source: src/libcfa/concurrency/preemption.c @ bede27b

aaron-thesisarm-ehcleanup-dtorsdeferred_resndemanglerjacob/cs343-translationjenkins-sandboxnew-astnew-ast-unique-exprnew-envno_listpersistent-indexerresolv-newwith_gc
Last change on this file since bede27b was bede27b, checked in by Peter A. Buhr <pabuhr@…>, 4 years ago

fix conflicts

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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 Feb  9 16:38:13 2018
13// Update Count     : 14
14//
15
16#include "preemption.h"
17
18extern "C" {
19#include <errno.h>
20#include <stdio.h>
21#include <string.h>
22#include <unistd.h>
23}
24
25#include "bits/signal.h"
26
27//TODO move to defaults
28#define __CFA_DEFAULT_PREEMPTION__ 10000
29
30//TODO move to defaults
31__attribute__((weak)) unsigned int default_preemption() {
32        return __CFA_DEFAULT_PREEMPTION__;
33}
34
35// FwdDeclarations : timeout handlers
36static void preempt( processor   * this );
37static void timeout( thread_desc * this );
38
39// FwdDeclarations : Signal handlers
40void sigHandler_ctxSwitch( __CFA_SIGPARMS__ );
41void sigHandler_segv     ( __CFA_SIGPARMS__ );
42void sigHandler_ill      ( __CFA_SIGPARMS__ );
43void sigHandler_fpe      ( __CFA_SIGPARMS__ );
44void sigHandler_abort    ( __CFA_SIGPARMS__ );
45
46// FwdDeclarations : alarm thread main
47void * alarm_loop( __attribute__((unused)) void * args );
48
49// Machine specific register name
50#if   defined( __i386 )
51#define CFA_REG_IP gregs[REG_EIP]
52#elif defined( __x86_64 )
53#define CFA_REG_IP gregs[REG_RIP]
54#elif defined( __ARM_ARCH )
55#define CFA_REG_IP arm_pc
56#else
57#error unknown hardware architecture
58#endif
59
60KERNEL_STORAGE(event_kernel_t, event_kernel);         // private storage for event kernel
61event_kernel_t * event_kernel;                        // kernel public handle to even kernel
62static pthread_t alarm_thread;                        // pthread handle to alarm thread
63
64void ?{}(event_kernel_t & this) with( this ) {
65        alarms{};
66        lock{};
67}
68
69enum {
70        PREEMPT_NORMAL    = 0,
71        PREEMPT_TERMINATE = 1,
72};
73
74//=============================================================================================
75// Kernel Preemption logic
76//=============================================================================================
77
78// Get next expired node
79static inline alarm_node_t * get_expired( alarm_list_t * alarms, __cfa_time_t currtime ) {
80        if( !alarms->head ) return NULL;                          // If no alarms return null
81        if( alarms->head->alarm >= currtime ) return NULL;        // If alarms head not expired return null
82        return pop(alarms);                                       // Otherwise just pop head
83}
84
85// Tick one frame of the Discrete Event Simulation for alarms
86void tick_preemption() {
87        alarm_node_t * node = NULL;                     // Used in the while loop but cannot be declared in the while condition
88        alarm_list_t * alarms = &event_kernel->alarms;  // Local copy for ease of reading
89        __cfa_time_t currtime = __kernel_get_time();    // Check current time once so we everything "happens at once"
90
91        //Loop throught every thing expired
92        while( node = get_expired( alarms, currtime ) ) {
93
94                // Check if this is a kernel
95                if( node->kernel_alarm ) {
96                        preempt( node->proc );
97                }
98                else {
99                        timeout( node->thrd );
100                }
101
102                // Check if this is a periodic alarm
103                __cfa_time_t period = node->period;
104                if( period > 0 ) {
105                        node->alarm = currtime + period;    // Alarm is periodic, add currtime to it (used cached current time)
106                        insert( alarms, node );             // Reinsert the node for the next time it triggers
107                }
108                else {
109                        node->set = false;                  // Node is one-shot, just mark it as not pending
110                }
111        }
112
113        // If there are still alarms pending, reset the timer
114        if( alarms->head ) { __kernel_set_timer( alarms->head->alarm - currtime ); }
115}
116
117// Update the preemption of a processor and notify interested parties
118void update_preemption( processor * this, __cfa_time_t duration ) {
119        alarm_node_t * alarm = this->preemption_alarm;
120
121        // Alarms need to be enabled
122        if ( duration > 0 && !alarm->set ) {
123                alarm->alarm = __kernel_get_time() + duration;
124                alarm->period = duration;
125                register_self( alarm );
126        }
127        // Zero duraction but alarm is set
128        else if ( duration == 0 && alarm->set ) {
129                unregister_self( alarm );
130                alarm->alarm = 0;
131                alarm->period = 0;
132        }
133        // If alarm is different from previous, change it
134        else if ( duration > 0 && alarm->period != duration ) {
135                unregister_self( alarm );
136                alarm->alarm = __kernel_get_time() + duration;
137                alarm->period = duration;
138                register_self( alarm );
139        }
140}
141
142//=============================================================================================
143// Kernel Signal Tools
144//=============================================================================================
145
