diff --git a/src/aio/aio.c b/src/aio/aio.c
new file mode 100644
index 00000000..7bf2b337
--- /dev/null
+++ b/src/aio/aio.c
@@ -0,0 +1,378 @@
+#include <aio.h>
+#include <pthread.h>
+#include <semaphore.h>
+#include <limits.h>
+#include <errno.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include "syscall.h"
+#include "atomic.h"
+#include "libc.h"
+#include "pthread_impl.h"
+
+/* The following is a threads-based implementation of AIO with minimal
+ * dependence on implementation details. Most synchronization is
+ * performed with pthread primitives, but atomics and futex operations
+ * are used for notification in a couple places where the pthread
+ * primitives would be inefficient or impractical.
+ *
+ * For each fd with outstanding aio operations, an aio_queue structure
+ * is maintained. These are reference-counted and destroyed by the last
+ * aio worker thread to exit. Accessing any member of the aio_queue
+ * structure requires a lock on the aio_queue. Adding and removing aio
+ * queues themselves requires a write lock on the global map object,
+ * a 4-level table mapping file descriptor numbers to aio queues. A
+ * read lock on the map is used to obtain locks on existing queues by
+ * excluding destruction of the queue by a different thread while it is
+ * being locked.
+ *
+ * Each aio queue has a list of active threads/operations. Presently there
+ * is a one to one relationship between threads and operations. The only
+ * members of the aio_thread structure which are accessed by other threads
+ * are the linked list pointers, op (which is immutable), running (which
+ * is updated atomically), and err (which is synchronized via running),
+ * so no locking is necessary. Most of the other other members are used
+ * for sharing data between the main flow of execution and cancellation
+ * cleanup handler.
+ *
+ * Taking any aio locks requires having all signals blocked. This is
+ * necessary because aio_cancel is needed by close, and close is required
+ * to be async-signal safe. All aio worker threads run with all signals
+ * blocked permanently.
+ */
+
+struct aio_args {
+	struct aiocb *cb;
+	int op;
+	int err;
+	sem_t sem;
+};
+
+struct aio_thread {
+	pthread_t td;
+	struct aiocb *cb;
+	struct aio_thread *next, *prev;
+	struct aio_queue *q;
+	int running, err, op;
+	ssize_t ret;
+};
+
+struct aio_queue {
+	int fd, seekable, append, ref, init;
+	pthread_mutex_t lock;
+	pthread_cond_t cond;
+	struct aio_thread *head;
+};
+
+static pthread_rwlock_t maplock = PTHREAD_RWLOCK_INITIALIZER;
+static struct aio_queue *****map;
+static volatile int aio_fd_cnt;
+volatile int __aio_fut;
+
+static struct aio_queue *__aio_get_queue(int fd, int need)
+{
+	if (fd < 0) return 0;
+	int a=fd>>24;
+	unsigned char b=fd>>16, c=fd>>8, d=fd;
+	struct aio_queue *q = 0;
+	pthread_rwlock_rdlock(&maplock);
+	if ((!map || !map[a] || !map[a][b] || !map[a][b][c] || !(q=map[a][b][c][d])) && need) {
