source: libcfa/src/concurrency/preemption.cfa @ c457dc4

arm-ehjacob/cs343-translationnew-ast-unique-expr
Last change on this file since c457dc4 was c457dc4, checked in by Thierry Delisle <tdelisle@…>, 4 months ago

Fix sequential handling of timers

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1//
2// Cforall Version 1.0.0 Copyright (C) 2016 University of Waterloo
3//
4// The contents of this file are covered under the licence agreement in the
5// file "LICENCE" distributed with Cforall.
6//
7// signal.c --
8//
9// Author           : Thierry Delisle
10// Created On       : Mon Jun 5 14:20:42 2017
11// Last Modified By : Peter A. Buhr
12// Last Modified On : Fri Nov  6 07:42:13 2020
13// Update Count     : 54
14//
15
16#define __cforall_thread__
17// #define __CFA_DEBUG_PRINT_PREEMPTION__
18
19#include "preemption.hfa"
20
21#include <assert.h>
22
23#include <errno.h>
24#include <stdio.h>
25#include <string.h>
26#include <unistd.h>
27#include <limits.h>                                                                             // PTHREAD_STACK_MIN
28
29#include "bits/debug.hfa"
30#include "bits/signal.hfa"
31#include "kernel_private.hfa"
32
33
34#if !defined(__CFA_DEFAULT_PREEMPTION__)
35#define __CFA_DEFAULT_PREEMPTION__ 10`ms
36#endif
37
38__attribute__((weak)) Duration default_preemption() {
39        const char * preempt_rate_s = getenv("CFA_DEFAULT_PREEMPTION");
40        if(!preempt_rate_s) {
41                __cfadbg_print_safe(preemption, "No CFA_DEFAULT_PREEMPTION in ENV\n");
42                return __CFA_DEFAULT_PREEMPTION__;
43        }
44
45        char * endptr = 0p;
46        long int preempt_rate_l = strtol(preempt_rate_s, &endptr, 10);
47        if(preempt_rate_l < 0 || preempt_rate_l > 65535) {
48                __cfadbg_print_safe(preemption, "CFA_DEFAULT_PREEMPTION out of range : %ld\n", preempt_rate_l);
49                return __CFA_DEFAULT_PREEMPTION__;
50        }
51        if('\0' != *endptr) {
52                __cfadbg_print_safe(preemption, "CFA_DEFAULT_PREEMPTION not a decimal number : %s\n", preempt_rate_s);
53                return __CFA_DEFAULT_PREEMPTION__;
54        }
55
56        return preempt_rate_l`ms;
57}
58
59// FwdDeclarations : timeout handlers
60static void preempt( processor   * this );
61static void timeout( $thread * this );
62
63// FwdDeclarations : Signal handlers
64static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ );
65static void sigHandler_alarm    ( __CFA_SIGPARMS__ );
66static void sigHandler_segv     ( __CFA_SIGPARMS__ );
67static void sigHandler_ill      ( __CFA_SIGPARMS__ );
68static void sigHandler_fpe      ( __CFA_SIGPARMS__ );
69static void sigHandler_abort    ( __CFA_SIGPARMS__ );
70
71// FwdDeclarations : alarm thread main
72static void * alarm_loop( __attribute__((unused)) void * args );
73
74// Machine specific register name
75#if   defined( __i386 )
76#define CFA_REG_IP gregs[REG_EIP]
77#elif defined( __x86_64 )
78#define CFA_REG_IP gregs[REG_RIP]
79#elif defined( __arm__ )
80#define CFA_REG_IP arm_pc
81#elif defined( __aarch64__ )
82#define CFA_REG_IP pc
83#else
84#error unsupported hardware architecture
85#endif
86
87KERNEL_STORAGE(event_kernel_t, event_kernel);         // private storage for event kernel
88event_kernel_t * event_kernel;                        // kernel public handle to even kernel
89static pthread_t alarm_thread;                        // pthread handle to alarm thread
90static void * alarm_stack;                                                        // pthread stack for alarm thread
91
92static void ?{}(event_kernel_t & this) with( this ) {
93        alarms{};
94        lock{};
95}
96
97enum {
98        PREEMPT_NORMAL    = 0,
99        PREEMPT_TERMINATE = 1,
100};
101
102//=============================================================================================
103// Kernel Preemption logic
104//=============================================================================================
105
106// Get next expired node
107static inline alarm_node_t * get_expired( alarm_list_t * alarms, Time currtime ) {
108        if( ! & (*alarms)`first ) return 0p;                                            // If no alarms return null
109        if( (*alarms)`first.timeval >= currtime ) return 0p;    // If alarms head not expired return null
110        return pop(alarms);                                                                     // Otherwise just pop head
111}
112
113// Tick one frame of the Discrete Event Simulation for alarms
114static void tick_preemption(void) {
115        alarm_node_t * node = 0p;                                                       // Used in the while loop but cannot be declared in the while condition
116        alarm_list_t * alarms = &event_kernel->alarms;          // Local copy for ease of reading
117        Time currtime = __kernel_get_time();                            // Check current time once so everything "happens at once"
