source: libcfa/src/concurrency/preemption.cfa @ adf34b3

arm-ehjacob/cs343-translationnew-ast-unique-expr
Last change on this file since adf34b3 was adf34b3, checked in by Thierry Delisle <tdelisle@…>, 12 months ago

check_preemption is now one of the interrupt protected functions.

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File size: 25.3 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
18#include "preemption.hfa"
19#include <assert.h>
20
21#include <errno.h>
22#include <stdio.h>
23#include <string.h>
24#include <unistd.h>
25#include <limits.h>                                                                             // PTHREAD_STACK_MIN
26
27#include "bits/signal.hfa"
28#include "kernel_private.hfa"
29
30#if !defined(__CFA_DEFAULT_PREEMPTION__)
31#define __CFA_DEFAULT_PREEMPTION__ 10`ms
32#endif
33
34Duration default_preemption() __attribute__((weak)) {
35        return __CFA_DEFAULT_PREEMPTION__;
36}
37
38// FwdDeclarations : timeout handlers
39static void preempt( processor   * this );
40static void timeout( $thread * this );
41
42// FwdDeclarations : Signal handlers
43static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ );
44static void sigHandler_alarm    ( __CFA_SIGPARMS__ );
45static void sigHandler_segv     ( __CFA_SIGPARMS__ );
46static void sigHandler_ill      ( __CFA_SIGPARMS__ );
47static void sigHandler_fpe      ( __CFA_SIGPARMS__ );
48static void sigHandler_abort    ( __CFA_SIGPARMS__ );
49
50// FwdDeclarations : alarm thread main
51static void * alarm_loop( __attribute__((unused)) void * args );
52
53// Machine specific register name
54#if   defined( __i386 )
55#define CFA_REG_IP gregs[REG_EIP]
56#elif defined( __x86_64 )
57#define CFA_REG_IP gregs[REG_RIP]
58#elif defined( __arm__ )
59#define CFA_REG_IP arm_pc
60#elif defined( __aarch64__ )
61#define CFA_REG_IP pc
62#else
63#error unsupported hardware architecture
64#endif
65
66KERNEL_STORAGE(event_kernel_t, event_kernel);         // private storage for event kernel
67event_kernel_t * event_kernel;                        // kernel public handle to even kernel
68static pthread_t alarm_thread;                        // pthread handle to alarm thread
69static void * alarm_stack;                                                        // pthread stack for alarm thread
70
71static void ?{}(event_kernel_t & this) with( this ) {
72        alarms{};
73        lock{};
74}
75
76enum {
77        PREEMPT_NORMAL    = 0,
78        PREEMPT_TERMINATE = 1,
79};
80
81//=============================================================================================
82// Kernel Preemption logic
83//=============================================================================================
84
85// Get next expired node
86static inline alarm_node_t * get_expired( alarm_list_t * alarms, Time currtime ) {
87        if( ! & (*alarms)`first ) return 0p;                                            // If no alarms return null
88        if( (*alarms)`first.alarm >= currtime ) return 0p;      // If alarms head not expired return null
89        return pop(alarms);                                                                     // Otherwise just pop head
90}
91
92// Tick one frame of the Discrete Event Simulation for alarms
93static void tick_preemption(void) {
94        alarm_node_t * node = 0p;                                                       // Used in the while loop but cannot be declared in the while condition
95        alarm_list_t * alarms = &event_kernel->alarms;          // Local copy for ease of reading
96        Time currtime = __kernel_get_time();                            // Check current time once so everything "happens at once"
97
98        //Loop throught every thing expired
99        while( node = get_expired( alarms, currtime ) ) {
100                // __cfaabi_dbg_print_buffer_decl( " KERNEL: preemption tick.\n" );
101                Duration period = node->period;
102                if( period == 0) {
103                        node->set = false;                  // Node is one-shot, just mark it as not pending
104                }
105
106                // Check if this is a kernel
107                if( node->type == Kernel ) {
108                        preempt( node->proc );
109                }
110                else if( node->type == User ) {
111                        timeout( node->thrd );
112                }
113                else {
114                        node->callback(*node);
115                }
116
117                // Check if this is a periodic alarm
118                if( period > 0 ) {
119                        // __cfaabi_dbg_print_buffer_local( " KERNEL: alarm period is %lu.\n", period.tv );
