source: libcfa/src/concurrency/preemption.cfa @ 54dcab1

arm-ehenumforall-pointer-decayjacob/cs343-translationnew-ast-unique-expr
Last change on this file since 54dcab1 was 54dcab1, checked in by Thierry Delisle <tdelisle@…>, 19 months ago

Merge branch 'master' of plg.uwaterloo.ca:software/cfa/cfa-cc

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