source: libcfa/src/concurrency/preemption.cfa @ d3ab183

arm-ehjacob/cs343-translationnew-astnew-ast-unique-expr
Last change on this file since d3ab183 was d3ab183, checked in by Michael Brooks <mlbrooks@…>, 18 months ago

Using dlist in alarm.

Minimal interface changes in alarm.hfa applied; some spill to preemption.cfa occured.

List management logic removed, including such helper functions from alarm.cfa. Remaining logic is concurrency-protection wrapping, and picking insertion point by traversing and comparing alarm-fire times.

Integrity checking definitions removed here. Calling version brought into list.hfa by change 4d741 instead.

  • Property mode set to 100644
File size: 16.9 KB
Line 
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 Dec  5 16:34:05 2019
13// Update Count     : 43
14//
15
16#define __cforall_thread__
17
18#include "preemption.hfa"
19#include <assert.h>
20
21extern "C" {
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
29#include "bits/signal.hfa"
30
31#if !defined(__CFA_DEFAULT_PREEMPTION__)
32#define __CFA_DEFAULT_PREEMPTION__ 10`ms
33#endif
34
35Duration default_preemption() __attribute__((weak)) {
36        return __CFA_DEFAULT_PREEMPTION__;
37}
38
39// FwdDeclarations : timeout handlers
40static void preempt( processor   * this );
41static void timeout( $thread * this );
42
43// FwdDeclarations : Signal handlers
44static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ );
45static void sigHandler_alarm    ( __CFA_SIGPARMS__ );
46static void sigHandler_segv     ( __CFA_SIGPARMS__ );
47static void sigHandler_ill      ( __CFA_SIGPARMS__ );
48static void sigHandler_fpe      ( __CFA_SIGPARMS__ );
49static void sigHandler_abort    ( __CFA_SIGPARMS__ );
50
51// FwdDeclarations : alarm thread main
52static void * alarm_loop( __attribute__((unused)) void * args );
53
54// Machine specific register name
55#if   defined( __i386 )
56#define CFA_REG_IP gregs[REG_EIP]
57#elif defined( __x86_64 )
58#define CFA_REG_IP gregs[REG_RIP]
59#elif defined( __ARM_ARCH )
60#define CFA_REG_IP arm_pc
61#else
62#error unknown hardware architecture
63#endif
64
65KERNEL_STORAGE(event_kernel_t, event_kernel);         // private storage for event kernel
66event_kernel_t * event_kernel;                        // kernel public handle to even kernel
67static pthread_t alarm_thread;                        // pthread handle to alarm thread
68static void * alarm_stack;                                                        // pthread stack for alarm thread
69
70static void ?{}(event_kernel_t & this) with( this ) {
71        alarms{};
72        lock{};
73}
74
75enum {
76        PREEMPT_NORMAL    = 0,
77        PREEMPT_TERMINATE = 1,
78};
79
80//=============================================================================================
81// Kernel Preemption logic
82//=============================================================================================
83
84// Get next expired node
85static inline alarm_node_t * get_expired( alarm_list_t * alarms, Time currtime ) {
86        if( ! & (*alarms)`first ) return 0p;                                            // If no alarms return null
87        if( (*alarms)`first.alarm >= currtime ) return 0p;      // If alarms head not expired return null
88        return pop(alarms);                                                                     // Otherwise just pop head
89}
90
91// Tick one frame of the Discrete Event Simulation for alarms
92static void tick_preemption() {
93        alarm_node_t * node = 0p;                                                       // Used in the while loop but cannot be declared in the while condition
94        alarm_list_t * alarms = &event_kernel->alarms;          // Local copy for ease of reading
95        Time currtime = __kernel_get_time();                            // Check current time once so everything "happens at once"
96
97        //Loop throught every thing expired
98        while( node = get_expired( alarms, currtime ) ) {
99                // __cfaabi_dbg_print_buffer_decl( " KERNEL: preemption tick.\n" );
100                Duration period = node->period;
101                if( period == 0) {
102                        node->set = false;                  // Node is one-shot, just mark it as not pending
103                }
104
105                // Check if this is a kernel
106                if( node->kernel_alarm ) {
107                        preempt( node->proc );
108                }
109                else {
110                        timeout( node->thrd );
111                }
112
113                // Check if this is a periodic alarm
114                if( period > 0 ) {
