source: libcfa/src/concurrency/preemption.cfa @ 357fae8

arm-ehenumforall-pointer-decayjacob/cs343-translationnew-ast-unique-exprpthread-emulationqualifiedEnum
Last change on this file since 357fae8 was 357fae8, checked in by Thierry Delisle <tdelisle@…>, 21 months ago

Fixed bad copy paste

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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 __CFA_DEBUG_PRINT_PREEMPTION__
18
19#include "preemption.hfa"
20#include <assert.h>
21
22#include <errno.h>
23#include <stdio.h>
24#include <string.h>
25#include <unistd.h>
26#include <limits.h>                                                                             // PTHREAD_STACK_MIN
27
28#include "bits/signal.hfa"
29#include "kernel_private.hfa"
30
31
32#if !defined(__CFA_DEFAULT_PREEMPTION__)
33#define __CFA_DEFAULT_PREEMPTION__ 10`ms
34#endif
35
36__attribute__((weak)) Duration default_preemption() {
37        const char * preempt_rate_s = getenv("CFA_DEFAULT_PREEMPTION");
38        if(!preempt_rate_s) {
39                __cfadbg_print_safe(preemption, "No CFA_DEFAULT_PREEMPTION in ENV\n");
40                return __CFA_DEFAULT_PREEMPTION__;
41        }
42
43        char * endptr = 0p;
44        long int preempt_rate_l = strtol(preempt_rate_s, &endptr, 10);
45        if(preempt_rate_l < 0 || preempt_rate_l > 65535) {
46                __cfadbg_print_safe(preemption, "CFA_DEFAULT_PREEMPTION out of range : %ld\n", preempt_rate_l);
47                return __CFA_DEFAULT_PREEMPTION__;
48        }
49        if('\0' != *endptr) {
50                __cfadbg_print_safe(preemption, "CFA_DEFAULT_PREEMPTION not a decimal number : %s\n", preempt_rate_s);
51                return __CFA_DEFAULT_PREEMPTION__;
52        }
53
54        return preempt_rate_l`ms;
55}
56
57// FwdDeclarations : timeout handlers
58static void preempt( processor   * this );
59static void timeout( $thread * this );
60
61// FwdDeclarations : Signal handlers
62static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ );
63static void sigHandler_alarm    ( __CFA_SIGPARMS__ );
64static void sigHandler_segv     ( __CFA_SIGPARMS__ );
65static void sigHandler_ill      ( __CFA_SIGPARMS__ );
66static void sigHandler_fpe      ( __CFA_SIGPARMS__ );
67static void sigHandler_abort    ( __CFA_SIGPARMS__ );
68
69// FwdDeclarations : alarm thread main
70static void * alarm_loop( __attribute__((unused)) void * args );
71
72// Machine specific register name
73#if   defined( __i386 )
74#define CFA_REG_IP gregs[REG_EIP]
75#elif defined( __x86_64 )
76#define CFA_REG_IP gregs[REG_RIP]
77#elif defined( __arm__ )
78#define CFA_REG_IP arm_pc
79#elif defined( __aarch64__ )
80#define CFA_REG_IP pc
81#else
82#error unsupported hardware architecture
83#endif
84
85KERNEL_STORAGE(event_kernel_t, event_kernel);         // private storage for event kernel
86event_kernel_t * event_kernel;                        // kernel public handle to even kernel
87static pthread_t alarm_thread;                        // pthread handle to alarm thread
88static void * alarm_stack;                                                        // pthread stack for alarm thread
89
90static void ?{}(event_kernel_t & this) with( this ) {
91        alarms{};
92        lock{};
93}
94
95enum {
96        PREEMPT_NORMAL    = 0,
97        PREEMPT_TERMINATE = 1,
98};
99
100//=============================================================================================
101// Kernel Preemption logic
102//=============================================================================================
103
104// Get next expired node
105static inline alarm_node_t * get_expired( alarm_list_t * alarms, Time currtime ) {
106        if( ! & (*alarms)`first ) return 0p;                                            // If no alarms return null
107        if( (*alarms)`first.alarm >= currtime ) return 0p;      // If alarms head not expired return null
108        return pop(alarms);                                                                     // Otherwise just pop head
109}
110
111// Tick one frame of the Discrete Event Simulation for alarms
112static void tick_preemption(void) {
113        alarm_node_t * node = 0p;                                                       // Used in the while loop but cannot be declared in the while condition
114        alarm_list_t * alarms = &event_kernel->alarms;          // Local copy for ease of reading
115        Time currtime = __kernel_get_time();                            // Check current time once so everything "happens at once"
116
117        //Loop throught every thing expired
