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io.cfa @ 4c4d854

ADTarm-ehast-experimentalenumforall-pointer-decayjacob/cs343-translationnew-ast-unique-exprpthread-emulationqualifiedEnum

Last change on this file since 4c4d854 was 4c4d854, checked in by Thierry Delisle <tdelisle@…>, 4 years ago
Fixed broken initialization and add verify.
Property mode set to `100644`
File size: 19.8 KB

Line
1	//
2	// Cforall Version 1.0.0 Copyright (C) 2020 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	// io.cfa --
8	//
9	// Author : Thierry Delisle
10	// Created On : Thu Apr 23 17:31:00 2020
11	// Last Modified By :
12	// Last Modified On :
13	// Update Count :
14	//
15
16	#define __cforall_thread__
17
18	#if defined(__CFA_DEBUG__)
19	// #define __CFA_DEBUG_PRINT_IO__
20	// #define __CFA_DEBUG_PRINT_IO_CORE__
21	#endif
22
23
24	#if defined(CFA_HAVE_LINUX_IO_URING_H)
25	#define _GNU_SOURCE /* See feature_test_macros(7) */
26	#include <errno.h>
27	#include <signal.h>
28	#include <stdint.h>
29	#include <string.h>
30	#include <unistd.h>
31
32	extern "C" {
33	#include <sys/syscall.h>
34
35	#include <linux/io_uring.h>
36	}
37
38	#include "stats.hfa"
39	#include "kernel.hfa"
40	#include "kernel/fwd.hfa"
41	#include "io/types.hfa"
42
43	__attribute__((unused)) static const char * opcodes[] = {
44	"OP_NOP",
45	"OP_READV",
46	"OP_WRITEV",
47	"OP_FSYNC",
48	"OP_READ_FIXED",
49	"OP_WRITE_FIXED",
50	"OP_POLL_ADD",
51	"OP_POLL_REMOVE",
52	"OP_SYNC_FILE_RANGE",
53	"OP_SENDMSG",
54	"OP_RECVMSG",
55	"OP_TIMEOUT",
56	"OP_TIMEOUT_REMOVE",
57	"OP_ACCEPT",
58	"OP_ASYNC_CANCEL",
59	"OP_LINK_TIMEOUT",
60	"OP_CONNECT",
61	"OP_FALLOCATE",
62	"OP_OPENAT",
63	"OP_CLOSE",
64	"OP_FILES_UPDATE",
65	"OP_STATX",
66	"OP_READ",
67	"OP_WRITE",
68	"OP_FADVISE",
69	"OP_MADVISE",
70	"OP_SEND",
71	"OP_RECV",
72	"OP_OPENAT2",
73	"OP_EPOLL_CTL",
74	"OP_SPLICE",
75	"OP_PROVIDE_BUFFERS",
76	"OP_REMOVE_BUFFERS",
77	"OP_TEE",
78	"INVALID_OP"
79	};
80
81	//=============================================================================================
82	// I/O Syscall
83	//=============================================================================================
84	static int __io_uring_enter( struct $io_context & ctx, unsigned to_submit, bool get ) {
85	__STATS__( false, io.calls.count++; )
86	bool need_sys_to_submit = false;
87	bool need_sys_to_complete = false;
88	unsigned flags = 0;
89
90	TO_SUBMIT:
91	if( to_submit > 0 ) {
92	if( !(ctx.ring_flags & IORING_SETUP_SQPOLL) ) {
93	need_sys_to_submit = true;
94	break TO_SUBMIT;
95	}
96	if( (*ctx.sq.flags) & IORING_SQ_NEED_WAKEUP ) {
97	need_sys_to_submit = true;
98	flags \|= IORING_ENTER_SQ_WAKEUP;
99	}
100	}
101
102	if( get && !(ctx.ring_flags & IORING_SETUP_SQPOLL) ) {
103	flags \|= IORING_ENTER_GETEVENTS;
104	if( (ctx.ring_flags & IORING_SETUP_IOPOLL) ) {
105	need_sys_to_complete = true;
106	}
107	}
108
109	int ret = 0;
110	if( need_sys_to_submit \|\| need_sys_to_complete ) {
111	__cfadbg_print_safe(io_core, "Kernel I/O : IO_URING enter %d %u %u\n", ctx.fd, to_submit, flags);
112	__STATS__( false, io.calls.blocks++; )
113	ret = syscall( __NR_io_uring_enter, ctx.fd, to_submit, 0, flags, (sigset_t *)0p, _NSIG / 8);
