source: libcfa/src/concurrency/preemption.cfa @ e874605

ADTast-experimental
Last change on this file since e874605 was 926d358, checked in by Thierry Delisle <tdelisle@…>, 2 years ago

Removed old asm_labels.
Modified preemption check to no longer poll interrupts.
Modified poll_interrupts to be lighter weight and remove redundant checks/safeties.

  • Property mode set to 100644
File size: 23.6 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 : Thu Feb 17 11:18:57 2022
13// Update Count     : 59
14//
15
16#define __cforall_thread__
17#define _GNU_SOURCE
18
19// #define __CFA_DEBUG_PRINT_PREEMPTION__
20
21#include "preemption.hfa"
22
23#include <assert.h>
24
25#include <errno.h>
26#include <stdio.h>
27#include <string.h>
28#include <unistd.h>
29#include <limits.h>                                                                             // PTHREAD_STACK_MIN
30
31#include "bits/debug.hfa"
32#include "bits/signal.hfa"
33#include "kernel/private.hfa"
34
35
36#if !defined(__CFA_DEFAULT_PREEMPTION__)
37#define __CFA_DEFAULT_PREEMPTION__ 10`ms
38#endif
39
40__attribute__((weak)) Duration default_preemption() libcfa_public {
41        const char * preempt_rate_s = getenv("CFA_DEFAULT_PREEMPTION");
42        if(!preempt_rate_s) {
43                __cfadbg_print_safe(preemption, "No CFA_DEFAULT_PREEMPTION in ENV\n");
44                return __CFA_DEFAULT_PREEMPTION__;
45        }
46
47        char * endptr = 0p;
48        long int preempt_rate_l = strtol(preempt_rate_s, &endptr, 10);
49        if(preempt_rate_l < 0 || preempt_rate_l > 65535) {
50                __cfadbg_print_safe(preemption, "CFA_DEFAULT_PREEMPTION out of range : %ld\n", preempt_rate_l);
51                return __CFA_DEFAULT_PREEMPTION__;
52        }
53        if('\0' != *endptr) {
54                __cfadbg_print_safe(preemption, "CFA_DEFAULT_PREEMPTION not a decimal number : %s\n", preempt_rate_s);
55                return __CFA_DEFAULT_PREEMPTION__;
56        }
57
58        return preempt_rate_l`ms;
59}
60
61// FwdDeclarations : timeout handlers
62static void preempt( processor   * this );
63static void timeout( thread$ * this );
64
65// FwdDeclarations : Signal handlers
66static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ );
67static void sigHandler_alarm    ( __CFA_SIGPARMS__ );
68static void sigHandler_segv     ( __CFA_SIGPARMS__ );
69static void sigHandler_ill      ( __CFA_SIGPARMS__ );
70static void sigHandler_fpe      ( __CFA_SIGPARMS__ );
71static void sigHandler_abort    ( __CFA_SIGPARMS__ );
72
73// FwdDeclarations : alarm thread main
74static void * alarm_loop( __attribute__((unused)) void * args );
75
76// Machine specific register name
77#if   defined( __i386 )
78#define CFA_REG_IP gregs[REG_EIP]
79#elif defined( __x86_64 )
80#define CFA_REG_IP gregs[REG_RIP]
81#elif defined( __arm__ )
82#define CFA_REG_IP arm_pc
83#elif defined( __aarch64__ )
84#define CFA_REG_IP pc
85#else
86#error unsupported hardware architecture
87#endif
88
89KERNEL_STORAGE(event_kernel_t, event_kernel);         // private storage for event kernel
90event_kernel_t * event_kernel;                        // kernel public handle to even kernel
91static pthread_t alarm_thread;                        // pthread handle to alarm thread
92static void * alarm_stack;                                                        // pthread stack for alarm thread
93
94static void ?{}(event_kernel_t & this) with( this ) {
95        alarms{};
96        lock{};
97}
98
99//=============================================================================================
100// Kernel Preemption logic
101//=============================================================================================
102
103// Get next expired node
104static inline alarm_node_t * get_expired( alarm_list_t * alarms, Time currtime ) {
105        if( ! & (*alarms)`first ) return 0p;                                            // If no alarms return null
106        if( (*alarms)`first.deadline >= currtime ) return 0p;   // If alarms head not expired return null
107        return pop(alarms);                                                                     // Otherwise just pop head
108}
109
110// Tick one frame of the Discrete Event Simulation for alarms
111static void tick_preemption(void) {
112        alarm_node_t * node = 0p;                                                       // Used in the while loop but cannot be declared in the while condition
113        alarm_list_t * alarms = &event_kernel->alarms;          // Local copy for ease of reading
114        Time currtime = __kernel_get_time();                            // Check current time once so everything "happens at once"
115
116        //Loop throught every thing expired
117        while( node = get_expired( alarms, currtime ) ) {
