source: libcfa/src/concurrency/preemption.cfa @ a3821fa

arm-ehjacob/cs343-translationnew-ast-unique-expr
Last change on this file since a3821fa was a3821fa, checked in by Thierry Delisle <tdelisle@…>, 5 months ago

Changed enable interrupts:

  • no longer save the caller for debugging
  • now polls based on parameter passed in
  • Property mode set to 100644
File size: 25.6 KB
Line 
1//
2// Cforall Version 1.0.0 Copyright (C) 2016 University of Waterloo
3//
4// The contents of this file are covered under the licence agreement in the
5// file "LICENCE" distributed with Cforall.
6//
7// signal.c --
8//
9// Author           : Thierry Delisle
10// Created On       : Mon Jun 5 14:20:42 2017
11// Last Modified By : Peter A. Buhr
12// Last Modified On : Fri Nov  6 07:42:13 2020
13// Update Count     : 54
14//
15
16#define __cforall_thread__
17// #define __CFA_DEBUG_PRINT_PREEMPTION__
18
19#include "preemption.hfa"
20#include <assert.h>
21
22#include <errno.h>
23#include <stdio.h>
24#include <string.h>
25#include <unistd.h>
26#include <limits.h>                                                                             // PTHREAD_STACK_MIN
27
28#include "bits/signal.hfa"
29#include "kernel_private.hfa"
30
31
32#if !defined(__CFA_DEFAULT_PREEMPTION__)
33#define __CFA_DEFAULT_PREEMPTION__ 10`ms
34#endif
35
36__attribute__((weak)) Duration default_preemption() {
37        const char * preempt_rate_s = getenv("CFA_DEFAULT_PREEMPTION");
38        if(!preempt_rate_s) {
39                __cfadbg_print_safe(preemption, "No CFA_DEFAULT_PREEMPTION in ENV\n");
40                return __CFA_DEFAULT_PREEMPTION__;
41        }
42
43        char * endptr = 0p;
44        long int preempt_rate_l = strtol(preempt_rate_s, &endptr, 10);
45        if(preempt_rate_l < 0 || preempt_rate_l > 65535) {
46                __cfadbg_print_safe(preemption, "CFA_DEFAULT_PREEMPTION out of range : %ld\n", preempt_rate_l);
47                return __CFA_DEFAULT_PREEMPTION__;
48        }
49        if('\0' != *endptr) {
50                __cfadbg_print_safe(preemption, "CFA_DEFAULT_PREEMPTION not a decimal number : %s\n", preempt_rate_s);
51                return __CFA_DEFAULT_PREEMPTION__;
52        }
53
54        return preempt_rate_l`ms;
55}
56
57// FwdDeclarations : timeout handlers
58static void preempt( processor   * this );
59static void timeout( $thread * this );
60
61// FwdDeclarations : Signal handlers
62static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ );
63static void sigHandler_alarm    ( __CFA_SIGPARMS__ );
64static void sigHandler_segv     ( __CFA_SIGPARMS__ );
65static void sigHandler_ill      ( __CFA_SIGPARMS__ );
66static void sigHandler_fpe      ( __CFA_SIGPARMS__ );
67static void sigHandler_abort    ( __CFA_SIGPARMS__ );
68
69// FwdDeclarations : alarm thread main
70static void * alarm_loop( __attribute__((unused)) void * args );
71
72// Machine specific register name
73#if   defined( __i386 )
74#define CFA_REG_IP gregs[REG_EIP]
75#elif defined( __x86_64 )
76#define CFA_REG_IP gregs[REG_RIP]
77#elif defined( __arm__ )
78#define CFA_REG_IP arm_pc
79#elif defined( __aarch64__ )
80#define CFA_REG_IP pc
81#else
82#error unsupported hardware architecture
83#endif
84
85KERNEL_STORAGE(event_kernel_t, event_kernel);         // private storage for event kernel
86event_kernel_t * event_kernel;                        // kernel public handle to even kernel
87static pthread_t alarm_thread;                        // pthread handle to alarm thread
88static void * alarm_stack;                                                        // pthread stack for alarm thread
89
90static void ?{}(event_kernel_t & this) with( this ) {
91        alarms{};
92        lock{};
93}
94
95enum {
96        PREEMPT_NORMAL    = 0,
97        PREEMPT_TERMINATE = 1,
98};
99
100//=============================================================================================
101// Kernel Preemption logic
102//=============================================================================================
103
104// Get next expired node
105static inline alarm_node_t * get_expired( alarm_list_t * alarms, Time currtime ) {
106        if( ! & (*alarms)`first ) return 0p;                                            // If no alarms return null
107        if( (*alarms)`first.alarm >= currtime ) return 0p;      // If alarms head not expired return null
108        return pop(alarms);                                                                     // Otherwise just pop head
109}
110
111// Tick one frame of the Discrete Event Simulation for alarms
112static void tick_preemption(void) {
113        alarm_node_t * node = 0p;                                                       // Used in the while loop but cannot be declared in the while condition
114        alarm_list_t * alarms = &event_kernel->alarms;          // Local copy for ease of reading
115        Time currtime = __kernel_get_time();                            // Check current time once so everything "happens at once"
