source: libcfa/src/concurrency/preemption.cfa@ e0c235c

ADT arm-eh ast-experimental enum forall-pointer-decay jacob/cs343-translation jenkins-sandbox new-ast new-ast-unique-expr pthread-emulation qualifiedEnum
Last change on this file since e0c235c was 09d4b22, checked in by Peter A. Buhr <pabuhr@…>, 6 years ago

move stack for preemptive pthread from TLS to static variable
  • Property mode set to 100644
File size: 16.7 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_desc * this );
42
43// FwdDeclarations : Signal handlers
44static void sigHandler_ctxSwitch( __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_ARCH )
59#define CFA_REG_IP arm_pc
60#else
61#error unknown hardware architecture
62#endif
63
64KERNEL_STORAGE(event_kernel_t, event_kernel); // private storage for event kernel
65event_kernel_t * event_kernel; // kernel public handle to even kernel
66static pthread_t alarm_thread; // pthread handle to alarm thread
67static void * alarm_stack; // pthread stack for alarm thread
68
69static void ?{}(event_kernel_t & this) with( this ) {
70 alarms{};
71 lock{};
72}
73
74enum {
75 PREEMPT_NORMAL = 0,
76 PREEMPT_TERMINATE = 1,
77};
78
79//=============================================================================================
80// Kernel Preemption logic
81//=============================================================================================
82
83// Get next expired node
84static inline alarm_node_t * get_expired( alarm_list_t * alarms, Time currtime ) {
85 if( !alarms->head ) return 0p; // If no alarms return null
86 if( alarms->head->alarm >= currtime ) return 0p; // If alarms head not expired return null
87 return pop(alarms); // Otherwise just pop head
88}
89
90// Tick one frame of the Discrete Event Simulation for alarms
91static void tick_preemption() {
92 alarm_node_t * node = 0p; // Used in the while loop but cannot be declared in the while condition
93 alarm_list_t * alarms = &event_kernel->alarms; // Local copy for ease of reading
94 Time currtime = __kernel_get_time(); // Check current time once so everything "happens at once"
95
96 //Loop throught every thing expired
97 while( node = get_expired( alarms, currtime ) ) {
98 // __cfaabi_dbg_print_buffer_decl( " KERNEL: preemption tick.\n" );
99
100 // Check if this is a kernel
101 if( node->kernel_alarm ) {
102 preempt( node->proc );
103 }
104 else {
105 timeout( node->thrd );
106 }
107
108 // Check if this is a periodic alarm
109 Duration period = node->period;
110 if( period > 0 ) {
111 // __cfaabi_dbg_print_buffer_local( " KERNEL: alarm period is %lu.\n", period.tv );
112 node->alarm = currtime + period; // Alarm is periodic, add currtime to it (used cached current time)
113 insert( alarms, node ); // Reinsert the node for the next time it triggers
114 }
115 else {
116 node->set = false; // Node is one-shot, just mark it as not pending
117 }
118 }
119
120 // If there are still alarms pending, reset the timer
121 if( alarms->head ) {
122 __cfaabi_dbg_print_buffer_decl( " KERNEL: @%ju(%ju) resetting alarm to %ju.\n", currtime.tv, __kernel_get_time().tv, (alarms->head->alarm - currtime).tv);
123 Duration delta = alarms->head->alarm - currtime;
124 Duration caped = max(delta, 50`us);
125 // itimerval tim = { caped };
126 // __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);
127
128 __kernel_set_timer( caped );
129 }
130}
131
132// Update the preemption of a processor and notify interested parties
133void update_preemption( processor * this, Duration duration ) {
134 alarm_node_t * alarm = this->preemption_alarm;
135
136 // Alarms need to be enabled
137 if ( duration > 0 && ! alarm->set ) {
138 alarm->alarm = __kernel_get_time() + duration;
139 alarm->period = duration;
140 register_self( alarm );
141 }
142 // Zero duration but alarm is set
143 else if ( duration == 0 && alarm->set ) {
144 unregister_self( alarm );
145 alarm->alarm = 0;
146 alarm->period = 0;
147 }
148 // If alarm is different from previous, change it
149 else if ( duration > 0 && alarm->period != duration ) {
150 unregister_self( alarm );
151 alarm->alarm = __kernel_get_time() + duration;
152 alarm->period = duration;
153 register_self( alarm );
154 }
155}
156
157//=============================================================================================
158// Kernel Signal Tools
159//=============================================================================================
160
161__cfaabi_dbg_debug_do( static thread_local void * last_interrupt = 0; )
162
163extern "C" {
164 // Disable interrupts by incrementing the counter
165 void disable_interrupts() {
166 with( kernelTLS.preemption_state ) {
167 #if GCC_VERSION > 50000
168 static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
169 #endif
170
171 // Set enabled flag to false
172 // should be atomic to avoid preemption in the middle of the operation.
