source: src/libcfa/concurrency/monitor.c @ 90c4df0

aaron-thesisarm-ehcleanup-dtorsdeferred_resndemanglerenumforall-pointer-decayjacob/cs343-translationjenkins-sandboxnew-astnew-ast-unique-exprnew-envno_listpersistent-indexerpthread-emulationqualifiedEnumresolv-newwith_gc
Last change on this file since 90c4df0 was 90c4df0, checked in by Thierry Delisle <tdelisle@…>, 5 years ago

Implemented search for external scheduling

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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// monitor_desc.c --
8//
9// Author           : Thierry Delisle
10// Created On       : Thd Feb 23 12:27:26 2017
11// Last Modified By : Peter A. Buhr
12// Last Modified On : Mon Jul 31 14:59:05 2017
13// Update Count     : 3
14//
15
16#include "monitor"
17
18#include <stdlib>
19
20#include "libhdr.h"
21#include "kernel_private.h"
22
23//-----------------------------------------------------------------------------
24// Forward declarations
25static inline void set_owner( monitor_desc * this, thread_desc * owner );
26static inline thread_desc * next_thread( monitor_desc * this );
27static inline int is_accepted( thread_desc * owner, monitor_desc * this, monitor_desc ** group, int group_cnt, void (*func)() );
28
29static inline void lock_all( spinlock ** locks, unsigned short count );
30static inline void lock_all( monitor_desc ** source, spinlock ** /*out*/ locks, unsigned short count );
31static inline void unlock_all( spinlock ** locks, unsigned short count );
32static inline void unlock_all( monitor_desc ** locks, unsigned short count );
33
34static inline void save_recursion   ( monitor_desc ** ctx, unsigned int * /*out*/ recursions, unsigned short count );
35static inline void restore_recursion( monitor_desc ** ctx, unsigned int * /*in */ recursions, unsigned short count );
36
37static inline void init     ( int count, monitor_desc ** monitors, __condition_node_t * waiter, __condition_criterion_t * criteria );
38static inline void init_push( int count, monitor_desc ** monitors, __condition_node_t * waiter, __condition_criterion_t * criteria );
39
40static inline thread_desc * check_condition( __condition_criterion_t * );
41static inline void brand_condition( condition * );
42static inline unsigned short insert_unique( thread_desc ** thrds, unsigned short end, thread_desc * val );
43
44static inline thread_desc * search_entry_queue( __acceptable_t * acceptables, int acc_count, monitor_desc ** monitors, int count );
45
46//-----------------------------------------------------------------------------
47// Useful defines
48#define wait_ctx(thrd, user_info)                               /* Create the necessary information to use the signaller stack       */ \
49        __condition_node_t waiter = { thrd, count, user_info };   /* Create the node specific to this wait operation                   */ \
50        __condition_criterion_t criteria[count];                  /* Create the creteria this wait operation needs to wake up          */ \
51        init( count, monitors, &waiter, criteria );               /* Link everything together                                          */ \
52
53#define wait_ctx_primed(thrd, user_info)                        /* Create the necessary information to use the signaller stack       */ \
54        __condition_node_t waiter = { thrd, count, user_info };   /* Create the node specific to this wait operation                   */ \
55        __condition_criterion_t criteria[count];                  /* Create the creteria this wait operation needs to wake up          */ \
56        init_push( count, monitors, &waiter, criteria );          /* Link everything together and push it to the AS-Stack              */ \
57
58#define monitor_ctx( mons, cnt )              /* Define that create the necessary struct for internal/external scheduling operations */ \
59        monitor_desc ** monitors = mons;        /* Save the targeted monitors                                                          */ \
60        unsigned short count = cnt;             /* Save the count to a local variable                                                  */ \
61        unsigned int recursions[ count ];       /* Save the current recursion levels to restore them later                             */ \
62        spinlock *   locks     [ count ];       /* We need to pass-in an array of locks to BlockInternal                               */ \
63
64//-----------------------------------------------------------------------------
65// Enter/Leave routines
66
67
68extern "C" {
69        // Enter single monitor
70        static void __enter_monitor_desc( monitor_desc * this, monitor_desc ** group, int group_cnt, void (*func)() ) {