114	__cfadbg_print_safe(io_core, "Kernel I/O : IO_URING %d returned %d\n", ctx.fd, ret);
115	}
116
117	// Memory barrier
118	__atomic_thread_fence( __ATOMIC_SEQ_CST );
119	return ret;
120	}
121
122	//=============================================================================================
123	// I/O Polling
124	//=============================================================================================
125	static inline unsigned __flush( struct $io_context & );
126	static inline __u32 __release_sqes( struct $io_context & );
127
128	static bool __drain_io( struct $io_context & ctx ) {
129	unsigned to_submit = __flush( ctx );
130	int ret = __io_uring_enter( ctx, to_submit, true );
131	if( ret < 0 ) {
132	switch((int)errno) {
133	case EAGAIN:
134	case EINTR:
135	case EBUSY:
136	// Update statistics
137	__STATS__( false, io.calls.errors.busy ++; )
138	return true;
139	break;
140	default:
141	abort( "KERNEL ERROR: IO_URING SYSCALL - (%d) %s\n", (int)errno, strerror(errno) );
142	}
143	}
144
145	// update statistics
146	if (to_submit > 0) {
147	__STATS__( false, io.calls.submitted += ret; )
148	/* paranoid / verify( ctx.sq.to_submit <= ctx.sq.num );
149
150	/* paranoid */ verify( ctx.sq.to_submit >= ret );
151	ctx.sq.to_submit -= ret;
152
153	/* paranoid / verify( ctx.sq.to_submit <= ctx.sq.num );
154
155	if(ret) {
156	__cfadbg_print_safe(io, "Kernel I/O : %u submitted to io_uring\n", ret);
157	}
158	}
159
160	// Release the consumed SQEs
161	__release_sqes( ctx );
162
163	// Drain the queue
164	unsigned head = *ctx.cq.head;
165	unsigned tail = *ctx.cq.tail;
166	const __u32 mask = *ctx.cq.mask;
167
168	// Nothing was new return 0
169	if (head == tail) {
170	return ctx.sq.to_submit > 0;
171	}
172
173	__u32 count = tail - head;
174	/* paranoid */ verify( count != 0 );
175	__STATS__( false, io.calls.submitted += count; )
176
177	for(i; count) {
178	unsigned idx = (head + i) & mask;
179	volatile struct io_uring_cqe & cqe = ctx.cq.cqes[idx];
180
181	/* paranoid */ verify(&cqe);
182
183	struct io_future_t * future = (struct io_future_t *)(uintptr_t)cqe.user_data;
184	__cfadbg_print_safe( io, "Kernel I/O : Syscall completed : cqe %p, result %d for %p\n", &cqe, cqe.res, future );
185
186	fulfil( *future, cqe.res );
187	}
188
189	if(count) {
190	__cfadbg_print_safe(io, "Kernel I/O : %u completed\n", count);
191	}
192
193	// Mark to the kernel that the cqe has been seen
194	// Ensure that the kernel only sees the new value of the head index after the CQEs have been read.
195	__atomic_store_n( ctx.cq.head, head + count, __ATOMIC_SEQ_CST );
196
197	return count > 0 \|\| to_submit > 0;
198	}
199
200	void main( $io_context & this ) {
201	__cfadbg_print_safe(io_core, "Kernel I/O : IO poller %d (%p) ready\n", this.fd, &this);
202
203	const int reset_cnt = 5;
204	int reset = reset_cnt;
205	// Then loop until we need to start
206	LOOP:
207	while() {
208	waitfor( ^?{} : this) {
209	break LOOP;
210	}
211	or else {}
212
213	// Drain the io
214	bool again = __drain_io( this );
215
216	if(!again) reset--;
217
218	// If we got something, just yield and check again
219	if(reset > 1) {
220	yield();
221	continue LOOP;
222	}
223
224	// We alread failed to find completed entries a few time.
