source: libcfa/src/concurrency/preemption.cfa @ b443db0

pthread-emulation
Last change on this file since b443db0 was b443db0, checked in by Thierry Delisle <tdelisle@…>, 7 months ago

Change how no preempts zone are implemented. From begin/end tags to specific sections.

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File size: 25.1 KB
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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 : 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.timeval >= 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->timeval = 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.timeval - 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// Some assembly required
236#define __cfaasm_label(label, when) when: asm volatile goto(".global __cfaasm_" #label "_" #when "\n" "__cfaasm_" #label "_" #when ":":::"memory":when)
237
238//----------
239// special case for preemption since used often
240__attribute__((optimize("no-reorder-blocks"))) bool __preemption_enabled() libcfa_nopreempt libcfa_public {
241        // create a assembler label before
242        // marked as clobber all to avoid movement
243        __cfaasm_label(check, before);
244
245        // access tls as normal
246        bool enabled = __cfaabi_tls.preemption_state.enabled;
247
248        // Check if there is a pending preemption
249        processor   * proc = __cfaabi_tls.this_processor;
250        bool pending = proc ? proc->pending_preemption : false;
251        if( enabled && pending ) proc->pending_preemption = false;
252
253        // create a assembler label after
254        // marked as clobber all to avoid movement
255        __cfaasm_label(check, after);
256
257        // If we can preempt and there is a pending one
258        // this is a good time to yield
259        if( enabled && pending ) {
260                force_yield( __POLL_PREEMPTION );
261        }
262        return enabled;
263}
264
265struct asm_region {
266        void * before;
267        void * after;
268};
269
270static inline bool __cfaasm_in( void * ip, struct asm_region & region ) {
271        return ip >= region.before && ip <= region.after;
272}
273
274extern "C" {
275        __attribute__((visibility("hidden"))) extern void * const __start_cfatext_nopreempt;
276        __attribute__((visibility("hidden"))) extern void * const __stop_cfatext_nopreempt;
277
278        extern const __cfa_nopreempt_region __libcfa_nopreempt;
279        __attribute__((visibility("protected"))) const __cfa_nopreempt_region __libcfathrd_nopreempt @= {
280                (void * const)&__start_cfatext_nopreempt,
281                (void * const)&__stop_cfatext_nopreempt
282        };
283}
284
285static inline bool __cfaabi_in( void * const ip, const struct __cfa_nopreempt_region & const region ) {
286        return ip >= region.start && ip <= region.stop;
287}
288
289
290//----------
291// Get data from the TLS block
292// struct asm_region __cfaasm_get;
293uintptr_t __cfatls_get( unsigned long int offset ) libcfa_nopreempt libcfa_public; //no inline to avoid problems
294uintptr_t __cfatls_get( unsigned long int offset ) {
295        // create a assembler label before
296        // marked as clobber all to avoid movement
297        __cfaasm_label(get, before);
298
299        // access tls as normal (except for pointer arithmetic)
300        uintptr_t val = *(uintptr_t*)((uintptr_t)&__cfaabi_tls + offset);
301
302        // create a assembler label after
303        // marked as clobber all to avoid movement
304        __cfaasm_label(get, after);
305
306        // This is used everywhere, to avoid cost, we DO NOT poll pending preemption
307        return val;
308}
309
310extern "C" {
311        // Disable interrupts by incrementing the counter
312        void disable_interrupts() libcfa_nopreempt libcfa_public {
313                // create a assembler label before
314                // marked as clobber all to avoid movement
315                __cfaasm_label(dsable, before);
316
317                with( __cfaabi_tls.preemption_state ) {
318                        #if GCC_VERSION > 50000
319                        static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
320                        #endif
321
322                        // Set enabled flag to false
323                        // should be atomic to avoid preemption in the middle of the operation.
324                        // use memory order RELAXED since there is no inter-thread on this variable requirements
325                        __atomic_store_n(&enabled, false, __ATOMIC_RELAXED);
326
327                        // Signal the compiler that a fence is needed but only for signal handlers
328                        __atomic_signal_fence(__ATOMIC_ACQUIRE);
329
330                        __attribute__((unused)) unsigned short new_val = disable_count + 1;
331                        disable_count = new_val;
332                        verify( new_val < 65_000u );              // If this triggers someone is disabling interrupts without enabling them
333                }
334
335                // create a assembler label after
336                // marked as clobber all to avoid movement
337                __cfaasm_label(dsable, after);
338
339        }
340
341        // Enable interrupts by decrementing the counter
342        // If counter reaches 0, execute any pending __cfactx_switch
343        void enable_interrupts( bool poll ) libcfa_nopreempt libcfa_public {
344                // Cache the processor now since interrupts can start happening after the atomic store
345                processor   * proc = __cfaabi_tls.this_processor;
346                /* paranoid */ verify( !poll || proc );
347
348                with( __cfaabi_tls.preemption_state ){
349                        unsigned short prev = disable_count;
350                        disable_count -= 1;
351
352                        // If this triggers someone is enabled already enabled interruptsverify( prev != 0u );
353                        /* paranoid */ verify( prev != 0u );
354
355                        // Check if we need to prempt the thread because an interrupt was missed
356                        if( prev == 1 ) {
357                                #if GCC_VERSION > 50000
358                                        static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
359                                #endif
360
361                                // Set enabled flag to true
362                                // should be atomic to avoid preemption in the middle of the operation.
