source: src/libcfa/concurrency/monitor.c @ 6b224a5

aaron-thesisarm-ehcleanup-dtorsdeferred_resndemanglerjacob/cs343-translationjenkins-sandboxnew-astnew-ast-unique-exprnew-envno_listpersistent-indexerresolv-newwith_gc
Last change on this file since 6b224a5 was 6b224a5, checked in by Thierry Delisle <tdelisle@…>, 4 years ago

Merge branch 'master' of plg.uwaterloo.ca:software/cfa/cfa-cc

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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
186// Leave multiple monitor
187// relies on the monitor array being sorted
188static inline void leave(monitor_desc ** monitors, int count) {
189        for(int i = count - 1; i >= 0; i--) {
190                __leave_monitor_desc( monitors[i] );
191        }
192}
193
194// Ctor for monitor guard
195// Sorts monitors before entering
196void ?{}( monitor_guard_t & this, monitor_desc ** m, int count, void (*func)() ) {
197        // Store current array
198        this.m = m;
199        this.count = count;
200
201        // Sort monitors based on address -> TODO use a sort specialized for small numbers
202        qsort(this.m, count);
203
204        // Save previous thread context
205        this.prev_mntrs = this_thread->current_monitors;
206        this.prev_count = this_thread->current_monitor_count;
207        this.prev_func  = this_thread->current_monitor_func;
208
209        // Update thread context (needed for conditions)
210        this_thread->current_monitors      = m;
211        this_thread->current_monitor_count = count;
212        this_thread->current_monitor_func  = func;
213
214        // Enter the monitors in order
215        enter( this.m, this.count, func );
216}
217
218
219// Dtor for monitor guard
220void ^?{}( monitor_guard_t & this ) {
221        // Leave the monitors in order
222        leave( this.m, this.count );
223
224        // Restore thread context
225        this_thread->current_monitors      = this.prev_mntrs;
226        this_thread->current_monitor_count = this.prev_count;
227        this_thread->current_monitor_func  = this.prev_func;
228}
229
230//-----------------------------------------------------------------------------
231// Internal scheduling types
232void ?{}(__condition_node_t & this, thread_desc * waiting_thread, unsigned short count, uintptr_t user_info ) {
233        this.waiting_thread = waiting_thread;
234        this.count = count;
235        this.next = NULL;
236        this.user_info = user_info;
237}
238
239void ?{}(__condition_criterion_t & this ) {
240        this.ready  = false;
241        this.target = NULL;
242        this.owner  = NULL;
243        this.next   = NULL;
244}
245
246void ?{}(__condition_criterion_t & this, monitor_desc * target, __condition_node_t * owner ) {
247        this.ready  = false;
248        this.target = target;
249        this.owner  = owner;
250        this.next   = NULL;
251}
252
253//-----------------------------------------------------------------------------
254// Internal scheduling
255void wait( condition * this, uintptr_t user_info = 0 ) {
256        brand_condition( this );
257
258        // Check that everything is as expected
259        assertf( this->monitors != NULL, "Waiting with no monitors (%p)", this->monitors );
260        verifyf( this->monitor_count != 0, "Waiting with 0 monitors (%i)", this->monitor_count );
261        verifyf( this->monitor_count < 32u, "Excessive monitor count (%i)", this->monitor_count );
262
263        // Create storage for monitor context
264        monitor_ctx( this->monitors, this->monitor_count );
265
266        // Create the node specific to this wait operation
267        wait_ctx( this_thread, user_info );
268
269        // Append the current wait operation to the ones already queued on the condition
270        // We don't need locks for that since conditions must always be waited on inside monitor mutual exclusion
271        append( &this->blocked, &waiter );
272
273        // Lock all monitors (aggregates the lock them as well)
274        lock_all( monitors, locks, count );
275
276        // DON'T unlock, ask the kernel to do it
277
278        // Save monitor state
279        save_recursion( monitors, recursions, count );