120                        node->alarm = currtime + period;    // Alarm is periodic, add currtime to it (used cached current time)
121                        insert( alarms, node );             // Reinsert the node for the next time it triggers
122                }
123        }
124
125        // If there are still alarms pending, reset the timer
126        if( & (*alarms)`first ) {
127                __cfadbg_print_buffer_decl(preemption, " KERNEL: @%ju(%ju) resetting alarm to %ju.\n", currtime.tv, __kernel_get_time().tv, (alarms->head->alarm - currtime).tv);
128                Duration delta = (*alarms)`first.alarm - currtime;
129                Duration capped = max(delta, 50`us);
130                // itimerval tim  = { caped };
131                // __cfaabi_dbg_print_buffer_local( "    Values are %lu, %lu, %lu %lu.\n", delta.tv, caped.tv, tim.it_value.tv_sec, tim.it_value.tv_usec);
132
133                __kernel_set_timer( capped );
134        }
135}
136
137// Update the preemption of a processor and notify interested parties
138void update_preemption( processor * this, Duration duration ) {
139        alarm_node_t * alarm = this->preemption_alarm;
140
141        // Alarms need to be enabled
142        if ( duration > 0 && ! alarm->set ) {
143                alarm->alarm = __kernel_get_time() + duration;
144                alarm->period = duration;
145                register_self( alarm );
146        }
147        // Zero duration but alarm is set
148        else if ( duration == 0 && alarm->set ) {
149                unregister_self( alarm );
150                alarm->alarm = 0;
151                alarm->period = 0;
152        }
153        // If alarm is different from previous, change it
154        else if ( duration > 0 && alarm->period != duration ) {
155                unregister_self( alarm );
156                alarm->alarm = __kernel_get_time() + duration;
157                alarm->period = duration;
158                register_self( alarm );
159        }
160}
161
162//=============================================================================================
163// Kernel Signal Tools
164//=============================================================================================
165// In a user-level threading system, there are handful of thread-local variables where this problem occurs on the ARM.
166//
167// For each kernel thread running user-level threads, there is a flag variable to indicate if interrupts are
168// enabled/disabled for that kernel thread. Therefore, this variable is made thread local.
169//
170// For example, this code fragment sets the state of the "interrupt" variable in thread-local memory.
171//
172// _Thread_local volatile int interrupts;
173// int main() {
174//     interrupts = 0; // disable interrupts }
175//
176// which generates the following code on the ARM
177//
178// (gdb) disassemble main
179// Dump of assembler code for function main:
180//    0x0000000000000610 <+0>:  mrs     x1, tpidr_el0
181//    0x0000000000000614 <+4>:  mov     w0, #0x0                        // #0
182//    0x0000000000000618 <+8>:  add     x1, x1, #0x0, lsl #12
183//    0x000000000000061c <+12>: add     x1, x1, #0x10
184//    0x0000000000000620 <+16>: str     wzr, [x1]
185//    0x0000000000000624 <+20>: ret
186//
187// The mrs moves a pointer from coprocessor register tpidr_el0 into register x1.  Register w0 is set to 0. The two adds
188// increase the TLS pointer with the displacement (offset) 0x10, which is the location in the TSL of variable
189// "interrupts".  Finally, 0 is stored into "interrupts" through the pointer in register x1 that points into the
190// TSL. Now once x1 has the pointer to the location of the TSL for kernel thread N, it can be be preempted at a
191// user-level and the user thread is put on the user-level ready-queue. When the preempted thread gets to the front of
192// the user-level ready-queue it is run on kernel thread M. It now stores 0 into "interrupts" back on kernel thread N,
193// turning off interrupt on the wrong kernel thread.
194//
195// On the x86, the following code is generated for the same code fragment.
196//
197// (gdb) disassemble main
198// Dump of assembler code for function main:
199//    0x0000000000400420 <+0>:  movl   $0x0,%fs:0xfffffffffffffffc
200//    0x000000000040042c <+12>: xor    %eax,%eax
201//    0x000000000040042e <+14>: retq
202//
203// and there is base-displacement addressing used to atomically reset variable "interrupts" off of the TSL pointer in
204// register "fs".
205//
206// Hence, the ARM has base-displacement address for the general purpose registers, BUT not to the coprocessor
207// registers. As a result, generating the address for the write into variable "interrupts" is no longer atomic.