116
117        //Loop throught every thing expired
118        while( node = get_expired( alarms, currtime ) ) {
119                __cfadbg_print_buffer_decl( preemption, " KERNEL: preemption tick %lu\n", currtime.tn);
120                Duration period = node->period;
121                if( period == 0) {
122                        node->set = false;                  // Node is one-shot, just mark it as not pending
123                }
124
125                __cfadbg_print_buffer_local( preemption, " KERNEL: alarm ticking node %p.\n", node );
126
127
128                // Check if this is a kernel
129                if( node->type == Kernel ) {
130                        preempt( node->proc );
131                }
132                else if( node->type == User ) {
133                        __cfadbg_print_buffer_local( preemption, " KERNEL: alarm unparking %p.\n", node->thrd );
134                        timeout( node->thrd );
135                }
136                else {
137                        node->callback(*node);
138                }
139
140                // Check if this is a periodic alarm
141                if( period > 0 ) {
142                        __cfadbg_print_buffer_local( preemption, " KERNEL: alarm period is %lu.\n", period`ns );
143                        node->alarm = currtime + period;    // Alarm is periodic, add currtime to it (used cached current time)
144                        insert( alarms, node );             // Reinsert the node for the next time it triggers
145                }
146        }
147
148        // If there are still alarms pending, reset the timer
149        if( & (*alarms)`first ) {
150                Duration delta = (*alarms)`first.alarm - currtime;
151                Duration capped = max(delta, 50`us);
152                __kernel_set_timer( capped );
153        }
154}
155
156// Update the preemption of a processor and notify interested parties
157void update_preemption( processor * this, Duration duration ) {
158        alarm_node_t * alarm = this->preemption_alarm;
159
160        // Alarms need to be enabled
161        if ( duration > 0 && ! alarm->set ) {
162                alarm->alarm = __kernel_get_time() + duration;
163                alarm->period = duration;
164                register_self( alarm );
165        }
166        // Zero duration but alarm is set
167        else if ( duration == 0 && alarm->set ) {
168                unregister_self( alarm );
169                alarm->alarm = 0;
170                alarm->period = 0;
171        }
172        // If alarm is different from previous, change it
173        else if ( duration > 0 && alarm->period != duration ) {
174                unregister_self( alarm );
175                alarm->alarm = __kernel_get_time() + duration;
176                alarm->period = duration;
177                register_self( alarm );
178        }
179}
180
181//=============================================================================================
182// Kernel Signal Tools
183//=============================================================================================
184// In a user-level threading system, there are handful of thread-local variables where this problem occurs on the ARM.
185//
186// For each kernel thread running user-level threads, there is a flag variable to indicate if interrupts are
187// enabled/disabled for that kernel thread. Therefore, this variable is made thread local.
188//
189// For example, this code fragment sets the state of the "interrupt" variable in thread-local memory.
190//
191// _Thread_local volatile int interrupts;
192// int main() {
193//     interrupts = 0; // disable interrupts }
194//
195// which generates the following code on the ARM
196//
197// (gdb) disassemble main
198// Dump of assembler code for function main:
199//    0x0000000000000610 <+0>:  mrs     x1, tpidr_el0
200//    0x0000000000000614 <+4>:  mov     w0, #0x0                        // #0
201//    0x0000000000000618 <+8>:  add     x1, x1, #0x0, lsl #12
202//    0x000000000000061c <+12>: add     x1, x1, #0x10
203//    0x0000000000000620 <+16>: str     wzr, [x1]
204//    0x0000000000000624 <+20>: ret
205//
206// The mrs moves a pointer from coprocessor register tpidr_el0 into register x1.  Register w0 is set to 0. The two adds
207// increase the TLS pointer with the displacement (offset) 0x10, which is the location in the TSL of variable
208// "interrupts".  Finally, 0 is stored into "interrupts" through the pointer in register x1 that points into the
209// TSL. Now once x1 has the pointer to the location of the TSL for kernel thread N, it can be be preempted at a
210// user-level and the user thread is put on the user-level ready-queue. When the preempted thread gets to the front of
211// the user-level ready-queue it is run on kernel thread M. It now stores 0 into "interrupts" back on kernel thread N,
212// turning off interrupt on the wrong kernel thread.