71                // Lock the monitor spinlock, lock_yield to reduce contention
72                lock_yield( &this->lock DEBUG_CTX2 );
73                thread_desc * thrd = this_thread;
74
75                LIB_DEBUG_PRINT_SAFE("Kernel : %10p Entering mon %p (%p)\n", thrd, this, this->owner);
76
77                this->accepted_index = -1;
78                if( !this->owner ) {
79                        // No one has the monitor, just take it
80                        set_owner( this, thrd );
81
82                        LIB_DEBUG_PRINT_SAFE("Kernel :  mon is free \n");
83                }
84                else if( this->owner == thrd) {
85                        // We already have the monitor, just not how many times we took it
86                        verify( this->recursion > 0 );
87                        this->recursion += 1;
88
89                        LIB_DEBUG_PRINT_SAFE("Kernel :  mon already owned \n");
90                }
91                else if( (this->accepted_index = is_accepted( thrd, this, group, group_cnt, func)) >= 0 ) {
92                        // Some one was waiting for us, enter
93                        set_owner( this, thrd );
94
95                        LIB_DEBUG_PRINT_SAFE("Kernel :  mon accepts \n");
96                }
97                else {
98                        LIB_DEBUG_PRINT_SAFE("Kernel :  blocking \n");
99
100                        // Some one else has the monitor, wait in line for it
101                        append( &this->entry_queue, thrd );
102                        BlockInternal( &this->lock );
103
104                        LIB_DEBUG_PRINT_SAFE("Kernel : %10p Entered  mon %p\n", thrd, this);
105
106                        // BlockInternal will unlock spinlock, no need to unlock ourselves
107                        return;
108                }
109
110                LIB_DEBUG_PRINT_SAFE("Kernel : %10p Entered  mon %p\n", thrd, this);
111
112                // Release the lock and leave
113                unlock( &this->lock );
114                return;
115        }
116
117        // Leave single monitor
118        void __leave_monitor_desc( monitor_desc * this ) {
119                // Lock the monitor spinlock, lock_yield to reduce contention
120                lock_yield( &this->lock DEBUG_CTX2 );
121
122                verifyf( this_thread == this->owner, "Expected owner to be %p, got %p (r: %i)", this_thread, this->owner, this->recursion );
123
124                // Leaving a recursion level, decrement the counter
125                this->recursion -= 1;
126
127                // If we haven't left the last level of recursion
128                // it means we don't need to do anything
129                if( this->recursion != 0) {
130                        unlock( &this->lock );
131                        return;
132                }
133
134                // Get the next thread, will be null on low contention monitor
135                thread_desc * new_owner = next_thread( this );
136
137                // We can now let other threads in safely
138                unlock( &this->lock );
139
140                //We need to wake-up the thread
141                WakeThread( new_owner );
142        }
143
144        // Leave the thread monitor
145        // last routine called by a thread.
146        // Should never return
147        void __leave_thread_monitor( thread_desc * thrd ) {
148                monitor_desc * this = &thrd->mon;
149
150                // Lock the monitor now
151                lock_yield( &this->lock DEBUG_CTX2 );
152
153                disable_interrupts();
154
155                thrd->cor.state = Halted;
156
157                verifyf( thrd == this->owner, "Expected owner to be %p, got %p (r: %i)", thrd, this->owner, this->recursion );
158
159                // Leaving a recursion level, decrement the counter
160                this->recursion -= 1;
161
162                // If we haven't left the last level of recursion
163                // it must mean there is an error
164                if( this->recursion != 0) { abortf("Thread internal monitor has unbalanced recursion"); }
165
166                // Fetch the next thread, can be null
167                thread_desc * new_owner = next_thread( this );
168
169                // Leave the thread, this will unlock the spinlock
170                // Use leave thread instead of BlockInternal which is
171                // specialized for this case and supports null new_owner
172                LeaveThread( &this->lock, new_owner );
173
174                // Control flow should never reach here!
