source: libcfa/src/concurrency/preemption.cfa @ c18bf9e

ADTast-experimentalpthread-emulationqualifiedEnum
Last change on this file since c18bf9e was c18bf9e, checked in by Thierry Delisle <tdelisle@…>, 22 months ago

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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_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
274
275//----------
276// Get data from the TLS block
277// struct asm_region __cfaasm_get;
278uintptr_t __cfatls_get( unsigned long int offset ) __attribute__((__noinline__, visibility("default"))); //no inline to avoid problems
279uintptr_t __cfatls_get( unsigned long int offset ) {
280        // create a assembler label before
281        // marked as clobber all to avoid movement
282        __cfaasm_label(get, before);
283
284        // access tls as normal (except for pointer arithmetic)
285        uintptr_t val = *(uintptr_t*)((uintptr_t)&__cfaabi_tls + offset);
286
287        // create a assembler label after
288        // marked as clobber all to avoid movement
289        __cfaasm_label(get, after);
290
291        // This is used everywhere, to avoid cost, we DO NOT poll pending preemption
292        return val;
293}
294
295extern "C" {
296        // Disable interrupts by incrementing the counter
297        __attribute__((__noinline__, visibility("default"))) void disable_interrupts() libcfa_public {
298                // create a assembler label before
299                // marked as clobber all to avoid movement
300                __cfaasm_label(dsable, before);
301
302                with( __cfaabi_tls.preemption_state ) {
303                        #if GCC_VERSION > 50000
304                        static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
305                        #endif
306
307                        // Set enabled flag to false
308                        // should be atomic to avoid preemption in the middle of the operation.
309                        // use memory order RELAXED since there is no inter-thread on this variable requirements
310                        __atomic_store_n(&enabled, false, __ATOMIC_RELAXED);
311
312                        // Signal the compiler that a fence is needed but only for signal handlers
313                        __atomic_signal_fence(__ATOMIC_ACQUIRE);
314
315                        __attribute__((unused)) unsigned short new_val = disable_count + 1;
316                        disable_count = new_val;
317                        verify( new_val < 65_000u );              // If this triggers someone is disabling interrupts without enabling them
318                }
319
320                // create a assembler label after
321                // marked as clobber all to avoid movement
322                __cfaasm_label(dsable, after);
323
324        }
325
326        // Enable interrupts by decrementing the counter
327        // If counter reaches 0, execute any pending __cfactx_switch
328        void enable_interrupts( bool poll ) libcfa_public {
329                // Cache the processor now since interrupts can start happening after the atomic store
330                processor   * proc = __cfaabi_tls.this_processor;
331                /* paranoid */ verify( !poll || proc );
332
333                with( __cfaabi_tls.preemption_state ){
334                        unsigned short prev = disable_count;
335                        disable_count -= 1;
336
337                        // If this triggers someone is enabled already enabled interruptsverify( prev != 0u );
338                        /* paranoid */ verify( prev != 0u );
339
340                        // Check if we need to prempt the thread because an interrupt was missed
341                        if( prev == 1 ) {
342                                #if GCC_VERSION > 50000
343                                        static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
344                                #endif
345
346                                // Set enabled flag to true
347                                // should be atomic to avoid preemption in the middle of the operation.
