source: libcfa/src/concurrency/preemption.cfa

Last change on this file was 5a05946, checked in by caparsons <caparson@…>, 17 months ago

cleanup up locks files and fixed a minor whitespace issue in preemption.cfa

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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 : Mon Jan  9 08:42:59 2023
13// Update Count     : 60
14//
15
16#define __cforall_thread__
17
18// #define __CFA_DEBUG_PRINT_PREEMPTION__
19
20#include "preemption.hfa"
21
22#include <assert.h>
23
24#include <errno.h>
25#include <stdio.h>
26#include <string.h>
27#include <unistd.h>
28#include <limits.h>                                                                             // PTHREAD_STACK_MIN
29
30#include "bits/debug.hfa"
31#include "bits/signal.hfa"
32#include "kernel/private.hfa"
33
34
35#if !defined(__CFA_DEFAULT_PREEMPTION__)
36#define __CFA_DEFAULT_PREEMPTION__ 10`ms
37#endif
38
39__attribute__((weak)) Duration default_preemption() libcfa_public {
40        const char * preempt_rate_s = getenv("CFA_DEFAULT_PREEMPTION");
41        if(!preempt_rate_s) {
42                __cfadbg_print_safe(preemption, "No CFA_DEFAULT_PREEMPTION in ENV\n");
43                return __CFA_DEFAULT_PREEMPTION__;
44        }
45
46        char * endptr = 0p;
47        long int preempt_rate_l = strtol(preempt_rate_s, &endptr, 10);
48        if(preempt_rate_l < 0 || preempt_rate_l > 65535) {
49                __cfadbg_print_safe(preemption, "CFA_DEFAULT_PREEMPTION out of range : %ld\n", preempt_rate_l);
50                return __CFA_DEFAULT_PREEMPTION__;
51        }
52        if('\0' != *endptr) {
53                __cfadbg_print_safe(preemption, "CFA_DEFAULT_PREEMPTION not a decimal number : %s\n", preempt_rate_s);
54                return __CFA_DEFAULT_PREEMPTION__;
55        }
56
57        return preempt_rate_l`ms;
58}
59
60// FwdDeclarations : timeout handlers
61static void preempt( processor   * this );
62static void timeout( thread$ * this );
63
64// FwdDeclarations : Signal handlers
65static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ );
66static void sigHandler_alarm    ( __CFA_SIGPARMS__ );
67static void sigHandler_segv     ( __CFA_SIGPARMS__ );
68static void sigHandler_ill      ( __CFA_SIGPARMS__ );
69static void sigHandler_fpe      ( __CFA_SIGPARMS__ );
70static void sigHandler_abort    ( __CFA_SIGPARMS__ );
71
72// FwdDeclarations : alarm thread main
73static void * alarm_loop( __attribute__((unused)) void * args );
74
75// Machine specific register name
76#if   defined( __i386 )
77#define CFA_REG_IP gregs[REG_EIP]
78#elif defined( __x86_64 )
79#define CFA_REG_IP gregs[REG_RIP]
80#elif defined( __arm__ )
81#define CFA_REG_IP arm_pc
82#elif defined( __aarch64__ )
83#define CFA_REG_IP pc
84#else
85#error unsupported hardware architecture
86#endif
87
88KERNEL_STORAGE(event_kernel_t, event_kernel);         // private storage for event kernel
89event_kernel_t * event_kernel;                        // kernel public handle to even kernel
90static pthread_t alarm_thread;                        // pthread handle to alarm thread
91static void * alarm_stack;                                                        // pthread stack for alarm thread
92
93static void ?{}(event_kernel_t & this) with( this ) {
94        alarms{};
95        lock{};
96}
97
98//=============================================================================================
99// Kernel Preemption logic
100//=============================================================================================
101
102// Get next expired node
103static inline alarm_node_t * get_expired( alarm_list_t * alarms, Time currtime ) {
104        if( ! & (*alarms)`first ) return 0p;                                            // If no alarms return null
105        if( (*alarms)`first.deadline >= currtime ) return 0p;   // If alarms head not expired return null
106        return pop(alarms);                                                                     // Otherwise just pop head
107}
108
109// Tick one frame of the Discrete Event Simulation for alarms
110static void tick_preemption(void) {
111        alarm_node_t * node = 0p;                                                       // Used in the while loop but cannot be declared in the while condition
112        alarm_list_t * alarms = &event_kernel->alarms;          // Local copy for ease of reading
113        Time currtime = __kernel_get_time();                            // Check current time once so everything "happens at once"
114
115        //Loop throught every thing expired
116        while( node = get_expired( alarms, currtime ) ) {
117                __cfadbg_print_buffer_decl( preemption, " KERNEL: preemption tick %lu\n", currtime.tn);
118                Duration period = node->period;
119                if( period == 0 ) {
120                        node->set = false;                  // Node is one-shot, just mark it as not pending