175        }
176}
177
178// Enter multiple monitor
179// relies on the monitor array being sorted
180static inline void enter(monitor_desc ** monitors, int count, void (*func)() ) {
181        for(int i = 0; i < count; i++) {
182                __enter_monitor_desc( monitors[i], monitors, count, func );
183        }
184
185        int acc_idx = monitors[0]->accepted_index;
186        if( acc_idx >= 0 && monitors[0]->acceptables[ acc_idx ].run_preaccept ) {
187                assert( monitors[0]->pre_accept );
188                monitors[0]->pre_accept();
189        }
190}
191
192// Leave multiple monitor
193// relies on the monitor array being sorted
194static inline void leave(monitor_desc ** monitors, int count) {
195        for(int i = count - 1; i >= 0; i--) {
196                __leave_monitor_desc( monitors[i] );
197        }
198}
199
200// Ctor for monitor guard
201// Sorts monitors before entering
202void ?{}( monitor_guard_t * this, monitor_desc ** m, int count, void (*func)() ) {
203        // Store current array
204        this->m = m;
205        this->count = count;
206
207        // Sort monitors based on address -> TODO use a sort specialized for small numbers
208        qsort(this->m, count);
209
210        // Save previous thread context
211        this->prev_mntrs = this_thread->current_monitors;
212        this->prev_count = this_thread->current_monitor_count;
213        this->prev_func  = this_thread->current_monitor_func;
214
215        // Update thread context (needed for conditions)
216        this_thread->current_monitors      = m;
217        this_thread->current_monitor_count = count;
218        this_thread->current_monitor_func  = func;
219
220        // Enter the monitors in order
221        enter( this->m, this->count, func );
222}
223
224// Dtor for monitor guard
225void ^?{}( monitor_guard_t * this ) {
226        // Leave the monitors in order
227        leave( this->m, this->count );
228
229        // Restore thread context
230        this_thread->current_monitors      = this->prev_mntrs;
231        this_thread->current_monitor_count = this->prev_count;
232        this_thread->current_monitor_func  = this->prev_func;
233}
234
235//-----------------------------------------------------------------------------
236// Internal scheduling types
237
238void ?{}(__condition_node_t * this, thread_desc * waiting_thread, unsigned short count, uintptr_t user_info ) {
239        this->waiting_thread = waiting_thread;
240        this->count = count;
241        this->next = NULL;
242        this->user_info = user_info;
243}
244
245void ?{}(__condition_criterion_t * this ) {
246        this->ready  = false;
247        this->target = NULL;
248        this->owner  = NULL;
249        this->next   = NULL;
250}
251
252void ?{}(__condition_criterion_t * this, monitor_desc * target, __condition_node_t * owner ) {
253        this->ready  = false;
254        this->target = target;
255        this->owner  = owner;
256        this->next   = NULL;
257}
258
259//-----------------------------------------------------------------------------
260// Internal scheduling
261void wait( condition * this, uintptr_t user_info = 0 ) {
262        brand_condition( this );
263
264        // Check that everything is as expected
265        assertf( this->monitors != NULL, "Waiting with no monitors (%p)", this->monitors );
266        verifyf( this->monitor_count != 0, "Waiting with 0 monitors (%i)", this->monitor_count );
267        verifyf( this->monitor_count < 32u, "Excessive monitor count (%i)", this->monitor_count );
268
269        // Create storage for monitor context
270        monitor_ctx( this->monitors, this->monitor_count );
271
272        // Create the node specific to this wait operation
273        wait_ctx( this_thread, user_info );
274
275        // Append the current wait operation to the ones already queued on the condition
276        // We don't need locks for that since conditions must always be waited on inside monitor mutual exclusion
277        append( &this->blocked, &waiter );
278
279        // Lock all monitors (aggregates the lock them as well)
280        lock_all( monitors, locks, count );
281
282        // DON'T unlock, ask the kernel to do it
283
284        // Save monitor state
285        save_recursion( monitors, recursions, count );
286
287        // Find the next thread(s) to run
288        unsigned short thread_count = 0;
289        thread_desc * threads[ count ];
290        for(int i = 0; i < count; i++) {
291                threads[i] = 0;
292        }
293
294        // Remove any duplicate threads
295        for( int i = 0; i < count; i++) {
296                thread_desc * new_owner = next_thread( monitors[i] );
297                thread_count = insert_unique( threads, thread_count, new_owner );
298        }
299
300        // Everything is ready to go to sleep
301        BlockInternal( locks, count, threads, thread_count );
