source: libcfa/src/concurrency/preemption.cfa @ 5c216b4

ADTast-experimentalenumpthread-emulationqualifiedEnum
Last change on this file since 5c216b4 was 250583e, checked in by Thierry Delisle <tdelisle@…>, 3 years ago

Some clean-up after preemption fix
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File size: 26.4 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 : Fri Nov  6 07:42:13 2020
13// Update Count     : 54
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() {
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
99enum {
100        PREEMPT_NORMAL    = 0,
101        PREEMPT_TERMINATE = 1,
102};
103
104//=============================================================================================
105// Kernel Preemption logic
106//=============================================================================================
107
108// Get next expired node
109static inline alarm_node_t * get_expired( alarm_list_t * alarms, Time currtime ) {
110        if( ! & (*alarms)`first ) return 0p;                                            // If no alarms return null
111        if( (*alarms)`first.timeval >= currtime ) return 0p;    // If alarms head not expired return null
112        return pop(alarms);                                                                     // Otherwise just pop head
113}
114
115// Tick one frame of the Discrete Event Simulation for alarms
116static void tick_preemption(void) {
117        alarm_node_t * node = 0p;                                                       // Used in the while loop but cannot be declared in the while condition
118        alarm_list_t * alarms = &event_kernel->alarms;          // Local copy for ease of reading
119        Time currtime = __kernel_get_time();                            // Check current time once so everything "happens at once"
120
121        //Loop throught every thing expired
122        while( node = get_expired( alarms, currtime ) ) {
123                __cfadbg_print_buffer_decl( preemption, " KERNEL: preemption tick %lu\n", currtime.tn);
124                Duration period = node->period;
125                if( period == 0) {
126                        node->set = false;                  // Node is one-shot, just mark it as not pending
127                }
128
129                __cfadbg_print_buffer_local( preemption, " KERNEL: alarm ticking node %p.\n", node );
130
131
132                // Check if this is a kernel
133                if( node->type == Kernel ) {
134                        preempt( node->proc );
135                }
136                else if( node->type == User ) {
137                        __cfadbg_print_buffer_local( preemption, " KERNEL: alarm unparking %p.\n", node->thrd );
138                        timeout( node->thrd );
139                }
140                else {
141                        node->callback(*node);
142                }
143
144                // Check if this is a periodic alarm
145                if( period > 0 ) {
146                        __cfadbg_print_buffer_local( preemption, " KERNEL: alarm period is %lu.\n", period`ns );
147                        node->timeval = currtime + period;  // Alarm is periodic, add currtime to it (used cached current time)
148                        insert( alarms, node );             // Reinsert the node for the next time it triggers
149                }
150        }
151
152        // If there are still alarms pending, reset the timer
153        if( & (*alarms)`first ) {
154                Duration delta = (*alarms)`first.timeval - currtime;
155                __kernel_set_timer( delta );
156        }
157}
158
159// Update the preemption of a processor and notify interested parties
160void update_preemption( processor * this, Duration duration ) {
161        alarm_node_t * alarm = this->preemption_alarm;
162
163        // Alarms need to be enabled
164        if ( duration > 0 && ! alarm->set ) {
165                alarm->initial = duration;
166                alarm->period  = duration;
167                register_self( alarm );
168        }
169        // Zero duration but alarm is set
170        else if ( duration == 0 && alarm->set ) {
171                unregister_self( alarm );
172                alarm->initial = 0;
173                alarm->period  = 0;
174        }
175        // If alarm is different from previous, change it
176        else if ( duration > 0 && alarm->period != duration ) {
177                unregister_self( alarm );
178                alarm->initial = duration;
179                alarm->period  = duration;
180                register_self( alarm );
181        }
182}
183
184//=============================================================================================
185// Kernel Signal Tools
186//=============================================================================================
187// In a user-level threading system, there are handful of thread-local variables where this problem occurs on the ARM.
188//
189// For each kernel thread running user-level threads, there is a flag variable to indicate if interrupts are
190// enabled/disabled for that kernel thread. Therefore, this variable is made thread local.