115                        // __cfaabi_dbg_print_buffer_local( " KERNEL: alarm period is %lu.\n", period.tv );
116                        node->alarm = currtime + period;    // Alarm is periodic, add currtime to it (used cached current time)
117                        insert( alarms, node );             // Reinsert the node for the next time it triggers
118                }
119        }
120
121        // If there are still alarms pending, reset the timer
122        if( & (*alarms)`first ) {
123                __cfaabi_dbg_print_buffer_decl( " KERNEL: @%ju(%ju) resetting alarm to %ju.\n", currtime.tv, __kernel_get_time().tv, (alarms->head->alarm - currtime).tv);
124                Duration delta = (*alarms)`first.alarm - currtime;
125                Duration capped = max(delta, 50`us);
126                // itimerval tim  = { caped };
127                // __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);
128
129                __kernel_set_timer( capped );
130        }
131}
132
133// Update the preemption of a processor and notify interested parties
134void update_preemption( processor * this, Duration duration ) {
135        alarm_node_t * alarm = this->preemption_alarm;
136
137        // Alarms need to be enabled
138        if ( duration > 0 && ! alarm->set ) {
139                alarm->alarm = __kernel_get_time() + duration;
140                alarm->period = duration;
141                register_self( alarm );
142        }
143        // Zero duration but alarm is set
144        else if ( duration == 0 && alarm->set ) {
145                unregister_self( alarm );
146                alarm->alarm = 0;
147                alarm->period = 0;
148        }
149        // If alarm is different from previous, change it
150        else if ( duration > 0 && alarm->period != duration ) {
151                unregister_self( alarm );
152                alarm->alarm = __kernel_get_time() + duration;
153                alarm->period = duration;
154                register_self( alarm );
155        }
156}
157
158//=============================================================================================
159// Kernel Signal Tools
160//=============================================================================================
161
162__cfaabi_dbg_debug_do( static thread_local void * last_interrupt = 0; )
163
164extern "C" {
165        // Disable interrupts by incrementing the counter
166        void disable_interrupts() {
167                with( kernelTLS.preemption_state ) {
168                        #if GCC_VERSION > 50000
169                        static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
170                        #endif
171
172                        // Set enabled flag to false
173                        // should be atomic to avoid preemption in the middle of the operation.
174                        // use memory order RELAXED since there is no inter-thread on this variable requirements
175                        __atomic_store_n(&enabled, false, __ATOMIC_RELAXED);
176
177                        // Signal the compiler that a fence is needed but only for signal handlers
178                        __atomic_signal_fence(__ATOMIC_ACQUIRE);
179
180                        __attribute__((unused)) unsigned short new_val = disable_count + 1;
181                        disable_count = new_val;
182                        verify( new_val < 65_000u );              // If this triggers someone is disabling interrupts without enabling them
183                }
184        }
185
186        // Enable interrupts by decrementing the counter
187        // If counter reaches 0, execute any pending __cfactx_switch
188        void enable_interrupts( __cfaabi_dbg_ctx_param ) {
189                processor   * proc = kernelTLS.this_processor; // Cache the processor now since interrupts can start happening after the atomic store
190
191                with( kernelTLS.preemption_state ){
192                        unsigned short prev = disable_count;
193                        disable_count -= 1;
194                        verify( prev != 0u );                     // If this triggers someone is enabled already enabled interruptsverify( prev != 0u );
195
196                        // Check if we need to prempt the thread because an interrupt was missed
197                        if( prev == 1 ) {
198                                #if GCC_VERSION > 50000
199                                static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
200                                #endif
201
202                                // Set enabled flag to true
203                                // should be atomic to avoid preemption in the middle of the operation.