+		pthread_rwlock_unlock(&maplock);
+		pthread_rwlock_wrlock(&maplock);
+		if (!map) map = calloc(sizeof *map, (-1U/2+1)>>24);
+		if (!map) goto out;
+		if (!map[a]) map[a] = calloc(sizeof **map, 256);
+		if (!map[a]) goto out;
+		if (!map[a][b]) map[a][b] = calloc(sizeof ***map, 256);
+		if (!map[a][b]) goto out;
+		if (!map[a][b][c]) map[a][b][c] = calloc(sizeof ****map, 256);
+		if (!map[a][b][c]) goto out;
+		if (!(q = map[a][b][c][d])) {
+			map[a][b][c][d] = q = calloc(sizeof *****map, 1);
+			if (q) {
+				q->fd = fd;
+				pthread_mutex_init(&q->lock, 0);
+				pthread_cond_init(&q->cond, 0);
+				a_inc(&aio_fd_cnt);
+			}
+		}
+	}
+	if (q) pthread_mutex_lock(&q->lock);
+out:
+	pthread_rwlock_unlock(&maplock);
+	return q;
+}
+
+static void __aio_unref_queue(struct aio_queue *q)
+{
+	if (q->ref > 1) {
+		q->ref--;
+		pthread_mutex_unlock(&q->lock);
+		return;
+	}
+
+	/* This is potentially the last reference, but a new reference
+	 * may arrive since we cannot free the queue object without first
+	 * taking the maplock, which requires releasing the queue lock. */
+	pthread_mutex_unlock(&q->lock);
+	pthread_rwlock_wrlock(&maplock);
+	pthread_mutex_lock(&q->lock);
+	if (q->ref == 1) {
+		int fd=q->fd;
+		int a=fd>>24;
+		unsigned char b=fd>>16, c=fd>>8, d=fd;
+		map[a][b][c][d] = 0;
+		a_dec(&aio_fd_cnt);
+		pthread_rwlock_unlock(&maplock);
+		pthread_mutex_unlock(&q->lock);
+		free(q);
+	} else {
+		q->ref--;
+		pthread_rwlock_unlock(&maplock);
+		pthread_mutex_unlock(&q->lock);
+	}
+}
+
+static void cleanup(void *ctx)
+{
+	struct aio_thread *at = ctx;
+	struct aio_queue *q = at->q;
+	struct aiocb *cb = at->cb;
+	struct sigevent sev = cb->aio_sigevent;
+
+	/* There are four potential types of waiters we could need to wake:
+	 *   1. Callers of aio_cancel/close.
+	 *   2. Callers of aio_suspend with a single aiocb.
+	 *   3. Callers of aio_suspend with a list.
+	 *   4. AIO worker threads waiting for sequenced operations.
+	 * Types 1-3 are notified via atomics/futexes, mainly for AS-safety
+	 * considerations. Type 4 is notified later via a cond var. */
+
+	a_store(&cb->__ret, at->ret);
+	if (a_swap(&at->running, 0) < 0)
+		__wake(&at->running, -1, 1);
+	if (a_swap(&cb->__err, at->err) != EINPROGRESS)
+		__wake(&cb->__err, -1, 1);
+	if (a_swap(&__aio_fut, 0))
+		__wake(&__aio_fut, -1, 1);
+
+	pthread_mutex_lock(&q->lock);
+
+	if (at->next) at->next->prev = at->prev;
+	if (at->prev) at->prev->next = at->next;
+	else q->head = at->next;
+
+	/* Signal aio worker threads waiting for sequenced operations. */
+	pthread_cond_broadcast(&q->cond);
+
+	__aio_unref_queue(q);
+
+	if (sev.sigev_notify == SIGEV_SIGNAL) {
+		siginfo_t si = {
+			.si_signo = sev.sigev_signo,
+			.si_value = sev.sigev_value,
+			.si_code = SI_ASYNCIO,
+			.si_pid = getpid(),
+			.si_uid = getuid()
+		};
+		__syscall(SYS_rt_sigqueueinfo, si.si_pid, si.si_signo, &si);
+	}
+	if (sev.sigev_notify == SIGEV_THREAD) {