118
119        //Loop throught every thing expired
120        while( node = get_expired( alarms, currtime ) ) {
121                __cfadbg_print_buffer_decl( preemption, " KERNEL: preemption tick %lu\n", currtime.tn);
122                Duration period = node->period;
123                if( period == 0) {
124                        node->set = false;                  // Node is one-shot, just mark it as not pending
125                }
126
127                __cfadbg_print_buffer_local( preemption, " KERNEL: alarm ticking node %p.\n", node );
128
129
130                // Check if this is a kernel
131                if( node->type == Kernel ) {
132                        preempt( node->proc );
133                }
134                else if( node->type == User ) {
135                        __cfadbg_print_buffer_local( preemption, " KERNEL: alarm unparking %p.\n", node->thrd );
136                        timeout( node->thrd );
137                }
138                else {
139                        node->callback(*node);
140                }
141
142                // Check if this is a periodic alarm
143                if( period > 0 ) {
144                        __cfadbg_print_buffer_local( preemption, " KERNEL: alarm period is %lu.\n", period`ns );
145                        node->timeval = currtime + period;  // Alarm is periodic, add currtime to it (used cached current time)
146                        insert( alarms, node );             // Reinsert the node for the next time it triggers
147                }
148        }
149
150        // If there are still alarms pending, reset the timer
151        if( & (*alarms)`first ) {
152                Duration delta = (*alarms)`first.timeval - currtime;
153                __kernel_set_timer( delta );
154        }
155}
156
157// Update the preemption of a processor and notify interested parties
158void update_preemption( processor * this, Duration duration ) {
159        alarm_node_t * alarm = this->preemption_alarm;
160
161        // Alarms need to be enabled
162        if ( duration > 0 && ! alarm->set ) {
163                alarm->initial = duration;
164                alarm->period  = duration;
165                register_self( alarm );
166        }
167        // Zero duration but alarm is set
168        else if ( duration == 0 && alarm->set ) {
169                unregister_self( alarm );
170                alarm->initial = 0;
171                alarm->period  = 0;
172        }
173        // If alarm is different from previous, change it
174        else if ( duration > 0 && alarm->period != duration ) {
175                unregister_self( alarm );
176                alarm->initial = duration;
177                alarm->period  = duration;
178                register_self( alarm );
179        }
180}
181
182//=============================================================================================
183// Kernel Signal Tools
184//=============================================================================================
185// In a user-level threading system, there are handful of thread-local variables where this problem occurs on the ARM.
186//
187// For each kernel thread running user-level threads, there is a flag variable to indicate if interrupts are
188// enabled/disabled for that kernel thread. Therefore, this variable is made thread local.
189//
190// For example, this code fragment sets the state of the "interrupt" variable in thread-local memory.
191//
192// _Thread_local volatile int interrupts;
193// int main() {
194//     interrupts = 0; // disable interrupts }
195//
196// which generates the following code on the ARM
197//
198// (gdb) disassemble main
199// Dump of assembler code for function main:
200//    0x0000000000000610 <+0>:  mrs     x1, tpidr_el0
201//    0x0000000000000614 <+4>:  mov     w0, #0x0                        // #0
202//    0x0000000000000618 <+8>:  add     x1, x1, #0x0, lsl #12
203//    0x000000000000061c <+12>: add     x1, x1, #0x10
204//    0x0000000000000620 <+16>: str     wzr, [x1]
205//    0x0000000000000624 <+20>: ret
206//
207// The mrs moves a pointer from coprocessor register tpidr_el0 into register x1.  Register w0 is set to 0. The two adds
208// increase the TLS pointer with the displacement (offset) 0x10, which is the location in the TSL of variable
209// "interrupts".  Finally, 0 is stored into "interrupts" through the pointer in register x1 that points into the
210// TSL. Now once x1 has the pointer to the location of the TSL for kernel thread N, it can be be preempted at a
211// user-level and the user thread is put on the user-level ready-queue. When the preempted thread gets to the front of
212// the user-level ready-queue it is run on kernel thread M. It now stores 0 into "interrupts" back on kernel thread N,
213// turning off interrupt on the wrong kernel thread.