204                                // use memory order RELAXED since there is no inter-thread on this variable requirements
205                                __atomic_store_n(&enabled, true, __ATOMIC_RELAXED);
206
207                                // Signal the compiler that a fence is needed but only for signal handlers
208                                __atomic_signal_fence(__ATOMIC_RELEASE);
209                                if( proc->pending_preemption ) {
210                                        proc->pending_preemption = false;
211                                        force_yield( __POLL_PREEMPTION );
212                                }
213                        }
214                }
215
216                // For debugging purposes : keep track of the last person to enable the interrupts
217                __cfaabi_dbg_debug_do( proc->last_enable = caller; )
218        }
219
220        // Disable interrupts by incrementint the counter
221        // Don't execute any pending __cfactx_switch even if counter reaches 0
222        void enable_interrupts_noPoll() {
223                unsigned short prev = kernelTLS.preemption_state.disable_count;
224                kernelTLS.preemption_state.disable_count -= 1;
225                verifyf( prev != 0u, "Incremented from %u\n", prev );                     // If this triggers someone is enabled already enabled interrupts
226                if( prev == 1 ) {
227                        #if GCC_VERSION > 50000
228                        static_assert(__atomic_always_lock_free(sizeof(kernelTLS.preemption_state.enabled), &kernelTLS.preemption_state.enabled), "Must be lock-free");
229                        #endif
230                        // Set enabled flag to true
231                        // should be atomic to avoid preemption in the middle of the operation.
232                        // use memory order RELAXED since there is no inter-thread on this variable requirements
233                        __atomic_store_n(&kernelTLS.preemption_state.enabled, true, __ATOMIC_RELAXED);
234
235                        // Signal the compiler that a fence is needed but only for signal handlers
236                        __atomic_signal_fence(__ATOMIC_RELEASE);
237                }
238        }
239}
240
241// sigprocmask wrapper : unblock a single signal
242static inline void signal_unblock( int sig ) {
243        sigset_t mask;
244        sigemptyset( &mask );
245        sigaddset( &mask, sig );
246
247        if ( pthread_sigmask( SIG_UNBLOCK, &mask, 0p ) == -1 ) {
248            abort( "internal error, pthread_sigmask" );
249        }
250}
251
252// sigprocmask wrapper : block a single signal
253static inline void signal_block( int sig ) {
254        sigset_t mask;
255        sigemptyset( &mask );
256        sigaddset( &mask, sig );
257
258        if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
259                abort( "internal error, pthread_sigmask" );
260        }
261}
262
263// kill wrapper : signal a processor
264static void preempt( processor * this ) {
265        sigval_t value = { PREEMPT_NORMAL };
266        pthread_sigqueue( this->kernel_thread, SIGUSR1, value );
267}
268
269// reserved for future use
270static void timeout( $thread * this ) {
271        __unpark( this __cfaabi_dbg_ctx2 );
272}
273
274// KERNEL ONLY
275// Check if a __cfactx_switch signal handler shoud defer
276// If true  : preemption is safe
277// If false : preemption is unsafe and marked as pending
278static inline bool preemption_ready() {
279        // Check if preemption is safe
280        bool ready = kernelTLS.preemption_state.enabled && ! kernelTLS.preemption_state.in_progress;
281
282        // Adjust the pending flag accordingly
283        kernelTLS.this_processor->pending_preemption = !ready;
284        return ready;
285}
286
287//=============================================================================================
288// Kernel Signal Startup/Shutdown logic
289//=============================================================================================