146__cfaabi_dbg_debug_do( static thread_local void * last_interrupt = 0; )
147
148extern "C" {
149        // Disable interrupts by incrementing the counter
150        void disable_interrupts() {
151                preemption_enabled = false;
152                __attribute__((unused)) unsigned short new_val = disable_preempt_count + 1;
153                disable_preempt_count = new_val;
154                verify( new_val < 65_000u );              // If this triggers someone is disabling interrupts without enabling them
155        }
156
157        // Enable interrupts by decrementing the counter
158        // If counter reaches 0, execute any pending CtxSwitch
159        void enable_interrupts( __cfaabi_dbg_ctx_param ) {
160                processor   * proc = this_processor;      // Cache the processor now since interrupts can start happening after the atomic add
161                thread_desc * thrd = this_thread;         // Cache the thread now since interrupts can start happening after the atomic add
162
163                unsigned short prev = disable_preempt_count;
164                disable_preempt_count -= 1;
165                verify( prev != 0u );                     // If this triggers someone is enabled already enabled interruptsverify( prev != 0u );
166
167                // Check if we need to prempt the thread because an interrupt was missed
168                if( prev == 1 ) {
169                        preemption_enabled = true;
170                        if( proc->pending_preemption ) {
171                                proc->pending_preemption = false;
172                                BlockInternal( thrd );
173                        }
174                }
175
176                // For debugging purposes : keep track of the last person to enable the interrupts
177                __cfaabi_dbg_debug_do( proc->last_enable = caller; )
178        }
179
180        // Disable interrupts by incrementint the counter
181        // Don't execute any pending CtxSwitch even if counter reaches 0
182        void enable_interrupts_noPoll() {
183                unsigned short prev = disable_preempt_count;
184                disable_preempt_count -= 1;
185                verifyf( prev != 0u, "Incremented from %u\n", prev );                     // If this triggers someone is enabled already enabled interrupts
186                if( prev == 1 ) {
187                        preemption_enabled = true;
188                }
189        }
190}
191
192// sigprocmask wrapper : unblock a single signal
193static inline void signal_unblock( int sig ) {
194        sigset_t mask;
195        sigemptyset( &mask );
196        sigaddset( &mask, sig );
197
198        if ( pthread_sigmask( SIG_UNBLOCK, &mask, NULL ) == -1 ) {
199            abort( "internal error, pthread_sigmask" );
200        }
201}
202
203// sigprocmask wrapper : block a single signal
204static inline void signal_block( int sig ) {
205        sigset_t mask;
206        sigemptyset( &mask );
207        sigaddset( &mask, sig );
208
209        if ( pthread_sigmask( SIG_BLOCK, &mask, NULL ) == -1 ) {
210            abort( "internal error, pthread_sigmask" );
211        }
212}
213
214// kill wrapper : signal a processor
215static void preempt( processor * this ) {
216        sigval_t value = { PREEMPT_NORMAL };
217        pthread_sigqueue( this->kernel_thread, SIGUSR1, value );
218}
219
220// kill wrapper : signal a processor
221void terminate(processor * this) {
222        this->do_terminate = true;
223        sigval_t value = { PREEMPT_TERMINATE };
224        pthread_sigqueue( this->kernel_thread, SIGUSR1, value );
225}
226
227// reserved for future use
228static void timeout( thread_desc * this ) {
229        //TODO : implement waking threads
230}
231
232
233// Check if a CtxSwitch signal handler shoud defer
234// If true  : preemption is safe
235// If false : preemption is unsafe and marked as pending
236static inline bool preemption_ready() {
237        bool ready = preemption_enabled && !preemption_in_progress; // Check if preemption is safe
238        this_processor->pending_preemption = !ready;                        // Adjust the pending flag accordingly
239        return ready;
240}
241
242//=============================================================================================
243// Kernel Signal Startup/Shutdown logic
244//=============================================================================================
245
246// Startup routine to activate preemption
247// Called from kernel_startup
248void kernel_start_preemption() {
249        __cfaabi_dbg_print_safe( "Kernel : Starting preemption\n" );
250
251        // Start with preemption disabled until ready
252        preemption_enabled = false;
253        disable_preempt_count = 1;
254
255        // Initialize the event kernel
256        event_kernel = (event_kernel_t *)&storage_event_kernel;
257        (*event_kernel){};
258
259        // Setup proper signal handlers
260        __cfaabi_sigaction( SIGUSR1, sigHandler_ctxSwitch, SA_SIGINFO | SA_RESTART );         // CtxSwitch handler
261
262        signal_block( SIGALRM );
263
264        pthread_create( &alarm_thread, NULL, alarm_loop, NULL );
265}
266
267// Shutdown routine to deactivate preemption
268// Called from kernel_shutdown
269void kernel_stop_preemption() {
270        __cfaabi_dbg_print_safe( "Kernel : Preemption stopping\n" );
271
272        // Block all signals since we are already shutting down
273        sigset_t mask;
274        sigfillset( &mask );
275        sigprocmask( SIG_BLOCK, &mask, NULL );
276
277        // Notify the alarm thread of the shutdown
278        sigval val = { 1 };