121                }
122
123                __cfadbg_print_buffer_local( preemption, " KERNEL: alarm ticking node %p.\n", node );
124
125
126                // Check if this is a kernel
127                if( node->type == Kernel ) {
128                        preempt( node->proc );
129                }
130                else if( node->type == User ) {
131                        __cfadbg_print_buffer_local( preemption, " KERNEL: alarm unparking %p.\n", node->thrd );
132                        timeout( node->thrd );
133                }
134                else {
135                        node->callback(*node);
136                }
137
138                // Check if this is a periodic alarm
139                if( period > 0 ) {
140                        __cfadbg_print_buffer_local( preemption, " KERNEL: alarm period is %lu.\n", period`ns );
141                        node->deadline = currtime + period;  // Alarm is periodic, add currtime to it (used cached current time)
142                        insert( alarms, node );             // Reinsert the node for the next time it triggers
143                }
144        }
145
146        // If there are still alarms pending, reset the timer
147        if( & (*alarms)`first ) {
148                Duration delta = (*alarms)`first.deadline - currtime;
149                __kernel_set_timer( delta );
150        }
151}
152
153// Update the preemption of a processor and notify interested parties
154void update_preemption( processor * this, Duration duration ) {
155        alarm_node_t * alarm = this->preemption_alarm;
156
157        // Alarms need to be enabled
158        if ( duration > 0 && ! alarm->set ) {
159                alarm->initial = duration;
160                alarm->period  = duration;
161                register_self( alarm );
162        }
163        // Zero duration but alarm is set
164        else if ( duration == 0 && alarm->set ) {
165                unregister_self( alarm );
166                alarm->initial = 0;
167                alarm->period  = 0;
168        }
169        // If alarm is different from previous, change it
170        else if ( duration > 0 && alarm->period != duration ) {
171                unregister_self( alarm );
172                alarm->initial = duration;
173                alarm->period  = duration;
174                register_self( alarm );
175        }
176}
177
178//=============================================================================================
179// Kernel Signal Tools
180//=============================================================================================
181// In a user-level threading system, there are handful of thread-local variables where this problem occurs on the ARM.
182//
183// For each kernel thread running user-level threads, there is a flag variable to indicate if interrupts are
184// enabled/disabled for that kernel thread. Therefore, this variable is made thread local.
185//
186// For example, this code fragment sets the state of the "interrupt" variable in thread-local memory.
187//
188// _Thread_local volatile int interrupts;
189// int main() {
190//     interrupts = 0; // disable interrupts }
191//
192// which generates the following code on the ARM
193//
194// (gdb) disassemble main
195// Dump of assembler code for function main:
196//    0x0000000000000610 <+0>:  mrs     x1, tpidr_el0
197//    0x0000000000000614 <+4>:  mov     w0, #0x0                        // #0
198//    0x0000000000000618 <+8>:  add     x1, x1, #0x0, lsl #12
199//    0x000000000000061c <+12>: add     x1, x1, #0x10
200//    0x0000000000000620 <+16>: str     wzr, [x1]
201//    0x0000000000000624 <+20>: ret
202//
203// The mrs moves a pointer from coprocessor register tpidr_el0 into register x1.  Register w0 is set to 0. The two adds
204// increase the TLS pointer with the displacement (offset) 0x10, which is the location in the TSL of variable
205// "interrupts".  Finally, 0 is stored into "interrupts" through the pointer in register x1 that points into the
206// TSL. Now once x1 has the pointer to the location of the TSL for kernel thread N, it can be be preempted at a
207// user-level and the user thread is put on the user-level ready-queue. When the preempted thread gets to the front of
208// the user-level ready-queue it is run on kernel thread M. It now stores 0 into "interrupts" back on kernel thread N,
209// turning off interrupt on the wrong kernel thread.
210//
211// On the x86, the following code is generated for the same code fragment.
212//
213// (gdb) disassemble main
214// Dump of assembler code for function main:
215//    0x0000000000400420 <+0>:  movl   $0x0,%fs:0xfffffffffffffffc
216//    0x000000000040042c <+12>: xor    %eax,%eax
217//    0x000000000040042e <+14>: retq
218//
219// and there is base-displacement addressing used to atomically reset variable "interrupts" off of the TSL pointer in
220// register "fs".