118        while( node = get_expired( alarms, currtime ) ) {
119                // __cfaabi_dbg_print_buffer_decl( " KERNEL: preemption tick.\n" );
120                Duration period = node->period;
121                if( period == 0) {
122                        node->set = false;                  // Node is one-shot, just mark it as not pending
123                }
124
125                // Check if this is a kernel
126                if( node->type == Kernel ) {
127                        preempt( node->proc );
128                }
129                else if( node->type == User ) {
130                        timeout( node->thrd );
131                }
132                else {
133                        node->callback(*node);
134                }
135
136                // Check if this is a periodic alarm
137                if( period > 0 ) {
138                        // __cfaabi_dbg_print_buffer_local( " KERNEL: alarm period is %lu.\n", period.tv );
139                        node->alarm = currtime + period;    // Alarm is periodic, add currtime to it (used cached current time)
140                        insert( alarms, node );             // Reinsert the node for the next time it triggers
141                }
142        }
143
144        // If there are still alarms pending, reset the timer
145        if( & (*alarms)`first ) {
146                Duration delta = (*alarms)`first.alarm - currtime;
147                Duration capped = max(delta, 50`us);
148                __kernel_set_timer( capped );
149        }
150}
151
152// Update the preemption of a processor and notify interested parties
153void update_preemption( processor * this, Duration duration ) {
154        alarm_node_t * alarm = this->preemption_alarm;
155
156        // Alarms need to be enabled
157        if ( duration > 0 && ! alarm->set ) {
158                alarm->alarm = __kernel_get_time() + duration;
159                alarm->period = duration;
160                register_self( alarm );
161        }
162        // Zero duration but alarm is set
163        else if ( duration == 0 && alarm->set ) {
164                unregister_self( alarm );
165                alarm->alarm = 0;
166                alarm->period = 0;
167        }
168        // If alarm is different from previous, change it
169        else if ( duration > 0 && alarm->period != duration ) {
170                unregister_self( alarm );
171                alarm->alarm = __kernel_get_time() + duration;
172                alarm->period = duration;
173                register_self( alarm );
174        }
175}
176
177//=============================================================================================
178// Kernel Signal Tools
179//=============================================================================================
180// In a user-level threading system, there are handful of thread-local variables where this problem occurs on the ARM.
181//
182// For each kernel thread running user-level threads, there is a flag variable to indicate if interrupts are
183// enabled/disabled for that kernel thread. Therefore, this variable is made thread local.
184//
185// For example, this code fragment sets the state of the "interrupt" variable in thread-local memory.
186//
187// _Thread_local volatile int interrupts;
188// int main() {
189//     interrupts = 0; // disable interrupts }
190//
191// which generates the following code on the ARM
192//
193// (gdb) disassemble main
194// Dump of assembler code for function main:
195//    0x0000000000000610 <+0>:  mrs     x1, tpidr_el0
196//    0x0000000000000614 <+4>:  mov     w0, #0x0                        // #0
197//    0x0000000000000618 <+8>:  add     x1, x1, #0x0, lsl #12
198//    0x000000000000061c <+12>: add     x1, x1, #0x10
199//    0x0000000000000620 <+16>: str     wzr, [x1]
200//    0x0000000000000624 <+20>: ret
201//
202// The mrs moves a pointer from coprocessor register tpidr_el0 into register x1.  Register w0 is set to 0. The two adds
203// increase the TLS pointer with the displacement (offset) 0x10, which is the location in the TSL of variable
204// "interrupts".  Finally, 0 is stored into "interrupts" through the pointer in register x1 that points into the
205// TSL. Now once x1 has the pointer to the location of the TSL for kernel thread N, it can be be preempted at a
206// user-level and the user thread is put on the user-level ready-queue. When the preempted thread gets to the front of
207// the user-level ready-queue it is run on kernel thread M. It now stores 0 into "interrupts" back on kernel thread N,
208// turning off interrupt on the wrong kernel thread.