+		a_store(&__pthread_self()->cancel, 0);
+		sev.sigev_notify_function(sev.sigev_value);
+	}
+}
+
+static void *io_thread_func(void *ctx)
+{
+	struct aio_thread at, *p;
+
+	struct aio_args *args = ctx;
+	struct aiocb *cb = args->cb;
+	int fd = cb->aio_fildes;
+	int op = args->op;
+	void *buf = (void *)cb->aio_buf;
+	size_t len = cb->aio_nbytes;
+	off_t off = cb->aio_offset;
+
+	struct aio_queue *q = __aio_get_queue(fd, 1);
+	ssize_t ret;
+
+	args->err = q ? 0 : EAGAIN;
+	sem_post(&args->sem);
+	if (!q) return 0;
+
+	at.op = op;
+	at.running = 1;
+	at.ret = -1;
+	at.err = ECANCELED;
+	at.q = q;
+	at.td = __pthread_self();
+	at.cb = cb;
+	at.prev = 0;
+	if ((at.next = q->head)) at.next->prev = &at;
+	q->head = &at;
+	q->ref++;
+
+	if (!q->init) {
+		int seekable = lseek(fd, 0, SEEK_CUR) >= 0;
+		q->seekable = seekable;
+		q->append = !seekable || (fcntl(fd, F_GETFL) & O_APPEND);
+		q->init = 1;
+	}
+
+	pthread_cleanup_push(cleanup, &at);
+
+	/* Wait for sequenced operations. */
+	if (op!=LIO_READ && (op!=LIO_WRITE || q->append)) {
+		for (;;) {
+			for (p=at.next; p && p->op!=LIO_WRITE; p=p->next);
+			if (!p) break;
+			pthread_cond_wait(&q->cond, &q->lock);
+		}
+	}
+
+	pthread_mutex_unlock(&q->lock);
+
+	switch (op) {
+	case LIO_WRITE:
+		ret = q->append ? write(fd, buf, len) : pwrite(fd, buf, len, off);
+		break;
+	case LIO_READ:
+		ret = !q->seekable ? read(fd, buf, len) : pread(fd, buf, len, off);
+		break;
+	case O_SYNC:
+		ret = fsync(fd);
+		break;
+	case O_DSYNC:
+		ret = fdatasync(fd);
+		break;
+	}
+	at.ret = ret;
+	at.err = ret<0 ? errno : 0;
+	
+	pthread_cleanup_pop(1);
+
+	return 0;
+}
+
+static int submit(struct aiocb *cb, int op)
+{
+	int ret = 0;
+	pthread_attr_t a;
+	sigset_t allmask, origmask;
+	pthread_t td;
+	struct aio_args args = { .cb = cb, .op = op };
+	sem_init(&args.sem, 0, 0);
+
+	if (cb->aio_sigevent.sigev_notify == SIGEV_THREAD) {
+		if (cb->aio_sigevent.sigev_notify_attributes)
+			a = *cb->aio_sigevent.sigev_notify_attributes;
+		else
+			pthread_attr_init(&a);
+	} else {
+		pthread_attr_init(&a);
+		pthread_attr_setstacksize(&a, PTHREAD_STACK_MIN);
+		pthread_attr_setguardsize(&a, 0);
+	}
+	pthread_attr_setdetachstate(&a, PTHREAD_CREATE_DETACHED);
+	sigfillset(&allmask);
+	pthread_sigmask(SIG_BLOCK, &allmask, &origmask);
+	cb->__err = EINPROGRESS;
+	if (pthread_create(&td, &a, io_thread_func, &args)) {
+		errno = EAGAIN;
+		ret = -1;
+	}
+	pthread_sigmask(SIG_SETMASK, &origmask, 0);
+
+	if (!ret) {
+		while (sem_wait(&args.sem));
+		if (args.err) {
+			errno = args.err;
+			ret = -1;
+		}
+	}
+
+	return ret;
+}
+
+int aio_read(struct aiocb *cb)
+{
+	return submit(cb, LIO_READ);
+}
+
+int aio_write(struct aiocb *cb)
+{
+	return submit(cb, LIO_WRITE);
+}
+
+int aio_fsync(int op, struct aiocb *cb)
+{
+	if (op != O_SYNC && op != O_DSYNC) {
+		errno = EINVAL;
+		return -1;
+	}
+	return submit(cb, op);
+}
+
+ssize_t aio_return(struct aiocb *cb)
+{