280
281        // Find the next thread(s) to run
282        unsigned short thread_count = 0;
283        thread_desc * threads[ count ];
284        for(int i = 0; i < count; i++) {
285                threads[i] = 0;
286        }
287
288        // Remove any duplicate threads
289        for( int i = 0; i < count; i++) {
290                thread_desc * new_owner = next_thread( monitors[i] );
291                thread_count = insert_unique( threads, thread_count, new_owner );
292        }
293
294        // Everything is ready to go to sleep
295        BlockInternal( locks, count, threads, thread_count );
296
297
298        // WE WOKE UP
299
300
301        // We are back, restore the owners and recursions
302        lock_all( locks, count );
303        restore_recursion( monitors, recursions, count );
304        unlock_all( locks, count );
305}
306
307bool signal( condition * this ) {
308        if( is_empty( this ) ) { return false; }
309
310        //Check that everything is as expected
311        verify( this->monitors );
312        verify( this->monitor_count != 0 );
313
314        //Some more checking in debug
315        LIB_DEBUG_DO(
316                thread_desc * this_thrd = this_thread;
317                if ( this->monitor_count != this_thrd->current_monitor_count ) {
318                        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 );
319                }
320
321                for(int i = 0; i < this->monitor_count; i++) {
322                        if ( this->monitors[i] != this_thrd->current_monitors[i] ) {
323                                abortf( "Signal on condition %p made with different monitor, expected %p got %i", this, this->monitors[i], this_thrd->current_monitors[i] );
324                        }
325                }
326        );
327
328        unsigned short count = this->monitor_count;
329
330        // Lock all monitors
331        lock_all( this->monitors, NULL, count );
332
333        //Pop the head of the waiting queue
334        __condition_node_t * node = pop_head( &this->blocked );
335
336        //Add the thread to the proper AS stack
337        for(int i = 0; i < count; i++) {
338                __condition_criterion_t * crit = &node->criteria[i];
339                assert( !crit->ready );
340                push( &crit->target->signal_stack, crit );
341        }
342
343        //Release
344        unlock_all( this->monitors, count );
345
346        return true;
347}
348
349bool signal_block( condition * this ) {
350        if( !this->blocked.head ) { return false; }
351
352        //Check that everything is as expected
353        verifyf( this->monitors != NULL, "Waiting with no monitors (%p)", this->monitors );
354        verifyf( this->monitor_count != 0, "Waiting with 0 monitors (%i)", this->monitor_count );
355
356        // Create storage for monitor context
357        monitor_ctx( this->monitors, this->monitor_count );
358
359        // Lock all monitors (aggregates the locks them as well)
360        lock_all( monitors, locks, count );
361
362        // Create the node specific to this wait operation
363        wait_ctx_primed( this_thread, 0 )
364
365        //save contexts
366        save_recursion( monitors, recursions, count );
367
368        //Find the thread to run
369        thread_desc * signallee = pop_head( &this->blocked )->waiting_thread;
370        for(int i = 0; i < count; i++) {
371                set_owner( monitors[i], signallee );
372        }
373
374        //Everything is ready to go to sleep
375        BlockInternal( locks, count, &signallee, 1 );
376
377
378        // WE WOKE UP
379
380
381        //We are back, restore the owners and recursions
382        lock_all( locks, count );
383        restore_recursion( monitors, recursions, count );
384        unlock_all( locks, count );
385
386        return true;
387}
388
389// Access the user_info of the thread waiting at the front of the queue
390uintptr_t front( condition * this ) {
391        verifyf( !is_empty(this),
392                "Attempt to access user data on an empty condition.\n"
393                "Possible cause is not checking if the condition is empty before reading stored data."