290
291// Startup routine to activate preemption
292// Called from kernel_startup
293void kernel_start_preemption() {
294        __cfaabi_dbg_print_safe( "Kernel : Starting preemption\n" );
295
296        // Start with preemption disabled until ready
297        kernelTLS.preemption_state.enabled = false;
298        kernelTLS.preemption_state.disable_count = 1;
299
300        // Initialize the event kernel
301        event_kernel = (event_kernel_t *)&storage_event_kernel;
302        (*event_kernel){};
303
304        // Setup proper signal handlers
305        __cfaabi_sigaction( SIGUSR1, sigHandler_ctxSwitch, SA_SIGINFO | SA_RESTART ); // __cfactx_switch handler
306        __cfaabi_sigaction( SIGALRM, sigHandler_alarm    , SA_SIGINFO | SA_RESTART ); // debug handler
307
308        signal_block( SIGALRM );
309
310        alarm_stack = __create_pthread( &alarm_thread, alarm_loop, 0p );
311}
312
313// Shutdown routine to deactivate preemption
314// Called from kernel_shutdown
315void kernel_stop_preemption() {
316        __cfaabi_dbg_print_safe( "Kernel : Preemption stopping\n" );
317
318        // Block all signals since we are already shutting down
319        sigset_t mask;
320        sigfillset( &mask );
321        sigprocmask( SIG_BLOCK, &mask, 0p );
322
323        // Notify the alarm thread of the shutdown
324        sigval val = { 1 };
325        pthread_sigqueue( alarm_thread, SIGALRM, val );
326
327        // Wait for the preemption thread to finish
328
329        pthread_join( alarm_thread, 0p );
330        free( alarm_stack );
331
332        // Preemption is now fully stopped
333
334        __cfaabi_dbg_print_safe( "Kernel : Preemption stopped\n" );
335}
336
337// Raii ctor/dtor for the preemption_scope
338// Used by thread to control when they want to receive preemption signals
339void ?{}( preemption_scope & this, processor * proc ) {
340        (this.alarm){ proc, (Time){ 0 }, 0`s };
341        this.proc = proc;
342        this.proc->preemption_alarm = &this.alarm;
343
344        update_preemption( this.proc, this.proc->cltr->preemption_rate );
345}
346
347void ^?{}( preemption_scope & this ) {
348        disable_interrupts();
349
350        update_preemption( this.proc, 0`s );
351}
352
353//=============================================================================================
354// Kernel Signal Handlers
355//=============================================================================================
356
357// Context switch signal handler
358// Receives SIGUSR1 signal and causes the current thread to yield
359static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ ) {
360        __cfaabi_dbg_debug_do( last_interrupt = (void *)(cxt->uc_mcontext.CFA_REG_IP); )
361
362        // SKULLDUGGERY: if a thread creates a processor and the immediately deletes it,
363        // the interrupt that is supposed to force the kernel thread to preempt might arrive
364        // before the kernel thread has even started running. When that happens an iterrupt
365        // we a null 'this_processor' will be caught, just ignore it.
366        if(! kernelTLS.this_processor ) return;
367
368        choose(sfp->si_value.sival_int) {
369                case PREEMPT_NORMAL   : ;// Normal case, nothing to do here
370                case PREEMPT_TERMINATE: verify( __atomic_load_n( &kernelTLS.this_processor->do_terminate, __ATOMIC_SEQ_CST ) );
371                default:
372                        abort( "internal error, signal value is %d", sfp->si_value.sival_int );
373        }
374
375        // Check if it is safe to preempt here
376        if( !preemption_ready() ) { return; }
377
378        __cfaabi_dbg_print_buffer_decl( " KERNEL: preempting core %p (%p @ %p).\n", kernelTLS.this_processor, kernelTLS.this_thread, (void *)(cxt->uc_mcontext.CFA_REG_IP) );
379
380        // Sync flag : prevent recursive calls to the signal handler
381        kernelTLS.preemption_state.in_progress = true;
382
383        // Clear sighandler mask before context switching.