221//
222// Hence, the ARM has base-displacement address for the general purpose registers, BUT not to the coprocessor
223// registers. As a result, generating the address for the write into variable "interrupts" is no longer atomic.
224//
225// Note this problem does NOT occur when just using multiple kernel threads because the preemption ALWAYS restarts the
226// thread on the same kernel thread.
227//
228// The obvious question is why does ARM use a coprocessor register to store the TSL pointer given that coprocessor
229// registers are second-class registers with respect to the instruction set. One possible answer is that they did not
230// want to dedicate one of the general registers to hold the TLS pointer and there was a free coprocessor register
231// available.
232
233//----------
234// special case for preemption since used often
235bool __preemption_enabled() libcfa_nopreempt libcfa_public {
236        // access tls as normal
237        return __cfaabi_tls.preemption_state.enabled;
238}
239
240extern "C" {
241        __attribute__((visibility("hidden"))) extern void * const __start_cfatext_nopreempt;
242        __attribute__((visibility("hidden"))) extern void * const __stop_cfatext_nopreempt;
243
244        extern const __cfa_nopreempt_region __libcfa_nopreempt;
245        __attribute__((visibility("protected"))) const __cfa_nopreempt_region __libcfathrd_nopreempt @= {
246                (void * const)&__start_cfatext_nopreempt,
247                (void * const)&__stop_cfatext_nopreempt
248        };
249}
250
251static inline bool __cfaabi_in( void * const ip, const struct __cfa_nopreempt_region & const region ) {
252        return ip >= region.start && ip <= region.stop;
253}
254
255
256//----------
257// Get data from the TLS block
258// struct asm_region __cfaasm_get;
259uintptr_t __cfatls_get( unsigned long int offset ) libcfa_nopreempt libcfa_public; //no inline to avoid problems
260uintptr_t __cfatls_get( unsigned long int offset ) {
261        // access tls as normal (except for pointer arithmetic)
262        uintptr_t val = *(uintptr_t*)((uintptr_t)&__cfaabi_tls + offset);
263
264        // This is used everywhere, to avoid cost, we DO NOT poll pending preemption
265        return val;
266}
267
268extern "C" {
269        // Disable interrupts by incrementing the counter
270        void disable_interrupts() libcfa_nopreempt libcfa_public with( __cfaabi_tls.preemption_state ) {
271                #if GCC_VERSION > 50000
272                static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
273                #endif
274
275                // Set enabled flag to false
276                // should be atomic to avoid preemption in the middle of the operation.
277                // use memory order RELAXED since there is no inter-thread on this variable requirements
278                __atomic_store_n(&enabled, false, __ATOMIC_RELAXED);
279
280                // Signal the compiler that a fence is needed but only for signal handlers
281                __atomic_signal_fence(__ATOMIC_ACQUIRE);
282
283                __attribute__((unused)) unsigned short new_val = disable_count + 1;
284                disable_count = new_val;
285                verify( new_val < 65_000u );              // If this triggers someone is disabling interrupts without enabling them
286        }
287
288        // Enable interrupts by decrementing the counter
289        // If counter reaches 0, execute any pending __cfactx_switch
290        void enable_interrupts( bool poll ) libcfa_nopreempt libcfa_public {
291                // Cache the processor now since interrupts can start happening after the atomic store
292                processor   * proc = __cfaabi_tls.this_processor;
293                /* paranoid */ verify( !poll || proc );
294
295                with( __cfaabi_tls.preemption_state ){
296                        unsigned short prev = disable_count;
297                        disable_count -= 1;
298
299                        // If this triggers someone is enabled already enabled interruptsverify( prev != 0u );
300                        /* paranoid */ verify( prev != 0u );
301
302                        // Check if we need to prempt the thread because an interrupt was missed
303                        if( prev == 1 ) {
304                                #if GCC_VERSION > 50000
305                                        static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
306                                #endif
307
308                                // Set enabled flag to true
309                                // should be atomic to avoid preemption in the middle of the operation.