394        );
395        return this->blocked.head->user_info;
396}
397
398//-----------------------------------------------------------------------------
399// Internal scheduling
400int __accept_internal( unsigned short acc_count, __acceptable_t * acceptables ) {
401        thread_desc * thrd = this_thread;
402
403        // Create storage for monitor context
404        monitor_ctx( acceptables->monitors, acceptables->count );
405
406        // Lock all monitors (aggregates the lock them as well)
407        lock_all( monitors, locks, count );
408
409        // Create the node specific to this wait operation
410        wait_ctx_primed( thrd, 0 );
411
412        // Check if the entry queue
413        thread_desc * next = search_entry_queue( acceptables, acc_count, monitors, count );
414
415        LIB_DEBUG_PRINT_SAFE("Owner(s) :");
416        for(int i = 0; i < count; i++) {
417                LIB_DEBUG_PRINT_SAFE(" %p", monitors[i]->owner );
418        }
419        LIB_DEBUG_PRINT_SAFE("\n");
420
421        LIB_DEBUG_PRINT_SAFE("Passing mon to %p\n", next);
422
423        if( !next ) {
424                // Update acceptables on the current monitors
425                for(int i = 0; i < count; i++) {
426                        monitors[i]->acceptables = acceptables;
427                        monitors[i]->acceptable_count = acc_count;
428                }
429        }
430        else {
431                for(int i = 0; i < count; i++) {
432                        set_owner( monitors[i], next );
433                }
434        }
435
436
437        save_recursion( monitors, recursions, count );
438
439
440        // Everything is ready to go to sleep
441        BlockInternal( locks, count, &next, next ? 1 : 0 );
442
443
444        //WE WOKE UP
445
446
447        //We are back, restore the owners and recursions
448        lock_all( locks, count );
449        restore_recursion( monitors, recursions, count );
450        int acc_idx = monitors[0]->accepted_index;
451        unlock_all( locks, count );
452
453        return acc_idx;
454}
455
456//-----------------------------------------------------------------------------
457// Utilities
458
459static inline void set_owner( monitor_desc * this, thread_desc * owner ) {
460        //Pass the monitor appropriately
461        this->owner = owner;
462
463        //We are passing the monitor to someone else, which means recursion level is not 0
464        this->recursion = owner ? 1 : 0;
465}
466
467static inline thread_desc * next_thread( monitor_desc * this ) {
468        //Check the signaller stack
469        __condition_criterion_t * urgent = pop( &this->signal_stack );
470        if( urgent ) {
471                //The signaller stack is not empty,
472                //regardless of if we are ready to baton pass,
473                //we need to set the monitor as in use
474                set_owner( this,  urgent->owner->waiting_thread );
475
476                return check_condition( urgent );
477        }
478
479        // No signaller thread
480        // Get the next thread in the entry_queue
481        thread_desc * new_owner = pop_head( &this->entry_queue );
482        set_owner( this, new_owner );
483
484        return new_owner;
485}
486
487static inline int is_accepted( thread_desc * owner, monitor_desc * this, monitor_desc ** group, int group_cnt, void (*func)() ) {
488        __acceptable_t* accs = this->acceptables; // Optim
489        int acc_cnt = this->acceptable_count;
490
491        // Check if there are any acceptable functions
492        if( !accs ) return -1;
493
494        // If this isn't the first monitor to test this, there is no reason to repeat the test.
495        if( this != group[0] ) return group[0]->accepted_index;
496
497        // For all acceptable functions check if this is the current function.
498        OUT_LOOP:
499        for( int i = 0; i < acc_cnt; i++ ) {
500                __acceptable_t * acc = &accs[i];
501
502                // if function matches, check the monitors
503                if( acc->func == func ) {
504
505                        // If the group count is different then it can't be a match
506                        if( acc->count != group_cnt ) return -1;
507
508                        // Check that all the monitors match
509                        for( int j = 0; j < group_cnt; j++ ) {
510                                // If not a match, check next function
511                                if( acc->monitors[j] != group[j] ) continue OUT_LOOP;
512                        }
513
514                        // It's a complete match, accept the call
515                        return i;
516                }
517        }
518
519        // No function matched
520        return -1;
521}
522
523static inline void init( int count, monitor_desc ** monitors, __condition_node_t * waiter, __condition_criterion_t * criteria ) {
524        for(int i = 0; i < count; i++) {
525                (criteria[i]){ monitors[i], waiter };
526        }
527
528        waiter->criteria = criteria;
529}
530
531static inline void init_push( int count, monitor_desc ** monitors, __condition_node_t * waiter, __condition_criterion_t * criteria ) {
532        for(int i = 0; i < count; i++) {
533                (criteria[i]){ monitors[i], waiter };
534                push( &criteria[i].target->signal_stack, &criteria[i] );
535        }
536
537        waiter->criteria = criteria;
538}
539
540static inline void lock_all( spinlock ** locks, unsigned short count ) {