225	if(reset == 1) {
226	// Rearm the context so it can block
227	// but don't block right away
228	// we need to retry one last time in case
229	// something completed just now
230	__ioctx_prepare_block( this );
231	continue LOOP;
232	}
233
234	__STATS__( false,
235	io.calls.blocks += 1;
236	)
237	__cfadbg_print_safe(io_core, "Kernel I/O : Parking io poller %d (%p)\n", this.fd, &this);
238
239	// block this thread
240	wait( this.sem );
241
242	// restore counter
243	reset = reset_cnt;
244	}
245
246	__cfadbg_print_safe(io_core, "Kernel I/O : Fast poller %d (%p) stopping\n", this.fd, &this);
247	}
248
249	//=============================================================================================
250	// I/O Submissions
251	//=============================================================================================
252
253	// Submition steps :
254	// 1 - Allocate a queue entry. The ring already has memory for all entries but only the ones
255	// listed in sq.array are visible by the kernel. For those not listed, the kernel does not
256	// offer any assurance that an entry is not being filled by multiple flags. Therefore, we
257	// need to write an allocator that allows allocating concurrently.
258	//
259	// 2 - Actually fill the submit entry, this is the only simple and straightforward step.
260	//
261	// 3 - Append the entry index to the array and adjust the tail accordingly. This operation
262	// needs to arrive to two concensus at the same time:
263	// A - The order in which entries are listed in the array: no two threads must pick the
264	// same index for their entries
265	// B - When can the tail be update for the kernel. EVERY entries in the array between
266	// head and tail must be fully filled and shouldn't ever be touched again.
267	//
268
269	static $io_context * __ioarbiter_allocate( $io_arbiter & mutex this, processor *, __u32 idxs[], __u32 want );
270	static void __ioarbiter_submit ( $io_arbiter & mutex this, $io_context * , __u32 idxs[], __u32 have );
271	static void __ioarbiter_flush ( $io_arbiter & mutex this, $io_context * );
272	static inline void __ioarbiter_notify( $io_context & ctx );
273
274	//=============================================================================================
275	// Allocation
276	// for user's convenience fill the sqes from the indexes
277	static inline void __fill(struct io_uring_sqe * out_sqes[], __u32 want, __u32 idxs[], struct $io_context * ctx) {
278	struct io_uring_sqe * sqes = ctx->sq.sqes;
279	for(i; want) {
280	out_sqes[i] = &sqes[idxs[i]];
281	}
282	}
283
284	// Try to directly allocate from the a given context
285	// Not thread-safe
286	static inline bool __alloc(struct $io_context * ctx, __u32 idxs[], __u32 want) {
287	__sub_ring_t & sq = ctx->sq;
288	const __u32 mask = *sq.mask;
289	__u32 fhead = sq.free_ring.head; // get the current head of the queue
290	__u32 ftail = sq.free_ring.tail; // get the current tail of the queue
291
292	// If we don't have enough sqes, fail
293	if((ftail - fhead) < want) { return false; }
294
295	// copy all the indexes we want from the available list
296	for(i; want) {
297	idxs[i] = sq.free_ring.array[(fhead + i) & mask];
298	}
299
300	// Advance the head to mark the indexes as consumed
301	__atomic_store_n(&sq.free_ring.head, fhead + want, __ATOMIC_RELEASE);
302
303	// return success
304	return true;
305	}
306
307	// Allocate an submit queue entry.
308	// The kernel cannot see these entries until they are submitted, but other threads must be
309	// able to see which entries can be used and which are already un used by an other thread
310	// for convenience, return both the index and the pointer to the sqe
311	// sqe == &sqes[idx]
312	struct $io_context * cfa_io_allocate(struct io_uring_sqe * sqes[], __u32 idxs[], __u32 want) {
313	__cfadbg_print_safe(io, "Kernel I/O : attempting to allocate %u\n", want);
314
315	disable_interrupts();
316	processor * proc = __cfaabi_tls.this_processor;
317	/* paranoid */ verify( __cfaabi_tls.this_processor );
318	/* paranoid */ verify( proc->io.lock == false );
319
320	__atomic_store_n( &proc->io.lock, true, __ATOMIC_SEQ_CST );
321	$io_context * ctx = proc->io.ctx;
322	$io_arbiter * ioarb = proc->cltr->io.arbiter;
323	/* paranoid */ verify( ioarb );
324
325	// Can we proceed to the fast path
326	if( ctx // We alreay have an instance?
327	&& !ctx->revoked ) // Our instance is still valid?