310                                // use memory order RELAXED since there is no inter-thread on this variable requirements
311                                __atomic_store_n(&enabled, true, __ATOMIC_RELAXED);
312
313                                // Signal the compiler that a fence is needed but only for signal handlers
314                                __atomic_signal_fence(__ATOMIC_RELEASE);
315                                if( poll && proc->pending_preemption ) {
316                                        proc->pending_preemption = false;
317                                        force_yield( __POLL_PREEMPTION );
318                                }
319                        }
320                }
321        }
322
323        // Check whether or not there is pending preemption
324        // force_yield( __POLL_PREEMPTION ) if appropriate
325        // return true if the thread was in an interruptable state
326        // i.e. on a real processor and not in the kernel
327        // (can return true even if no preemption was pending)
328        bool poll_interrupts() libcfa_nopreempt libcfa_public {
329                // Cache the processor now since interrupts can start happening after the atomic store
330                processor   * proc =  __cfaabi_tls.this_processor;
331                if ( ! proc ) return false;
332                if ( ! __cfaabi_tls.preemption_state.enabled ) return false;
333
334                // Signal the compiler that a fence is needed but only for signal handlers
335                __atomic_signal_fence(__ATOMIC_RELEASE);
336                if( unlikely( proc->pending_preemption ) ) {
337                        proc->pending_preemption = false;
338                        force_yield( __POLL_PREEMPTION );
339                }
340
341                return true;
342        }
343}
344
345//-----------------------------------------------------------------------------
346// Kernel Signal Debug
347void __cfaabi_check_preemption() libcfa_public {
348        bool ready = __preemption_enabled();
349        if(!ready) { abort("Preemption should be ready"); }
350
351        sigset_t oldset;
352        int ret;
353        ret = __cfaabi_pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset);  // workaround trac#208: cast should be unnecessary
354        if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
355
356        ret = sigismember(&oldset, SIGUSR1);
357        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
358        if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
359
360        ret = sigismember(&oldset, SIGALRM);
361        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
362        if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
363
364        ret = sigismember(&oldset, SIGTERM);
365        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
366        if(ret == 1) { abort("ERROR SIGTERM is disabled"); }
367}
368
369#ifdef __CFA_WITH_VERIFY__
370bool __cfaabi_dbg_in_kernel() {
371        return !__preemption_enabled();
372}
373#endif
374
375#undef __cfaasm_label
376
377//-----------------------------------------------------------------------------
378// Signal handling
379
380// sigprocmask wrapper : unblock a single signal
381static inline void signal_unblock( int sig ) {
382        sigset_t mask;
383        sigemptyset( &mask );
384        sigaddset( &mask, sig );
385
386        if ( __cfaabi_pthread_sigmask( SIG_UNBLOCK, &mask, 0p ) == -1 ) {
387            abort( "internal error, pthread_sigmask" );
388        }
389}
390
391// sigprocmask wrapper : block a single signal
392static inline void signal_block( int sig ) {
393        sigset_t mask;
394        sigemptyset( &mask );
395        sigaddset( &mask, sig );
396
397        if ( __cfaabi_pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
398                abort( "internal error, pthread_sigmask" );
399        }
400}
401
402// kill wrapper : signal a processor
403static void preempt( processor * this ) {
404        sigval_t value = { PREEMPT_NORMAL };
405        __cfaabi_pthread_sigqueue( this->kernel_thread, SIGUSR1, value );
406}
407
408// reserved for future use
409static void timeout( thread$ * this ) {
410        unpark( this );
411}
412
413void __disable_interrupts_hard() {
414        sigset_t oldset;
415        int ret;
416        ret = __cfaabi_pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset);  // workaround trac#208: cast should be unnecessary
417        if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
418
419        ret = sigismember(&oldset, SIGUSR1);
420        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
421        if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
422
423        ret = sigismember(&oldset, SIGALRM);
424        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
425        if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
426
427        signal_block( SIGUSR1 );
428}
429
430void __enable_interrupts_hard() {
431        signal_unblock( SIGUSR1 );
432
433        sigset_t oldset;
434        int ret;
435        ret = __cfaabi_pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset);  // workaround trac#208: cast should be unnecessary
436        if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
437
438        ret = sigismember(&oldset, SIGUSR1);
439        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
440        if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
441
442        ret = sigismember(&oldset, SIGALRM);
443        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
444        if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