213//
214// On the x86, the following code is generated for the same code fragment.
215//
216// (gdb) disassemble main
217// Dump of assembler code for function main:
218//    0x0000000000400420 <+0>:  movl   $0x0,%fs:0xfffffffffffffffc
219//    0x000000000040042c <+12>: xor    %eax,%eax
220//    0x000000000040042e <+14>: retq
221//
222// and there is base-displacement addressing used to atomically reset variable "interrupts" off of the TSL pointer in
223// register "fs".
224//
225// Hence, the ARM has base-displacement address for the general purpose registers, BUT not to the coprocessor
226// registers. As a result, generating the address for the write into variable "interrupts" is no longer atomic.
227//
228// Note this problem does NOT occur when just using multiple kernel threads because the preemption ALWAYS restarts the
229// thread on the same kernel thread.
230//
231// The obvious question is why does ARM use a coprocessor register to store the TSL pointer given that coprocessor
232// registers are second-class registers with respect to the instruction set. One possible answer is that they did not
233// want to dedicate one of the general registers to hold the TLS pointer and there was a free coprocessor register
234// available.
235
236//-----------------------------------------------------------------------------
237// Some assembly required
238#define __cfaasm_label(label, when) when: asm volatile goto(".global __cfaasm_" #label "_" #when "\n" "__cfaasm_" #label "_" #when ":":::"memory":when)
239
240//----------
241// special case for preemption since used often
242bool __preemption_enabled() {
243        // create a assembler label before
244        // marked as clobber all to avoid movement
245        __cfaasm_label(check, before);
246
247        // access tls as normal
248        bool enabled = __cfaabi_tls.preemption_state.enabled;
249
250        // create a assembler label after
251        // marked as clobber all to avoid movement
252        __cfaasm_label(check, after);
253        return enabled;
254}
255
256struct asm_region {
257        void * before;
258        void * after;
259};
260
261static inline bool __cfaasm_in( void * ip, struct asm_region & region ) {
262        return ip >= region.before && ip <= region.after;
263}
264
265
266//----------
267// Get data from the TLS block
268// struct asm_region __cfaasm_get;
269uintptr_t __cfatls_get( unsigned long int offset ) __attribute__((__noinline__)); //no inline to avoid problems
270uintptr_t __cfatls_get( unsigned long int offset ) {
271        // create a assembler label before
272        // marked as clobber all to avoid movement
273        __cfaasm_label(get, before);
274
275        // access tls as normal (except for pointer arithmetic)
276        uintptr_t val = *(uintptr_t*)((uintptr_t)&__cfaabi_tls + offset);
277
278        // create a assembler label after
279        // marked as clobber all to avoid movement
280        __cfaasm_label(get, after);
281        return val;
282}
283
284extern "C" {
285        // Disable interrupts by incrementing the counter
286        void disable_interrupts() {
287                // create a assembler label before
288                // marked as clobber all to avoid movement
289                __cfaasm_label(dsable, before);
290
291                with( __cfaabi_tls.preemption_state ) {
292                        #if GCC_VERSION > 50000
293                        static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
294                        #endif
295
296                        // Set enabled flag to false
297                        // should be atomic to avoid preemption in the middle of the operation.