214//
215// On the x86, the following code is generated for the same code fragment.
216//
217// (gdb) disassemble main
218// Dump of assembler code for function main:
219//    0x0000000000400420 <+0>:  movl   $0x0,%fs:0xfffffffffffffffc
220//    0x000000000040042c <+12>: xor    %eax,%eax
221//    0x000000000040042e <+14>: retq
222//
223// and there is base-displacement addressing used to atomically reset variable "interrupts" off of the TSL pointer in
224// register "fs".
225//
226// Hence, the ARM has base-displacement address for the general purpose registers, BUT not to the coprocessor
227// registers. As a result, generating the address for the write into variable "interrupts" is no longer atomic.
228//
229// Note this problem does NOT occur when just using multiple kernel threads because the preemption ALWAYS restarts the
230// thread on the same kernel thread.
231//
232// The obvious question is why does ARM use a coprocessor register to store the TSL pointer given that coprocessor
233// registers are second-class registers with respect to the instruction set. One possible answer is that they did not
234// want to dedicate one of the general registers to hold the TLS pointer and there was a free coprocessor register
235// available.
236
237//-----------------------------------------------------------------------------
238// Some assembly required
239#define __cfaasm_label(label, when) when: asm volatile goto(".global __cfaasm_" #label "_" #when "\n" "__cfaasm_" #label "_" #when ":":::"memory":when)
240
241//----------
242// special case for preemption since used often
243bool __preemption_enabled() {
244        // create a assembler label before
245        // marked as clobber all to avoid movement
246        __cfaasm_label(check, before);
247
248        // access tls as normal
249        bool enabled = __cfaabi_tls.preemption_state.enabled;
250
251        // create a assembler label after
252        // marked as clobber all to avoid movement
253        __cfaasm_label(check, after);
254        return enabled;
255}
256
257struct asm_region {
258        void * before;
259        void * after;
260};
261
262static inline bool __cfaasm_in( void * ip, struct asm_region & region ) {
263        return ip >= region.before && ip <= region.after;
264}
265
266
267//----------
268// Get data from the TLS block
269// struct asm_region __cfaasm_get;
270uintptr_t __cfatls_get( unsigned long int offset ) __attribute__((__noinline__)); //no inline to avoid problems
271uintptr_t __cfatls_get( unsigned long int offset ) {
272        // create a assembler label before
273        // marked as clobber all to avoid movement
274        __cfaasm_label(get, before);
275
276        // access tls as normal (except for pointer arithmetic)
277        uintptr_t val = *(uintptr_t*)((uintptr_t)&__cfaabi_tls + offset);
278
279        // create a assembler label after
280        // marked as clobber all to avoid movement
281        __cfaasm_label(get, after);
282        return val;
283}
284
285extern "C" {
286        // Disable interrupts by incrementing the counter
287        void disable_interrupts() {
288                // create a assembler label before
289                // marked as clobber all to avoid movement
290                __cfaasm_label(dsable, before);
291
292                with( __cfaabi_tls.preemption_state ) {
293                        #if GCC_VERSION > 50000
294                        static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
295                        #endif
296
297                        // Set enabled flag to false
298                        // should be atomic to avoid preemption in the middle of the operation.