191//
192// For example, this code fragment sets the state of the "interrupt" variable in thread-local memory.
193//
194// _Thread_local volatile int interrupts;
195// int main() {
196//     interrupts = 0; // disable interrupts }
197//
198// which generates the following code on the ARM
199//
200// (gdb) disassemble main
201// Dump of assembler code for function main:
202//    0x0000000000000610 <+0>:  mrs     x1, tpidr_el0
203//    0x0000000000000614 <+4>:  mov     w0, #0x0                        // #0
204//    0x0000000000000618 <+8>:  add     x1, x1, #0x0, lsl #12
205//    0x000000000000061c <+12>: add     x1, x1, #0x10
206//    0x0000000000000620 <+16>: str     wzr, [x1]
207//    0x0000000000000624 <+20>: ret
208//
209// The mrs moves a pointer from coprocessor register tpidr_el0 into register x1.  Register w0 is set to 0. The two adds
210// increase the TLS pointer with the displacement (offset) 0x10, which is the location in the TSL of variable
211// "interrupts".  Finally, 0 is stored into "interrupts" through the pointer in register x1 that points into the
212// TSL. Now once x1 has the pointer to the location of the TSL for kernel thread N, it can be be preempted at a
213// user-level and the user thread is put on the user-level ready-queue. When the preempted thread gets to the front of
214// the user-level ready-queue it is run on kernel thread M. It now stores 0 into "interrupts" back on kernel thread N,
215// turning off interrupt on the wrong kernel thread.
216//
217// On the x86, the following code is generated for the same code fragment.
218//
219// (gdb) disassemble main
220// Dump of assembler code for function main:
221//    0x0000000000400420 <+0>:  movl   $0x0,%fs:0xfffffffffffffffc
222//    0x000000000040042c <+12>: xor    %eax,%eax
223//    0x000000000040042e <+14>: retq
224//
225// and there is base-displacement addressing used to atomically reset variable "interrupts" off of the TSL pointer in
226// register "fs".
227//
228// Hence, the ARM has base-displacement address for the general purpose registers, BUT not to the coprocessor
229// registers. As a result, generating the address for the write into variable "interrupts" is no longer atomic.
230//
231// Note this problem does NOT occur when just using multiple kernel threads because the preemption ALWAYS restarts the
232// thread on the same kernel thread.
233//
234// The obvious question is why does ARM use a coprocessor register to store the TSL pointer given that coprocessor
235// registers are second-class registers with respect to the instruction set. One possible answer is that they did not
236// want to dedicate one of the general registers to hold the TLS pointer and there was a free coprocessor register
237// available.
238
239//-----------------------------------------------------------------------------
240// Some assembly required
241#define __cfaasm_label(label, when) when: asm volatile goto(".global __cfaasm_" #label "_" #when "\n" "__cfaasm_" #label "_" #when ":":::"memory":when)
242
243//----------
244// special case for preemption since used often
245bool __preemption_enabled() {
246        // create a assembler label before
247        // marked as clobber all to avoid movement
248        __cfaasm_label(check, before);
249
250        // access tls as normal
251        bool enabled = __cfaabi_tls.preemption_state.enabled;
252
253        // Check if there is a pending preemption
254        processor   * proc = __cfaabi_tls.this_processor;
255        bool pending = proc ? proc->pending_preemption : false;
256        if( enabled && pending ) proc->pending_preemption = false;
257
258        // create a assembler label after
259        // marked as clobber all to avoid movement
260        __cfaasm_label(check, after);
261
262        // If we can preempt and there is a pending one
263        // this is a good time to yield
264        if( enabled && pending ) {
265                force_yield( __POLL_PREEMPTION );