298                        // use memory order RELAXED since there is no inter-thread on this variable requirements
299                        __atomic_store_n(&enabled, false, __ATOMIC_RELAXED);
300
301                        // Signal the compiler that a fence is needed but only for signal handlers
302                        __atomic_signal_fence(__ATOMIC_ACQUIRE);
303
304                        __attribute__((unused)) unsigned short new_val = disable_count + 1;
305                        disable_count = new_val;
306                        verify( new_val < 65_000u );              // If this triggers someone is disabling interrupts without enabling them
307                }
308
309                // create a assembler label after
310                // marked as clobber all to avoid movement
311                __cfaasm_label(dsable, after);
312
313        }
314
315        // Enable interrupts by decrementing the counter
316        // If counter reaches 0, execute any pending __cfactx_switch
317        void enable_interrupts( bool poll ) {
318                // Cache the processor now since interrupts can start happening after the atomic store
319                processor   * proc = __cfaabi_tls.this_processor;
320                /* paranoid */ verify( !poll || proc );
321
322                with( __cfaabi_tls.preemption_state ){
323                        unsigned short prev = disable_count;
324                        disable_count -= 1;
325
326                        // If this triggers someone is enabled already enabled interruptsverify( prev != 0u );
327                        /* paranoid */ verify( prev != 0u );
328
329                        // Check if we need to prempt the thread because an interrupt was missed
330                        if( prev == 1 ) {
331                                #if GCC_VERSION > 50000
332                                        static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
333                                #endif
334
335                                // Set enabled flag to true
336                                // should be atomic to avoid preemption in the middle of the operation.
337                                // use memory order RELAXED since there is no inter-thread on this variable requirements
338                                __atomic_store_n(&enabled, true, __ATOMIC_RELAXED);
339
340                                // Signal the compiler that a fence is needed but only for signal handlers
341                                __atomic_signal_fence(__ATOMIC_RELEASE);
342                                if( poll && proc->pending_preemption ) {
343                                        proc->pending_preemption = false;
344                                        force_yield( __POLL_PREEMPTION );
345                                }
346                        }
347                }
348        }
349}
350
351//-----------------------------------------------------------------------------
352// Kernel Signal Debug
353void __cfaabi_check_preemption() {
354        bool ready = __preemption_enabled();
355        if(!ready) { abort("Preemption should be ready"); }
356
357        __cfaasm_label(debug, before);
358
359                sigset_t oldset;
360                int ret;
361                ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset);  // workaround trac#208: cast should be unnecessary
362                if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
363
364                ret = sigismember(&oldset, SIGUSR1);
365                if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
366                if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
367
368                ret = sigismember(&oldset, SIGALRM);
369                if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
370                if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
371
372                ret = sigismember(&oldset, SIGTERM);
373                if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
374                if(ret == 1) { abort("ERROR SIGTERM is disabled"); }
375
376        __cfaasm_label(debug, after);
377}
378
379#ifdef __CFA_WITH_VERIFY__
380bool __cfaabi_dbg_in_kernel() {
381        return !__preemption_enabled();
382}
383#endif
384
385#undef __cfaasm_label
386
387//-----------------------------------------------------------------------------
388// Signal handling
389
390// sigprocmask wrapper : unblock a single signal
391static inline void signal_unblock( int sig ) {
392        sigset_t mask;
393        sigemptyset( &mask );
394        sigaddset( &mask, sig );
395
396        if ( pthread_sigmask( SIG_UNBLOCK, &mask, 0p ) == -1 ) {
397            abort( "internal error, pthread_sigmask" );
398        }
399}
400
401// sigprocmask wrapper : block a single signal
402static inline void signal_block( int sig ) {
403        sigset_t mask;
404        sigemptyset( &mask );
405        sigaddset( &mask, sig );
406
407        if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
408                abort( "internal error, pthread_sigmask" );
409        }
410}
411
412// kill wrapper : signal a processor
413static void preempt( processor * this ) {
414        sigval_t value = { PREEMPT_NORMAL };