299                        // use memory order RELAXED since there is no inter-thread on this variable requirements
300                        __atomic_store_n(&enabled, false, __ATOMIC_RELAXED);
301
302                        // Signal the compiler that a fence is needed but only for signal handlers
303                        __atomic_signal_fence(__ATOMIC_ACQUIRE);
304
305                        __attribute__((unused)) unsigned short new_val = disable_count + 1;
306                        disable_count = new_val;
307                        verify( new_val < 65_000u );              // If this triggers someone is disabling interrupts without enabling them
308                }
309
310                // create a assembler label after
311                // marked as clobber all to avoid movement
312                __cfaasm_label(dsable, after);
313
314        }
315
316        // Enable interrupts by decrementing the counter
317        // If counter reaches 0, execute any pending __cfactx_switch
318        void enable_interrupts( bool poll ) {
319                // Cache the processor now since interrupts can start happening after the atomic store
320                processor   * proc = __cfaabi_tls.this_processor;
321                /* paranoid */ verify( !poll || proc );
322
323                with( __cfaabi_tls.preemption_state ){
324                        unsigned short prev = disable_count;
325                        disable_count -= 1;
326
327                        // If this triggers someone is enabled already enabled interruptsverify( prev != 0u );
328                        /* paranoid */ verify( prev != 0u );
329
330                        // Check if we need to prempt the thread because an interrupt was missed
331                        if( prev == 1 ) {
332                                #if GCC_VERSION > 50000
333                                        static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
334                                #endif
335
336                                // Set enabled flag to true
337                                // should be atomic to avoid preemption in the middle of the operation.
338                                // use memory order RELAXED since there is no inter-thread on this variable requirements
339                                __atomic_store_n(&enabled, true, __ATOMIC_RELAXED);
340
341                                // Signal the compiler that a fence is needed but only for signal handlers
342                                __atomic_signal_fence(__ATOMIC_RELEASE);
343                                if( poll && proc->pending_preemption ) {
344                                        proc->pending_preemption = false;
345                                        force_yield( __POLL_PREEMPTION );
346                                }
347                        }
348                }
349        }
350}
351
352//-----------------------------------------------------------------------------
353// Kernel Signal Debug
354void __cfaabi_check_preemption() {
355        bool ready = __preemption_enabled();
356        if(!ready) { abort("Preemption should be ready"); }
357
358        __cfaasm_label(debug, before);
359
360                sigset_t oldset;
361                int ret;
362                ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset);  // workaround trac#208: cast should be unnecessary
363                if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
364
365                ret = sigismember(&oldset, SIGUSR1);
366                if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
367                if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
368
369                ret = sigismember(&oldset, SIGALRM);
370                if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
371                if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
372
373                ret = sigismember(&oldset, SIGTERM);
374                if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
375                if(ret == 1) { abort("ERROR SIGTERM is disabled"); }
376
377        __cfaasm_label(debug, after);
378}
379
380#ifdef __CFA_WITH_VERIFY__
381bool __cfaabi_dbg_in_kernel() {
382        return !__preemption_enabled();
383}
384#endif
385
386#undef __cfaasm_label
387
388//-----------------------------------------------------------------------------
389// Signal handling
390
391// sigprocmask wrapper : unblock a single signal
392static inline void signal_unblock( int sig ) {
393        sigset_t mask;
394        sigemptyset( &mask );
395        sigaddset( &mask, sig );
396
397        if ( pthread_sigmask( SIG_UNBLOCK, &mask, 0p ) == -1 ) {
398            abort( "internal error, pthread_sigmask" );
399        }
400}
401
402// sigprocmask wrapper : block a single signal
403static inline void signal_block( int sig ) {
404        sigset_t mask;
405        sigemptyset( &mask );
406        sigaddset( &mask, sig );
407
408        if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
409                abort( "internal error, pthread_sigmask" );
410        }
411}
412
413// kill wrapper : signal a processor
414static void preempt( processor * this ) {
415        sigval_t value = { PREEMPT_NORMAL };