209//
210// On the x86, the following code is generated for the same code fragment.
211//
212// (gdb) disassemble main
213// Dump of assembler code for function main:
214//    0x0000000000400420 <+0>:  movl   $0x0,%fs:0xfffffffffffffffc
215//    0x000000000040042c <+12>: xor    %eax,%eax
216//    0x000000000040042e <+14>: retq
217//
218// and there is base-displacement addressing used to atomically reset variable "interrupts" off of the TSL pointer in
219// register "fs".
220//
221// Hence, the ARM has base-displacement address for the general purpose registers, BUT not to the coprocessor
222// registers. As a result, generating the address for the write into variable "interrupts" is no longer atomic.
223//
224// Note this problem does NOT occur when just using multiple kernel threads because the preemption ALWAYS restarts the
225// thread on the same kernel thread.
226//
227// The obvious question is why does ARM use a coprocessor register to store the TSL pointer given that coprocessor
228// registers are second-class registers with respect to the instruction set. One possible answer is that they did not
229// want to dedicate one of the general registers to hold the TLS pointer and there was a free coprocessor register
230// available.
231
232//-----------------------------------------------------------------------------
233// Some assembly required
234#define __cfaasm_label(label, when) when: asm volatile goto(".global __cfaasm_" #label "_" #when "\n" "__cfaasm_" #label "_" #when ":":::"memory":when)
235
236//----------
237// special case for preemption since used often
238bool __preemption_enabled() {
239        // create a assembler label before
240        // marked as clobber all to avoid movement
241        __cfaasm_label(check, before);
242
243        // access tls as normal
244        bool enabled = __cfaabi_tls.preemption_state.enabled;
245
246        // create a assembler label after
247        // marked as clobber all to avoid movement
248        __cfaasm_label(check, after);
249        return enabled;
250}
251
252struct asm_region {
253        void * before;
254        void * after;
255};
256
257static inline bool __cfaasm_in( void * ip, struct asm_region & region ) {
258        return ip >= region.before && ip <= region.after;
259}
260
261
262//----------
263// Get data from the TLS block
264// struct asm_region __cfaasm_get;
265uintptr_t __cfatls_get( unsigned long int offset ) __attribute__((__noinline__)); //no inline to avoid problems
266uintptr_t __cfatls_get( unsigned long int offset ) {
267        // create a assembler label before
268        // marked as clobber all to avoid movement
269        __cfaasm_label(get, before);
270
271        // access tls as normal (except for pointer arithmetic)
272        uintptr_t val = *(uintptr_t*)((uintptr_t)&__cfaabi_tls + offset);
273
274        // create a assembler label after
275        // marked as clobber all to avoid movement
276        __cfaasm_label(get, after);
277        return val;
278}
279
280extern "C" {
281        // Disable interrupts by incrementing the counter
282        void disable_interrupts() {
283                // create a assembler label before
284                // marked as clobber all to avoid movement
285                __cfaasm_label(dsable, before);
286
287                with( __cfaabi_tls.preemption_state ) {
288                        #if GCC_VERSION > 50000
289                        static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
290                        #endif
291
292                        // Set enabled flag to false
293                        // should be atomic to avoid preemption in the middle of the operation.