266        }
267        return enabled;
268}
269
270struct asm_region {
271        void * before;
272        void * after;
273};
274
275static inline bool __cfaasm_in( void * ip, struct asm_region & region ) {
276        return ip >= region.before && ip <= region.after;
277}
278
279
280//----------
281// Get data from the TLS block
282// struct asm_region __cfaasm_get;
283uintptr_t __cfatls_get( unsigned long int offset ) __attribute__((__noinline__)); //no inline to avoid problems
284uintptr_t __cfatls_get( unsigned long int offset ) {
285        // create a assembler label before
286        // marked as clobber all to avoid movement
287        __cfaasm_label(get, before);
288
289        // access tls as normal (except for pointer arithmetic)
290        uintptr_t val = *(uintptr_t*)((uintptr_t)&__cfaabi_tls + offset);
291
292        // create a assembler label after
293        // marked as clobber all to avoid movement
294        __cfaasm_label(get, after);
295
296        // This is used everywhere, to avoid cost, we DO NOT poll pending preemption
297        return val;
298}
299
300extern "C" {
301        // Disable interrupts by incrementing the counter
302        void disable_interrupts() {
303                // create a assembler label before
304                // marked as clobber all to avoid movement
305                __cfaasm_label(dsable, before);
306
307                with( __cfaabi_tls.preemption_state ) {
308                        #if GCC_VERSION > 50000
309                        static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
310                        #endif
311
312                        // Set enabled flag to false
313                        // should be atomic to avoid preemption in the middle of the operation.
314                        // use memory order RELAXED since there is no inter-thread on this variable requirements
315                        __atomic_store_n(&enabled, false, __ATOMIC_RELAXED);
316
317                        // Signal the compiler that a fence is needed but only for signal handlers
318                        __atomic_signal_fence(__ATOMIC_ACQUIRE);
319
320                        __attribute__((unused)) unsigned short new_val = disable_count + 1;
321                        disable_count = new_val;
322                        verify( new_val < 65_000u );              // If this triggers someone is disabling interrupts without enabling them
323                }
324
325                // create a assembler label after
326                // marked as clobber all to avoid movement
327                __cfaasm_label(dsable, after);
328
329        }
330
331        // Enable interrupts by decrementing the counter
332        // If counter reaches 0, execute any pending __cfactx_switch
333        void enable_interrupts( bool poll ) {
334                // Cache the processor now since interrupts can start happening after the atomic store
335                processor   * proc = __cfaabi_tls.this_processor;
336                /* paranoid */ verify( !poll || proc );
337
338                with( __cfaabi_tls.preemption_state ){
339                        unsigned short prev = disable_count;
340                        disable_count -= 1;
341
342                        // If this triggers someone is enabled already enabled interruptsverify( prev != 0u );
343                        /* paranoid */ verify( prev != 0u );
344
345                        // Check if we need to prempt the thread because an interrupt was missed
346                        if( prev == 1 ) {
347                                #if GCC_VERSION > 50000
348                                        static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
349                                #endif
350
351                                // Set enabled flag to true
352                                // should be atomic to avoid preemption in the middle of the operation.