279        pthread_sigqueue( alarm_thread, SIGALRM, val );
280
281        // Wait for the preemption thread to finish
282        pthread_join( alarm_thread, NULL );
283
284        // Preemption is now fully stopped
285
286        __cfaabi_dbg_print_safe( "Kernel : Preemption stopped\n" );
287}
288
289// Raii ctor/dtor for the preemption_scope
290// Used by thread to control when they want to receive preemption signals
291void ?{}( preemption_scope & this, processor * proc ) {
292        (this.alarm){ proc, zero_time, zero_time };
293        this.proc = proc;
294        this.proc->preemption_alarm = &this.alarm;
295
296        update_preemption( this.proc, from_us(this.proc->cltr->preemption) );
297}
298
299void ^?{}( preemption_scope & this ) {
300        disable_interrupts();
301
302        update_preemption( this.proc, zero_time );
303}
304
305//=============================================================================================
306// Kernel Signal Handlers
307//=============================================================================================
308
309// Context switch signal handler
310// Receives SIGUSR1 signal and causes the current thread to yield
311void sigHandler_ctxSwitch( __CFA_SIGPARMS__ ) {
312        __cfaabi_dbg_debug_do( last_interrupt = (void *)(cxt->uc_mcontext.CFA_REG_IP); )
313
314        // SKULLDUGGERY: if a thread creates a processor and the immediately deletes it,
315        // the interrupt that is supposed to force the kernel thread to preempt might arrive
316        // before the kernel thread has even started running. When that happens an iterrupt
317        // we a null 'this_processor' will be caught, just ignore it.
318        if(!this_processor) return;
319
320        choose(sfp->si_value.sival_int) {
321                case PREEMPT_NORMAL   : ;// Normal case, nothing to do here
322                case PREEMPT_TERMINATE: verify(this_processor->do_terminate);
323                default:
324                        abort( "internal error, signal value is %d", sfp->si_value.sival_int );
325        }
326
327        // Check if it is safe to preempt here
328        if( !preemption_ready() ) { return; }
329
330        __cfaabi_dbg_print_buffer_decl( " KERNEL: preempting core %p (%p).\n", this_processor, this_thread);
331
332        preemption_in_progress = true;                      // Sync flag : prevent recursive calls to the signal handler
333        signal_unblock( SIGUSR1 );                          // We are about to CtxSwitch out of the signal handler, let other handlers in
334        preemption_in_progress = false;                     // Clear the in progress flag
335
336        // Preemption can occur here
337
338        BlockInternal( (thread_desc*)this_thread );         // Do the actual CtxSwitch
339}
340
341// Main of the alarm thread
342// Waits on SIGALRM and send SIGUSR1 to whom ever needs it
343void * alarm_loop( __attribute__((unused)) void * args ) {
344        // Block sigalrms to control when they arrive
345        sigset_t mask;
346        sigemptyset( &mask );
347        sigaddset( &mask, SIGALRM );
348
349        if ( pthread_sigmask( SIG_BLOCK, &mask, NULL ) == -1 ) {
350            abort( "internal error, pthread_sigmask" );
351        }
352
353        // Main loop
354        while( true ) {
355                // Wait for a sigalrm
356                siginfo_t info;
357                int sig = sigwaitinfo( &mask, &info );
358
359                if( sig < 0 ) {
360                        //Error!
361                        int err = errno;
362                        switch( err ) {
363                                case EAGAIN :
364                                case EINTR :
365                                        continue;
366                        case EINVAL :
367                                        abort( "Timeout was invalid." );
368                                default:
369                                        abort( "Unhandled error %d", err);
370                        }
371                }
372
373                // If another signal arrived something went wrong
374                assertf(sig == SIGALRM, "Kernel Internal Error, sigwait: Unexpected signal %d (%d : %d)\n", sig, info.si_code, info.si_value.sival_int);
375
376                // __cfaabi_dbg_print_safe( "Kernel : Caught alarm from %d with %d\n", info.si_code, info.si_value.sival_int );
377                // Switch on the code (a.k.a. the sender) to
378                switch( info.si_code )
379                {
380                // Timers can apparently be marked as sent for the kernel
381                // In either case, tick preemption
382                case SI_TIMER:
383                case SI_KERNEL:
384                        // __cfaabi_dbg_print_safe( "Kernel : Preemption thread tick\n" );
385                        lock( event_kernel->lock __cfaabi_dbg_ctx2 );
386                        tick_preemption();
387                        unlock( event_kernel->lock );
388                        break;
389                // Signal was not sent by the kernel but by an other thread
390                case SI_QUEUE:
391                        // For now, other thread only signal the alarm thread to shut it down
392                        // If this needs to change use info.si_value and handle the case here
393                        goto EXIT;
394                }
395        }
396
397EXIT:
398        __cfaabi_dbg_print_safe( "Kernel : Preemption thread stopping\n" );
399        return NULL;
400}
401
402// Local Variables: //
403// mode: c //
404// tab-width: 4 //
405// End: //
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