118                __cfadbg_print_buffer_decl( preemption, " KERNEL: preemption tick %lu\n", currtime.tn);
119                Duration period = node->period;
120                if( period == 0) {
121                        node->set = false;                  // Node is one-shot, just mark it as not pending
122                }
123
124                __cfadbg_print_buffer_local( preemption, " KERNEL: alarm ticking node %p.\n", node );
125
126
127                // Check if this is a kernel
128                if( node->type == Kernel ) {
129                        preempt( node->proc );
130                }
131                else if( node->type == User ) {
132                        __cfadbg_print_buffer_local( preemption, " KERNEL: alarm unparking %p.\n", node->thrd );
133                        timeout( node->thrd );
134                }
135                else {
136                        node->callback(*node);
137                }
138
139                // Check if this is a periodic alarm
140                if( period > 0 ) {
141                        __cfadbg_print_buffer_local( preemption, " KERNEL: alarm period is %lu.\n", period`ns );
142                        node->deadline = currtime + period;  // Alarm is periodic, add currtime to it (used cached current time)
143                        insert( alarms, node );             // Reinsert the node for the next time it triggers
144                }
145        }
146
147        // If there are still alarms pending, reset the timer
148        if( & (*alarms)`first ) {
149                Duration delta = (*alarms)`first.deadline - currtime;
150                __kernel_set_timer( delta );
151        }
152}
153
154// Update the preemption of a processor and notify interested parties
155void update_preemption( processor * this, Duration duration ) {
156        alarm_node_t * alarm = this->preemption_alarm;
157
158        // Alarms need to be enabled
159        if ( duration > 0 && ! alarm->set ) {
160                alarm->initial = duration;
161                alarm->period  = duration;
162                register_self( alarm );
163        }
164        // Zero duration but alarm is set
165        else if ( duration == 0 && alarm->set ) {
166                unregister_self( alarm );
167                alarm->initial = 0;
168                alarm->period  = 0;
169        }
170        // If alarm is different from previous, change it
171        else if ( duration > 0 && alarm->period != duration ) {
172                unregister_self( alarm );
173                alarm->initial = duration;
174                alarm->period  = duration;
175                register_self( alarm );
176        }
177}
178
179//=============================================================================================
180// Kernel Signal Tools
181//=============================================================================================
182// In a user-level threading system, there are handful of thread-local variables where this problem occurs on the ARM.
183//
184// For each kernel thread running user-level threads, there is a flag variable to indicate if interrupts are
185// enabled/disabled for that kernel thread. Therefore, this variable is made thread local.
186//
187// For example, this code fragment sets the state of the "interrupt" variable in thread-local memory.
188//
189// _Thread_local volatile int interrupts;
190// int main() {
191//     interrupts = 0; // disable interrupts }
192//
193// which generates the following code on the ARM
194//
195// (gdb) disassemble main
196// Dump of assembler code for function main:
197//    0x0000000000000610 <+0>:  mrs     x1, tpidr_el0
198//    0x0000000000000614 <+4>:  mov     w0, #0x0                        // #0
199//    0x0000000000000618 <+8>:  add     x1, x1, #0x0, lsl #12
200//    0x000000000000061c <+12>: add     x1, x1, #0x10
201//    0x0000000000000620 <+16>: str     wzr, [x1]
202//    0x0000000000000624 <+20>: ret
203//
204// The mrs moves a pointer from coprocessor register tpidr_el0 into register x1.  Register w0 is set to 0. The two adds
205// increase the TLS pointer with the displacement (offset) 0x10, which is the location in the TSL of variable
206// "interrupts".  Finally, 0 is stored into "interrupts" through the pointer in register x1 that points into the
207// TSL. Now once x1 has the pointer to the location of the TSL for kernel thread N, it can be be preempted at a
208// user-level and the user thread is put on the user-level ready-queue. When the preempted thread gets to the front of
209// the user-level ready-queue it is run on kernel thread M. It now stores 0 into "interrupts" back on kernel thread N,
210// turning off interrupt on the wrong kernel thread.
211//
212// On the x86, the following code is generated for the same code fragment.