363                                // use memory order RELAXED since there is no inter-thread on this variable requirements
364                                __atomic_store_n(&enabled, true, __ATOMIC_RELAXED);
365
366                                // Signal the compiler that a fence is needed but only for signal handlers
367                                __atomic_signal_fence(__ATOMIC_RELEASE);
368                                if( poll && proc->pending_preemption ) {
369                                        proc->pending_preemption = false;
370                                        force_yield( __POLL_PREEMPTION );
371                                }
372                        }
373                }
374        }
375
376        // Check whether or not there is pending preemption
377        // force_yield( __POLL_PREEMPTION ) if appropriate
378        // return true if the thread was in an interruptable state
379        // i.e. on a real processor and not in the kernel
380        // (can return true even if no preemption was pending)
381        bool poll_interrupts() libcfa_public {
382                // Cache the processor now since interrupts can start happening after the atomic store
383                processor   * proc = publicTLS_get( this_processor );
384                if ( ! proc ) return false;
385                if ( ! __preemption_enabled() ) return false;
386
387                with( __cfaabi_tls.preemption_state ){
388                        // Signal the compiler that a fence is needed but only for signal handlers
389                        __atomic_signal_fence(__ATOMIC_RELEASE);
390                        if( proc->pending_preemption ) {
391                                proc->pending_preemption = false;
392                                force_yield( __POLL_PREEMPTION );
393                        }
394                }
395
396                return true;
397        }
398}
399
400//-----------------------------------------------------------------------------
401// Kernel Signal Debug
402void __cfaabi_check_preemption() libcfa_public {
403        bool ready = __preemption_enabled();
404        if(!ready) { abort("Preemption should be ready"); }
405
406        sigset_t oldset;
407        int ret;
408        ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset);  // workaround trac#208: cast should be unnecessary
409        if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
410
411        ret = sigismember(&oldset, SIGUSR1);
412        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
413        if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
414
415        ret = sigismember(&oldset, SIGALRM);
416        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
417        if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
418
419        ret = sigismember(&oldset, SIGTERM);
420        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
421        if(ret == 1) { abort("ERROR SIGTERM is disabled"); }
422}
423
424#ifdef __CFA_WITH_VERIFY__
425bool __cfaabi_dbg_in_kernel() {
426        return !__preemption_enabled();
427}
428#endif
429
430#undef __cfaasm_label
431
432//-----------------------------------------------------------------------------
433// Signal handling
434
435// sigprocmask wrapper : unblock a single signal
436static inline void signal_unblock( int sig ) {
437        sigset_t mask;
438        sigemptyset( &mask );
439        sigaddset( &mask, sig );
440
441        if ( pthread_sigmask( SIG_UNBLOCK, &mask, 0p ) == -1 ) {
442            abort( "internal error, pthread_sigmask" );
443        }
444}
445
446// sigprocmask wrapper : block a single signal
447static inline void signal_block( int sig ) {
448        sigset_t mask;
449        sigemptyset( &mask );
450        sigaddset( &mask, sig );
451
452        if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
453                abort( "internal error, pthread_sigmask" );
454        }
455}
456
457// kill wrapper : signal a processor
458static void preempt( processor * this ) {
459        sigval_t value = { PREEMPT_NORMAL };
460        pthread_sigqueue( this->kernel_thread, SIGUSR1, value );
461}
462
463// reserved for future use
464static void timeout( thread$ * this ) {
465        unpark( this );
466}
467
468void __disable_interrupts_hard() {
469        sigset_t oldset;
470        int ret;
471        ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset);  // workaround trac#208: cast should be unnecessary
472        if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
473
474        ret = sigismember(&oldset, SIGUSR1);
475        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
476        if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
477
478        ret = sigismember(&oldset, SIGALRM);
479        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
480        if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
481
482        signal_block( SIGUSR1 );
483}
484
485void __enable_interrupts_hard() {
486        signal_unblock( SIGUSR1 );
487