328	{
329	__cfadbg_print_safe(io, "Kernel I/O : attempting to fast allocation\n");
330
331	// We can proceed to the fast path
332	if( __alloc(ctx, idxs, want) ) {
333	// Allocation was successful
334	// Mark the instance as no longer in-use and re-enable interrupts
335	__atomic_store_n( &proc->io.lock, false, __ATOMIC_RELEASE );
336	__STATS__( true, io.alloc.fast += 1; )
337	enable_interrupts( __cfaabi_dbg_ctx );
338
339	__cfadbg_print_safe(io, "Kernel I/O : fast allocation successful\n");
340
341	__fill( sqes, want, idxs, ctx );
342	return ctx;
343	}
344	// The fast path failed, fallback
345	__STATS__( true, io.alloc.fail += 1; )
346	}
347
348	// Fast path failed, fallback on arbitration
349	__atomic_store_n( &proc->io.lock, false, __ATOMIC_RELEASE );
350	__STATS__( true, io.alloc.slow += 1; )
351	enable_interrupts( __cfaabi_dbg_ctx );
352
353	__cfadbg_print_safe(io, "Kernel I/O : falling back on arbiter for allocation\n");
354
355	struct $io_context * ret = __ioarbiter_allocate(*ioarb, proc, idxs, want);
356
357	__cfadbg_print_safe(io, "Kernel I/O : slow allocation completed\n");
358
359	__fill( sqes, want, idxs,ret );
360	return ret;
361	}
362
363
364	//=============================================================================================
365	// submission
366	static inline void __submit( struct $io_context * ctx, __u32 idxs[], __u32 have) {
367	// We can proceed to the fast path
368	// Get the right objects
369	__sub_ring_t & sq = ctx->sq;
370	const __u32 mask = *sq.mask;
371	__u32 tail = sq.kring.ready;
372
373	// Add the sqes to the array
374	for( i; have ) {
375	sq.kring.array[ (tail + i) & mask ] = idxs[i];
376	}
377
378	// Make the sqes visible to the submitter
379	__atomic_store_n(&sq.kring.ready, tail + have, __ATOMIC_RELEASE);
380
381	// Make sure the poller is awake
382	__cfadbg_print_safe(io, "Kernel I/O : waking the poller\n");
383	post( ctx->sem );
384	}
385
386	void cfa_io_submit( struct $io_context * inctx, __u32 idxs[], __u32 have ) __attribute__((nonnull (1))) {
387	__cfadbg_print_safe(io, "Kernel I/O : attempting to submit %u\n", have);
388
389	disable_interrupts();
390	processor * proc = __cfaabi_tls.this_processor;
391	/* paranoid */ verify( __cfaabi_tls.this_processor );
392	/* paranoid */ verify( proc->io.lock == false );
393
394	__atomic_store_n( &proc->io.lock, true, __ATOMIC_SEQ_CST );
395	$io_context * ctx = proc->io.ctx;
396
397	// Can we proceed to the fast path
398	if( ctx // We alreay have an instance?
399	&& !ctx->revoked // Our instance is still valid?
400	&& ctx == inctx ) // We have the right instance?
401	{
402	__submit(ctx, idxs, have);
403
404	// Mark the instance as no longer in-use, re-enable interrupts and return
405	__atomic_store_n( &proc->io.lock, false, __ATOMIC_RELEASE );
406	__STATS__( true, io.submit.fast += 1; )
407	enable_interrupts( __cfaabi_dbg_ctx );
408
409	__cfadbg_print_safe(io, "Kernel I/O : submitted on fast path\n");
410	return;
411	}
412
413	// Fast path failed, fallback on arbitration
414	__atomic_store_n( &proc->io.lock, false, __ATOMIC_RELEASE );
415	__STATS__( true, io.submit.slow += 1; )
416	enable_interrupts( __cfaabi_dbg_ctx );
417
418	__cfadbg_print_safe(io, "Kernel I/O : falling back on arbiter for submission\n");
419
420	__ioarbiter_submit(*inctx->arbiter, inctx, idxs, have);
421	}
422
423	//=============================================================================================
424	// Flushing
425	static unsigned __flush( struct $io_context & ctx ) {
426	// First check for external
427	if( !__atomic_load_n(&ctx.ext_sq.empty, __ATOMIC_SEQ_CST) ) {