+	return cb->__ret;
+}
+
+int aio_error(const struct aiocb *cb)
+{
+	a_barrier();
+	return cb->__err & 0x7fffffff;
+}
+
+int aio_cancel(int fd, struct aiocb *cb)
+{
+	sigset_t allmask, origmask;
+	int ret = AIO_ALLDONE;
+	struct aio_thread *p;
+	struct aio_queue *q;
+
+	/* Unspecified behavior case. Report an error. */
+	if (cb && fd != cb->aio_fildes) {
+		errno = EINVAL;
+		return -1;
+	}
+
+	sigfillset(&allmask);
+	pthread_sigmask(SIG_BLOCK, &allmask, &origmask);
+
+	if (!(q = __aio_get_queue(fd, 0))) {
+		if (fcntl(fd, F_GETFD) < 0) ret = -1;
+		goto done;
+	}
+
+	for (p = q->head; p; p = p->next) {
+		if (cb && cb != p->cb) continue;
+		/* Transition target from running to running-with-waiters */
+		if (a_cas(&p->running, 1, -1)) {
+			pthread_cancel(p->td);
+			__wait(&p->running, 0, -1, 1);
+			if (p->err == ECANCELED) ret = AIO_CANCELED;
+		}
+	}
+
+	pthread_mutex_unlock(&q->lock);
+done:
+	pthread_sigmask(SIG_SETMASK, &origmask, 0);
+	return ret;
+}
+
+int __aio_close(int fd)
+{
+	a_barrier();
+	if (aio_fd_cnt) aio_cancel(fd, 0);
+	return fd;
+}
+
+LFS64(aio_cancel);
+LFS64(aio_error);
+LFS64(aio_fsync);
+LFS64(aio_read);
+LFS64(aio_write);
+LFS64(aio_return);
diff --git a/src/aio/aio_cancel.c b/src/aio/aio_cancel.c
deleted file mode 100644
index 16fc431f..00000000
--- a/src/aio/aio_cancel.c
+++ /dev/null
@@ -1,19 +0,0 @@
-#include <aio.h>
-#include <pthread.h>
-#include <errno.h>
-#include "libc.h"
-
-int aio_cancel(int fd, struct aiocb *cb)
-{
-	if (!cb) {
-		/* FIXME: for correctness, we should return AIO_ALLDONE
-		 * if there are no outstanding aio operations on this
-		 * file descriptor, but that would require making aio
-		 * much slower, and seems to have little advantage since
-		 * we don't support cancellation anyway. */
-		return AIO_NOTCANCELED;
-	}
-	return cb->__err==EINPROGRESS ? AIO_NOTCANCELED : AIO_ALLDONE;
-}
-
-LFS64(aio_cancel);
diff --git a/src/aio/aio_error.c b/src/aio/aio_error.c
deleted file mode 100644
index fd42ea11..00000000
--- a/src/aio/aio_error.c
+++ /dev/null
@@ -1,9 +0,0 @@
-#include <aio.h>
-#include "libc.h"
-
-int aio_error(const struct aiocb *cb)
-{
-	return cb->__err;
-}
-
-LFS64(aio_error);
diff --git a/src/aio/aio_fsync.c b/src/aio/aio_fsync.c
deleted file mode 100644
index 6e1a70ab..00000000
--- a/src/aio/aio_fsync.c
+++ /dev/null
@@ -1,12 +0,0 @@
-#include <aio.h>
-#include <errno.h>
-#include "libc.h"
-
-int aio_fsync(int op, struct aiocb *cb)
-{
-	/* FIXME: unsupported */
-	errno = EINVAL;
-	return -1;
-}
-
-LFS64(aio_fsync);
diff --git a/src/aio/aio_readwrite.c b/src/aio/aio_readwrite.c
deleted file mode 100644
index 8753ffda..00000000
--- a/src/aio/aio_readwrite.c
+++ /dev/null
@@ -1,110 +0,0 @@
-#include <aio.h>
-#include <fcntl.h>
-#include <errno.h>
-#include <unistd.h>
-#include "pthread_impl.h"
-#include "libc.h"
-
-static void dummy(void)
-{
-}
-
-weak_alias(dummy, __aio_wake);
-
-static void notify_signal(struct sigevent *sev)