416        pthread_sigqueue( this->kernel_thread, SIGUSR1, value );
417}
418
419// reserved for future use
420static void timeout( $thread * this ) {
421        unpark( this );
422}
423
424void __disable_interrupts_hard() {
425        sigset_t oldset;
426        int ret;
427        ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset);  // workaround trac#208: cast should be unnecessary
428        if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
429
430        ret = sigismember(&oldset, SIGUSR1);
431        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
432        if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
433
434        ret = sigismember(&oldset, SIGALRM);
435        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
436        if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
437
438        signal_block( SIGUSR1 );
439}
440
441void __enable_interrupts_hard() {
442        signal_unblock( SIGUSR1 );
443
444        sigset_t oldset;
445        int ret;
446        ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset);  // workaround trac#208: cast should be unnecessary
447        if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
448
449        ret = sigismember(&oldset, SIGUSR1);
450        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
451        if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
452
453        ret = sigismember(&oldset, SIGALRM);
454        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
455        if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
456}
457
458//-----------------------------------------------------------------------------
459// Some assembly required
460#if defined( __i386 )
461        #ifdef __PIC__
462                #define RELOC_PRELUDE( label ) \
463                        "calll   .Lcfaasm_prelude_" #label "$pb\n\t" \
464                        ".Lcfaasm_prelude_" #label "$pb:\n\t" \
465                        "popl    %%eax\n\t" \
466                        ".Lcfaasm_prelude_" #label "_end:\n\t" \
467                        "addl    $_GLOBAL_OFFSET_TABLE_+(.Lcfaasm_prelude_" #label "_end-.Lcfaasm_prelude_" #label "$pb), %%eax\n\t"
468                #define RELOC_PREFIX ""
469                #define RELOC_SUFFIX "@GOT(%%eax)"
470        #else
471                #define RELOC_PREFIX "$"
472                #define RELOC_SUFFIX ""
473        #endif
474        #define __cfaasm_label( label ) struct asm_region label = \
475                ({ \
476                        struct asm_region region; \
477                        asm( \
478                                RELOC_PRELUDE( label ) \
479                                "movl " RELOC_PREFIX "__cfaasm_" #label "_before" RELOC_SUFFIX ", %[vb]\n\t" \
480                                "movl " RELOC_PREFIX "__cfaasm_" #label "_after"  RELOC_SUFFIX ", %[va]\n\t" \
481                                 : [vb]"=r"(region.before), [va]"=r"(region.after) \
482                        ); \
483                        region; \
484                });
485#elif defined( __x86_64 )
486        #ifdef __PIC__
487                #define RELOC_PREFIX ""
488                #define RELOC_SUFFIX "@GOTPCREL(%%rip)"
489        #else
490                #define RELOC_PREFIX "$"
491                #define RELOC_SUFFIX ""
492        #endif
493        #define __cfaasm_label( label ) struct asm_region label = \
494                ({ \
495                        struct asm_region region; \
496                        asm( \
497                                "movq " RELOC_PREFIX "__cfaasm_" #label "_before" RELOC_SUFFIX ", %[vb]\n\t" \
498                                "movq " RELOC_PREFIX "__cfaasm_" #label "_after"  RELOC_SUFFIX ", %[va]\n\t" \
499                                 : [vb]"=r"(region.before), [va]"=r"(region.after) \
500                        ); \
501                        region; \
502                });
503#elif defined( __aarch64__ )
504        #ifdef __PIC__
505                // Note that this works only for gcc
506                #define __cfaasm_label( label ) struct asm_region label = \
507                ({ \
508                        struct asm_region region; \
509                        asm( \
510                                "adrp %[vb], _GLOBAL_OFFSET_TABLE_"                              "\n\t" \
511                                "ldr  %[vb], [%[vb], #:gotpage_lo15:__cfaasm_" #label "_before]" "\n\t" \
512                                "adrp %[va], _GLOBAL_OFFSET_TABLE_"                              "\n\t" \
513                                "ldr  %[va], [%[va], #:gotpage_lo15:__cfaasm_" #label "_after]"  "\n\t" \
514                                 : [vb]"=r"(region.before), [va]"=r"(region.after) \
515                        ); \
516                        region; \
517                });
518        #else
519                #error this is not the right thing to do
520                /*
521                #define __cfaasm_label( label ) struct asm_region label = \
522                ({ \
523                        struct asm_region region; \
524                        asm( \
525                                "adrp %[vb], __cfaasm_" #label "_before"              "\n\t" \