488        sigset_t oldset;
489        int ret;
490        ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset);  // workaround trac#208: cast should be unnecessary
491        if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
492
493        ret = sigismember(&oldset, SIGUSR1);
494        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
495        if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
496
497        ret = sigismember(&oldset, SIGALRM);
498        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
499        if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
500}
501
502//-----------------------------------------------------------------------------
503// KERNEL ONLY
504// Check if a __cfactx_switch signal handler shoud defer
505// If true  : preemption is safe
506// If false : preemption is unsafe and marked as pending
507static inline bool preemption_ready( void * ip ) {
508        // Check if preemption is safe
509        bool ready = true;
510        if( __cfaabi_in( ip, __libcfa_nopreempt ) ) { ready = false; goto EXIT; };
511        if( __cfaabi_in( ip, __libcfathrd_nopreempt ) ) { ready = false; goto EXIT; };
512
513        if( !__cfaabi_tls.preemption_state.enabled) { ready = false; goto EXIT; };
514        if( __cfaabi_tls.preemption_state.in_progress ) { ready = false; goto EXIT; };
515
516EXIT:
517        // Adjust the pending flag accordingly
518        __cfaabi_tls.this_processor->pending_preemption = !ready;
519        return ready;
520}
521
522//=============================================================================================
523// Kernel Signal Startup/Shutdown logic
524//=============================================================================================
525
526// Startup routine to activate preemption
527// Called from kernel_startup
528void __kernel_alarm_startup() {
529        __cfaabi_dbg_print_safe( "Kernel : Starting preemption\n" );
530
531        // Start with preemption disabled until ready
532        __cfaabi_tls.preemption_state.enabled = false;
533        __cfaabi_tls.preemption_state.disable_count = 1;
534
535        // Initialize the event kernel
536        event_kernel = (event_kernel_t *)&storage_event_kernel;
537        (*event_kernel){};
538
539        // Setup proper signal handlers
540        __cfaabi_sigaction( SIGUSR1, sigHandler_ctxSwitch, SA_SIGINFO ); // __cfactx_switch handler
541        __cfaabi_sigaction( SIGALRM, sigHandler_alarm    , SA_SIGINFO ); // debug handler
542
543        signal_block( SIGALRM );
544
545        alarm_stack = __create_pthread( &alarm_thread, alarm_loop, 0p );
546}
547
548// Shutdown routine to deactivate preemption
549// Called from kernel_shutdown
550void __kernel_alarm_shutdown() {
551        __cfaabi_dbg_print_safe( "Kernel : Preemption stopping\n" );
552
553        // Block all signals since we are already shutting down
554        sigset_t mask;
555        sigfillset( &mask );
556        sigprocmask( SIG_BLOCK, &mask, 0p );
557
558        // Notify the alarm thread of the shutdown
559        sigval val;
560        val.sival_int = 0;
561        pthread_sigqueue( alarm_thread, SIGALRM, val );
562
563        // Wait for the preemption thread to finish
564
565        __destroy_pthread( alarm_thread, alarm_stack, 0p );
566
567        // Preemption is now fully stopped
568
569        __cfaabi_dbg_print_safe( "Kernel : Preemption stopped\n" );
570}
571
572// Prevent preemption since we are about to start terminating things
573void __kernel_abort_lock(void) {
574        signal_block( SIGUSR1 );
575}
576
577// Raii ctor/dtor for the preemption_scope
578// Used by thread to control when they want to receive preemption signals
579void ?{}( preemption_scope & this, processor * proc ) {
580        (this.alarm){ proc, 0`s, 0`s };
581        this.proc = proc;
582        this.proc->preemption_alarm = &this.alarm;
583
584        update_preemption( this.proc, this.proc->cltr->preemption_rate );
585}
586
587void ^?{}( preemption_scope & this ) {
588        disable_interrupts();
589
590        update_preemption( this.proc, 0`s );
591}
592
593//=============================================================================================
594// Kernel Signal Handlers
595//=============================================================================================
596__cfaabi_dbg_debug_do( static __thread void * last_interrupt = 0; )
597
598// Context switch signal handler
599// Receives SIGUSR1 signal and causes the current thread to yield
600static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ ) {
601        void * ip = (void *)(cxt->uc_mcontext.CFA_REG_IP);
602        __cfaabi_dbg_debug_do( last_interrupt = ip; )
603
604        // SKULLDUGGERY: if a thread creates a processor and the immediately deletes it,
605        // the interrupt that is supposed to force the kernel thread to preempt might arrive
606        // before the kernel thread has even started running. When that happens, an interrupt
607        // with a null 'this_processor' will be caught, just ignore it.