541        for( int i = 0; i < count; i++ ) {
542                lock_yield( locks[i] DEBUG_CTX2 );
543        }
544}
545
546static inline void lock_all( monitor_desc ** source, spinlock ** /*out*/ locks, unsigned short count ) {
547        for( int i = 0; i < count; i++ ) {
548                spinlock * l = &source[i]->lock;
549                lock_yield( l DEBUG_CTX2 );
550                if(locks) locks[i] = l;
551        }
552}
553
554static inline void unlock_all( spinlock ** locks, unsigned short count ) {
555        for( int i = 0; i < count; i++ ) {
556                unlock( locks[i] );
557        }
558}
559
560static inline void unlock_all( monitor_desc ** locks, unsigned short count ) {
561        for( int i = 0; i < count; i++ ) {
562                unlock( &locks[i]->lock );
563        }
564}
565
566
567static inline void save_recursion   ( monitor_desc ** ctx, unsigned int * /*out*/ recursions, unsigned short count ) {
568        for( int i = 0; i < count; i++ ) {
569                recursions[i] = ctx[i]->recursion;
570        }
571}
572
573static inline void restore_recursion( monitor_desc ** ctx, unsigned int * /*in */ recursions, unsigned short count ) {
574        for( int i = 0; i < count; i++ ) {
575                ctx[i]->recursion = recursions[i];
576        }
577}
578
579// Function has 2 different behavior
580// 1 - Marks a monitors as being ready to run
581// 2 - Checks if all the monitors are ready to run
582//     if so return the thread to run
583static inline thread_desc * check_condition( __condition_criterion_t * target ) {
584        __condition_node_t * node = target->owner;
585        unsigned short count = node->count;
586        __condition_criterion_t * criteria = node->criteria;
587
588        bool ready2run = true;
589
590        for(    int i = 0; i < count; i++ ) {
591
592                // LIB_DEBUG_PRINT_SAFE( "Checking %p for %p\n", &criteria[i], target );
593                if( &criteria[i] == target ) {
594                        criteria[i].ready = true;
595                        // LIB_DEBUG_PRINT_SAFE( "True\n" );
596                }
597
598                ready2run = criteria[i].ready && ready2run;
599        }
600
601        // LIB_DEBUG_PRINT_SAFE( "Runing %i\n", ready2run );
602        return ready2run ? node->waiting_thread : NULL;
603}
604
605static inline void brand_condition( condition * this ) {
606        thread_desc * thrd = this_thread;
607        if( !this->monitors ) {
608                // LIB_DEBUG_PRINT_SAFE("Branding\n");
609                assertf( thrd->current_monitors != NULL, "No current monitor to brand condition %p", thrd->current_monitors );
610                this->monitor_count = thrd->current_monitor_count;
611
612                this->monitors = malloc( this->monitor_count * sizeof( *this->monitors ) );
613                for( int i = 0; i < this->monitor_count; i++ ) {
614                        this->monitors[i] = thrd->current_monitors[i];
615                }
616        }
617}
618
619static inline unsigned short insert_unique( thread_desc ** thrds, unsigned short end, thread_desc * val ) {
620        if( !val ) return end;
621
622        for(int i = 0; i <= end; i++) {
623                if( thrds[i] == val ) return end;
624        }
625
626        thrds[end] = val;
627        return end + 1;
628}
629
630
631static inline bool match( __acceptable_t * acc, thread_desc * thrd ) {
632        verify( thrd );
633        verify( acc );
634        if( acc->func != thrd->current_monitor_func ) return false;
635
636        return true;
637}
638
639static inline thread_desc * search_entry_queue( __acceptable_t * acceptables, int acc_count, monitor_desc ** monitors, int count ) {
640
641        __thread_queue_t * entry_queue = &monitors[0]->entry_queue;
642
643        // For each thread in the entry-queue
644        for(    thread_desc ** thrd_it = &entry_queue->head;
645                *thrd_it;
646                thrd_it = &(*thrd_it)->next)
647        {
648                // For each acceptable check if it matches
649                __acceptable_t * acc_end = acceptables + acc_count;
650                for( __acceptable_t * acc_it = acceptables; acc_it != acc_end; acc_it++ ) {
651                        // Check if we have a match
652                        if( match( acc_it, *thrd_it ) ) {
653
654                                // If we have a match return it
655                                // after removeing it from the entry queue
656                                return remove( entry_queue, thrd_it );
657                        }
658                }
659        }
660
661        return NULL;
662}
663void ?{}( __condition_blocked_queue_t & this ) {
664        this.head = NULL;
665        this.tail = &this.head;
666}
667
668void append( __condition_blocked_queue_t * this, __condition_node_t * c ) {
669        verify(this->tail != NULL);
670        *this->tail = c;
671        this->tail = &c->next;
672}
673
674__condition_node_t * pop_head( __condition_blocked_queue_t * this ) {
675        __condition_node_t * head = this->head;
676        if( head ) {
677                this->head = head->next;
678                if( !head->next ) {
679                        this->tail = &this->head;
680                }
681                head->next = NULL;
682        }
683        return head;
684}
685
686// Local Variables: //
687// mode: c //
688// tab-width: 4 //
689// End: //
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