415        pthread_sigqueue( this->kernel_thread, SIGUSR1, value );
416}
417
418// reserved for future use
419static void timeout( $thread * this ) {
420        unpark( this );
421}
422
423void __disable_interrupts_hard() {
424        sigset_t oldset;
425        int ret;
426        ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset);  // workaround trac#208: cast should be unnecessary
427        if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
428
429        ret = sigismember(&oldset, SIGUSR1);
430        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
431        if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
432
433        ret = sigismember(&oldset, SIGALRM);
434        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
435        if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
436
437        signal_block( SIGUSR1 );
438}
439
440void __enable_interrupts_hard() {
441        signal_unblock( SIGUSR1 );
442
443        sigset_t oldset;
444        int ret;
445        ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset);  // workaround trac#208: cast should be unnecessary
446        if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
447
448        ret = sigismember(&oldset, SIGUSR1);
449        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
450        if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
451
452        ret = sigismember(&oldset, SIGALRM);
453        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
454        if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
455}
456
457//-----------------------------------------------------------------------------
458// Some assembly required
459#if defined( __i386 )
460        #ifdef __PIC__
461                #define RELOC_PRELUDE( label ) \
462                        "calll   .Lcfaasm_prelude_" #label "$pb\n\t" \
463                        ".Lcfaasm_prelude_" #label "$pb:\n\t" \
464                        "popl    %%eax\n\t" \
465                        ".Lcfaasm_prelude_" #label "_end:\n\t" \
466                        "addl    $_GLOBAL_OFFSET_TABLE_+(.Lcfaasm_prelude_" #label "_end-.Lcfaasm_prelude_" #label "$pb), %%eax\n\t"
467                #define RELOC_PREFIX ""
468                #define RELOC_SUFFIX "@GOT(%%eax)"
469        #else
470                #define RELOC_PREFIX "$"
471                #define RELOC_SUFFIX ""
472        #endif
473        #define __cfaasm_label( label ) struct asm_region label = \
474                ({ \
475                        struct asm_region region; \
476                        asm( \
477                                RELOC_PRELUDE( label ) \
478                                "movl " RELOC_PREFIX "__cfaasm_" #label "_before" RELOC_SUFFIX ", %[vb]\n\t" \
479                                "movl " RELOC_PREFIX "__cfaasm_" #label "_after"  RELOC_SUFFIX ", %[va]\n\t" \
480                                 : [vb]"=r"(region.before), [va]"=r"(region.after) \
481                        ); \
482                        region; \
483                });
484#elif defined( __x86_64 )
485        #ifdef __PIC__
486                #define RELOC_PREFIX ""
487                #define RELOC_SUFFIX "@GOTPCREL(%%rip)"
488        #else
489                #define RELOC_PREFIX "$"
490                #define RELOC_SUFFIX ""
491        #endif
492        #define __cfaasm_label( label ) struct asm_region label = \
493                ({ \
494                        struct asm_region region; \
495                        asm( \
496                                "movq " RELOC_PREFIX "__cfaasm_" #label "_before" RELOC_SUFFIX ", %[vb]\n\t" \
497                                "movq " RELOC_PREFIX "__cfaasm_" #label "_after"  RELOC_SUFFIX ", %[va]\n\t" \
498                                 : [vb]"=r"(region.before), [va]"=r"(region.after) \
499                        ); \
500                        region; \
501                });
502#elif defined( __aarch64__ )
503        #ifdef __PIC__
504                // Note that this works only for gcc
505                #define __cfaasm_label( label ) struct asm_region label = \
506                ({ \
507                        struct asm_region region; \
508                        asm( \
509                                "adrp %[vb], _GLOBAL_OFFSET_TABLE_"                              "\n\t" \
510                                "ldr  %[vb], [%[vb], #:gotpage_lo15:__cfaasm_" #label "_before]" "\n\t" \
511                                "adrp %[va], _GLOBAL_OFFSET_TABLE_"                              "\n\t" \
512                                "ldr  %[va], [%[va], #:gotpage_lo15:__cfaasm_" #label "_after]"  "\n\t" \
513                                 : [vb]"=r"(region.before), [va]"=r"(region.after) \
514                        ); \
515                        region; \
516                });
517        #else
518                #error this is not the right thing to do
519                /*
520                #define __cfaasm_label( label ) struct asm_region label = \
521                ({ \
522                        struct asm_region region; \
523                        asm( \
524                                "adrp %[vb], __cfaasm_" #label "_before"              "\n\t" \