353                                // use memory order RELAXED since there is no inter-thread on this variable requirements
354                                __atomic_store_n(&enabled, true, __ATOMIC_RELAXED);
355
356                                // Signal the compiler that a fence is needed but only for signal handlers
357                                __atomic_signal_fence(__ATOMIC_RELEASE);
358                                if( poll && proc->pending_preemption ) {
359                                        proc->pending_preemption = false;
360                                        force_yield( __POLL_PREEMPTION );
361                                }
362                        }
363                }
364        }
365}
366
367//-----------------------------------------------------------------------------
368// Kernel Signal Debug
369void __cfaabi_check_preemption() {
370        bool ready = __preemption_enabled();
371        if(!ready) { abort("Preemption should be ready"); }
372
373        sigset_t oldset;
374        int ret;
375        ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset);  // workaround trac#208: cast should be unnecessary
376        if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
377
378        ret = sigismember(&oldset, SIGUSR1);
379        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
380        if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
381
382        ret = sigismember(&oldset, SIGALRM);
383        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
384        if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
385
386        ret = sigismember(&oldset, SIGTERM);
387        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
388        if(ret == 1) { abort("ERROR SIGTERM is disabled"); }
389}
390
391#ifdef __CFA_WITH_VERIFY__
392bool __cfaabi_dbg_in_kernel() {
393        return !__preemption_enabled();
394}
395#endif
396
397#undef __cfaasm_label
398
399//-----------------------------------------------------------------------------
400// Signal handling
401
402// sigprocmask wrapper : unblock a single signal
403static inline void signal_unblock( int sig ) {
404        sigset_t mask;
405        sigemptyset( &mask );
406        sigaddset( &mask, sig );
407
408        if ( pthread_sigmask( SIG_UNBLOCK, &mask, 0p ) == -1 ) {
409            abort( "internal error, pthread_sigmask" );
410        }
411}
412
413// sigprocmask wrapper : block a single signal
414static inline void signal_block( int sig ) {
415        sigset_t mask;
416        sigemptyset( &mask );
417        sigaddset( &mask, sig );
418
419        if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
420                abort( "internal error, pthread_sigmask" );
421        }
422}
423
424// kill wrapper : signal a processor
425static void preempt( processor * this ) {
426        sigval_t value = { PREEMPT_NORMAL };
427        pthread_sigqueue( this->kernel_thread, SIGUSR1, value );
428}
429
430// reserved for future use
431static void timeout( thread$ * this ) {
432        unpark( this );
433}
434
435void __disable_interrupts_hard() {
436        sigset_t oldset;
437        int ret;
438        ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset);  // workaround trac#208: cast should be unnecessary
439        if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
440
441        ret = sigismember(&oldset, SIGUSR1);
442        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
443        if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
444
445        ret = sigismember(&oldset, SIGALRM);
446        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
447        if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
448
449        signal_block( SIGUSR1 );
450}
451
452void __enable_interrupts_hard() {
453        signal_unblock( SIGUSR1 );
454
455        sigset_t oldset;
456        int ret;
457        ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset);  // workaround trac#208: cast should be unnecessary
458        if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
459
460        ret = sigismember(&oldset, SIGUSR1);
461        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
462        if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
463
464        ret = sigismember(&oldset, SIGALRM);
465        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
466        if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
467}
468
469//-----------------------------------------------------------------------------
470// Some assembly required
471#if defined( __i386 )
472        #ifdef __PIC__
473                #define RELOC_PRELUDE( label ) \
474                        "calll   .Lcfaasm_prelude_" #label "$pb\n\t" \
475                        ".Lcfaasm_prelude_" #label "$pb:\n\t" \