213//
214// (gdb) disassemble main
215// Dump of assembler code for function main:
216//    0x0000000000400420 <+0>:  movl   $0x0,%fs:0xfffffffffffffffc
217//    0x000000000040042c <+12>: xor    %eax,%eax
218//    0x000000000040042e <+14>: retq
219//
220// and there is base-displacement addressing used to atomically reset variable "interrupts" off of the TSL pointer in
221// register "fs".
222//
223// Hence, the ARM has base-displacement address for the general purpose registers, BUT not to the coprocessor
224// registers. As a result, generating the address for the write into variable "interrupts" is no longer atomic.
225//
226// Note this problem does NOT occur when just using multiple kernel threads because the preemption ALWAYS restarts the
227// thread on the same kernel thread.
228//
229// The obvious question is why does ARM use a coprocessor register to store the TSL pointer given that coprocessor
230// registers are second-class registers with respect to the instruction set. One possible answer is that they did not
231// want to dedicate one of the general registers to hold the TLS pointer and there was a free coprocessor register
232// available.
233
234//----------
235// special case for preemption since used often
236bool __preemption_enabled() libcfa_nopreempt libcfa_public {
237        // access tls as normal
238        return __cfaabi_tls.preemption_state.enabled;
239}
240
241extern "C" {
242        __attribute__((visibility("hidden"))) extern void * const __start_cfatext_nopreempt;
243        __attribute__((visibility("hidden"))) extern void * const __stop_cfatext_nopreempt;
244
245        extern const __cfa_nopreempt_region __libcfa_nopreempt;
246        __attribute__((visibility("protected"))) const __cfa_nopreempt_region __libcfathrd_nopreempt @= {
247                (void * const)&__start_cfatext_nopreempt,
248                (void * const)&__stop_cfatext_nopreempt
249        };
250}
251
252static inline bool __cfaabi_in( void * const ip, const struct __cfa_nopreempt_region & const region ) {
253        return ip >= region.start && ip <= region.stop;
254}
255
256
257//----------
258// Get data from the TLS block
259// struct asm_region __cfaasm_get;
260uintptr_t __cfatls_get( unsigned long int offset ) libcfa_nopreempt libcfa_public; //no inline to avoid problems
261uintptr_t __cfatls_get( unsigned long int offset ) {
262        // access tls as normal (except for pointer arithmetic)
263        uintptr_t val = *(uintptr_t*)((uintptr_t)&__cfaabi_tls + offset);
264
265        // This is used everywhere, to avoid cost, we DO NOT poll pending preemption
266        return val;
267}
268
269extern "C" {
270        // Disable interrupts by incrementing the counter
271        void disable_interrupts() libcfa_nopreempt libcfa_public with( __cfaabi_tls.preemption_state ) {
272                #if GCC_VERSION > 50000
273                static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
274                #endif
275
276                // Set enabled flag to false
277                // should be atomic to avoid preemption in the middle of the operation.
278                // use memory order RELAXED since there is no inter-thread on this variable requirements
279                __atomic_store_n(&enabled, false, __ATOMIC_RELAXED);
280
281                // Signal the compiler that a fence is needed but only for signal handlers
282                __atomic_signal_fence(__ATOMIC_ACQUIRE);
283
284                __attribute__((unused)) unsigned short new_val = disable_count + 1;
285                disable_count = new_val;
286                verify( new_val < 65_000u );              // If this triggers someone is disabling interrupts without enabling them
287        }
288
289        // Enable interrupts by decrementing the counter
290        // If counter reaches 0, execute any pending __cfactx_switch
291        void enable_interrupts( bool poll ) libcfa_nopreempt libcfa_public {
292                // Cache the processor now since interrupts can start happening after the atomic store
293                processor   * proc = __cfaabi_tls.this_processor;
294                /* paranoid */ verify( !poll || proc );
295
296                with( __cfaabi_tls.preemption_state ){
297                        unsigned short prev = disable_count;
298                        disable_count -= 1;
299
300                        // If this triggers someone is enabled already enabled interruptsverify( prev != 0u );
301                        /* paranoid */ verify( prev != 0u );
302
303                        // Check if we need to prempt the thread because an interrupt was missed
304                        if( prev == 1 ) {
305                                #if GCC_VERSION > 50000
306                                        static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
307                                #endif
308
309                                // Set enabled flag to true
310                                // should be atomic to avoid preemption in the middle of the operation.