428	// We have external submissions, delegate to the arbiter
429	__ioarbiter_flush( *ctx.arbiter, &ctx );
430	}
431
432	__u32 tail = *ctx.sq.kring.tail;
433	__u32 ready = ctx.sq.kring.ready;
434
435	/* paranoid / verify( ctx.sq.to_submit <= ctx.sq.num );
436	ctx.sq.to_submit += (ready - tail);
437	/* paranoid / verify( ctx.sq.to_submit <= ctx.sq.num );
438
439	if(ctx.sq.to_submit) {
440	__cfadbg_print_safe(io, "Kernel I/O : %u ready to submit\n", ctx.sq.to_submit);
441	}
442
443	__atomic_store_n(ctx.sq.kring.tail, ready, __ATOMIC_RELEASE);
444
445	return ctx.sq.to_submit;
446	}
447
448
449	// Go through the ring's submit queue and release everything that has already been consumed
450	// by io_uring
451	// This cannot be done by multiple threads
452	static __u32 __release_sqes( struct $io_context & ctx ) {
453	const __u32 mask = *ctx.sq.mask;
454
455	__attribute__((unused))
456	__u32 ctail = *ctx.sq.kring.tail; // get the current tail of the queue
457	__u32 chead = *ctx.sq.kring.head; // get the current head of the queue
458	__u32 phead = ctx.sq.kring.released; // get the head the last time we were here
459
460	__u32 ftail = ctx.sq.free_ring.tail; // get the current tail of the queue
461
462	// the 3 fields are organized like this diagram
463	// except it's are ring
464	// ---+--------+--------+----
465	// ---+--------+--------+----
466	// ^ ^ ^
467	// phead chead ctail
468
469	// make sure ctail doesn't wrap around and reach phead
470	/* paranoid */ verify(
471	(ctail >= chead && chead >= phead)
472	\|\| (chead >= phead && phead >= ctail)
473	\|\| (phead >= ctail && ctail >= chead)
474	);
475
476	// find the range we need to clear
477	__u32 count = chead - phead;
478
479	if(count == 0) {
480	return 0;
481	}
482
483	// We acquired an previous-head/current-head range
484	// go through the range and release the sqes
485	for( i; count ) {
486	__u32 idx = ctx.sq.kring.array[ (phead + i) & mask ];
487	ctx.sq.free_ring.array[ (ftail + i) & mask ] = idx;
488	}
489
490	ctx.sq.kring.released = chead; // note up to were we processed
491	__atomic_store_n(&ctx.sq.free_ring.tail, ftail + count, __ATOMIC_SEQ_CST);
492
493	__ioarbiter_notify(ctx);
494
495	return count;
496	}
497
498	//=============================================================================================
499	// I/O Arbiter
500	//=============================================================================================
501	static inline void __revoke( $io_arbiter & this, $io_context * ctx ) {
502	if(ctx->revoked) return;
503
504	/* paranoid */ verify( ctx->proc );
505	remove( this.assigned, *ctx );
506
507	// Mark as revoked
508	__atomic_store_n(&ctx->revoked, true, __ATOMIC_SEQ_CST);
509
510	// Wait for the processor to no longer use it
511	while(ctx->proc->io.lock) Pause();
512
513	// Remove the coupling with the processor
514	ctx->proc->io.ctx = 0p;
515	ctx->proc = 0p;
516
517	// add to available contexts
518	addHead( this.available, *ctx );
519	}
520
521	static inline void __assign( $io_arbiter & this, $io_context * ctx, processor * proc ) {
522	remove( this.available, *ctx );
523
524	ctx->revoked = false;
525	ctx->proc = proc;
526	__atomic_store_n(&proc->io.ctx, ctx, __ATOMIC_SEQ_CST);
527
528	// add to assigned contexts
529	addTail( this.assigned, *ctx );
530	}
531
532	static $io_context * __ioarbiter_allocate( $io_arbiter & mutex this, processor * proc, __u32 idxs[], __u32 want ) {
533	__cfadbg_print_safe(io, "Kernel I/O : arbiter allocating\n");
534
535	SeqIter($io_context) iter;
536	$io_context & ci;
537	// Do we already have something available?