208//
209// Note this problem does NOT occur when just using multiple kernel threads because the preemption ALWAYS restarts the
210// thread on the same kernel thread.
211//
212// The obvious question is why does ARM use a coprocessor register to store the TSL pointer given that coprocessor
213// registers are second-class registers with respect to the instruction set. One possible answer is that they did not
214// want to dedicate one of the general registers to hold the TLS pointer and there was a free coprocessor register
215// available.
216
217//-----------------------------------------------------------------------------
218// Some assembly required
219#define __cfaasm_label(label, when) when: asm volatile goto(".global __cfaasm_" #label "_" #when "\n" "__cfaasm_" #label "_" #when ":":::"memory":when)
220
221//----------
222// special case for preemption since used often
223bool __preemption_enabled() {
224        // create a assembler label before
225        // marked as clobber all to avoid movement
226        __cfaasm_label(check, before);
227
228        // access tls as normal
229        bool enabled = __cfaabi_tls.preemption_state.enabled;
230
231        // create a assembler label after
232        // marked as clobber all to avoid movement
233        __cfaasm_label(check, after);
234        return enabled;
235}
236
237struct asm_region {
238        void * before;
239        void * after;
240};
241
242static inline bool __cfaasm_in( void * ip, struct asm_region & region ) {
243        return ip >= region.before && ip <= region.after;
244}
245
246
247//----------
248// Get data from the TLS block
249// struct asm_region __cfaasm_get;
250uintptr_t __cfatls_get( unsigned long int offset ) __attribute__((__noinline__)); //no inline to avoid problems
251uintptr_t __cfatls_get( unsigned long int offset ) {
252        // create a assembler label before
253        // marked as clobber all to avoid movement
254        __cfaasm_label(get, before);
255
256        // access tls as normal (except for pointer arithmetic)
257        uintptr_t val = *(uintptr_t*)((uintptr_t)&__cfaabi_tls + offset);
258
259        // create a assembler label after
260        // marked as clobber all to avoid movement
261        __cfaasm_label(get, after);
262        return val;
263}
264
265extern "C" {
266        // Disable interrupts by incrementing the counter
267        void disable_interrupts() {
268                // create a assembler label before
269                // marked as clobber all to avoid movement
270                __cfaasm_label(dsable, before);
271
272                with( __cfaabi_tls.preemption_state ) {
273                        #if GCC_VERSION > 50000
274                        static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
275                        #endif
276
277                        // Set enabled flag to false
278                        // should be atomic to avoid preemption in the middle of the operation.
279                        // use memory order RELAXED since there is no inter-thread on this variable requirements
280                        __atomic_store_n(&enabled, false, __ATOMIC_RELAXED);
281
282                        // Signal the compiler that a fence is needed but only for signal handlers
283                        __atomic_signal_fence(__ATOMIC_ACQUIRE);
284
285                        __attribute__((unused)) unsigned short new_val = disable_count + 1;
286                        disable_count = new_val;
287                        verify( new_val < 65_000u );              // If this triggers someone is disabling interrupts without enabling them
288                }
289
290                // create a assembler label after
291                // marked as clobber all to avoid movement
292                __cfaasm_label(dsable, after);
293
294        }
295
296        // Enable interrupts by decrementing the counter
297        // If counter reaches 0, execute any pending __cfactx_switch
298        void enable_interrupts( __cfaabi_dbg_ctx_param ) {
299                // Cache the processor now since interrupts can start happening after the atomic store
300                processor   * proc = __cfaabi_tls.this_processor;
301                /* paranoid */ verify( proc );
302
303                with( __cfaabi_tls.preemption_state ){
304                        unsigned short prev = disable_count;
305                        disable_count -= 1;
306
307                        // If this triggers someone is enabled already enabled interruptsverify( prev != 0u );
308                        /* paranoid */ verify( prev != 0u );
309
310                        // Check if we need to prempt the thread because an interrupt was missed
311                        if( prev == 1 ) {
312                                #if GCC_VERSION > 50000
313                                        static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
314                                #endif
315
316                                // Set enabled flag to true
317                                // should be atomic to avoid preemption in the middle of the operation.
