREFIX "__cfaasm_" #label "_after" RELOC_SUFFIX ", %[va]\n\t" \
485	: [vb]"=r"(region.before), [va]"=r"(region.after) \
486	); \
487	region; \
488	});
489	#elif defined( __x86_64 )
490	#ifdef __PIC__
491	#define RELOC_PREFIX ""
492	#define RELOC_SUFFIX "@GOTPCREL(%%rip)"
493	#else
494	#define RELOC_PREFIX "$"
495	#define RELOC_SUFFIX ""
496	#endif
497	#define __cfaasm_label( label ) struct asm_region label = \
498	({ \
499	struct asm_region region; \
500	asm( \
501	"movq " RELOC_PREFIX "__cfaasm_" #label "_before" RELOC_SUFFIX ", %[vb]\n\t" \
502	"movq " RELOC_PREFIX "__cfaasm_" #label "_after" RELOC_SUFFIX ", %[va]\n\t" \
503	: [vb]"=r"(region.before), [va]"=r"(region.after) \
504	); \
505	region; \
506	});
507	#elif defined( __aarch64__ )
508	#ifdef __PIC__
509	// Note that this works only for gcc
510	#define __cfaasm_label( label ) struct asm_region label = \
511	({ \
512	struct asm_region region; \
513	asm( \
514	"adrp %[vb], _GLOBAL_OFFSET_TABLE_" "\n\t" \
515	"ldr %[vb], [%[vb], #:gotpage_lo15:__cfaasm_" #label "_before]" "\n\t" \
516	"adrp %[va], _GLOBAL_OFFSET_TABLE_" "\n\t" \
517	"ldr %[va], [%[va], #:gotpage_lo15:__cfaasm_" #label "_after]" "\n\t" \
518	: [vb]"=r"(region.before), [va]"=r"(region.after) \
519	); \
520	region; \
521	});
522	#else
523	#error this is not the right thing to do
524	/*
525	#define __cfaasm_label( label ) struct asm_region label = \
526	({ \
527	struct asm_region region; \
528	asm( \
529	"adrp %[vb], __cfaasm_" #label "_before" "\n\t" \
530	"add %[vb], %[vb], :lo12:__cfaasm_" #label "_before" "\n\t" \
531	"adrp %[va], :got:__cfaasm_" #label "_after" "\n\t" \
532	"add %[va], %[va], :lo12:__cfaasm_" #label "_after" "\n\t" \
533	: [vb]"=r"(region.before), [va]"=r"(region.after) \
534	); \
535	region; \
536	});
537	*/
538	#endif
539	#else
540	#error unknown hardware architecture
541	#endif
542
543	// KERNEL ONLY
544	// Check if a __cfactx_switch signal handler shoud defer
545	// If true : preemption is safe
546	// If false : preemption is unsafe and marked as pending
547	static inline bool preemption_ready( void * ip ) {
548	// Get all the region for which it is not safe to preempt
549	__cfaasm_label( get );
550	__cfaasm_label( check );
551	__cfaasm_label( dsable );
552	__cfaasm_label( debug );
553
554	// Check if preemption is safe
555	bool ready = true;
556	if( __cfaasm_in( ip, get ) ) { ready = false; goto EXIT; };
557	if( __cfaasm_in( ip, check ) ) { ready = false; goto EXIT; };
558	if( __cfaasm_in( ip, dsable ) ) { ready = false; goto EXIT; };
559	if( __cfaasm_in( ip, debug ) ) { ready = false; goto EXIT; };
560	if( !__cfaabi_tls.preemption_state.enabled) { ready = false; goto EXIT; };
561	if( __cfaabi_tls.preemption_state.in_progress ) { ready = false; goto EXIT; };
562
563	EXIT:
564	// Adjust the pending flag accordingly
565	__cfaabi_tls.this_processor->pending_preemption = !ready;
566	return ready;
567	}
568
569	//=============================================================================================
570	// Kernel Signal Startup/Shutdown logic
571	//=============================================================================================
572
573	// Startup routine to activate preemption
574	// Called from kernel_startup
575	void __kernel_alarm_startup() {
576	__cfaabi_dbg_print_safe( "Kernel : Starting preemption\n" );
577
578	// Start with preemption disabled until ready
579	__cfaabi_tls.preemption_state.enabled = false;
580	__cfaabi_tls.preemption_state.disable_count = 1;