348                                // use memory order RELAXED since there is no inter-thread on this variable requirements
349                                __atomic_store_n(&enabled, true, __ATOMIC_RELAXED);
350
351                                // Signal the compiler that a fence is needed but only for signal handlers
352                                __atomic_signal_fence(__ATOMIC_RELEASE);
353                                if( poll && proc->pending_preemption ) {
354                                        proc->pending_preemption = false;
355                                        force_yield( __POLL_PREEMPTION );
356                                }
357                        }
358                }
359        }
360}
361
362//-----------------------------------------------------------------------------
363// Kernel Signal Debug
364void __cfaabi_check_preemption() libcfa_public {
365        bool ready = __preemption_enabled();
366        if(!ready) { abort("Preemption should be ready"); }
367
368        sigset_t oldset;
369        int ret;
370        ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset);  // workaround trac#208: cast should be unnecessary
371        if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
372
373        ret = sigismember(&oldset, SIGUSR1);
374        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
375        if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
376
377        ret = sigismember(&oldset, SIGALRM);
378        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
379        if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
380
381        ret = sigismember(&oldset, SIGTERM);
382        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
383        if(ret == 1) { abort("ERROR SIGTERM is disabled"); }
384}
385
386#ifdef __CFA_WITH_VERIFY__
387bool __cfaabi_dbg_in_kernel() {
388        return !__preemption_enabled();
389}
390#endif
391
392#undef __cfaasm_label
393
394//-----------------------------------------------------------------------------
395// Signal handling
396
397// sigprocmask wrapper : unblock a single signal
398static inline void signal_unblock( int sig ) {
399        sigset_t mask;
400        sigemptyset( &mask );
401        sigaddset( &mask, sig );
402
403        if ( pthread_sigmask( SIG_UNBLOCK, &mask, 0p ) == -1 ) {
404            abort( "internal error, pthread_sigmask" );
405        }
406}
407
408// sigprocmask wrapper : block a single signal
409static inline void signal_block( int sig ) {
410        sigset_t mask;
411        sigemptyset( &mask );
412        sigaddset( &mask, sig );
413
414        if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
415                abort( "internal error, pthread_sigmask" );
416        }
417}
418
419// kill wrapper : signal a processor
420static void preempt( processor * this ) {
421        sigval_t value = { PREEMPT_NORMAL };
422        pthread_sigqueue( this->kernel_thread, SIGUSR1, value );
423}
424
425// reserved for future use
426static void timeout( thread$ * this ) {
427        unpark( this );
428}
429
430void __disable_interrupts_hard() {
431        sigset_t oldset;
432        int ret;
433        ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset);  // workaround trac#208: cast should be unnecessary
434        if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
435
436        ret = sigismember(&oldset, SIGUSR1);
437        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
438        if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
439
440        ret = sigismember(&oldset, SIGALRM);
441        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
442        if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
443
444        signal_block( SIGUSR1 );
445}
446
447void __enable_interrupts_hard() {
448        signal_unblock( SIGUSR1 );
449
450        sigset_t oldset;
451        int ret;
452        ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset);  // workaround trac#208: cast should be unnecessary
453        if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
454
455        ret = sigismember(&oldset, SIGUSR1);
456        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
457        if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
458
459        ret = sigismember(&oldset, SIGALRM);
460        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
461        if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
462}
463
464//-----------------------------------------------------------------------------
465// Some assembly required
466#if defined( __i386 )
467        #ifdef __PIC__
468                #define RELOC_PRELUDE( label ) \
469                        "calll   .Lcfaasm_prelude_" #label "$pb\n\t" \
470                        ".Lcfaasm_prelude_" #label "$pb:\n\t" \
471                        "popl    %%eax\n\t" \
