Add a "fork" of musl as //fusl.

fusl/src/aio/aio.c

+#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;
+        volatile int running;
+        int 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. */
+
+        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);