476                        "popl    %%eax\n\t" \
477                        ".Lcfaasm_prelude_" #label "_end:\n\t" \
478                        "addl    $_GLOBAL_OFFSET_TABLE_+(.Lcfaasm_prelude_" #label "_end-.Lcfaasm_prelude_" #label "$pb), %%eax\n\t"
479                #define RELOC_PREFIX ""
480                #define RELOC_SUFFIX "@GOT(%%eax)"
481        #else
482                #define RELOC_PREFIX "$"
483                #define RELOC_SUFFIX ""
484        #endif
485        #define __cfaasm_label( label ) struct asm_region label = \
486                ({ \
487                        struct asm_region region; \
488                        asm( \
489                                RELOC_PRELUDE( label ) \
490                                "movl " RELOC_PREFIX "__cfaasm_" #label "_before" RELOC_SUFFIX ", %[vb]\n\t" \
491                                "movl " RELOC_PREFIX "__cfaasm_" #label "_after"  RELOC_SUFFIX ", %[va]\n\t" \
492                                 : [vb]"=r"(region.before), [va]"=r"(region.after) \
493                        ); \
494                        region; \
495                });
496#elif defined( __x86_64 )
497        #ifdef __PIC__
498                #define RELOC_PREFIX ""
499                #define RELOC_SUFFIX "@GOTPCREL(%%rip)"
500        #else
501                #define RELOC_PREFIX "$"
502                #define RELOC_SUFFIX ""
503        #endif
504        #define __cfaasm_label( label ) struct asm_region label = \
505                ({ \
506                        struct asm_region region; \
507                        asm( \
508                                "movq " RELOC_PREFIX "__cfaasm_" #label "_before" RELOC_SUFFIX ", %[vb]\n\t" \
509                                "movq " RELOC_PREFIX "__cfaasm_" #label "_after"  RELOC_SUFFIX ", %[va]\n\t" \
510                                 : [vb]"=r"(region.before), [va]"=r"(region.after) \
511                        ); \
512                        region; \
513                });
514#elif defined( __aarch64__ )
515        #ifdef __PIC__
516                // Note that this works only for gcc
517                #define __cfaasm_label( label ) struct asm_region label = \
518                ({ \
519                        struct asm_region region; \
520                        asm( \
521                                "adrp %[vb], _GLOBAL_OFFSET_TABLE_"                              "\n\t" \
522                                "ldr  %[vb], [%[vb], #:gotpage_lo15:__cfaasm_" #label "_before]" "\n\t" \
523                                "adrp %[va], _GLOBAL_OFFSET_TABLE_"                              "\n\t" \
524                                "ldr  %[va], [%[va], #:gotpage_lo15:__cfaasm_" #label "_after]"  "\n\t" \
525                                 : [vb]"=r"(region.before), [va]"=r"(region.after) \
526                        ); \
527                        region; \
528                });
529        #else
530                #error this is not the right thing to do
531                /*
532                #define __cfaasm_label( label ) struct asm_region label = \
533                ({ \
534                        struct asm_region region; \
535                        asm( \
536                                "adrp %[vb], __cfaasm_" #label "_before"              "\n\t" \
537                                "add  %[vb], %[vb], :lo12:__cfaasm_" #label "_before" "\n\t" \
538                                "adrp %[va], :got:__cfaasm_" #label "_after"          "\n\t" \
539                                "add  %[va], %[va], :lo12:__cfaasm_" #label "_after"  "\n\t" \
540                                 : [vb]"=r"(region.before), [va]"=r"(region.after) \
541                        ); \
542                        region; \
543                });
544                */
545        #endif
546#else
547        #error unknown hardware architecture
548#endif
549
550// KERNEL ONLY
551// Check if a __cfactx_switch signal handler shoud defer
552// If true  : preemption is safe
553// If false : preemption is unsafe and marked as pending
554static inline bool preemption_ready( void * ip ) {
555        // Get all the region for which it is not safe to preempt
556        __cfaasm_label( get    );
557        __cfaasm_label( check  );
558        __cfaasm_label( dsable );
559        // __cfaasm_label( debug  );
560
561        // Check if preemption is safe
562        bool ready = true;
563        if( __cfaasm_in( ip, get    ) ) { ready = false; goto EXIT; };
564        if( __cfaasm_in( ip, check  ) ) { ready = false; goto EXIT; };
565        if( __cfaasm_in( ip, dsable ) ) { ready = false; goto EXIT; };
566        // if( __cfaasm_in( ip, debug  ) ) { ready = false; goto EXIT; };
567        if( !__cfaabi_tls.preemption_state.enabled) { ready = false; goto EXIT; };