581
582	// Initialize the event kernel
583	event_kernel = (event_kernel_t *)&storage_event_kernel;
584	(*event_kernel){};
585
586	// Setup proper signal handlers
587	__cfaabi_sigaction( SIGUSR1, sigHandler_ctxSwitch, SA_SIGINFO ); // __cfactx_switch handler
588	__cfaabi_sigaction( SIGALRM, sigHandler_alarm , SA_SIGINFO ); // debug handler
589
590	signal_block( SIGALRM );
591
592	alarm_stack = __create_pthread( &alarm_thread, alarm_loop, 0p );
593	}
594
595	// Shutdown routine to deactivate preemption
596	// Called from kernel_shutdown
597	void __kernel_alarm_shutdown() {
598	__cfaabi_dbg_print_safe( "Kernel : Preemption stopping\n" );
599
600	// Block all signals since we are already shutting down
601	sigset_t mask;
602	sigfillset( &mask );
603	sigprocmask( SIG_BLOCK, &mask, 0p );
604
605	// Notify the alarm thread of the shutdown
606	sigval val = { 1 };
607	pthread_sigqueue( alarm_thread, SIGALRM, val );
608
609	// Wait for the preemption thread to finish
610
611	__destroy_pthread( alarm_thread, alarm_stack, 0p );
612
613	// Preemption is now fully stopped
614
615	__cfaabi_dbg_print_safe( "Kernel : Preemption stopped\n" );
616	}
617
618	// Prevent preemption since we are about to start terminating things
619	void __kernel_abort_lock(void) {
620	signal_block( SIGUSR1 );
621	}
622
623	// Raii ctor/dtor for the preemption_scope
624	// Used by thread to control when they want to receive preemption signals
625	void ?{}( preemption_scope & this, processor * proc ) {
626	(this.alarm){ proc, (Time){ 0 }, 0`s };
627	this.proc = proc;
628	this.proc->preemption_alarm = &this.alarm;
629
630	update_preemption( this.proc, this.proc->cltr->preemption_rate );
631	}
632
633	void ^?{}( preemption_scope & this ) {
634	disable_interrupts();
635
636	update_preemption( this.proc, 0`s );
637	}
638
639	//=============================================================================================
640	// Kernel Signal Handlers
641	//=============================================================================================
642	__cfaabi_dbg_debug_do( static thread_local void * last_interrupt = 0; )
643
644	// Context switch signal handler
645	// Receives SIGUSR1 signal and causes the current thread to yield
646	static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ ) {
647	void * ip = (void *)(cxt->uc_mcontext.CFA_REG_IP);
648	__cfaabi_dbg_debug_do( last_interrupt = ip; )
649
650	// SKULLDUGGERY: if a thread creates a processor and the immediately deletes it,
651	// the interrupt that is supposed to force the kernel thread to preempt might arrive
652	// before the kernel thread has even started running. When that happens, an interrupt
653	// with a null 'this_processor' will be caught, just ignore it.
654	if(! __cfaabi_tls.this_processor ) return;
655
656	choose(sfp->si_value.sival_int) {
657	case PREEMPT_NORMAL : ;// Normal case, nothing to do here
658	case PREEMPT_TERMINATE: verify( __atomic_load_n( &__cfaabi_tls.this_processor->do_terminate, __ATOMIC_SEQ_CST ) );
659	default:
660	abort( "internal error, signal value is %d", sfp->si_value.sival_int );
661	}
662
663	// Check if it is safe to preempt here
664	if( !preemption_ready( ip ) ) { return; }
665
666	__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) );
667
668	// Sync flag : prevent recursive calls to the signal handler
669	__cfaabi_tls.preemption_state.in_progress = true;
670
671	// Clear sighandler mask before context switching.