294                        // use memory order RELAXED since there is no inter-thread on this variable requirements
295                        __atomic_store_n(&enabled, false, __ATOMIC_RELAXED);
296
297                        // Signal the compiler that a fence is needed but only for signal handlers
298                        __atomic_signal_fence(__ATOMIC_ACQUIRE);
299
300                        __attribute__((unused)) unsigned short new_val = disable_count + 1;
301                        disable_count = new_val;
302                        verify( new_val < 65_000u );              // If this triggers someone is disabling interrupts without enabling them
303                }
304
305                // create a assembler label after
306                // marked as clobber all to avoid movement
307                __cfaasm_label(dsable, after);
308
309        }
310
311        // Enable interrupts by decrementing the counter
312        // If counter reaches 0, execute any pending __cfactx_switch
313        void enable_interrupts( __cfaabi_dbg_ctx_param ) {
314                // Cache the processor now since interrupts can start happening after the atomic store
315                processor   * proc = __cfaabi_tls.this_processor;
316                /* paranoid */ verify( proc );
317
318                with( __cfaabi_tls.preemption_state ){
319                        unsigned short prev = disable_count;
320                        disable_count -= 1;
321
322                        // If this triggers someone is enabled already enabled interruptsverify( prev != 0u );
323                        /* paranoid */ verify( prev != 0u );
324
325                        // Check if we need to prempt the thread because an interrupt was missed
326                        if( prev == 1 ) {
327                                #if GCC_VERSION > 50000
328                                        static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
329                                #endif
330
331                                // Set enabled flag to true
332                                // should be atomic to avoid preemption in the middle of the operation.
333                                // use memory order RELAXED since there is no inter-thread on this variable requirements
334                                __atomic_store_n(&enabled, true, __ATOMIC_RELAXED);
335
336                                // Signal the compiler that a fence is needed but only for signal handlers
337                                __atomic_signal_fence(__ATOMIC_RELEASE);
338                                if( proc->pending_preemption ) {
339                                        proc->pending_preemption = false;
340                                        force_yield( __POLL_PREEMPTION );
341                                }
342                        }
343                }
344
345                // For debugging purposes : keep track of the last person to enable the interrupts
346                __cfaabi_dbg_debug_do( proc->last_enable = caller; )
347        }
348
349        // Disable interrupts by incrementint the counter
350        // Don't execute any pending __cfactx_switch even if counter reaches 0
351        void enable_interrupts_noPoll() {
352                unsigned short prev = __cfaabi_tls.preemption_state.disable_count;
353                __cfaabi_tls.preemption_state.disable_count -= 1;
354                // If this triggers someone is enabled already enabled interrupts
355                /* paranoid */ verifyf( prev != 0u, "Incremented from %u\n", prev );
356                if( prev == 1 ) {
357                        #if GCC_VERSION > 50000
358                                static_assert(__atomic_always_lock_free(sizeof(__cfaabi_tls.preemption_state.enabled), &__cfaabi_tls.preemption_state.enabled), "Must be lock-free");
359                        #endif
360                        // Set enabled flag to true
361                        // should be atomic to avoid preemption in the middle of the operation.