538	for( over( iter, this.available ); iter \| ci;) {
539	__cfadbg_print_safe(io, "Kernel I/O : attempting available context\n");
540
541	$io_context * c = &ci;
542	if(__alloc(c, idxs, want)) {
543	__assign( this, c, proc);
544	return c;
545	}
546	}
547
548
549	// Otherwise, we have no choice but to revoke everyone to check if other instance have available data
550	for( over( iter, this.assigned ); iter \| ci; ) {
551	__cfadbg_print_safe(io, "Kernel I/O : revoking context for allocation\n");
552
553	$io_context * c = &ci;
554	__revoke( this, c );
555
556	__STATS__( false, io.alloc.revoke += 1; )
557
558	if(__alloc(c, idxs, want)) {
559	__assign( this, c, proc);
560	return c;
561	}
562	}
563
564	__cfadbg_print_safe(io, "Kernel I/O : waiting for available resources\n");
565
566	__STATS__( false, io.alloc.block += 1; )
567
568	// No one has any resources left, wait for something to finish
569	// Mark as pending
570	__atomic_store_n( &this.pending.flag, true, __ATOMIC_SEQ_CST );
571
572	// Wait for our turn to submit
573	wait( this.pending.blocked, want );
574
575	__attribute((unused)) bool ret =
576	__alloc( this.pending.ctx, idxs, want);
577	/* paranoid */ verify( ret );
578
579	__assign( this, this.pending.ctx, proc);
580	return this.pending.ctx;
581	}
582
583	static void __ioarbiter_notify( $io_arbiter & mutex this, $io_context * ctx ) {
584	/* paranoid */ verify( !is_empty(this.pending.blocked) );
585	this.pending.ctx = ctx;
586
587	while( !is_empty(this.pending.blocked) ) {
588	__u32 have = ctx->sq.free_ring.tail - ctx->sq.free_ring.head;
589	__u32 want = front( this.pending.blocked );
590
591	if( have > want ) return;
592
593	signal_block( this.pending.blocked );
594	}
595
596	this.pending.flag = false;
597	}
598
599	static void __ioarbiter_notify( $io_context & ctx ) {
600	if(__atomic_load_n( &ctx.arbiter->pending.flag, __ATOMIC_SEQ_CST)) {
601	__ioarbiter_notify( *ctx.arbiter, &ctx );
602	}
603	}
604
605	// Simply append to the pending
606	static void __ioarbiter_submit( $io_arbiter & mutex this, $io_context * ctx, __u32 idxs[], __u32 have ) {
607	__cfadbg_print_safe(io, "Kernel I/O : submitting %u from the arbiter to context %u\n", have, ctx->fd);
608
609	/* paranoid */ verify( &this == ctx->arbiter );
610
611	// Mark as pending
612	__atomic_store_n( &ctx->ext_sq.empty, false, __ATOMIC_SEQ_CST );
613
614	// Wake-up the poller
615	post( ctx->sem );
616
617	__cfadbg_print_safe(io, "Kernel I/O : waiting to submit %u\n", have);
618
619	// Wait for our turn to submit
620	wait( ctx->ext_sq.blocked );
621
622	// Submit our indexes
623	__submit(ctx, idxs, have);
624
625	__cfadbg_print_safe(io, "Kernel I/O : %u submitted from arbiter\n", have);
626	}
627
628	static void __ioarbiter_flush( $io_arbiter & mutex this, $io_context * ctx ) {
629	/* paranoid */ verify( &this == ctx->arbiter );
630
631	__STATS__( false, io.flush.external += 1; )
632
633	__revoke( this, ctx );
634
635	__cfadbg_print_safe(io, "Kernel I/O : arbiter flushing\n");
636
637	condition & blcked = ctx->ext_sq.blocked;
638	/* paranoid */ verify( ctx->ext_sq.empty == is_empty( blcked ) );
639	while(!is_empty( blcked )) {
640	signal_block( blcked );
641	}
642
643	ctx->ext_sq.empty = true;
644	}
645
646	void __ioarbiter_register( $io_arbiter & mutex this, $io_context & ctx ) {
647	__cfadbg_print_safe(io, "Kernel I/O : registering new context\n");
648
649	ctx.arbiter = &this;
650
651	// add to available contexts
652	addHead( this.available, ctx );
653
654	// Check if this solves pending allocations
655	if(this.pending.flag) {
656	__ioarbiter_notify( ctx );
657	}
658	}
659
660	void __ioarbiter_unregister( $io_arbiter & mutex this, $io_context & ctx ) {
661	/* paranoid */ verify( &this == ctx.arbiter );
662
663	__revoke( this, &ctx );
664
665	remove( this.available, ctx );
666	}
667	#endif

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