568        if( __cfaabi_tls.preemption_state.in_progress ) { ready = false; goto EXIT; };
569
570EXIT:
571        // Adjust the pending flag accordingly
572        __cfaabi_tls.this_processor->pending_preemption = !ready;
573        return ready;
574}
575
576//=============================================================================================
577// Kernel Signal Startup/Shutdown logic
578//=============================================================================================
579
580// Startup routine to activate preemption
581// Called from kernel_startup
582void __kernel_alarm_startup() {
583        __cfaabi_dbg_print_safe( "Kernel : Starting preemption\n" );
584
585        // Start with preemption disabled until ready
586        __cfaabi_tls.preemption_state.enabled = false;
587        __cfaabi_tls.preemption_state.disable_count = 1;
588
589        // Initialize the event kernel
590        event_kernel = (event_kernel_t *)&storage_event_kernel;
591        (*event_kernel){};
592
593        // Setup proper signal handlers
594        __cfaabi_sigaction( SIGUSR1, sigHandler_ctxSwitch, SA_SIGINFO ); // __cfactx_switch handler
595        __cfaabi_sigaction( SIGALRM, sigHandler_alarm    , SA_SIGINFO ); // debug handler
596
597        signal_block( SIGALRM );
598
599        alarm_stack = __create_pthread( &alarm_thread, alarm_loop, 0p );
600}
601
602// Shutdown routine to deactivate preemption
603// Called from kernel_shutdown
604void __kernel_alarm_shutdown() {
605        __cfaabi_dbg_print_safe( "Kernel : Preemption stopping\n" );
606
607        // Block all signals since we are already shutting down
608        sigset_t mask;
609        sigfillset( &mask );
610        sigprocmask( SIG_BLOCK, &mask, 0p );
611
612        // Notify the alarm thread of the shutdown
613        sigval val;
614        val.sival_int = 0;
615        pthread_sigqueue( alarm_thread, SIGALRM, val );
616
617        // Wait for the preemption thread to finish
618
619        __destroy_pthread( alarm_thread, alarm_stack, 0p );
620
621        // Preemption is now fully stopped
622
623        __cfaabi_dbg_print_safe( "Kernel : Preemption stopped\n" );
624}
625
626// Prevent preemption since we are about to start terminating things
627void __kernel_abort_lock(void) {
628        signal_block( SIGUSR1 );
629}
630
631// Raii ctor/dtor for the preemption_scope
632// Used by thread to control when they want to receive preemption signals
633void ?{}( preemption_scope & this, processor * proc ) {
634        (this.alarm){ proc, 0`s, 0`s };
635        this.proc = proc;
636        this.proc->preemption_alarm = &this.alarm;
637
638        update_preemption( this.proc, this.proc->cltr->preemption_rate );
639}
640
641void ^?{}( preemption_scope & this ) {
642        disable_interrupts();
643
644        update_preemption( this.proc, 0`s );
645}
646
647//=============================================================================================
648// Kernel Signal Handlers
649//=============================================================================================
650__cfaabi_dbg_debug_do( static thread_local void * last_interrupt = 0; )
651
652// Context switch signal handler
653// Receives SIGUSR1 signal and causes the current thread to yield
654static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ ) {
655        void * ip = (void *)(cxt->uc_mcontext.CFA_REG_IP);
656        __cfaabi_dbg_debug_do( last_interrupt = ip; )
657
658        // SKULLDUGGERY: if a thread creates a processor and the immediately deletes it,
659        // the interrupt that is supposed to force the kernel thread to preempt might arrive
660        // before the kernel thread has even started running. When that happens, an interrupt
661        // with a null 'this_processor' will be caught, just ignore it.
662        if(! __cfaabi_tls.this_processor ) return;
663
664        choose(sfp->si_value.sival_int) {
665                case PREEMPT_NORMAL   : ;// Normal case, nothing to do here
666                case PREEMPT_TERMINATE: verify( __atomic_load_n( &__cfaabi_tls.this_processor->do_terminate, __ATOMIC_SEQ_CST ) );
667                default:
668                        abort( "internal error, signal value is %d", sfp->si_value.sival_int );
669        }
670
671        // Check if it is safe to preempt here
672        if( !preemption_ready( ip ) ) {
673                #if !defined(__CFA_NO_STATISTICS__)
674                        __cfaabi_tls.this_stats->ready.threads.preempt.rllfwd++;
675                #endif
676                return;
677        }
678
679        __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) );
680
681        // Sync flag : prevent recursive calls to the signal handler
682        __cfaabi_tls.preemption_state.in_progress = true;
683
684        // Clear sighandler mask before context switching.