362                        // use memory order RELAXED since there is no inter-thread on this variable requirements
363                        __atomic_store_n(&__cfaabi_tls.preemption_state.enabled, true, __ATOMIC_RELAXED);
364
365                        // Signal the compiler that a fence is needed but only for signal handlers
366                        __atomic_signal_fence(__ATOMIC_RELEASE);
367                }
368        }
369}
370
371//-----------------------------------------------------------------------------
372// Kernel Signal Debug
373void __cfaabi_check_preemption() {
374        bool ready = __preemption_enabled();
375        if(!ready) { abort("Preemption should be ready"); }
376
377        __cfaasm_label(debug, before);
378
379                sigset_t oldset;
380                int ret;
381                ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset);  // workaround trac#208: cast should be unnecessary
382                if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
383
384                ret = sigismember(&oldset, SIGUSR1);
385                if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
386                if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
387
388                ret = sigismember(&oldset, SIGALRM);
389                if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
390                if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
391
392                ret = sigismember(&oldset, SIGTERM);
393                if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
394                if(ret == 1) { abort("ERROR SIGTERM is disabled"); }
395
396        __cfaasm_label(debug, after);
397}
398
399#ifdef __CFA_WITH_VERIFY__
400bool __cfaabi_dbg_in_kernel() {
401        return !__preemption_enabled();
402}
403#endif
404
405#undef __cfaasm_label
406
407//-----------------------------------------------------------------------------
408// Signal handling
409
410// sigprocmask wrapper : unblock a single signal
411static inline void signal_unblock( int sig ) {
412        sigset_t mask;
413        sigemptyset( &mask );
414        sigaddset( &mask, sig );
415
416        if ( pthread_sigmask( SIG_UNBLOCK, &mask, 0p ) == -1 ) {
417            abort( "internal error, pthread_sigmask" );
418        }
419}
420
421// sigprocmask wrapper : block a single signal
422static inline void signal_block( int sig ) {
423        sigset_t mask;
424        sigemptyset( &mask );
425        sigaddset( &mask, sig );
426
427        if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
428                abort( "internal error, pthread_sigmask" );
429        }
430}
431
432// kill wrapper : signal a processor
433static void preempt( processor * this ) {
434        sigval_t value = { PREEMPT_NORMAL };
435        pthread_sigqueue( this->kernel_thread, SIGUSR1, value );
436}
437
438// reserved for future use
439static void timeout( $thread * this ) {
440        unpark( this );
441}
442
443void __disable_interrupts_hard() {
444        sigset_t oldset;
445        int ret;
446        ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset);  // workaround trac#208: cast should be unnecessary
447        if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
448
449        ret = sigismember(&oldset, SIGUSR1);
450        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
451        if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
452
453        ret = sigismember(&oldset, SIGALRM);
454        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
455        if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
456
457        signal_block( SIGUSR1 );
458}
459
460void __enable_interrupts_hard() {
461        signal_unblock( SIGUSR1 );
462
463        sigset_t oldset;
464        int ret;
465        ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset);  // workaround trac#208: cast should be unnecessary
466        if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
467
468        ret = sigismember(&oldset, SIGUSR1);
469        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
470        if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
471
472        ret = sigismember(&oldset, SIGALRM);
473        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
474        if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
475}
476
477//-----------------------------------------------------------------------------
478// Some assembly required
479#if defined( __i386 )
480        #ifdef __PIC__
481                #define RELOC_PRELUDE( label ) \
482                        "calll   .Lcfaasm_prelude_" #label "$pb\n\t" \
483                        ".Lcfaasm_prelude_" #label "$pb:\n\t" \