318                                // use memory order RELAXED since there is no inter-thread on this variable requirements
319                                __atomic_store_n(&enabled, true, __ATOMIC_RELAXED);
320
321                                // Signal the compiler that a fence is needed but only for signal handlers
322                                __atomic_signal_fence(__ATOMIC_RELEASE);
323                                if( proc->pending_preemption ) {
324                                        proc->pending_preemption = false;
325                                        force_yield( __POLL_PREEMPTION );
326                                }
327                        }
328                }
329
330                // For debugging purposes : keep track of the last person to enable the interrupts
331                __cfaabi_dbg_debug_do( proc->last_enable = caller; )
332        }
333
334        // Disable interrupts by incrementint the counter
335        // Don't execute any pending __cfactx_switch even if counter reaches 0
336        void enable_interrupts_noPoll() {
337                unsigned short prev = __cfaabi_tls.preemption_state.disable_count;
338                __cfaabi_tls.preemption_state.disable_count -= 1;
339                // If this triggers someone is enabled already enabled interrupts
340                /* paranoid */ verifyf( prev != 0u, "Incremented from %u\n", prev );
341                if( prev == 1 ) {
342                        #if GCC_VERSION > 50000
343                                static_assert(__atomic_always_lock_free(sizeof(__cfaabi_tls.preemption_state.enabled), &__cfaabi_tls.preemption_state.enabled), "Must be lock-free");
344                        #endif
345                        // Set enabled flag to true
346                        // should be atomic to avoid preemption in the middle of the operation.
347                        // use memory order RELAXED since there is no inter-thread on this variable requirements
348                        __atomic_store_n(&__cfaabi_tls.preemption_state.enabled, true, __ATOMIC_RELAXED);
349
350                        // Signal the compiler that a fence is needed but only for signal handlers
351                        __atomic_signal_fence(__ATOMIC_RELEASE);
352                }
353        }
354}
355
356//-----------------------------------------------------------------------------
357// Kernel Signal Debug
358void __cfaabi_check_preemption() {
359        bool ready = __preemption_enabled();
360        if(!ready) { abort("Preemption should be ready"); }
361
362        __cfaasm_label(debug, before);
363
364                sigset_t oldset;
365                int ret;
366                ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset);  // workaround trac#208: cast should be unnecessary
367                if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
368
369                ret = sigismember(&oldset, SIGUSR1);
370                if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
371                if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
372
373                ret = sigismember(&oldset, SIGALRM);
374                if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
375                if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
376
377                ret = sigismember(&oldset, SIGTERM);
378                if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
379                if(ret == 1) { abort("ERROR SIGTERM is disabled"); }
380
381        __cfaasm_label(debug, after);
382}
383
384#ifdef __CFA_WITH_VERIFY__
385bool __cfaabi_dbg_in_kernel() {
386        return !__preemption_enabled();
387}
388#endif
389
390#undef __cfaasm_label
391
392//-----------------------------------------------------------------------------
393// Signal handling
394
395// sigprocmask wrapper : unblock a single signal
396static inline void signal_unblock( int sig ) {
397        sigset_t mask;
398        sigemptyset( &mask );
399        sigaddset( &mask, sig );
400
401        if ( pthread_sigmask( SIG_UNBLOCK, &mask, 0p ) == -1 ) {
402            abort( "internal error, pthread_sigmask" );
403        }
404}
405
406// sigprocmask wrapper : block a single signal
407static inline void signal_block( int sig ) {
408        sigset_t mask;
409        sigemptyset( &mask );
410        sigaddset( &mask, sig );
411
412        if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
413                abort( "internal error, pthread_sigmask" );
414        }
415}
416
417// kill wrapper : signal a processor
418static void preempt( processor * this ) {
419        sigval_t value = { PREEMPT_NORMAL };
420        pthread_sigqueue( this->kernel_thread, SIGUSR1, value );
421}
422
423// reserved for future use
424static void timeout( $thread * this ) {
425        unpark( this );