685        #if GCC_VERSION > 50000
686        static_assert( sizeof( sigset_t ) == sizeof( cxt->uc_sigmask ), "Expected cxt->uc_sigmask to be of sigset_t" );
687        #endif
688        if ( pthread_sigmask( SIG_SETMASK, (sigset_t *)&(cxt->uc_sigmask), 0p ) == -1 ) {
689                abort( "internal error, sigprocmask" );
690        }
691
692        // Clear the in progress flag
693        __cfaabi_tls.preemption_state.in_progress = false;
694
695        // Preemption can occur here
696
697        #if !defined(__CFA_NO_STATISTICS__)
698                __cfaabi_tls.this_stats->ready.threads.preempt.yield++;
699        #endif
700
701        force_yield( __ALARM_PREEMPTION ); // Do the actual __cfactx_switch
702}
703
704static void sigHandler_alarm( __CFA_SIGPARMS__ ) {
705        abort("SIGALRM should never reach the signal handler");
706}
707
708// Main of the alarm thread
709// Waits on SIGALRM and send SIGUSR1 to whom ever needs it
710static void * alarm_loop( __attribute__((unused)) void * args ) {
711        unsigned id = register_proc_id();
712
713        // Block sigalrms to control when they arrive
714        sigset_t mask;
715        sigfillset(&mask);
716        if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
717            abort( "internal error, pthread_sigmask" );
718        }
719
720        sigemptyset( &mask );
721        sigaddset( &mask, SIGALRM );
722
723        // Main loop
724        while( true ) {
725                // Wait for a sigalrm
726                siginfo_t info;
727                int sig = sigwaitinfo( &mask, &info );
728
729                __cfadbg_print_buffer_decl ( preemption, " KERNEL: sigwaitinfo returned %d, c: %d, v: %d\n", sig, info.si_code, info.si_value.sival_int );
730                __cfadbg_print_buffer_local( preemption, " KERNEL: SI_QUEUE %d, SI_TIMER %d, SI_KERNEL %d\n", SI_QUEUE, SI_TIMER, SI_KERNEL );
731
732                if( sig < 0 ) {
733                        //Error!
734                        int err = errno;
735                        switch( err ) {
736                                case EAGAIN :
737                                case EINTR :
738                                        {__cfadbg_print_buffer_local( preemption, " KERNEL: Spurious wakeup %d.\n", err );}
739                                        continue;
740                                case EINVAL :
741                                        abort( "Timeout was invalid." );
742                                default:
743                                        abort( "Unhandled error %d", err);
744                        }
745                }
746
747                // If another signal arrived something went wrong
748                assertf(sig == SIGALRM, "Kernel Internal Error, sigwait: Unexpected signal %d (%d : %d)\n", sig, info.si_code, info.si_value.sival_int);
749
750                // Switch on the code (a.k.a. the sender) to
751                switch( info.si_code )
752                {
753                // Signal was not sent by the kernel but by an other thread
754                case SI_QUEUE:
755                        // other threads may signal the alarm thread to shut it down
756                        // or to manual cause the preemption tick
757                        // use info.si_value and handle the case here
758                        switch( info.si_value.sival_int ) {
759                        case 0:
760                                goto EXIT;
761                        default:
762                                abort( "SI_QUEUE with val %d", info.si_value.sival_int);
763                        }
764                        // fallthrough
765                // Timers can apparently be marked as sent for the kernel
766                // In either case, tick preemption
767                case SI_TIMER:
768                case SI_KERNEL:
769                        // __cfaabi_dbg_print_safe( "Kernel : Preemption thread tick\n" );
770                        lock( event_kernel->lock __cfaabi_dbg_ctx2 );
771                        tick_preemption();
772                        unlock( event_kernel->lock );
773                        break;
774                }
775        }
776
777EXIT:
778        __cfaabi_dbg_print_safe( "Kernel : Preemption thread stopping\n" );
779        unregister_proc_id(id);
780
781        return 0p;
782}
783
784// Local Variables: //
785// mode: c //
786// tab-width: 4 //
787// End: //
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