484                        "popl    %%eax\n\t" \
485                        ".Lcfaasm_prelude_" #label "_end:\n\t" \
486                        "addl    $_GLOBAL_OFFSET_TABLE_+(.Lcfaasm_prelude_" #label "_end-.Lcfaasm_prelude_" #label "$pb), %%eax\n\t"
487                #define RELOC_PREFIX ""
488                #define RELOC_SUFFIX "@GOT(%%eax)"
489        #else
490                #define RELOC_PREFIX "$"
491                #define RELOC_SUFFIX ""
492        #endif
493        #define __cfaasm_label( label ) struct asm_region label = \
494                ({ \
495                        struct asm_region region; \
496                        asm( \
497                                RELOC_PRELUDE( label ) \
498                                "movl " RELOC_PREFIX "__cfaasm_" #label "_before" RELOC_SUFFIX ", %[vb]\n\t" \
499                                "movl " RELOC_PREFIX "__cfaasm_" #label "_after"  RELOC_SUFFIX ", %[va]\n\t" \
500                                 : [vb]"=r"(region.before), [va]"=r"(region.after) \
501                        ); \
502                        region; \
503                });
504#elif defined( __x86_64 )
505        #ifdef __PIC__
506                #define RELOC_PREFIX ""
507                #define RELOC_SUFFIX "@GOTPCREL(%%rip)"
508        #else
509                #define RELOC_PREFIX "$"
510                #define RELOC_SUFFIX ""
511        #endif
512        #define __cfaasm_label( label ) struct asm_region label = \
513                ({ \
514                        struct asm_region region; \
515                        asm( \
516                                "movq " RELOC_PREFIX "__cfaasm_" #label "_before" RELOC_SUFFIX ", %[vb]\n\t" \
517                                "movq " RELOC_PREFIX "__cfaasm_" #label "_after"  RELOC_SUFFIX ", %[va]\n\t" \
518                                 : [vb]"=r"(region.before), [va]"=r"(region.after) \
519                        ); \
520                        region; \
521                });
522#elif defined( __aarch64__ )
523        #ifdef __PIC__
524                // Note that this works only for gcc
525                #define __cfaasm_label( label ) struct asm_region label = \
526                ({ \
527                        struct asm_region region; \
528                        asm( \
529                                "adrp %[vb], _GLOBAL_OFFSET_TABLE_"                              "\n\t" \
530                                "ldr  %[vb], [%[vb], #:gotpage_lo15:__cfaasm_" #label "_before]" "\n\t" \
531                                "adrp %[va], _GLOBAL_OFFSET_TABLE_"                              "\n\t" \
532                                "ldr  %[va], [%[va], #:gotpage_lo15:__cfaasm_" #label "_after]"  "\n\t" \
533                                 : [vb]"=r"(region.before), [va]"=r"(region.after) \
534                        ); \
535                        region; \
536                });
537        #else
538                #error this is not the right thing to do
539                /*
540                #define __cfaasm_label( label ) struct asm_region label = \
541                ({ \
542                        struct asm_region region; \
543                        asm( \
544                                "adrp %[vb], __cfaasm_" #label "_before"              "\n\t" \
545                                "add  %[vb], %[vb], :lo12:__cfaasm_" #label "_before" "\n\t" \
546                                "adrp %[va], :got:__cfaasm_" #label "_after"          "\n\t" \
547                                "add  %[va], %[va], :lo12:__cfaasm_" #label "_after"  "\n\t" \
548                                 : [vb]"=r"(region.before), [va]"=r"(region.after) \
549                        ); \
550                        region; \
551                });
552                */
553        #endif
554#else
555        #error unknown hardware architecture
556#endif
557
558// KERNEL ONLY
559// Check if a __cfactx_switch signal handler shoud defer
560// If true  : preemption is safe
561// If false : preemption is unsafe and marked as pending
562static inline bool preemption_ready( void * ip ) {
563        // Get all the region for which it is not safe to preempt
564        __cfaasm_label( get    );
565        __cfaasm_label( check  );
566        __cfaasm_label( dsable );
567        __cfaasm_label( debug  );
568
569        // Check if preemption is safe
570        bool ready = true;
571        if( __cfaasm_in( ip, get    ) ) { ready = false; goto EXIT; };
572        if( __cfaasm_in( ip, check  ) ) { ready = false; goto EXIT; };
573        if( __cfaasm_in( ip, dsable ) ) { ready = false; goto EXIT; };
574        if( __cfaasm_in( ip, debug  ) ) { ready = false; goto EXIT; };