472                        ".Lcfaasm_prelude_" #label "_end:\n\t" \
473                        "addl    $_GLOBAL_OFFSET_TABLE_+(.Lcfaasm_prelude_" #label "_end-.Lcfaasm_prelude_" #label "$pb), %%eax\n\t"
474                #define RELOC_PREFIX ""
475                #define RELOC_SUFFIX "@GOT(%%eax)"
476        #else
477                #define RELOC_PREFIX "$"
478                #define RELOC_SUFFIX ""
479        #endif
480        #define __cfaasm_label( label ) struct asm_region label = \
481                ({ \
482                        struct asm_region region; \
483                        asm( \
484                                RELOC_PRELUDE( label ) \
485                                "movl " RELOC_PREFIX "__cfaasm_" #label "_before" RELOC_SUFFIX ", %[vb]\n\t" \
486                                "movl " RELOC_PREFIX "__cfaasm_" #label "_after"  RELOC_SUFFIX ", %[va]\n\t" \
487                                 : [vb]"=r"(region.before), [va]"=r"(region.after) \
488                        ); \
489                        region; \
490                });
491#elif defined( __x86_64 )
492        #ifdef __PIC__
493                #define RELOC_PREFIX ""
494                #define RELOC_SUFFIX "@GOTPCREL(%%rip)"
495        #else
496                #define RELOC_PREFIX "$"
497                #define RELOC_SUFFIX ""
498        #endif
499        #define __cfaasm_label( label ) struct asm_region label = \
500                ({ \
501                        struct asm_region region; \
502                        asm( \
503                                "movq " RELOC_PREFIX "__cfaasm_" #label "_before" RELOC_SUFFIX ", %[vb]\n\t" \
504                                "movq " RELOC_PREFIX "__cfaasm_" #label "_after"  RELOC_SUFFIX ", %[va]\n\t" \
505                                 : [vb]"=r"(region.before), [va]"=r"(region.after) \
506                        ); \
507                        region; \
508                });
509#elif defined( __aarch64__ )
510        #ifdef __PIC__
511                // Note that this works only for gcc
512                #define __cfaasm_label( label ) struct asm_region label = \
513                ({ \
514                        struct asm_region region; \
515                        asm( \
516                                "adrp %[vb], _GLOBAL_OFFSET_TABLE_"                              "\n\t" \
517                                "ldr  %[vb], [%[vb], #:gotpage_lo15:__cfaasm_" #label "_before]" "\n\t" \
518                                "adrp %[va], _GLOBAL_OFFSET_TABLE_"                              "\n\t" \
519                                "ldr  %[va], [%[va], #:gotpage_lo15:__cfaasm_" #label "_after]"  "\n\t" \
520                                 : [vb]"=r"(region.before), [va]"=r"(region.after) \
521                        ); \
522                        region; \
523                });
524        #else
525                #error this is not the right thing to do
526                /*
527                #define __cfaasm_label( label ) struct asm_region label = \
528                ({ \
529                        struct asm_region region; \
530                        asm( \
531                                "adrp %[vb], __cfaasm_" #label "_before"              "\n\t" \
532                                "add  %[vb], %[vb], :lo12:__cfaasm_" #label "_before" "\n\t" \
533                                "adrp %[va], :got:__cfaasm_" #label "_after"          "\n\t" \
534                                "add  %[va], %[va], :lo12:__cfaasm_" #label "_after"  "\n\t" \
535                                 : [vb]"=r"(region.before), [va]"=r"(region.after) \
536                        ); \
537                        region; \
538                });
539                */
540        #endif
541#else
542        #error unknown hardware architecture
543#endif
544
545// KERNEL ONLY
546// Check if a __cfactx_switch signal handler shoud defer
547// If true  : preemption is safe
548// If false : preemption is unsafe and marked as pending
549static inline bool preemption_ready( void * ip ) {
550        // Get all the region for which it is not safe to preempt
551        __cfaasm_label( get    );
552        __cfaasm_label( check  );
553        __cfaasm_label( dsable );
554        // __cfaasm_label( debug  );
555
556        // Check if preemption is safe
557        bool ready = true;
558        if( __cfaasm_in( ip, get    ) ) { ready = false; goto EXIT; };
559        if( __cfaasm_in( ip, check  ) ) { ready = false; goto EXIT; };
560        if( __cfaasm_in( ip, dsable ) ) { ready = false; goto EXIT; };
561        // if( __cfaasm_in( ip, debug  ) ) { ready = false; goto EXIT; };
562        if( !__cfaabi_tls.preemption_state.enabled) { ready = false; goto EXIT; };
563        if( __cfaabi_tls.preemption_state.in_progress ) { ready = false; goto EXIT; };