302
303
304        // WE WOKE UP
305
306
307        // We are back, restore the owners and recursions
308        lock_all( locks, count );
309        restore_recursion( monitors, recursions, count );
310        unlock_all( locks, count );
311}
312
313bool signal( condition * this ) {
314        if( is_empty( this ) ) { return false; }
315
316        //Check that everything is as expected
317        verify( this->monitors );
318        verify( this->monitor_count != 0 );
319
320        //Some more checking in debug
321        LIB_DEBUG_DO(
322                thread_desc * this_thrd = this_thread;
323                if ( this->monitor_count != this_thrd->current_monitor_count ) {
324                        abortf( "Signal on condition %p made with different number of monitor(s), expected %i got %i", this, this->monitor_count, this_thrd->current_monitor_count );
325                }
326
327                for(int i = 0; i < this->monitor_count; i++) {
328                        if ( this->monitors[i] != this_thrd->current_monitors[i] ) {
329                                abortf( "Signal on condition %p made with different monitor, expected %p got %i", this, this->monitors[i], this_thrd->current_monitors[i] );
330                        }
331                }
332        );
333
334        unsigned short count = this->monitor_count;
335
336        // Lock all monitors
337        lock_all( this->monitors, NULL, count );
338
339        //Pop the head of the waiting queue
340        __condition_node_t * node = pop_head( &this->blocked );
341
342        //Add the thread to the proper AS stack
343        for(int i = 0; i < count; i++) {
344                __condition_criterion_t * crit = &node->criteria[i];
345                assert( !crit->ready );
346                push( &crit->target->signal_stack, crit );
347        }
348
349        //Release
350        unlock_all( this->monitors, count );
351
352        return true;
353}
354
355bool signal_block( condition * this ) {
356        if( !this->blocked.head ) { return false; }
357
358        //Check that everything is as expected
359        verifyf( this->monitors != NULL, "Waiting with no monitors (%p)", this->monitors );
360        verifyf( this->monitor_count != 0, "Waiting with 0 monitors (%i)", this->monitor_count );
361
362        // Create storage for monitor context
363        monitor_ctx( this->monitors, this->monitor_count );
364
365        // Lock all monitors (aggregates the locks them as well)
366        lock_all( monitors, locks, count );
367
368        // Create the node specific to this wait operation
369        wait_ctx_primed( this_thread, 0 )
370
371        //save contexts
372        save_recursion( monitors, recursions, count );
373
374        //Find the thread to run
375        thread_desc * signallee = pop_head( &this->blocked )->waiting_thread;
376        for(int i = 0; i < count; i++) {
377                set_owner( monitors[i], signallee );
378        }
379
380        //Everything is ready to go to sleep
381        BlockInternal( locks, count, &signallee, 1 );
382
383
384        // WE WOKE UP
385
386
387        //We are back, restore the owners and recursions
388        lock_all( locks, count );
389        restore_recursion( monitors, recursions, count );
390        unlock_all( locks, count );
391
392        return true;
393}
394
395// Access the user_info of the thread waiting at the front of the queue
396uintptr_t front( condition * this ) {
397        verifyf( !is_empty(this),
398                "Attempt to access user data on an empty condition.\n"
399                "Possible cause is not checking if the condition is empty before reading stored data."
400        );
401        return this->blocked.head->user_info;
402}
403
404//-----------------------------------------------------------------------------
405// Internal scheduling
406int __accept_internal( unsigned short acc_count, __acceptable_t * acceptables ) {
407        thread_desc * thrd = this_thread;
408
409        // Create storage for monitor context
410        monitor_ctx( acceptables->monitors, acceptables->count );
411
412        // Lock all monitors (aggregates the lock them as well)
413        lock_all( monitors, locks, count );
414
415        // Create the node specific to this wait operation
416        wait_ctx_primed( thrd, 0 );
417
418        // Check if the entry queue
419        thread_desc * next = search_entry_queue( acceptables, acc_count, monitors, count );
420
421        LIB_DEBUG_PRINT_SAFE("Owner(s) :");
422        for(int i = 0; i < count; i++) {
423                LIB_DEBUG_PRINT_SAFE(" %p", monitors[i]->owner );
424        }
425        LIB_DEBUG_PRINT_SAFE("\n");
426
427        LIB_DEBUG_PRINT_SAFE("Passing mon to %p\n", next);
428
429        if( !next ) {
430                // Update acceptables on the current monitors
431                for(int i = 0; i < count; i++) {