525                                "add  %[vb], %[vb], :lo12:__cfaasm_" #label "_before" "\n\t" \
526                                "adrp %[va], :got:__cfaasm_" #label "_after"          "\n\t" \
527                                "add  %[va], %[va], :lo12:__cfaasm_" #label "_after"  "\n\t" \
528                                 : [vb]"=r"(region.before), [va]"=r"(region.after) \
529                        ); \
530                        region; \
531                });
532                */
533        #endif
534#else
535        #error unknown hardware architecture
536#endif
537
538// KERNEL ONLY
539// Check if a __cfactx_switch signal handler shoud defer
540// If true  : preemption is safe
541// If false : preemption is unsafe and marked as pending
542static inline bool preemption_ready( void * ip ) {
543        // Get all the region for which it is not safe to preempt
544        __cfaasm_label( get    );
545        __cfaasm_label( check  );
546        __cfaasm_label( dsable );
547        __cfaasm_label( debug  );
548
549        // Check if preemption is safe
550        bool ready = true;
551        if( __cfaasm_in( ip, get    ) ) { ready = false; goto EXIT; };
552        if( __cfaasm_in( ip, check  ) ) { ready = false; goto EXIT; };
553        if( __cfaasm_in( ip, dsable ) ) { ready = false; goto EXIT; };
554        if( __cfaasm_in( ip, debug  ) ) { ready = false; goto EXIT; };
555        if( !__cfaabi_tls.preemption_state.enabled) { ready = false; goto EXIT; };
556        if( __cfaabi_tls.preemption_state.in_progress ) { ready = false; goto EXIT; };
557
558EXIT:
559        // Adjust the pending flag accordingly
560        __cfaabi_tls.this_processor->pending_preemption = !ready;
561        return ready;
562}
563
564//=============================================================================================
565// Kernel Signal Startup/Shutdown logic
566//=============================================================================================
567
568// Startup routine to activate preemption
569// Called from kernel_startup
570void __kernel_alarm_startup() {
571        __cfaabi_dbg_print_safe( "Kernel : Starting preemption\n" );
572
573        // Start with preemption disabled until ready
574        __cfaabi_tls.preemption_state.enabled = false;
575        __cfaabi_tls.preemption_state.disable_count = 1;
576
577        // Initialize the event kernel
578        event_kernel = (event_kernel_t *)&storage_event_kernel;
579        (*event_kernel){};
580
581        // Setup proper signal handlers
582        __cfaabi_sigaction( SIGUSR1, sigHandler_ctxSwitch, SA_SIGINFO ); // __cfactx_switch handler
583        __cfaabi_sigaction( SIGALRM, sigHandler_alarm    , SA_SIGINFO ); // debug handler
584
585        signal_block( SIGALRM );
586
587        alarm_stack = __create_pthread( &alarm_thread, alarm_loop, 0p );
588}
589
590// Shutdown routine to deactivate preemption
591// Called from kernel_shutdown
592void __kernel_alarm_shutdown() {
593        __cfaabi_dbg_print_safe( "Kernel : Preemption stopping\n" );
594
595        // Block all signals since we are already shutting down
596        sigset_t mask;
597        sigfillset( &mask );
598        sigprocmask( SIG_BLOCK, &mask, 0p );
599
600        // Notify the alarm thread of the shutdown
601        sigval val = { 1 };
602        pthread_sigqueue( alarm_thread, SIGALRM, val );
603
604        // Wait for the preemption thread to finish
605
606        __destroy_pthread( alarm_thread, alarm_stack, 0p );
607
608        // Preemption is now fully stopped
609
610        __cfaabi_dbg_print_safe( "Kernel : Preemption stopped\n" );
611}
612
613// Prevent preemption since we are about to start terminating things
614void __kernel_abort_lock(void) {
615        signal_block( SIGUSR1 );
616}
617
618// Raii ctor/dtor for the preemption_scope
619// Used by thread to control when they want to receive preemption signals
620void ?{}( preemption_scope & this, processor * proc ) {
621        (this.alarm){ proc, (Time){ 0 }, 0`s };
622        this.proc = proc;
623        this.proc->preemption_alarm = &this.alarm;
624
625        update_preemption( this.proc, this.proc->cltr->preemption_rate );
626}
627
628void ^?{}( preemption_scope & this ) {
629        disable_interrupts();
630
631        update_preemption( this.proc, 0`s );
632}
633
634//=============================================================================================
635// Kernel Signal Handlers
636//=============================================================================================
637__cfaabi_dbg_debug_do( static thread_local void * last_interrupt = 0; )
638
639// Context switch signal handler
640// Receives SIGUSR1 signal and causes the current thread to yield
641static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ ) {
642        void * ip = (void *)(cxt->uc_mcontext.CFA_REG_IP);
643        __cfaabi_dbg_debug_do( last_interrupt = ip; )
644
645        // SKULLDUGGERY: if a thread creates a processor and the immediately deletes it,
646        // the interrupt that is supposed to force the kernel thread to preempt might arrive
647        // before the kernel thread has even started running. When that happens, an interrupt
648        // with a null 'this_processor' will be caught, just ignore it.