426}
427
428//-----------------------------------------------------------------------------
429// Some assembly required
430#if defined( __i386 )
431        #ifdef __PIC__
432                #define RELOC_PRELUDE( label ) \
433                        "calll   .Lcfaasm_prelude_" #label "$pb\n\t" \
434                        ".Lcfaasm_prelude_" #label "$pb:\n\t" \
435                        "popl    %%eax\n\t" \
436                        ".Lcfaasm_prelude_" #label "_end:\n\t" \
437                        "addl    $_GLOBAL_OFFSET_TABLE_+(.Lcfaasm_prelude_" #label "_end-.Lcfaasm_prelude_" #label "$pb), %%eax\n\t"
438                #define RELOC_PREFIX ""
439                #define RELOC_SUFFIX "@GOT(%%eax)"
440        #else
441                #define RELOC_PREFIX "$"
442                #define RELOC_SUFFIX ""
443        #endif
444        #define __cfaasm_label( label ) struct asm_region label = \
445                ({ \
446                        struct asm_region region; \
447                        asm( \
448                                RELOC_PRELUDE( label ) \
449                                "movl " RELOC_PREFIX "__cfaasm_" #label "_before" RELOC_SUFFIX ", %[vb]\n\t" \
450                                "movl " RELOC_PREFIX "__cfaasm_" #label "_after"  RELOC_SUFFIX ", %[va]\n\t" \
451                                 : [vb]"=r"(region.before), [va]"=r"(region.after) \
452                        ); \
453                        region; \
454                });
455#elif defined( __x86_64 )
456        #ifdef __PIC__
457                #define RELOC_PREFIX ""
458                #define RELOC_SUFFIX "@GOTPCREL(%%rip)"
459        #else
460                #define RELOC_PREFIX "$"
461                #define RELOC_SUFFIX ""
462        #endif
463        #define __cfaasm_label( label ) struct asm_region label = \
464                ({ \
465                        struct asm_region region; \
466                        asm( \
467                                "movq " RELOC_PREFIX "__cfaasm_" #label "_before" RELOC_SUFFIX ", %[vb]\n\t" \
468                                "movq " RELOC_PREFIX "__cfaasm_" #label "_after"  RELOC_SUFFIX ", %[va]\n\t" \
469                                 : [vb]"=r"(region.before), [va]"=r"(region.after) \
470                        ); \
471                        region; \
472                });
473#elif defined( __aarch64__ )
474        #ifdef __PIC__
475                // Note that this works only for gcc
476                #define __cfaasm_label( label ) struct asm_region label = \
477                ({ \
478                        struct asm_region region; \
479                        asm( \
480                                "adrp %[vb], _GLOBAL_OFFSET_TABLE_"                              "\n\t" \
481                                "ldr  %[vb], [%[vb], #:gotpage_lo15:__cfaasm_" #label "_before]" "\n\t" \
482                                "adrp %[va], _GLOBAL_OFFSET_TABLE_"                              "\n\t" \
483                                "ldr  %[va], [%[va], #:gotpage_lo15:__cfaasm_" #label "_after]"  "\n\t" \
484                                 : [vb]"=r"(region.before), [va]"=r"(region.after) \
485                        ); \
486                        region; \
487                });
488        #else
489                #error this is not the right thing to do
490                /*
491                #define __cfaasm_label( label ) struct asm_region label = \
492                ({ \
493                        struct asm_region region; \
494                        asm( \
495                                "adrp %[vb], __cfaasm_" #label "_before"              "\n\t" \
496                                "add  %[vb], %[vb], :lo12:__cfaasm_" #label "_before" "\n\t" \
497                                "adrp %[va], :got:__cfaasm_" #label "_after"          "\n\t" \
498                                "add  %[va], %[va], :lo12:__cfaasm_" #label "_after"  "\n\t" \
499                                 : [vb]"=r"(region.before), [va]"=r"(region.after) \
500                        ); \
501                        region; \
502                });
503                */
504        #endif
505#else
506        #error unknown hardware architecture
507#endif
508
509// KERNEL ONLY
510// Check if a __cfactx_switch signal handler shoud defer
511// If true  : preemption is safe
512// If false : preemption is unsafe and marked as pending
513static inline bool preemption_ready( void * ip ) {
514        // Get all the region for which it is not safe to preempt
515        __cfaasm_label( get    );
516        __cfaasm_label( check  );
517        __cfaasm_label( dsable );
518        __cfaasm_label( debug  );
519
520        // Check if preemption is safe
521        bool ready = true;
522        if( __cfaasm_in( ip, get    ) ) { ready = false; goto EXIT; };