311                                // use memory order RELAXED since there is no inter-thread on this variable requirements
312                                __atomic_store_n(&enabled, true, __ATOMIC_RELAXED);
313
314                                // Signal the compiler that a fence is needed but only for signal handlers
315                                __atomic_signal_fence(__ATOMIC_RELEASE);
316                                if( poll && proc->pending_preemption ) {
317                                        proc->pending_preemption = false;
318                                        force_yield( __POLL_PREEMPTION );
319                                }
320                        }
321                }
322        }
323
324        // Check whether or not there is pending preemption
325        // force_yield( __POLL_PREEMPTION ) if appropriate
326        // return true if the thread was in an interruptable state
327        // i.e. on a real processor and not in the kernel
328        // (can return true even if no preemption was pending)
329        bool poll_interrupts() libcfa_nopreempt libcfa_public {
330                // Cache the processor now since interrupts can start happening after the atomic store
331                processor   * proc =  __cfaabi_tls.this_processor;
332                if ( ! proc ) return false;
333                if ( ! __cfaabi_tls.preemption_state.enabled ) return false;
334
335                // Signal the compiler that a fence is needed but only for signal handlers
336                __atomic_signal_fence(__ATOMIC_RELEASE);
337                if( unlikely( proc->pending_preemption ) ) {
338                        proc->pending_preemption = false;
339                        force_yield( __POLL_PREEMPTION );
340                }
341
342                return true;
343        }
344}
345
346//-----------------------------------------------------------------------------
347// Kernel Signal Debug
348void __cfaabi_check_preemption() libcfa_public {
349        bool ready = __preemption_enabled();
350        if(!ready) { abort("Preemption should be ready"); }
351
352        sigset_t oldset;
353        int ret;
354        ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset);  // workaround trac#208: cast should be unnecessary
355        if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
356
357        ret = sigismember(&oldset, SIGUSR1);
358        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
359        if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
360
361        ret = sigismember(&oldset, SIGALRM);
362        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
363        if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
364
365        ret = sigismember(&oldset, SIGTERM);
366        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
367        if(ret == 1) { abort("ERROR SIGTERM is disabled"); }
368}
369
370#ifdef __CFA_WITH_VERIFY__
371bool __cfaabi_dbg_in_kernel() {
372        return !__preemption_enabled();
373}
374#endif
375
376#undef __cfaasm_label
377
378//-----------------------------------------------------------------------------
379// Signal handling
380
381// sigprocmask wrapper : unblock a single signal
382static inline void signal_unblock( int sig ) {
383        sigset_t mask;
384        sigemptyset( &mask );
385        sigaddset( &mask, sig );
386
387        if ( pthread_sigmask( SIG_UNBLOCK, &mask, 0p ) == -1 ) {
388            abort( "internal error, pthread_sigmask" );
389        }
390}
391
392// sigprocmask wrapper : block a single signal
393static inline void signal_block( int sig ) {
394        sigset_t mask;
395        sigemptyset( &mask );
396        sigaddset( &mask, sig );
397
398        if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
399                abort( "internal error, pthread_sigmask" );
400        }
401}
402
403// kill wrapper : signal a processor
404static void preempt( processor * this ) {
405        sigval_t value = { PREEMPT_NORMAL };
406        pthread_sigqueue( this->kernel_thread, SIGUSR1, value );
407}
408
409// reserved for future use
410static void timeout( thread$ * this ) {
411        unpark( this );
412}
413
414void __disable_interrupts_hard() {
415        sigset_t oldset;
416        int ret;
417        ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset);  // workaround trac#208: cast should be unnecessary
418        if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
419
420        ret = sigismember(&oldset, SIGUSR1);
421        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
422        if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
423
424        ret = sigismember(&oldset, SIGALRM);
425        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
426        if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
427
428        signal_block( SIGUSR1 );
429}
430
431void __enable_interrupts_hard() {
432        signal_unblock( SIGUSR1 );
433
434        sigset_t oldset;
435        int ret;
436        ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset);  // workaround trac#208: cast should be unnecessary
437        if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
438
439        ret = sigismember(&oldset, SIGUSR1);
440        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
441        if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
442
443        ret = sigismember(&oldset, SIGALRM);
444        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
445        if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
446}
447