575        if( !__cfaabi_tls.preemption_state.enabled) { ready = false; goto EXIT; };
576        if( __cfaabi_tls.preemption_state.in_progress ) { ready = false; goto EXIT; };
577
578EXIT:
579        // Adjust the pending flag accordingly
580        __cfaabi_tls.this_processor->pending_preemption = !ready;
581        return ready;
582}
583
584//=============================================================================================
585// Kernel Signal Startup/Shutdown logic
586//=============================================================================================
587
588// Startup routine to activate preemption
589// Called from kernel_startup
590void __kernel_alarm_startup() {
591        __cfaabi_dbg_print_safe( "Kernel : Starting preemption\n" );
592
593        // Start with preemption disabled until ready
594        __cfaabi_tls.preemption_state.enabled = false;
595        __cfaabi_tls.preemption_state.disable_count = 1;
596
597        // Initialize the event kernel
598        event_kernel = (event_kernel_t *)&storage_event_kernel;
599        (*event_kernel){};
600
601        // Setup proper signal handlers
602        __cfaabi_sigaction( SIGUSR1, sigHandler_ctxSwitch, SA_SIGINFO ); // __cfactx_switch handler
603        __cfaabi_sigaction( SIGALRM, sigHandler_alarm    , SA_SIGINFO ); // debug handler
604
605        signal_block( SIGALRM );
606
607        alarm_stack = __create_pthread( &alarm_thread, alarm_loop, 0p );
608}
609
610// Shutdown routine to deactivate preemption
611// Called from kernel_shutdown
612void __kernel_alarm_shutdown() {
613        __cfaabi_dbg_print_safe( "Kernel : Preemption stopping\n" );
614
615        // Block all signals since we are already shutting down
616        sigset_t mask;
617        sigfillset( &mask );
618        sigprocmask( SIG_BLOCK, &mask, 0p );
619
620        // Notify the alarm thread of the shutdown
621        sigval val = { 1 };
622        pthread_sigqueue( alarm_thread, SIGALRM, val );
623
624        // Wait for the preemption thread to finish
625
626        __destroy_pthread( alarm_thread, alarm_stack, 0p );
627
628        // Preemption is now fully stopped
629
630        __cfaabi_dbg_print_safe( "Kernel : Preemption stopped\n" );
631}
632
633// Prevent preemption since we are about to start terminating things
634void __kernel_abort_lock(void) {
635        signal_block( SIGUSR1 );
636}
637
638// Raii ctor/dtor for the preemption_scope
639// Used by thread to control when they want to receive preemption signals
640void ?{}( preemption_scope & this, processor * proc ) {
641        (this.alarm){ proc, (Time){ 0 }, 0`s };
642        this.proc = proc;
643        this.proc->preemption_alarm = &this.alarm;
644
645        update_preemption( this.proc, this.proc->cltr->preemption_rate );
646}
647
648void ^?{}( preemption_scope & this ) {
649        disable_interrupts();
650
651        update_preemption( this.proc, 0`s );
652}
653
654//=============================================================================================
655// Kernel Signal Handlers
656//=============================================================================================
657__cfaabi_dbg_debug_do( static thread_local void * last_interrupt = 0; )
658
659// Context switch signal handler
660// Receives SIGUSR1 signal and causes the current thread to yield
661static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ ) {
662        void * ip = (void *)(cxt->uc_mcontext.CFA_REG_IP);
663        __cfaabi_dbg_debug_do( last_interrupt = ip; )
664
665        // SKULLDUGGERY: if a thread creates a processor and the immediately deletes it,
666        // the interrupt that is supposed to force the kernel thread to preempt might arrive
667        // before the kernel thread has even started running. When that happens, an interrupt
668        // with a null 'this_processor' will be caught, just ignore it.
669        if(! __cfaabi_tls.this_processor ) return;
670
671        choose(sfp->si_value.sival_int) {
672                case PREEMPT_NORMAL   : ;// Normal case, nothing to do here
673                case PREEMPT_TERMINATE: verify( __atomic_load_n( &__cfaabi_tls.this_processor->do_terminate, __ATOMIC_SEQ_CST ) );
674                default:
675                        abort( "internal error, signal value is %d", sfp->si_value.sival_int );
676        }
677
678        // Check if it is safe to preempt here
679        if( !preemption_ready( ip ) ) { return; }
680
681        __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) );
682
683        // Sync flag : prevent recursive calls to the signal handler
684        __cfaabi_tls.preemption_state.in_progress = true;
685
686        // Clear sighandler mask before context switching.