564
565EXIT:
566        // Adjust the pending flag accordingly
567        __cfaabi_tls.this_processor->pending_preemption = !ready;
568        return ready;
569}
570
571//=============================================================================================
572// Kernel Signal Startup/Shutdown logic
573//=============================================================================================
574
575// Startup routine to activate preemption
576// Called from kernel_startup
577void __kernel_alarm_startup() {
578        __cfaabi_dbg_print_safe( "Kernel : Starting preemption\n" );
579
580        // Start with preemption disabled until ready
581        __cfaabi_tls.preemption_state.enabled = false;
582        __cfaabi_tls.preemption_state.disable_count = 1;
583
584        // Initialize the event kernel
585        event_kernel = (event_kernel_t *)&storage_event_kernel;
586        (*event_kernel){};
587
588        // Setup proper signal handlers
589        __cfaabi_sigaction( SIGUSR1, sigHandler_ctxSwitch, SA_SIGINFO ); // __cfactx_switch handler
590        __cfaabi_sigaction( SIGALRM, sigHandler_alarm    , SA_SIGINFO ); // debug handler
591
592        signal_block( SIGALRM );
593
594        alarm_stack = __create_pthread( &alarm_thread, alarm_loop, 0p );
595}
596
597// Shutdown routine to deactivate preemption
598// Called from kernel_shutdown
599void __kernel_alarm_shutdown() {
600        __cfaabi_dbg_print_safe( "Kernel : Preemption stopping\n" );
601
602        // Block all signals since we are already shutting down
603        sigset_t mask;
604        sigfillset( &mask );
605        sigprocmask( SIG_BLOCK, &mask, 0p );
606
607        // Notify the alarm thread of the shutdown
608        sigval val;
609        val.sival_int = 0;
610        pthread_sigqueue( alarm_thread, SIGALRM, val );
611
612        // Wait for the preemption thread to finish
613
614        __destroy_pthread( alarm_thread, alarm_stack, 0p );
615
616        // Preemption is now fully stopped
617
618        __cfaabi_dbg_print_safe( "Kernel : Preemption stopped\n" );
619}
620
621// Prevent preemption since we are about to start terminating things
622void __kernel_abort_lock(void) {
623        signal_block( SIGUSR1 );
624}
625
626// Raii ctor/dtor for the preemption_scope
627// Used by thread to control when they want to receive preemption signals
628void ?{}( preemption_scope & this, processor * proc ) {
629        (this.alarm){ proc, 0`s, 0`s };
630        this.proc = proc;
631        this.proc->preemption_alarm = &this.alarm;
632
633        update_preemption( this.proc, this.proc->cltr->preemption_rate );
634}
635
636void ^?{}( preemption_scope & this ) {
637        disable_interrupts();
638
639        update_preemption( this.proc, 0`s );
640}
641
642//=============================================================================================
643// Kernel Signal Handlers
644//=============================================================================================
645__cfaabi_dbg_debug_do( static thread_local void * last_interrupt = 0; )
646
647// Context switch signal handler
648// Receives SIGUSR1 signal and causes the current thread to yield
649static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ ) {
650        void * ip = (void *)(cxt->uc_mcontext.CFA_REG_IP);
651        __cfaabi_dbg_debug_do( last_interrupt = ip; )
652
653        // SKULLDUGGERY: if a thread creates a processor and the immediately deletes it,
654        // the interrupt that is supposed to force the kernel thread to preempt might arrive
655        // before the kernel thread has even started running. When that happens, an interrupt
656        // with a null 'this_processor' will be caught, just ignore it.
657        if(! __cfaabi_tls.this_processor ) return;
658
659        choose(sfp->si_value.sival_int) {
660                case PREEMPT_NORMAL   : ;// Normal case, nothing to do here
661                case PREEMPT_IO       : ;// I/O asked to stop spinning, nothing to do here
662                case PREEMPT_TERMINATE: verify( __atomic_load_n( &__cfaabi_tls.this_processor->do_terminate, __ATOMIC_SEQ_CST ) );
663                default:
664                        abort( "internal error, signal value is %d", sfp->si_value.sival_int );
665        }
666
667        // Check if it is safe to preempt here
668        if( !preemption_ready( ip ) ) {
669                #if !defined(__CFA_NO_STATISTICS__)
670                        __cfaabi_tls.this_stats->ready.threads.preempt.rllfwd++;
671                #endif
672                return;
673        }
674
675        __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) );
676
677        // Sync flag : prevent recursive calls to the signal handler
678        __cfaabi_tls.preemption_state.in_progress = true;
679
680        // Clear sighandler mask before context switching.