526                                "add  %[vb], %[vb], :lo12:__cfaasm_" #label "_before" "\n\t" \
527                                "adrp %[va], :got:__cfaasm_" #label "_after"          "\n\t" \
528                                "add  %[va], %[va], :lo12:__cfaasm_" #label "_after"  "\n\t" \
529                                 : [vb]"=r"(region.before), [va]"=r"(region.after) \
530                        ); \
531                        region; \
532                });
533                */
534        #endif
535#else
536        #error unknown hardware architecture
537#endif
538
539// KERNEL ONLY
540// Check if a __cfactx_switch signal handler shoud defer
541// If true  : preemption is safe
542// If false : preemption is unsafe and marked as pending
543static inline bool preemption_ready( void * ip ) {
544        // Get all the region for which it is not safe to preempt
545        __cfaasm_label( get    );
546        __cfaasm_label( check  );
547        __cfaasm_label( dsable );
548        __cfaasm_label( debug  );
549
550        // Check if preemption is safe
551        bool ready = true;
552        if( __cfaasm_in( ip, get    ) ) { ready = false; goto EXIT; };
553        if( __cfaasm_in( ip, check  ) ) { ready = false; goto EXIT; };
554        if( __cfaasm_in( ip, dsable ) ) { ready = false; goto EXIT; };
555        if( __cfaasm_in( ip, debug  ) ) { ready = false; goto EXIT; };
556        if( !__cfaabi_tls.preemption_state.enabled) { ready = false; goto EXIT; };
557        if( __cfaabi_tls.preemption_state.in_progress ) { ready = false; goto EXIT; };
558
559EXIT:
560        // Adjust the pending flag accordingly
561        __cfaabi_tls.this_processor->pending_preemption = !ready;
562        return ready;
563}
564
565//=============================================================================================
566// Kernel Signal Startup/Shutdown logic
567//=============================================================================================
568
569// Startup routine to activate preemption
570// Called from kernel_startup
571void __kernel_alarm_startup() {
572        __cfaabi_dbg_print_safe( "Kernel : Starting preemption\n" );
573
574        // Start with preemption disabled until ready
575        __cfaabi_tls.preemption_state.enabled = false;
576        __cfaabi_tls.preemption_state.disable_count = 1;
577
578        // Initialize the event kernel
579        event_kernel = (event_kernel_t *)&storage_event_kernel;
580        (*event_kernel){};
581
582        // Setup proper signal handlers
583        __cfaabi_sigaction( SIGUSR1, sigHandler_ctxSwitch, SA_SIGINFO ); // __cfactx_switch handler
584        __cfaabi_sigaction( SIGALRM, sigHandler_alarm    , SA_SIGINFO ); // debug handler
585
586        signal_block( SIGALRM );
587
588        alarm_stack = __create_pthread( &alarm_thread, alarm_loop, 0p );
589}
590
591// Shutdown routine to deactivate preemption
592// Called from kernel_shutdown
593void __kernel_alarm_shutdown() {
594        __cfaabi_dbg_print_safe( "Kernel : Preemption stopping\n" );
595
596        // Block all signals since we are already shutting down
597        sigset_t mask;
598        sigfillset( &mask );
599        sigprocmask( SIG_BLOCK, &mask, 0p );
600
601        // Notify the alarm thread of the shutdown
602        sigval val;
603        val.sival_int = 0;
604        pthread_sigqueue( alarm_thread, SIGALRM, val );
605
606        // Wait for the preemption thread to finish
607
608        __destroy_pthread( alarm_thread, alarm_stack, 0p );
609
610        // Preemption is now fully stopped
611
612        __cfaabi_dbg_print_safe( "Kernel : Preemption stopped\n" );
613}
614
615// Prevent preemption since we are about to start terminating things
616void __kernel_abort_lock(void) {
617        signal_block( SIGUSR1 );
618}
619
620// Raii ctor/dtor for the preemption_scope
621// Used by thread to control when they want to receive preemption signals
622void ?{}( preemption_scope & this, processor * proc ) {
623        (this.alarm){ proc, 0`s, 0`s };
624        this.proc = proc;
625        this.proc->preemption_alarm = &this.alarm;
626
627        update_preemption( this.proc, this.proc->cltr->preemption_rate );
628}
629
630void ^?{}( preemption_scope & this ) {
631        disable_interrupts();
632
633        update_preemption( this.proc, 0`s );
634}
635
636//=============================================================================================
637// Kernel Signal Handlers
638//=============================================================================================
639__cfaabi_dbg_debug_do( static thread_local void * last_interrupt = 0; )
640
641// Context switch signal handler
642// Receives SIGUSR1 signal and causes the current thread to yield
643static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ ) {
644        void * ip = (void *)(cxt->uc_mcontext.CFA_REG_IP);
645        __cfaabi_dbg_debug_do( last_interrupt = ip; )
646
647        // SKULLDUGGERY: if a thread creates a processor and the immediately deletes it,
648        // the interrupt that is supposed to force the kernel thread to preempt might arrive
649        // before the kernel thread has even started running. When that happens, an interrupt
650        // with a null 'this_processor' will be caught, just ignore it.