649        if(! __cfaabi_tls.this_processor ) return;
650
651        choose(sfp->si_value.sival_int) {
652                case PREEMPT_NORMAL   : ;// Normal case, nothing to do here
653                case PREEMPT_TERMINATE: verify( __atomic_load_n( &__cfaabi_tls.this_processor->do_terminate, __ATOMIC_SEQ_CST ) );
654                default:
655                        abort( "internal error, signal value is %d", sfp->si_value.sival_int );
656        }
657
658        // Check if it is safe to preempt here
659        if( !preemption_ready( ip ) ) { return; }
660
661        __cfaabi_dbg_print_buffer_decl( " KERNEL: preempting core %p (%p @ %p).\n", __cfaabi_tls.this_processor, __cfaabi_tls.this_thread, (void *)(cxt->uc_mcontext.CFA_REG_IP) );
662
663        // Sync flag : prevent recursive calls to the signal handler
664        __cfaabi_tls.preemption_state.in_progress = true;
665
666        // Clear sighandler mask before context switching.
667        #if GCC_VERSION > 50000
668        static_assert( sizeof( sigset_t ) == sizeof( cxt->uc_sigmask ), "Expected cxt->uc_sigmask to be of sigset_t" );
669        #endif
670        if ( pthread_sigmask( SIG_SETMASK, (sigset_t *)&(cxt->uc_sigmask), 0p ) == -1 ) {
671                abort( "internal error, sigprocmask" );
672        }
673
674        // Clear the in progress flag
675        __cfaabi_tls.preemption_state.in_progress = false;
676
677        // Preemption can occur here
678
679        force_yield( __ALARM_PREEMPTION ); // Do the actual __cfactx_switch
680}
681
682static void sigHandler_alarm( __CFA_SIGPARMS__ ) {
683        abort("SIGALRM should never reach the signal handler");
684}
685
686// Main of the alarm thread
687// Waits on SIGALRM and send SIGUSR1 to whom ever needs it
688static void * alarm_loop( __attribute__((unused)) void * args ) {
689        __processor_id_t id;
690        register_proc_id(&id);
691        __cfaabi_tls.this_proc_id = &id;
692
693
694        // Block sigalrms to control when they arrive
695        sigset_t mask;
696        sigfillset(&mask);
697        if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
698            abort( "internal error, pthread_sigmask" );
699        }
700
701        sigemptyset( &mask );
702        sigaddset( &mask, SIGALRM );
703
704        // Main loop
705        while( true ) {
706                // Wait for a sigalrm
707                siginfo_t info;
708                int sig = sigwaitinfo( &mask, &info );
709
710                if( sig < 0 ) {
711                        //Error!
712                        int err = errno;
713                        switch( err ) {
714                                case EAGAIN :
715                                case EINTR :
716                                        {__cfaabi_dbg_print_buffer_decl( " KERNEL: Spurious wakeup %d.\n", err );}
717                                        continue;
718                                case EINVAL :
719                                        abort( "Timeout was invalid." );
720                                default:
721                                        abort( "Unhandled error %d", err);
722                        }
723                }
724
725                // If another signal arrived something went wrong
726                assertf(sig == SIGALRM, "Kernel Internal Error, sigwait: Unexpected signal %d (%d : %d)\n", sig, info.si_code, info.si_value.sival_int);
727
728                // __cfaabi_dbg_print_safe( "Kernel : Caught alarm from %d with %d\n", info.si_code, info.si_value.sival_int );
729                // Switch on the code (a.k.a. the sender) to
730                switch( info.si_code )
731                {
732                // Timers can apparently be marked as sent for the kernel
733                // In either case, tick preemption
734                case SI_TIMER:
735                case SI_KERNEL:
736                        // __cfaabi_dbg_print_safe( "Kernel : Preemption thread tick\n" );
737                        lock( event_kernel->lock __cfaabi_dbg_ctx2 );
738                        tick_preemption();
739                        unlock( event_kernel->lock );
740                        break;
741                // Signal was not sent by the kernel but by an other thread
742                case SI_QUEUE:
743                        // For now, other thread only signal the alarm thread to shut it down
744                        // If this needs to change use info.si_value and handle the case here
745                        goto EXIT;
746                }
747        }
748
749EXIT:
750        __cfaabi_dbg_print_safe( "Kernel : Preemption thread stopping\n" );
751        register_proc_id(&id);
752
753        return 0p;
754}
755
756// Local Variables: //
757// mode: c //
758// tab-width: 4 //
759// End: //
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