687        #if GCC_VERSION > 50000
688        static_assert( sizeof( sigset_t ) == sizeof( cxt->uc_sigmask ), "Expected cxt->uc_sigmask to be of sigset_t" );
689        #endif
690        if ( pthread_sigmask( SIG_SETMASK, (sigset_t *)&(cxt->uc_sigmask), 0p ) == -1 ) {
691                abort( "internal error, sigprocmask" );
692        }
693
694        // Clear the in progress flag
695        __cfaabi_tls.preemption_state.in_progress = false;
696
697        // Preemption can occur here
698
699        force_yield( __ALARM_PREEMPTION ); // Do the actual __cfactx_switch
700}
701
702static void sigHandler_alarm( __CFA_SIGPARMS__ ) {
703        abort("SIGALRM should never reach the signal handler");
704}
705
706#if !defined(__CFA_NO_STATISTICS__)
707        int __print_alarm_stats = 0;
708#endif
709
710// Main of the alarm thread
711// Waits on SIGALRM and send SIGUSR1 to whom ever needs it
712static void * alarm_loop( __attribute__((unused)) void * args ) {
713        __processor_id_t id;
714        id.full_proc = false;
715        id.id = doregister(&id);
716        __cfaabi_tls.this_proc_id = &id;
717
718        #if !defined(__CFA_NO_STATISTICS__)
719                struct __stats_t local_stats;
720                __cfaabi_tls.this_stats = &local_stats;
721                __init_stats( &local_stats );
722        #endif
723
724        // Block sigalrms to control when they arrive
725        sigset_t mask;
726        sigfillset(&mask);
727        if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
728            abort( "internal error, pthread_sigmask" );
729        }
730
731        sigemptyset( &mask );
732        sigaddset( &mask, SIGALRM );
733
734        // Main loop
735        while( true ) {
736                // Wait for a sigalrm
737                siginfo_t info;
738                int sig = sigwaitinfo( &mask, &info );
739
740                if( sig < 0 ) {
741                        //Error!
742                        int err = errno;
743                        switch( err ) {
744                                case EAGAIN :
745                                case EINTR :
746                                        {__cfaabi_dbg_print_buffer_decl( " KERNEL: Spurious wakeup %d.\n", err );}
747                                        continue;
748                                case EINVAL :
749                                        abort( "Timeout was invalid." );
750                                default:
751                                        abort( "Unhandled error %d", err);
752                        }
753                }
754
755                // If another signal arrived something went wrong
756                assertf(sig == SIGALRM, "Kernel Internal Error, sigwait: Unexpected signal %d (%d : %d)\n", sig, info.si_code, info.si_value.sival_int);
757
758                // __cfaabi_dbg_print_safe( "Kernel : Caught alarm from %d with %d\n", info.si_code, info.si_value.sival_int );
759                // Switch on the code (a.k.a. the sender) to
760                switch( info.si_code )
761                {
762                // Timers can apparently be marked as sent for the kernel
763                // In either case, tick preemption
764                case SI_TIMER:
765                case SI_KERNEL:
766                        // __cfaabi_dbg_print_safe( "Kernel : Preemption thread tick\n" );
767                        lock( event_kernel->lock __cfaabi_dbg_ctx2 );
768                        tick_preemption();
769                        unlock( event_kernel->lock );
770                        break;
771                // Signal was not sent by the kernel but by an other thread
772                case SI_QUEUE:
773                        // For now, other thread only signal the alarm thread to shut it down
774                        // If this needs to change use info.si_value and handle the case here
775                        goto EXIT;
776                }
777        }
778
779EXIT:
780        __cfaabi_dbg_print_safe( "Kernel : Preemption thread stopping\n" );
781        unregister(&id);
782
783        #if !defined(__CFA_NO_STATISTICS__)
784                if( 0 != __print_alarm_stats ) {
785                        __print_stats( &local_stats, __print_alarm_stats, "Alarm", "Thread", 0p );
786                }
787        #endif
788        return 0p;
789}
790
791// Local Variables: //
792// mode: c //
793// tab-width: 4 //
794// End: //
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