523        if( __cfaasm_in( ip, check  ) ) { ready = false; goto EXIT; };
524        if( __cfaasm_in( ip, dsable ) ) { ready = false; goto EXIT; };
525        if( __cfaasm_in( ip, debug  ) ) { ready = false; goto EXIT; };
526        if( !__cfaabi_tls.preemption_state.enabled) { ready = false; goto EXIT; };
527        if( __cfaabi_tls.preemption_state.in_progress ) { ready = false; goto EXIT; };
528
529EXIT:
530        // Adjust the pending flag accordingly
531        __cfaabi_tls.this_processor->pending_preemption = !ready;
532        return ready;
533}
534
535//=============================================================================================
536// Kernel Signal Startup/Shutdown logic
537//=============================================================================================
538
539// Startup routine to activate preemption
540// Called from kernel_startup
541void __kernel_alarm_startup() {
542        __cfaabi_dbg_print_safe( "Kernel : Starting preemption\n" );
543
544        // Start with preemption disabled until ready
545        __cfaabi_tls.preemption_state.enabled = false;
546        __cfaabi_tls.preemption_state.disable_count = 1;
547
548        // Initialize the event kernel
549        event_kernel = (event_kernel_t *)&storage_event_kernel;
550        (*event_kernel){};
551
552        // Setup proper signal handlers
553        __cfaabi_sigaction( SIGUSR1, sigHandler_ctxSwitch, SA_SIGINFO | SA_RESTART ); // __cfactx_switch handler
554        __cfaabi_sigaction( SIGALRM, sigHandler_alarm    , SA_SIGINFO | SA_RESTART ); // debug handler
555
556        signal_block( SIGALRM );
557
558        alarm_stack = __create_pthread( &alarm_thread, alarm_loop, 0p );
559}
560
561// Shutdown routine to deactivate preemption
562// Called from kernel_shutdown
563void __kernel_alarm_shutdown() {
564        __cfaabi_dbg_print_safe( "Kernel : Preemption stopping\n" );
565
566        // Block all signals since we are already shutting down
567        sigset_t mask;
568        sigfillset( &mask );
569        sigprocmask( SIG_BLOCK, &mask, 0p );
570
571        // Notify the alarm thread of the shutdown
572        sigval val = { 1 };
573        pthread_sigqueue( alarm_thread, SIGALRM, val );
574
575        // Wait for the preemption thread to finish
576
577        pthread_join( alarm_thread, 0p );
578        free( alarm_stack );
579
580        // Preemption is now fully stopped
581
582        __cfaabi_dbg_print_safe( "Kernel : Preemption stopped\n" );
583}
584
585// Raii ctor/dtor for the preemption_scope
586// Used by thread to control when they want to receive preemption signals
587void ?{}( preemption_scope & this, processor * proc ) {
588        (this.alarm){ proc, (Time){ 0 }, 0`s };
589        this.proc = proc;
590        this.proc->preemption_alarm = &this.alarm;
591
592        update_preemption( this.proc, this.proc->cltr->preemption_rate );
593}
594
595void ^?{}( preemption_scope & this ) {
596        disable_interrupts();
597
598        update_preemption( this.proc, 0`s );
599}
600
601//=============================================================================================
602// Kernel Signal Handlers
603//=============================================================================================
604__cfaabi_dbg_debug_do( static thread_local void * last_interrupt = 0; )
605
606// Context switch signal handler
607// Receives SIGUSR1 signal and causes the current thread to yield
608static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ ) {
609        void * ip = (void *)(cxt->uc_mcontext.CFA_REG_IP);
610        __cfaabi_dbg_debug_do( last_interrupt = ip; )
611
612        // SKULLDUGGERY: if a thread creates a processor and the immediately deletes it,
613        // the interrupt that is supposed to force the kernel thread to preempt might arrive
614        // before the kernel thread has even started running. When that happens, an interrupt
615        // with a null 'this_processor' will be caught, just ignore it.
616        if(! __cfaabi_tls.this_processor ) return;
617
618        choose(sfp->si_value.sival_int) {
619                case PREEMPT_NORMAL   : ;// Normal case, nothing to do here
620                case PREEMPT_TERMINATE: verify( __atomic_load_n( &__cfaabi_tls.this_processor->do_terminate, __ATOMIC_SEQ_CST ) );
621                default:
622                        abort( "internal error, signal value is %d", sfp->si_value.sival_int );
623        }
624
625        // Check if it is safe to preempt here
626        if( !preemption_ready( ip ) ) { return; }
627
628        __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) );
629
630        // Sync flag : prevent recursive calls to the signal handler
631        __cfaabi_tls.preemption_state.in_progress = true;
632
633        // Clear sighandler mask before context switching.