445}
446
447//-----------------------------------------------------------------------------
448// KERNEL ONLY
449// Check if a __cfactx_switch signal handler shoud defer
450// If true  : preemption is safe
451// If false : preemption is unsafe and marked as pending
452static inline bool preemption_ready( void * ip ) {
453        // Check if preemption is safe
454        bool ready = true;
455        if( __cfaabi_in( ip, __libcfa_nopreempt ) ) { ready = false; goto EXIT; };
456        if( __cfaabi_in( ip, __libcfathrd_nopreempt ) ) { ready = false; goto EXIT; };
457
458        if( !__cfaabi_tls.preemption_state.enabled) { ready = false; goto EXIT; };
459        if( __cfaabi_tls.preemption_state.in_progress ) { ready = false; goto EXIT; };
460
461EXIT:
462        // Adjust the pending flag accordingly
463        __cfaabi_tls.this_processor->pending_preemption = !ready;
464        return ready;
465}
466
467//=============================================================================================
468// Kernel Signal Startup/Shutdown logic
469//=============================================================================================
470
471// Startup routine to activate preemption
472// Called from kernel_startup
473void __kernel_alarm_startup() {
474        __cfaabi_dbg_print_safe( "Kernel : Starting preemption\n" );
475
476        // Start with preemption disabled until ready
477        __cfaabi_tls.preemption_state.enabled = false;
478        __cfaabi_tls.preemption_state.disable_count = 1;
479
480        // Initialize the event kernel
481        event_kernel = (event_kernel_t *)&storage_event_kernel;
482        (*event_kernel){};
483
484        // Setup proper signal handlers
485        __cfaabi_sigaction( SIGUSR1, sigHandler_ctxSwitch, SA_SIGINFO ); // __cfactx_switch handler
486        __cfaabi_sigaction( SIGALRM, sigHandler_alarm    , SA_SIGINFO ); // debug handler
487
488        signal_block( SIGALRM );
489
490        alarm_stack = __create_pthread( &alarm_thread, alarm_loop, 0p );
491}
492
493// Shutdown routine to deactivate preemption
494// Called from kernel_shutdown
495void __kernel_alarm_shutdown() {
496        __cfaabi_dbg_print_safe( "Kernel : Preemption stopping\n" );
497
498        // Block all signals since we are already shutting down
499        sigset_t mask;
500        sigfillset( &mask );
501        sigprocmask( SIG_BLOCK, &mask, 0p );
502
503        // Notify the alarm thread of the shutdown
504        sigval val;
505        val.sival_int = 0;
506        __cfaabi_pthread_sigqueue( alarm_thread, SIGALRM, val );
507
508        // Wait for the preemption thread to finish
509
510        __destroy_pthread( alarm_thread, alarm_stack, 0p );
511
512        // Preemption is now fully stopped
513
514        __cfaabi_dbg_print_safe( "Kernel : Preemption stopped\n" );
515}
516
517// Prevent preemption since we are about to start terminating things
518void __kernel_abort_lock(void) {
519        signal_block( SIGUSR1 );
520}
521
522// Raii ctor/dtor for the preemption_scope
523// Used by thread to control when they want to receive preemption signals
524void ?{}( preemption_scope & this, processor * proc ) {
525        (this.alarm){ proc, 0`s, 0`s };
526        this.proc = proc;
527        this.proc->preemption_alarm = &this.alarm;
528
529        update_preemption( this.proc, this.proc->cltr->preemption_rate );
530}
531
532void ^?{}( preemption_scope & this ) {
533        disable_interrupts();
534
535        update_preemption( this.proc, 0`s );
536}
537
538//=============================================================================================
539// Kernel Signal Handlers
540//=============================================================================================
541__cfaabi_dbg_debug_do( static __thread void * last_interrupt = 0; )
542
543// Context switch signal handler
544// Receives SIGUSR1 signal and causes the current thread to yield
545static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ ) {
546        void * ip = (void *)(cxt->uc_mcontext.CFA_REG_IP);
547        __cfaabi_dbg_debug_do( last_interrupt = ip; )
548
549        // SKULLDUGGERY: if a thread creates a processor and the immediately deletes it,
550        // the interrupt that is supposed to force the kernel thread to preempt might arrive
551        // before the kernel thread has even started running. When that happens, an interrupt
552        // with a null 'this_processor' will be caught, just ignore it.
553        if(! __cfaabi_tls.this_processor ) return;
554
555        choose(sfp->si_value.sival_int) {
556                case PREEMPT_NORMAL   : ;// Normal case, nothing to do here
557                case PREEMPT_IO       : ;// I/O asked to stop spinning, nothing to do here
558                case PREEMPT_TERMINATE: verify( __atomic_load_n( &__cfaabi_tls.this_processor->do_terminate, __ATOMIC_SEQ_CST ) );
559                default:
560                        abort( "internal error, signal value is %d", sfp->si_value.sival_int );
561        }
562
563        // Check if it is safe to preempt here
564        if( !preemption_ready( ip ) ) {
565                #if !defined(__CFA_NO_STATISTICS__)
566                        __cfaabi_tls.this_stats->ready.threads.preempt.rllfwd++;
567                #endif
568                return;
569        }
570
571        __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) );
572
573        // Sync flag : prevent recursive calls to the signal handler
574        __cfaabi_tls.preemption_state.in_progress = true;
575
576        // Clear sighandler mask before context switching.