432                        monitors[i]->acceptables = acceptables;
433                        monitors[i]->acceptable_count = acc_count;
434                }
435        }
436        else {
437                for(int i = 0; i < count; i++) {
438                        set_owner( monitors[i], next );
439                }
440        }
441
442
443        save_recursion( monitors, recursions, count );
444
445
446        // Everything is ready to go to sleep
447        BlockInternal( locks, count, &next, next ? 1 : 0 );
448
449
450        //WE WOKE UP
451
452
453        //We are back, restore the owners and recursions
454        lock_all( locks, count );
455        restore_recursion( monitors, recursions, count );
456        int acc_idx = monitors[0]->accepted_index;
457        unlock_all( locks, count );
458
459        return acc_idx;
460}
461
462//-----------------------------------------------------------------------------
463// Utilities
464
465static inline void set_owner( monitor_desc * this, thread_desc * owner ) {
466        //Pass the monitor appropriately
467        this->owner = owner;
468
469        //We are passing the monitor to someone else, which means recursion level is not 0
470        this->recursion = owner ? 1 : 0;
471}
472
473static inline thread_desc * next_thread( monitor_desc * this ) {
474        //Check the signaller stack
475        __condition_criterion_t * urgent = pop( &this->signal_stack );
476        if( urgent ) {
477                //The signaller stack is not empty,
478                //regardless of if we are ready to baton pass,
479                //we need to set the monitor as in use
480                set_owner( this,  urgent->owner->waiting_thread );
481
482                return check_condition( urgent );
483        }
484
485        // No signaller thread
486        // Get the next thread in the entry_queue
487        thread_desc * new_owner = pop_head( &this->entry_queue );
488        set_owner( this, new_owner );
489
490        return new_owner;
491}
492
493static inline int is_accepted( thread_desc * owner, monitor_desc * this, monitor_desc ** group, int group_cnt, void (*func)() ) {
494        __acceptable_t* accs = this->acceptables; // Optim
495        int acc_cnt = this->acceptable_count;
496
497        // Check if there are any acceptable functions
498        if( !accs ) return -1;
499
500        // If this isn't the first monitor to test this, there is no reason to repeat the test.
501        if( this != group[0] ) return group[0]->accepted_index;
502
503        // For all acceptable functions check if this is the current function.
504        OUT_LOOP:
505        for( int i = 0; i < acc_cnt; i++ ) {
506                __acceptable_t * acc = &accs[i];
507
508                // if function matches, check the monitors
509                if( acc->func == func ) {
510
511                        // If the group count is different then it can't be a match
512                        if( acc->count != group_cnt ) return -1;
513
514                        // Check that all the monitors match
515                        for( int j = 0; j < group_cnt; j++ ) {
516                                // If not a match, check next function
517                                if( acc->monitors[j] != group[j] ) continue OUT_LOOP;
518                        }
519
520                        // It's a complete match, accept the call
521                        return i;
522                }
523        }
524
525        // No function matched
526        return -1;
527}
528
529static inline void init( int count, monitor_desc ** monitors, __condition_node_t * waiter, __condition_criterion_t * criteria ) {
530        for(int i = 0; i < count; i++) {
531                (&criteria[i]){ monitors[i], waiter };
532        }
533
534        waiter->criteria = criteria;
535}
536
537static inline void init_push( int count, monitor_desc ** monitors, __condition_node_t * waiter, __condition_criterion_t * criteria ) {
538        for(int i = 0; i < count; i++) {
539                (&criteria[i]){ monitors[i], waiter };
540                push( &criteria[i].target->signal_stack, &criteria[i] );
541        }
542
543        waiter->criteria = criteria;
544}
545
546static inline void lock_all( spinlock ** locks, unsigned short count ) {
547        for( int i = 0; i < count; i++ ) {
548                lock_yield( locks[i] DEBUG_CTX2 );
549        }
550}
551
552static inline void lock_all( monitor_desc ** source, spinlock ** /*out*/ locks, unsigned short count ) {
553        for( int i = 0; i < count; i++ ) {
554                spinlock * l = &source[i]->lock;
555                lock_yield( l DEBUG_CTX2 );
556                if(locks) locks[i] = l;
557        }
558}
559
560static inline void unlock_all( spinlock ** locks, unsigned short count ) {
561        for( int i = 0; i < count; i++ ) {
562                unlock( locks[i] );