634        #if GCC_VERSION > 50000
635        static_assert( sizeof( sigset_t ) == sizeof( cxt->uc_sigmask ), "Expected cxt->uc_sigmask to be of sigset_t" );
636        #endif
637        if ( pthread_sigmask( SIG_SETMASK, (sigset_t *)&(cxt->uc_sigmask), 0p ) == -1 ) {
638                abort( "internal error, sigprocmask" );
639        }
640
641        // Clear the in progress flag
642        __cfaabi_tls.preemption_state.in_progress = false;
643
644        // Preemption can occur here
645
646        force_yield( __ALARM_PREEMPTION ); // Do the actual __cfactx_switch
647}
648
649static void sigHandler_alarm( __CFA_SIGPARMS__ ) {
650        abort("SIGALRM should never reach the signal handler");
651}
652
653#if !defined(__CFA_NO_STATISTICS__)
654        int __print_alarm_stats = 0;
655#endif
656
657// Main of the alarm thread
658// Waits on SIGALRM and send SIGUSR1 to whom ever needs it
659static void * alarm_loop( __attribute__((unused)) void * args ) {
660        __processor_id_t id;
661        id.full_proc = false;
662        id.id = doregister(&id);
663        __cfaabi_tls.this_proc_id = &id;
664
665        #if !defined(__CFA_NO_STATISTICS__)
666                struct __stats_t local_stats;
667                __cfaabi_tls.this_stats = &local_stats;
668                __init_stats( &local_stats );
669        #endif
670
671        // Block sigalrms to control when they arrive
672        sigset_t mask;
673        sigfillset(&mask);
674        if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
675            abort( "internal error, pthread_sigmask" );
676        }
677
678        sigemptyset( &mask );
679        sigaddset( &mask, SIGALRM );
680
681        // Main loop
682        while( true ) {
683                // Wait for a sigalrm
684                siginfo_t info;
685                int sig = sigwaitinfo( &mask, &info );
686
687                if( sig < 0 ) {
688                        //Error!
689                        int err = errno;
690                        switch( err ) {
691                                case EAGAIN :
692                                case EINTR :
693                                        {__cfaabi_dbg_print_buffer_decl( " KERNEL: Spurious wakeup %d.\n", err );}
694                                        continue;
695                                case EINVAL :
696                                        abort( "Timeout was invalid." );
697                                default:
698                                        abort( "Unhandled error %d", err);
699                        }
700                }
701
702                // If another signal arrived something went wrong
703                assertf(sig == SIGALRM, "Kernel Internal Error, sigwait: Unexpected signal %d (%d : %d)\n", sig, info.si_code, info.si_value.sival_int);
704
705                // __cfaabi_dbg_print_safe( "Kernel : Caught alarm from %d with %d\n", info.si_code, info.si_value.sival_int );
706                // Switch on the code (a.k.a. the sender) to
707                switch( info.si_code )
708                {
709                // Timers can apparently be marked as sent for the kernel
710                // In either case, tick preemption
711                case SI_TIMER:
712                case SI_KERNEL:
713                        // __cfaabi_dbg_print_safe( "Kernel : Preemption thread tick\n" );
714                        lock( event_kernel->lock __cfaabi_dbg_ctx2 );
715                        tick_preemption();
716                        unlock( event_kernel->lock );
717                        break;
718                // Signal was not sent by the kernel but by an other thread
719                case SI_QUEUE:
720                        // For now, other thread only signal the alarm thread to shut it down
721                        // If this needs to change use info.si_value and handle the case here
722                        goto EXIT;
723                }
724        }
725
726EXIT:
727        __cfaabi_dbg_print_safe( "Kernel : Preemption thread stopping\n" );
728        unregister(&id);
729
730        #if !defined(__CFA_NO_STATISTICS__)
731                if( 0 != __print_alarm_stats ) {
732                        __print_stats( &local_stats, __print_alarm_stats, "Alarm", "Thread", 0p );
733                }
734        #endif
735        return 0p;
736}
737
738// Local Variables: //
739// mode: c //
740// tab-width: 4 //
741// End: //
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