577        #if GCC_VERSION > 50000
578        static_assert( sizeof( sigset_t ) == sizeof( cxt->uc_sigmask ), "Expected cxt->uc_sigmask to be of sigset_t" );
579        #endif
580        if ( __cfaabi_pthread_sigmask( SIG_SETMASK, (sigset_t *)&(cxt->uc_sigmask), 0p ) == -1 ) {
581                abort( "internal error, sigprocmask" );
582        }
583
584        // Clear the in progress flag
585        __cfaabi_tls.preemption_state.in_progress = false;
586
587        // Preemption can occur here
588
589        #if !defined(__CFA_NO_STATISTICS__)
590                __cfaabi_tls.this_stats->ready.threads.preempt.yield++;
591        #endif
592
593        force_yield( __ALARM_PREEMPTION ); // Do the actual __cfactx_switch
594}
595
596static void sigHandler_alarm( __CFA_SIGPARMS__ ) {
597        abort("SIGALRM should never reach the signal handler");
598}
599
600// Main of the alarm thread
601// Waits on SIGALRM and send SIGUSR1 to whom ever needs it
602static void * alarm_loop( __attribute__((unused)) void * args ) {
603        unsigned id = register_proc_id();
604
605        // Block sigalrms to control when they arrive
606        sigset_t mask;
607        sigfillset(&mask);
608        if ( __cfaabi_pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
609            abort( "internal error, pthread_sigmask" );
610        }
611
612        sigemptyset( &mask );
613        sigaddset( &mask, SIGALRM );
614
615        // Main loop
616        while( true ) {
617                // Wait for a sigalrm
618                siginfo_t info;
619                int sig = sigwaitinfo( &mask, &info );
620
621                __cfadbg_print_buffer_decl ( preemption, " KERNEL: sigwaitinfo returned %d, c: %d, v: %d\n", sig, info.si_code, info.si_value.sival_int );
622                __cfadbg_print_buffer_local( preemption, " KERNEL: SI_QUEUE %d, SI_TIMER %d, SI_KERNEL %d\n", SI_QUEUE, SI_TIMER, SI_KERNEL );
623
624                if( sig < 0 ) {
625                        //Error!
626                        int err = errno;
627                        switch( err ) {
628                                case EAGAIN :
629                                case EINTR :
630                                        {__cfadbg_print_buffer_local( preemption, " KERNEL: Spurious wakeup %d.\n", err );}
631                                        continue;
632                                case EINVAL :
633                                        abort( "Timeout was invalid." );
634                                default:
635                                        abort( "Unhandled error %d", err);
636                        }
637                }
638
639                // If another signal arrived something went wrong
640                assertf(sig == SIGALRM, "Kernel Internal Error, sigwait: Unexpected signal %d (%d : %d)\n", sig, info.si_code, info.si_value.sival_int);
641
642                // Switch on the code (a.k.a. the sender) to
643                switch( info.si_code )
644                {
645                // Signal was not sent by the kernel but by an other thread
646                case SI_QUEUE:
647                        // other threads may signal the alarm thread to shut it down
648                        // or to manual cause the preemption tick
649                        // use info.si_value and handle the case here
650                        switch( info.si_value.sival_int ) {
651                        case 0:
652                                goto EXIT;
653                        default:
654                                abort( "SI_QUEUE with val %d", info.si_value.sival_int);
655                        }
656                        // fallthrough
657                // Timers can apparently be marked as sent for the kernel
658                // In either case, tick preemption
659                case SI_TIMER:
660                case SI_KERNEL:
661                        // __cfaabi_dbg_print_safe( "Kernel : Preemption thread tick\n" );
662                        lock( event_kernel->lock __cfaabi_dbg_ctx2 );
663                        tick_preemption();
664                        unlock( event_kernel->lock );
665                        break;
666                }
667        }
668
669EXIT:
670        __cfaabi_dbg_print_safe( "Kernel : Preemption thread stopping\n" );
671        unregister_proc_id(id);
672
673        return 0p;
674}
675
676// Local Variables: //
677// mode: c //
678// tab-width: 4 //
679// End: //
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