-{
-	siginfo_t si = {
-		.si_signo = sev->sigev_signo,
-		.si_value = sev->sigev_value,
-		.si_code = SI_ASYNCIO,
-		.si_pid = getpid(),
-		.si_uid = getuid()
-	};
-	__syscall(SYS_rt_sigqueueinfo, si.si_pid, si.si_signo, &si);
-}
-
-static void *io_thread(void *p)
-{
-	struct aiocb *cb = p;
-	int fd = cb->aio_fildes;
-	void *buf = (void *)cb->aio_buf;
-	size_t len = cb->aio_nbytes;
-	off_t off = cb->aio_offset;
-	int op = cb->aio_lio_opcode;
-	struct sigevent sev = cb->aio_sigevent;
-	ssize_t ret;
-
-	if (op == LIO_WRITE) {
-		if (  (fcntl(fd, F_GETFL) & O_APPEND)
-		    ||((ret = pwrite(fd, buf, len, off))<0 && errno==ESPIPE) )
-			ret = write(fd, buf, len);
-	} else if (op == LIO_READ) {
-		if ( (ret = pread(fd, buf, len, off))<0 && errno==ESPIPE )
-			ret = read(fd, buf, len);
-	} else {
-		ret = 0;
-	}
-	cb->__ret = ret;
-
-	if (ret < 0) a_store(&cb->__err, errno);
-	else a_store(&cb->__err, 0);
-
-	__aio_wake();
-
-	switch (sev.sigev_notify) {
-	case SIGEV_SIGNAL:
-		notify_signal(&sev);
-		break;
-	case SIGEV_THREAD:
-		sev.sigev_notify_function(sev.sigev_value);
-		break;
-	}
-
-	return 0;
-}
-
-static int new_req(struct aiocb *cb)
-{
-	int ret = 0;
-	pthread_attr_t a;
-	sigset_t set;
-	pthread_t td;
-
-	if (cb->aio_sigevent.sigev_notify == SIGEV_THREAD) {
-		if (cb->aio_sigevent.sigev_notify_attributes)
-			a = *cb->aio_sigevent.sigev_notify_attributes;
-		else
-			pthread_attr_init(&a);
-	} else {
-		pthread_attr_init(&a);
-		pthread_attr_setstacksize(&a, PAGE_SIZE);
-		pthread_attr_setguardsize(&a, 0);
-	}
-	pthread_attr_setdetachstate(&a, PTHREAD_CREATE_DETACHED);
-	sigfillset(&set);
-	pthread_sigmask(SIG_BLOCK, &set, &set);
-	cb->__err = EINPROGRESS;
-	if (pthread_create(&td, &a, io_thread, cb)) {
-		errno = EAGAIN;
-		ret = -1;
-	}
-	pthread_sigmask(SIG_SETMASK, &set, 0);
-	cb->__td = td;
-
-	return ret;
-}
-
-int aio_read(struct aiocb *cb)
-{
-	cb->aio_lio_opcode = LIO_READ;
-	return new_req(cb);
-}
-
-int aio_write(struct aiocb *cb)
-{
-	cb->aio_lio_opcode = LIO_WRITE;
-	return new_req(cb);
-}
-
-LFS64(aio_read);
-LFS64(aio_write);
diff --git a/src/aio/aio_return.c b/src/aio/aio_return.c
deleted file mode 100644
index c1ce450c..00000000
--- a/src/aio/aio_return.c
+++ /dev/null
@@ -1,9 +0,0 @@
-#include <aio.h>
-#include "libc.h"
-
-ssize_t aio_return(struct aiocb *cb)
-{
-	return cb->__ret;
-}
-
-LFS64(aio_return);
diff --git a/src/aio/aio_suspend.c b/src/aio/aio_suspend.c
index dcdf6019..2391d786 100644
--- a/src/aio/aio_suspend.c
+++ b/src/aio/aio_suspend.c
@@ -1,57 +1,70 @@
 #include <aio.h>
 #include <errno.h>
-#include "pthread_impl.h"
+#include <time.h>
+#include "atomic.h"
 #include "libc.h"
+#include "pthread_impl.h"
 
-/* Due to the requirement that aio_suspend be async-signal-safe, we cannot
- * use any locks, wait queues, etc. that would make it more efficient. The
- * only obviously-correct algorithm is to generate a wakeup every time any