173 // use memory order RELAXED since there is no inter-thread on this variable requirements
174 __atomic_store_n(&enabled, false, __ATOMIC_RELAXED);
175
176 // Signal the compiler that a fence is needed but only for signal handlers
177 __atomic_signal_fence(__ATOMIC_ACQUIRE);
178
179 __attribute__((unused)) unsigned short new_val = disable_count + 1;
180 disable_count = new_val;
181 verify( new_val < 65_000u ); // If this triggers someone is disabling interrupts without enabling them
182 }
183 }
184
185 // Enable interrupts by decrementing the counter
186 // If counter reaches 0, execute any pending CtxSwitch
187 void enable_interrupts( __cfaabi_dbg_ctx_param ) {
188 processor * proc = kernelTLS.this_processor; // Cache the processor now since interrupts can start happening after the atomic store
189 thread_desc * thrd = kernelTLS.this_thread; // Cache the thread 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 BlockInternal( thrd );
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 CtxSwitch 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_desc * this ) {
271 //TODO : implement waking threads
272}
273
274// KERNEL ONLY
275// Check if a CtxSwitch 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 ); // CtxSwitch handler
306
307 signal_block( SIGALRM );
308
309 alarm_stack = create_pthread( &alarm_thread, alarm_loop, 0p );
310}
311
312// Shutdown routine to deactivate preemption
313// Called from kernel_shutdown
314void kernel_stop_preemption() {
315 __cfaabi_dbg_print_safe( "Kernel : Preemption stopping\n" );
316
317 // Block all signals since we are already shutting down
318 sigset_t mask;
319 sigfillset( &mask );
320 sigprocmask( SIG_BLOCK, &mask, 0p );
321
322 // Notify the alarm thread of the shutdown
323 sigval val = { 1 };
324 pthread_sigqueue( alarm_thread, SIGALRM, val );
325
326 // Wait for the preemption thread to finish
327
328 pthread_join( alarm_thread, 0p );
329 free( alarm_stack );
330
331 // Preemption is now fully stopped
332
333 __cfaabi_dbg_print_safe( "Kernel : Preemption stopped\n" );
334}
335
336// Raii ctor/dtor for the preemption_scope
337// Used by thread to control when they want to receive preemption signals
338void ?{}( preemption_scope & this, processor * proc ) {
339 (this.alarm){ proc, (Time){ 0 }, 0`s };
340 this.proc = proc;
341 this.proc->preemption_alarm = &this.alarm;
342
343 update_preemption( this.proc, this.proc->cltr->preemption_rate );
344}
345
346void ^?{}( preemption_scope & this ) {
347 disable_interrupts();
348
349 update_preemption( this.proc, 0`s );
350}
351
352//=============================================================================================
353// Kernel Signal Handlers
354//=============================================================================================
355
356// Context switch signal handler
357// Receives SIGUSR1 signal and causes the current thread to yield
358static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ ) {
359 __cfaabi_dbg_debug_do( last_interrupt = (void *)(cxt->uc_mcontext.CFA_REG_IP); )
360
361 // SKULLDUGGERY: if a thread creates a processor and the immediately deletes it,
362 // the interrupt that is supposed to force the kernel thread to preempt might arrive
363 // before the kernel thread has even started running. When that happens an iterrupt
364 // we a null 'this_processor' will be caught, just ignore it.
365 if(! kernelTLS.this_processor ) return;
366
367 choose(sfp->si_value.sival_int) {
368 case PREEMPT_NORMAL : ;// Normal case, nothing to do here
369 case PREEMPT_TERMINATE: verify( __atomic_load_n( &kernelTLS.this_processor->do_terminate, __ATOMIC_SEQ_CST ) );
370 default:
371 abort( "internal error, signal value is %d", sfp->si_value.sival_int );
372 }
373
374 // Check if it is safe to preempt here
375 if( !preemption_ready() ) { return; }
376
377 __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) );
378
379 // Sync flag : prevent recursive calls to the signal handler
380 kernelTLS.preemption_state.in_progress = true;
381
382 // Clear sighandler mask before context switching.