672	#if GCC_VERSION > 50000
673	static_assert( sizeof( sigset_t ) == sizeof( cxt->uc_sigmask ), "Expected cxt->uc_sigmask to be of sigset_t" );
674	#endif
675	if ( pthread_sigmask( SIG_SETMASK, (sigset_t *)&(cxt->uc_sigmask), 0p ) == -1 ) {
676	abort( "internal error, sigprocmask" );
677	}
678
679	// Clear the in progress flag
680	__cfaabi_tls.preemption_state.in_progress = false;
681
682	// Preemption can occur here
683
684	force_yield( __ALARM_PREEMPTION ); // Do the actual __cfactx_switch
685	}
686
687	static void sigHandler_alarm( __CFA_SIGPARMS__ ) {
688	abort("SIGALRM should never reach the signal handler");
689	}
690
691	#if !defined(__CFA_NO_STATISTICS__)
692	int __print_alarm_stats = 0;
693	#endif
694
695	// Main of the alarm thread
696	// Waits on SIGALRM and send SIGUSR1 to whom ever needs it
697	static void * alarm_loop( __attribute__((unused)) void * args ) {
698	__processor_id_t id;
699	id.full_proc = false;
700	id.id = doregister(&id);
701	__cfaabi_tls.this_proc_id = &id;
702
703	#if !defined(__CFA_NO_STATISTICS__)
704	struct __stats_t local_stats;
705	__cfaabi_tls.this_stats = &local_stats;
706	__init_stats( &local_stats );
707	#endif
708
709	// Block sigalrms to control when they arrive
710	sigset_t mask;
711	sigfillset(&mask);
712	if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
713	abort( "internal error, pthread_sigmask" );
714	}
715
716	sigemptyset( &mask );
717	sigaddset( &mask, SIGALRM );
718
719	// Main loop
720	while( true ) {
721	// Wait for a sigalrm
722	siginfo_t info;
723	int sig = sigwaitinfo( &mask, &info );
724
725	if( sig < 0 ) {
726	//Error!
727	int err = errno;
728	switch( err ) {
729	case EAGAIN :
730	case EINTR :
731	{__cfaabi_dbg_print_buffer_decl( " KERNEL: Spurious wakeup %d.\n", err );}
732	continue;
733	case EINVAL :
734	abort( "Timeout was invalid." );
735	default:
736	abort( "Unhandled error %d", err);
737	}
738	}
739
740	// If another signal arrived something went wrong
741	assertf(sig == SIGALRM, "Kernel Internal Error, sigwait: Unexpected signal %d (%d : %d)\n", sig, info.si_code, info.si_value.sival_int);
742
743	// __cfaabi_dbg_print_safe( "Kernel : Caught alarm from %d with %d\n", info.si_code, info.si_value.sival_int );
744	// Switch on the code (a.k.a. the sender) to
745	switch( info.si_code )
746	{
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	// Signal was not sent by the kernel but by an other thread
757	case SI_QUEUE:
758	// For now, other thread only signal the alarm thread to shut it down
759	// If this needs to change use info.si_value and handle the case here
760	goto EXIT;
761	}
762	}
763
764	EXIT:
765	__cfaabi_dbg_print_safe( "Kernel : Preemption thread stopping\n" );
766	unregister(&id);
767
768	#if !defined(__CFA_NO_STATISTICS__)
769	if( 0 != __print_alarm_stats ) {
770	__print_stats( &local_stats, __print_alarm_stats, "Alarm", "Thread", 0p );
771	}
772	#endif
773	return 0p;
774	}
775
776	// Local Variables: //
777	// mode: c //
778	// tab-width: 4 //
779	// End: //

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