651        if(! __cfaabi_tls.this_processor ) return;
652
653        choose(sfp->si_value.sival_int) {
654                case PREEMPT_NORMAL   : ;// Normal case, nothing to do here
655                case PREEMPT_TERMINATE: verify( __atomic_load_n( &__cfaabi_tls.this_processor->do_terminate, __ATOMIC_SEQ_CST ) );
656                default:
657                        abort( "internal error, signal value is %d", sfp->si_value.sival_int );
658        }
659
660        // Check if it is safe to preempt here
661        if( !preemption_ready( ip ) ) { return; }
662
663        __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) );
664
665        // Sync flag : prevent recursive calls to the signal handler
666        __cfaabi_tls.preemption_state.in_progress = true;
667
668        // Clear sighandler mask before context switching.
669        #if GCC_VERSION > 50000
670        static_assert( sizeof( sigset_t ) == sizeof( cxt->uc_sigmask ), "Expected cxt->uc_sigmask to be of sigset_t" );
671        #endif
672        if ( pthread_sigmask( SIG_SETMASK, (sigset_t *)&(cxt->uc_sigmask), 0p ) == -1 ) {
673                abort( "internal error, sigprocmask" );
674        }
675
676        // Clear the in progress flag
677        __cfaabi_tls.preemption_state.in_progress = false;
678
679        // Preemption can occur here
680
681        force_yield( __ALARM_PREEMPTION ); // Do the actual __cfactx_switch
682}
683
684static void sigHandler_alarm( __CFA_SIGPARMS__ ) {
685        abort("SIGALRM should never reach the signal handler");
686}
687
688// Main of the alarm thread
689// Waits on SIGALRM and send SIGUSR1 to whom ever needs it
690static void * alarm_loop( __attribute__((unused)) void * args ) {
691        unsigned id = register_proc_id();
692
693        // Block sigalrms to control when they arrive
694        sigset_t mask;
695        sigfillset(&mask);
696        if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
697            abort( "internal error, pthread_sigmask" );
698        }
699
700        sigemptyset( &mask );
701        sigaddset( &mask, SIGALRM );
702
703        // Main loop
704        while( true ) {
705                // Wait for a sigalrm
706                siginfo_t info;
707                int sig = sigwaitinfo( &mask, &info );
708
709                __cfadbg_print_buffer_decl ( preemption, " KERNEL: sigwaitinfo returned %d, c: %d, v: %d\n", sig, info.si_code, info.si_value.sival_int );
710                __cfadbg_print_buffer_local( preemption, " KERNEL: SI_QUEUE %d, SI_TIMER %d, SI_KERNEL %d\n", SI_QUEUE, SI_TIMER, SI_KERNEL );
711
712                if( sig < 0 ) {
713                        //Error!
714                        int err = errno;
715                        switch( err ) {
716                                case EAGAIN :
717                                case EINTR :
718                                        {__cfadbg_print_buffer_local( preemption, " KERNEL: Spurious wakeup %d.\n", err );}
719                                        continue;
720                                case EINVAL :
721                                        abort( "Timeout was invalid." );
722                                default:
723                                        abort( "Unhandled error %d", err);
724                        }
725                }
726
727                // If another signal arrived something went wrong
728                assertf(sig == SIGALRM, "Kernel Internal Error, sigwait: Unexpected signal %d (%d : %d)\n", sig, info.si_code, info.si_value.sival_int);
729
730                // Switch on the code (a.k.a. the sender) to
731                switch( info.si_code )
732                {
733                // Signal was not sent by the kernel but by an other thread
734                case SI_QUEUE:
735                        // other threads may signal the alarm thread to shut it down
736                        // or to manual cause the preemption tick
737                        // use info.si_value and handle the case here
738                        switch( info.si_value.sival_int ) {
739                        case 0:
740                                goto EXIT;
741                        default:
742                                abort( "SI_QUEUE with val %d", info.si_value.sival_int);
743                        }
744                        // fallthrough
745                // Timers can apparently be marked as sent for the kernel
746                // In either case, tick preemption
747                case SI_TIMER:
748                case SI_KERNEL:
749                        // __cfaabi_dbg_print_safe( "Kernel : Preemption thread tick\n" );
750                        lock( event_kernel->lock __cfaabi_dbg_ctx2 );
751                        tick_preemption();
752                        unlock( event_kernel->lock );
753                        break;
754                }
755        }
756
757EXIT:
758        __cfaabi_dbg_print_safe( "Kernel : Preemption thread stopping\n" );
759        unregister_proc_id(id);
760
761        return 0p;
762}
763
764// Local Variables: //
765// mode: c //
766// tab-width: 4 //
767// End: //
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