source: libcfa/src/concurrency/preemption.cfa @ 43784ac

jacob/cs343-translationnew-ast-unique-expr
Last change on this file since 43784ac was 43784ac, checked in by Thierry Delisle <tdelisle@…>, 3 months ago

Changed libcfathread to consistently define _GNU_SOURCE

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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
62static void preempt( processor   * this );
63static void timeout( $thread * this );
64
65// FwdDeclarations : Signal handlers
66static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ );
67static void sigHandler_alarm    ( __CFA_SIGPARMS__ );
68static void sigHandler_segv     ( __CFA_SIGPARMS__ );
69static void sigHandler_ill      ( __CFA_SIGPARMS__ );
70static void sigHandler_fpe      ( __CFA_SIGPARMS__ );
71static void sigHandler_abort    ( __CFA_SIGPARMS__ );
72
73// FwdDeclarations : alarm thread main
74static void * alarm_loop( __attribute__((unused)) void * args );
75
76// Machine specific register name
77#if   defined( __i386 )
78#define CFA_REG_IP gregs[REG_EIP]
79#elif defined( __x86_64 )
80#define CFA_REG_IP gregs[REG_RIP]
81#elif defined( __arm__ )
82#define CFA_REG_IP arm_pc
83#elif defined( __aarch64__ )
84#define CFA_REG_IP pc
85#else
86#error unsupported hardware architecture
87#endif
88
89KERNEL_STORAGE(event_kernel_t, event_kernel);         // private storage for event kernel
90event_kernel_t * event_kernel;                        // kernel public handle to even kernel
91static pthread_t alarm_thread;                        // pthread handle to alarm thread
92static void * alarm_stack;                                                        // pthread stack for alarm thread
93
94static void ?{}(event_kernel_t & this) with( this ) {
95        alarms{};
96        lock{};
97}
98
99enum {
100        PREEMPT_NORMAL    = 0,
101        PREEMPT_TERMINATE = 1,
102};
103
104//=============================================================================================
105// Kernel Preemption logic
106//=============================================================================================
107
108// Get next expired node
109static 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
116static 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
160void 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
245bool __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
259struct asm_region {
260        void * before;
261        void * after;
262};
263
264static 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;
272uintptr_t __cfatls_get( unsigned long int offset ) __attribute__((__noinline__)); //no inline to avoid problems
273uintptr_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
287extern "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
356void __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__
383bool __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
394static 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
405static 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
416static 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
422static void timeout( $thread * this ) {
423        unpark( this );
424}
425
426void __disable_interrupts_hard() {
427        sigset_t oldset;
428        int ret;
429        ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset);  // workaround trac#208: cast should be unnecessary
430        if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
431
432        ret = sigismember(&oldset, SIGUSR1);
433        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
434        if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
435
436        ret = sigismember(&oldset, SIGALRM);
437        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
438        if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
439
440        signal_block( SIGUSR1 );
441}
442
443void __enable_interrupts_hard() {
444        signal_unblock( SIGUSR1 );
445
446        sigset_t oldset;
447        int ret;
448        ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset);  // workaround trac#208: cast should be unnecessary
449        if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
450
451        ret = sigismember(&oldset, SIGUSR1);
452        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
453        if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
454
455        ret = sigismember(&oldset, SIGALRM);
456        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
457        if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
458}
459
460//-----------------------------------------------------------------------------
461// Some assembly required
462#if defined( __i386 )
463        #ifdef __PIC__
464                #define RELOC_PRELUDE( label ) \
465                        "calll   .Lcfaasm_prelude_" #label "$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
545static 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
561EXIT:
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
573void __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
595void __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
618void __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
624void ?{}( 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
632void ^?{}( 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
645static 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
686static 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
692static 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
759EXIT:
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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