681        #if GCC_VERSION > 50000
682        static_assert( sizeof( sigset_t ) == sizeof( cxt->uc_sigmask ), "Expected cxt->uc_sigmask to be of sigset_t" );
683        #endif
684        if ( pthread_sigmask( SIG_SETMASK, (sigset_t *)&(cxt->uc_sigmask), 0p ) == -1 ) {
685                abort( "internal error, sigprocmask" );
686        }
687
688        // Clear the in progress flag
689        __cfaabi_tls.preemption_state.in_progress = false;
690
691        // Preemption can occur here
692
693        #if !defined(__CFA_NO_STATISTICS__)
694                __cfaabi_tls.this_stats->ready.threads.preempt.yield++;
695        #endif
696
697        force_yield( __ALARM_PREEMPTION ); // Do the actual __cfactx_switch
698}
699
700static void sigHandler_alarm( __CFA_SIGPARMS__ ) {
701        abort("SIGALRM should never reach the signal handler");
702}
703
704// Main of the alarm thread
705// Waits on SIGALRM and send SIGUSR1 to whom ever needs it
706static void * alarm_loop( __attribute__((unused)) void * args ) {
707        unsigned id = register_proc_id();
708
709        // Block sigalrms to control when they arrive
710        sigset_t mask;
711        sigfillset(&mask);
712        if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
713            abort( "internal error, pthread_sigmask" );
714        }
715
716        sigemptyset( &mask );
717        sigaddset( &mask, SIGALRM );
718
719        // Main loop
720        while( true ) {
721                // Wait for a sigalrm
722                siginfo_t info;
723                int sig = sigwaitinfo( &mask, &info );
724
725                __cfadbg_print_buffer_decl ( preemption, " KERNEL: sigwaitinfo returned %d, c: %d, v: %d\n", sig, info.si_code, info.si_value.sival_int );
726                __cfadbg_print_buffer_local( preemption, " KERNEL: SI_QUEUE %d, SI_TIMER %d, SI_KERNEL %d\n", SI_QUEUE, SI_TIMER, SI_KERNEL );
727
728                if( sig < 0 ) {
729                        //Error!
730                        int err = errno;
731                        switch( err ) {
732                                case EAGAIN :
733                                case EINTR :
734                                        {__cfadbg_print_buffer_local( preemption, " KERNEL: Spurious wakeup %d.\n", err );}
735                                        continue;
736                                case EINVAL :
737                                        abort( "Timeout was invalid." );
738                                default:
739                                        abort( "Unhandled error %d", err);
740                        }
741                }
742
743                // If another signal arrived something went wrong
744                assertf(sig == SIGALRM, "Kernel Internal Error, sigwait: Unexpected signal %d (%d : %d)\n", sig, info.si_code, info.si_value.sival_int);
745
746                // Switch on the code (a.k.a. the sender) to
747                switch( info.si_code )
748                {
749                // Signal was not sent by the kernel but by an other thread
750                case SI_QUEUE:
751                        // other threads may signal the alarm thread to shut it down
752                        // or to manual cause the preemption tick
753                        // use info.si_value and handle the case here
754                        switch( info.si_value.sival_int ) {
755                        case 0:
756                                goto EXIT;
757                        default:
758                                abort( "SI_QUEUE with val %d", info.si_value.sival_int);
759                        }
760                        // fallthrough
761                // Timers can apparently be marked as sent for the kernel
762                // In either case, tick preemption
763                case SI_TIMER:
764                case SI_KERNEL:
765                        // __cfaabi_dbg_print_safe( "Kernel : Preemption thread tick\n" );
766                        lock( event_kernel->lock __cfaabi_dbg_ctx2 );
767                        tick_preemption();
768                        unlock( event_kernel->lock );
769                        break;
770                }
771        }
772
773EXIT:
774        __cfaabi_dbg_print_safe( "Kernel : Preemption thread stopping\n" );
775        unregister_proc_id(id);
776
777        return 0p;
778}
779
780// Local Variables: //
781// mode: c //
782// tab-width: 4 //
783// End: //
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