608        if(! __cfaabi_tls.this_processor ) return;
609
610        choose(sfp->si_value.sival_int) {
611                case PREEMPT_NORMAL   : ;// Normal case, nothing to do here
612                case PREEMPT_IO       : ;// I/O asked to stop spinning, nothing to do here
613                case PREEMPT_TERMINATE: verify( __atomic_load_n( &__cfaabi_tls.this_processor->do_terminate, __ATOMIC_SEQ_CST ) );
614                default:
615                        abort( "internal error, signal value is %d", sfp->si_value.sival_int );
616        }
617
618        // Check if it is safe to preempt here
619        if( !preemption_ready( ip ) ) {
620                #if !defined(__CFA_NO_STATISTICS__)
621                        __cfaabi_tls.this_stats->ready.threads.preempt.rllfwd++;
622                #endif
623                return;
624        }
625
626        __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) );
627
628        // Sync flag : prevent recursive calls to the signal handler
629        __cfaabi_tls.preemption_state.in_progress = true;
630
631        // Clear sighandler mask before context switching.
632        #if GCC_VERSION > 50000
633        static_assert( sizeof( sigset_t ) == sizeof( cxt->uc_sigmask ), "Expected cxt->uc_sigmask to be of sigset_t" );
634        #endif
635        if ( pthread_sigmask( SIG_SETMASK, (sigset_t *)&(cxt->uc_sigmask), 0p ) == -1 ) {
636                abort( "internal error, sigprocmask" );
637        }
638
639        // Clear the in progress flag
640        __cfaabi_tls.preemption_state.in_progress = false;
641
642        // Preemption can occur here
643
644        #if !defined(__CFA_NO_STATISTICS__)
645                __cfaabi_tls.this_stats->ready.threads.preempt.yield++;
646        #endif
647
648        force_yield( __ALARM_PREEMPTION ); // Do the actual __cfactx_switch
649}
650
651static void sigHandler_alarm( __CFA_SIGPARMS__ ) {
652        abort("SIGALRM should never reach the signal handler");
653}
654
655// Main of the alarm thread
656// Waits on SIGALRM and send SIGUSR1 to whom ever needs it
657static void * alarm_loop( __attribute__((unused)) void * args ) {
658        unsigned id = register_proc_id();
659
660        // Block sigalrms to control when they arrive
661        sigset_t mask;
662        sigfillset(&mask);
663        if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
664            abort( "internal error, pthread_sigmask" );
665        }
666
667        sigemptyset( &mask );
668        sigaddset( &mask, SIGALRM );
669
670        // Main loop
671        while( true ) {
672                // Wait for a sigalrm
673                siginfo_t info;
674                int sig = sigwaitinfo( &mask, &info );
675
676                __cfadbg_print_buffer_decl ( preemption, " KERNEL: sigwaitinfo returned %d, c: %d, v: %d\n", sig, info.si_code, info.si_value.sival_int );
677                __cfadbg_print_buffer_local( preemption, " KERNEL: SI_QUEUE %d, SI_TIMER %d, SI_KERNEL %d\n", SI_QUEUE, SI_TIMER, SI_KERNEL );
678
679                if( sig < 0 ) {
680                        //Error!
681                        int err = errno;
682                        switch( err ) {
683                                case EAGAIN :
684                                case EINTR :
685                                        {__cfadbg_print_buffer_local( preemption, " KERNEL: Spurious wakeup %d.\n", err );}
686                                        continue;
687                                case EINVAL :
688                                        abort( "Timeout was invalid." );
689                                default:
690                                        abort( "Unhandled error %d", err);
691                        }
692                }
693
694                // If another signal arrived something went wrong
695                assertf(sig == SIGALRM, "Kernel Internal Error, sigwait: Unexpected signal %d (%d : %d)\n", sig, info.si_code, info.si_value.sival_int);
696
697                // Switch on the code (a.k.a. the sender) to
698                switch( info.si_code )
699                {
700                // Signal was not sent by the kernel but by an other thread
701                case SI_QUEUE:
702                        // other threads may signal the alarm thread to shut it down
703                        // or to manual cause the preemption tick
704                        // use info.si_value and handle the case here
705                        switch( info.si_value.sival_int ) {
706                        case 0:
707                                goto EXIT;
708                        default:
709                                abort( "SI_QUEUE with val %d", info.si_value.sival_int);
710                        }
711                        // fallthrough
712                // Timers can apparently be marked as sent for the kernel
713                // In either case, tick preemption
714                case SI_TIMER:
715                case SI_KERNEL:
716                        // __cfaabi_dbg_print_safe( "Kernel : Preemption thread tick\n" );
717                        lock( event_kernel->lock __cfaabi_dbg_ctx2 );
718                        tick_preemption();
719                        unlock( event_kernel->lock );
720                        break;
721                }
722        }
723
724EXIT:
725        __cfaabi_dbg_print_safe( "Kernel : Preemption thread stopping\n" );
726        unregister_proc_id(id);
727
728        return 0p;
729}
730
731// Local Variables: //
732// mode: c //
733// tab-width: 4 //
734// End: //
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