- * aio operation finishes and have aio_suspend re-evaluate the completion
- * status of each aiocb it was waiting on. */
-
-static volatile int seq;
-
-void __aio_wake(void)
-{
-	a_inc(&seq);
-	__wake(&seq, -1, 1);
-}
+extern volatile int __aio_fut;
 
 int aio_suspend(const struct aiocb *const cbs[], int cnt, const struct timespec *ts)
 {
-	int i, last, first=1, ret=0;
+	int i, tid = 0, ret, expect = 0;
 	struct timespec at;
+	volatile int dummy_fut, *pfut;
+	int nzcnt = 0;
+	const struct aiocb *cb = 0;
 
 	if (cnt<0) {
 		errno = EINVAL;
 		return -1;
 	}
 
+	for (i=0; i<cnt; i++) if (cbs[i]) {
+		if (aio_error(cbs[i]) != EINPROGRESS) return 0;
+		nzcnt++;
+		cb = cbs[i];
+	}
+
+	if (ts) {
+		clock_gettime(CLOCK_MONOTONIC, &at);
+		at.tv_sec += ts->tv_sec;
+		if ((at.tv_nsec += ts->tv_nsec) >= 1000000000) {
+			at.tv_nsec -= 1000000000;
+			at.tv_sec++;
+		}
+	}
+
 	for (;;) {
-		last = seq;
-
-		for (i=0; i<cnt; i++) {
-			if (cbs[i] && cbs[i]->__err != EINPROGRESS)
+		for (i=0; i<cnt; i++)
+			if (cbs[i] && aio_error(cbs[i]) != EINPROGRESS)
 				return 0;
+
+		switch (nzcnt) {
+		case 0:
+			pfut = &dummy_fut;
+			break;
+		case 1:
+			pfut = (void *)&cb->__err;
+			expect = EINPROGRESS | 0x80000000;
+			a_cas(pfut, EINPROGRESS, expect);
+			break;
+		default:
+			pfut = &__aio_fut;
+			if (!tid) tid = __pthread_self()->tid;
+			expect = a_cas(pfut, 0, tid);
+			if (!expect) expect = tid;
+			/* Need to recheck the predicate before waiting. */
+			for (i=0; i<cnt; i++)
+				if (cbs[i] && aio_error(cbs[i]) != EINPROGRESS)
+					return 0;
+			break;
 		}
 
-		if (first && ts) {
-			clock_gettime(CLOCK_MONOTONIC, &at);
-			at.tv_sec += ts->tv_sec;
-			if ((at.tv_nsec += ts->tv_nsec) >= 1000000000) {
-				at.tv_nsec -= 1000000000;
-				at.tv_sec++;
-			}
-			first = 0;
-		}
-
-		ret = __timedwait(&seq, last, CLOCK_MONOTONIC,
-			ts ? &at : 0, 0, 0, 1);
-
-		if (ret == ETIMEDOUT) ret = EAGAIN;
+		ret = __timedwait(pfut, expect, CLOCK_MONOTONIC, ts?&at:0, 0, 0, 1);
 
 		if (ret) {
-			errno = ret;
+			errno = ret==ETIMEDOUT ? EAGAIN : ret;
 			return -1;
 		}
 	}
diff --git a/src/stdio/__stdio_close.c b/src/stdio/__stdio_close.c
index 9f7ee18c..79452bdb 100644
--- a/src/stdio/__stdio_close.c
+++ b/src/stdio/__stdio_close.c
@@ -1,6 +1,13 @@
 #include "stdio_impl.h"
 
+static int dummy(int fd)
+{
+	return fd;
+}
+
+weak_alias(dummy, __aio_close);
+
 int __stdio_close(FILE *f)
 {
-	return syscall(SYS_close, f->fd);
+	return syscall(SYS_close, __aio_close(f->fd));
 }
diff --git a/src/unistd/close.c b/src/unistd/close.c
index e8f813d6..2f1eabd7 100644
--- a/src/unistd/close.c
+++ b/src/unistd/close.c
@@ -3,8 +3,16 @@
 #include "syscall.h"
 #include "libc.h"
 
+static int dummy(int fd)
+{
+	return fd;
+}
+
+weak_alias(dummy, __aio_close);
+
 int close(int fd)
 {
+	fd = __aio_close(fd);
 	int r = __syscall_cp(SYS_close, fd);
 	if (r == -EINTR) r = -EINPROGRESS;
 	return __syscall_ret(r);