448//-----------------------------------------------------------------------------
449// KERNEL ONLY
450// Check if a __cfactx_switch signal handler shoud defer
451// If true  : preemption is safe
452// If false : preemption is unsafe and marked as pending
453static inline bool preemption_ready( void * ip ) {
454        // Check if preemption is safe
455        bool ready = true;
456        if( __cfaabi_in( ip, __libcfa_nopreempt ) ) { ready = false; goto EXIT; };
457        if( __cfaabi_in( ip, __libcfathrd_nopreempt ) ) { ready = false; goto EXIT; };
458
459        if( !__cfaabi_tls.preemption_state.enabled) { ready = false; goto EXIT; };
460        if( __cfaabi_tls.preemption_state.in_progress ) { ready = false; goto EXIT; };
461
462EXIT:
463        // Adjust the pending flag accordingly
464        __cfaabi_tls.this_processor->pending_preemption = !ready;
465        return ready;
466}
467
468//=============================================================================================
469// Kernel Signal Startup/Shutdown logic
470//=============================================================================================
471
472// Startup routine to activate preemption
473// Called from kernel_startup
474void __kernel_alarm_startup() {
475        __cfaabi_dbg_print_safe( "Kernel : Starting preemption\n" );
476
477        // Start with preemption disabled until ready
478        __cfaabi_tls.preemption_state.enabled = false;
479        __cfaabi_tls.preemption_state.disable_count = 1;
480
481        // Initialize the event kernel
482        event_kernel = (event_kernel_t *)&storage_event_kernel;
483        (*event_kernel){};
484
485        // Setup proper signal handlers
486        __cfaabi_sigaction( SIGUSR1, sigHandler_ctxSwitch, SA_SIGINFO ); // __cfactx_switch handler
487        __cfaabi_sigaction( SIGALRM, sigHandler_alarm    , SA_SIGINFO ); // debug handler
488
489        signal_block( SIGALRM );
490
491        alarm_stack = __create_pthread( &alarm_thread, alarm_loop, 0p );
492}
493
494// Shutdown routine to deactivate preemption
495// Called from kernel_shutdown
496void __kernel_alarm_shutdown() {
497        __cfaabi_dbg_print_safe( "Kernel : Preemption stopping\n" );
498
499        // Block all signals since we are already shutting down
500        sigset_t mask;
501        sigfillset( &mask );
502        sigprocmask( SIG_BLOCK, &mask, 0p );
503
504        // Notify the alarm thread of the shutdown
505        sigval val;
506        val.sival_int = 0;
507        pthread_sigqueue( alarm_thread, SIGALRM, val );
508
509        // Wait for the preemption thread to finish
510
511        __destroy_pthread( alarm_thread, alarm_stack, 0p );
512
513        // Preemption is now fully stopped
514
515        __cfaabi_dbg_print_safe( "Kernel : Preemption stopped\n" );
516}
517
518// Prevent preemption since we are about to start terminating things
519void __kernel_abort_lock(void) {
520        signal_block( SIGUSR1 );
521}
522
523// Raii ctor/dtor for the preemption_scope
524// Used by thread to control when they want to receive preemption signals
525void ?{}( preemption_scope & this, processor * proc ) {
526        (this.alarm){ proc, 0`s, 0`s };
527        this.proc = proc;
528        this.proc->preemption_alarm = &this.alarm;
529
530        update_preemption( this.proc, this.proc->cltr->preemption_rate );
531}
532
533void ^?{}( preemption_scope & this ) {
534        disable_interrupts();
535
536        update_preemption( this.proc, 0`s );
537}
538
539//=============================================================================================
540// Kernel Signal Handlers
541//=============================================================================================
542__cfaabi_dbg_debug_do( static __thread void * last_interrupt = 0; )
543
544// Context switch signal handler
545// Receives SIGUSR1 signal and causes the current thread to yield
546static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ ) {
547        void * ip = (void *)(cxt->uc_mcontext.CFA_REG_IP);
548        __cfaabi_dbg_debug_do( last_interrupt = ip; )
549
550        // SKULLDUGGERY: if a thread creates a processor and the immediately deletes it,
551        // the interrupt that is supposed to force the kernel thread to preempt might arrive
552        // before the kernel thread has even started running. When that happens, an interrupt
553        // with a null 'this_processor' will be caught, just ignore it.
554        if(! __cfaabi_tls.this_processor ) return;
555
556        choose(sfp->si_value.sival_int) {
557                case PREEMPT_NORMAL   : ;// Normal case, nothing to do here
558                case PREEMPT_IO       : ;// I/O asked to stop spinning, nothing to do here
559                case PREEMPT_TERMINATE: verify( __atomic_load_n( &__cfaabi_tls.this_processor->do_terminate, __ATOMIC_SEQ_CST ) );
560                default:
561                        abort( "internal error, signal value is %d", sfp->si_value.sival_int );
562        }
563
564        // Check if it is safe to preempt here
565        if( !preemption_ready( ip ) ) {
566                #if !defined(__CFA_NO_STATISTICS__)
567                        __cfaabi_tls.this_stats->ready.threads.preempt.rllfwd++;
568                #endif
569                return;
570        }
571
572        __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) );
573
574        // Sync flag : prevent recursive calls to the signal handler
575        __cfaabi_tls.preemption_state.in_progress = true;
576
577        // Clear sighandler mask before context switching.