383 #if GCC_VERSION > 50000
384 static_assert( sizeof( sigset_t ) == sizeof( cxt->uc_sigmask ), "Expected cxt->uc_sigmask to be of sigset_t" );
385 #endif
386 if ( pthread_sigmask( SIG_SETMASK, (sigset_t *)&(cxt->uc_sigmask), 0p ) == -1 ) {
387 abort( "internal error, sigprocmask" );
388 }
389
390 // TODO: this should go in finish action
391 // Clear the in progress flag
392 kernelTLS.preemption_state.in_progress = false;
393
394 // Preemption can occur here
395
396 BlockInternal( kernelTLS.this_thread ); // Do the actual CtxSwitch
397}
398
399// Main of the alarm thread
400// Waits on SIGALRM and send SIGUSR1 to whom ever needs it
401static void * alarm_loop( __attribute__((unused)) void * args ) {
402 // Block sigalrms to control when they arrive
403 sigset_t mask;
404 sigfillset(&mask);
405 if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
406 abort( "internal error, pthread_sigmask" );
407 }
408
409 sigemptyset( &mask );
410 sigaddset( &mask, SIGALRM );
411
412 // Main loop
413 while( true ) {
414 // Wait for a sigalrm
415 siginfo_t info;
416 int sig = sigwaitinfo( &mask, &info );
417
418 if( sig < 0 ) {
419 //Error!
420 int err = errno;
421 switch( err ) {
422 case EAGAIN :
423 case EINTR :
424 {__cfaabi_dbg_print_buffer_decl( " KERNEL: Spurious wakeup %d.\n", err );}
425 continue;
426 case EINVAL :
427 abort( "Timeout was invalid." );
428 default:
429 abort( "Unhandled error %d", err);
430 }
431 }
432
433 // If another signal arrived something went wrong
434 assertf(sig == SIGALRM, "Kernel Internal Error, sigwait: Unexpected signal %d (%d : %d)\n", sig, info.si_code, info.si_value.sival_int);
435
436 // __cfaabi_dbg_print_safe( "Kernel : Caught alarm from %d with %d\n", info.si_code, info.si_value.sival_int );
437 // Switch on the code (a.k.a. the sender) to
438 switch( info.si_code )
439 {
440 // Timers can apparently be marked as sent for the kernel
441 // In either case, tick preemption
442 case SI_TIMER:
443 case SI_KERNEL:
444 // __cfaabi_dbg_print_safe( "Kernel : Preemption thread tick\n" );
445 lock( event_kernel->lock __cfaabi_dbg_ctx2 );
446 tick_preemption();
447 unlock( event_kernel->lock );
448 break;
449 // Signal was not sent by the kernel but by an other thread
450 case SI_QUEUE:
451 // For now, other thread only signal the alarm thread to shut it down
452 // If this needs to change use info.si_value and handle the case here
453 goto EXIT;
454 }
455 }
456
457EXIT:
458 __cfaabi_dbg_print_safe( "Kernel : Preemption thread stopping\n" );
459 return 0p;
460}
461
462//=============================================================================================
463// Kernel Signal Debug
464//=============================================================================================
465
466void __cfaabi_check_preemption() {
467 bool ready = kernelTLS.preemption_state.enabled;
468 if(!ready) { abort("Preemption should be ready"); }
469
470 sigset_t oldset;
471 int ret;
472 ret = pthread_sigmask(0, 0p, &oldset);
473 if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
474
475 ret = sigismember(&oldset, SIGUSR1);
476 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
477 if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
478
479 ret = sigismember(&oldset, SIGALRM);
480 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
481 if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
482
483 ret = sigismember(&oldset, SIGTERM);
484 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
485 if(ret == 1) { abort("ERROR SIGTERM is disabled"); }
486}
487
488#ifdef __CFA_WITH_VERIFY__
489bool __cfaabi_dbg_in_kernel() {
490 return !kernelTLS.preemption_state.enabled;
491}
492#endif
493
494// Local Variables: //
495// mode: c //
496// tab-width: 4 //
497// End: //
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