563        }
564}
565
566static inline void unlock_all( monitor_desc ** locks, unsigned short count ) {
567        for( int i = 0; i < count; i++ ) {
568                unlock( &locks[i]->lock );
569        }
570}
571
572
573static inline void save_recursion   ( monitor_desc ** ctx, unsigned int * /*out*/ recursions, unsigned short count ) {
574        for( int i = 0; i < count; i++ ) {
575                recursions[i] = ctx[i]->recursion;
576        }
577}
578
579static inline void restore_recursion( monitor_desc ** ctx, unsigned int * /*in */ recursions, unsigned short count ) {
580        for( int i = 0; i < count; i++ ) {
581                ctx[i]->recursion = recursions[i];
582        }
583}
584
585// Function has 2 different behavior
586// 1 - Marks a monitors as being ready to run
587// 2 - Checks if all the monitors are ready to run
588//     if so return the thread to run
589static inline thread_desc * check_condition( __condition_criterion_t * target ) {
590        __condition_node_t * node = target->owner;
591        unsigned short count = node->count;
592        __condition_criterion_t * criteria = node->criteria;
593
594        bool ready2run = true;
595
596        for(    int i = 0; i < count; i++ ) {
597
598                // LIB_DEBUG_PRINT_SAFE( "Checking %p for %p\n", &criteria[i], target );
599                if( &criteria[i] == target ) {
600                        criteria[i].ready = true;
601                        // LIB_DEBUG_PRINT_SAFE( "True\n" );
602                }
603
604                ready2run = criteria[i].ready && ready2run;
605        }
606
607        // LIB_DEBUG_PRINT_SAFE( "Runing %i\n", ready2run );
608        return ready2run ? node->waiting_thread : NULL;
609}
610
611static inline void brand_condition( condition * this ) {
612        thread_desc * thrd = this_thread;
613        if( !this->monitors ) {
614                // LIB_DEBUG_PRINT_SAFE("Branding\n");
615                assertf( thrd->current_monitors != NULL, "No current monitor to brand condition %p", thrd->current_monitors );
616                this->monitor_count = thrd->current_monitor_count;
617
618                this->monitors = malloc( this->monitor_count * sizeof( *this->monitors ) );
619                for( int i = 0; i < this->monitor_count; i++ ) {
620                        this->monitors[i] = thrd->current_monitors[i];
621                }
622        }
623}
624
625static inline unsigned short insert_unique( thread_desc ** thrds, unsigned short end, thread_desc * val ) {
626        if( !val ) return end;
627
628        for(int i = 0; i <= end; i++) {
629                if( thrds[i] == val ) return end;
630        }
631
632        thrds[end] = val;
633        return end + 1;
634}
635
636static inline bool match( __acceptable_t * acc, thread_desc * thrd ) {
637        verify( thrd );
638        verify( acc );
639        if( acc->func != thrd->current_monitor_func ) return false;
640
641        return true;
642}
643
644static inline thread_desc * search_entry_queue( __acceptable_t * acceptables, int acc_count, monitor_desc ** monitors, int count ) {
645
646        __thread_queue_t * entry_queue = &monitors[0]->entry_queue;
647
648        // For each thread in the entry-queue
649        for(    thread_desc ** thrd_it = &entry_queue->head;
650                *thrd_it;
651                thrd_it = &(*thrd_it)->next)
652        {
653                // For each acceptable check if it matches
654                __acceptable_t * acc_end = acceptables + acc_count;
655                for( __acceptable_t * acc_it = acceptables; acc_it != acc_end; acc_it++ ) {
656                        // Check if we have a match
657                        if( match( acc_it, *thrd_it ) ) {
658
659                                // If we have a match return it
660                                // after removeing it from the entry queue
661                                return remove( entry_queue, thrd_it );
662                        }
663                }
664        }
665
666        return NULL;
667}
668
669void ?{}( __condition_blocked_queue_t * this ) {
670        this->head = NULL;
671        this->tail = &this->head;
672}
673
674void append( __condition_blocked_queue_t * this, __condition_node_t * c ) {
675        verify(this->tail != NULL);
676        *this->tail = c;
677        this->tail = &c->next;
678}
679
680__condition_node_t * pop_head( __condition_blocked_queue_t * this ) {
681        __condition_node_t * head = this->head;
682        if( head ) {
683                this->head = head->next;
684                if( !head->next ) {
685                        this->tail = &this->head;
686                }
687                head->next = NULL;
688        }
689        return head;
690}
691
692// Local Variables: //
693// mode: c //
694// tab-width: 4 //
695// End: //
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