578        #if GCC_VERSION > 50000
579        static_assert( sizeof( sigset_t ) == sizeof( cxt->uc_sigmask ), "Expected cxt->uc_sigmask to be of sigset_t" );
580        #endif
581        if ( pthread_sigmask( SIG_SETMASK, (sigset_t *)&(cxt->uc_sigmask), 0p ) == -1 ) {
582                abort( "internal error, sigprocmask" );
583        }
584
585        // Clear the in progress flag
586        __cfaabi_tls.preemption_state.in_progress = false;
587
588        // Preemption can occur here
589
590        #if !defined(__CFA_NO_STATISTICS__)
591                __cfaabi_tls.this_stats->ready.threads.preempt.yield++;
592        #endif
593
594        force_yield( __ALARM_PREEMPTION ); // Do the actual __cfactx_switch
595}
596
597static void sigHandler_alarm( __CFA_SIGPARMS__ ) {
598        abort("SIGALRM should never reach the signal handler");
599}
600
601// Main of the alarm thread
602// Waits on SIGALRM and send SIGUSR1 to whom ever needs it
603static void * alarm_loop( __attribute__((unused)) void * args ) {
604        unsigned id = register_proc_id();
605
606        // Block sigalrms to control when they arrive
607        sigset_t mask;
608        sigfillset(&mask);
609        if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
610            abort( "internal error, pthread_sigmask" );
611        }
612
613        sigemptyset( &mask );
614        sigaddset( &mask, SIGALRM );
615
616        // Main loop
617        while( true ) {
618                // Wait for a sigalrm
619                siginfo_t info;
620                int sig = sigwaitinfo( &mask, &info );
621
622                __cfadbg_print_buffer_decl ( preemption, " KERNEL: sigwaitinfo returned %d, c: %d, v: %d\n", sig, info.si_code, info.si_value.sival_int );
623                __cfadbg_print_buffer_local( preemption, " KERNEL: SI_QUEUE %d, SI_TIMER %d, SI_KERNEL %d\n", SI_QUEUE, SI_TIMER, SI_KERNEL );
624
625                if( sig < 0 ) {
626                        //Error!
627                        int err = errno;
628                        switch( err ) {
629                                case EAGAIN :
630                                case EINTR :
631                                        {__cfadbg_print_buffer_local( preemption, " KERNEL: Spurious wakeup %d.\n", err );}
632                                        continue;
633                                case EINVAL :
634                                        abort( "Timeout was invalid." );
635                                default:
636                                        abort( "Unhandled error %d", err);
637                        }
638                }
639
640                // If another signal arrived something went wrong
641                assertf(sig == SIGALRM, "Kernel Internal Error, sigwait: Unexpected signal %d (%d : %d)\n", sig, info.si_code, info.si_value.sival_int);
642
643                // Switch on the code (a.k.a. the sender) to
644                switch( info.si_code )
645                {
646                // Signal was not sent by the kernel but by an other thread
647                case SI_QUEUE:
648                        // other threads may signal the alarm thread to shut it down
649                        // or to manual cause the preemption tick
650                        // use info.si_value and handle the case here
651                        switch( info.si_value.sival_int ) {
652                        case 0:
653                                goto EXIT;
654                        default:
655                                abort( "SI_QUEUE with val %d", info.si_value.sival_int);
656                        }
657                        // fallthrough
658                // Timers can apparently be marked as sent for the kernel
659                // In either case, tick preemption
660                case SI_TIMER:
661                case SI_KERNEL:
662                        // __cfaabi_dbg_print_safe( "Kernel : Preemption thread tick\n" );
663                        lock( event_kernel->lock __cfaabi_dbg_ctx2 );
664                        tick_preemption();
665                        unlock( event_kernel->lock );
666                        break;
667                }
668        }
669
670EXIT:
671        __cfaabi_dbg_print_safe( "Kernel : Preemption thread stopping\n" );
672        unregister_proc_id(id);
673
674        return 0p;
675}
676
677// Local Variables: //
678// mode: c //
679// tab-width: 4 //
680// End: //
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