384        #if GCC_VERSION > 50000
385        static_assert( sizeof( sigset_t ) == sizeof( cxt->uc_sigmask ), "Expected cxt->uc_sigmask to be of sigset_t" );
386        #endif
387        if ( pthread_sigmask( SIG_SETMASK, (sigset_t *)&(cxt->uc_sigmask), 0p ) == -1 ) {
388                abort( "internal error, sigprocmask" );
389        }
390
391        // TODO: this should go in finish action
392        // Clear the in progress flag
393        kernelTLS.preemption_state.in_progress = false;
394
395        // Preemption can occur here
396
397        force_yield( __ALARM_PREEMPTION ); // Do the actual __cfactx_switch
398}
399
400static void sigHandler_alarm( __CFA_SIGPARMS__ ) {
401        abort("SIGALRM should never reach the signal handler");
402}
403
404// Main of the alarm thread
405// Waits on SIGALRM and send SIGUSR1 to whom ever needs it
406static void * alarm_loop( __attribute__((unused)) void * args ) {
407        // Block sigalrms to control when they arrive
408        sigset_t mask;
409        sigfillset(&mask);
410        if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
411            abort( "internal error, pthread_sigmask" );
412        }
413
414        sigemptyset( &mask );
415        sigaddset( &mask, SIGALRM );
416
417        // Main loop
418        while( true ) {
419                // Wait for a sigalrm
420                siginfo_t info;
421                int sig = sigwaitinfo( &mask, &info );
422
423                if( sig < 0 ) {
424                        //Error!
425                        int err = errno;
426                        switch( err ) {
427                                case EAGAIN :
428                                case EINTR :
429                                        {__cfaabi_dbg_print_buffer_decl( " KERNEL: Spurious wakeup %d.\n", err );}
430                                        continue;
431                                case EINVAL :
432                                        abort( "Timeout was invalid." );
433                                default:
434                                        abort( "Unhandled error %d", err);
435                        }
436                }
437
438                // If another signal arrived something went wrong
439                assertf(sig == SIGALRM, "Kernel Internal Error, sigwait: Unexpected signal %d (%d : %d)\n", sig, info.si_code, info.si_value.sival_int);
440
441                // __cfaabi_dbg_print_safe( "Kernel : Caught alarm from %d with %d\n", info.si_code, info.si_value.sival_int );
442                // Switch on the code (a.k.a. the sender) to
443                switch( info.si_code )
444                {
445                // Timers can apparently be marked as sent for the kernel
446                // In either case, tick preemption
447                case SI_TIMER:
448                case SI_KERNEL:
449                        // __cfaabi_dbg_print_safe( "Kernel : Preemption thread tick\n" );
450                        lock( event_kernel->lock __cfaabi_dbg_ctx2 );
451                        tick_preemption();
452                        unlock( event_kernel->lock );
453                        break;
454                // Signal was not sent by the kernel but by an other thread
455                case SI_QUEUE:
456                        // For now, other thread only signal the alarm thread to shut it down
457                        // If this needs to change use info.si_value and handle the case here
458                        goto EXIT;
459                }
460        }
461
462EXIT:
463        __cfaabi_dbg_print_safe( "Kernel : Preemption thread stopping\n" );
464        return 0p;
465}
466
467//=============================================================================================
468// Kernel Signal Debug
469//=============================================================================================
470
471void __cfaabi_check_preemption() {
472        bool ready = kernelTLS.preemption_state.enabled;
473        if(!ready) { abort("Preemption should be ready"); }
474
475        sigset_t oldset;
476        int ret;
477        ret = pthread_sigmask(0, 0p, &oldset);
478        if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
479
480        ret = sigismember(&oldset, SIGUSR1);
481        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
482        if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
483
484        ret = sigismember(&oldset, SIGALRM);
485        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
486        if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
487
488        ret = sigismember(&oldset, SIGTERM);
489        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
490        if(ret == 1) { abort("ERROR SIGTERM is disabled"); }
491}
492
493#ifdef __CFA_WITH_VERIFY__
494bool __cfaabi_dbg_in_kernel() {
495        return !kernelTLS.preemption_state.enabled;
496}
497#endif
498
499// Local Variables: //
500// mode: c //
501// tab-width: 4 //
502// End: //
Note: See TracBrowser for help on using the repository browser.