git.sesse.net Git - plocate/blob - io_uring_engine.cpp

   1 #include <string.h>
   2 #ifndef WITHOUT_URING
   3 #include <liburing.h>
   4 #endif
   5 #include "io_uring_engine.h"
   6
   7 #include <functional>
   8 #include <memory>
   9 #include <stdint.h>
  10 #include <unistd.h>
  11
  12 using namespace std;
  13
  14 IOUringEngine::IOUringEngine()
  15 {
  16 #ifdef WITHOUT_URING
  17         int ret = -1;
  18 #else
  19         int ret = io_uring_queue_init(queue_depth, &ring, 0);
  20 #endif
  21         using_uring = (ret >= 0);
  22 }
  23
  24 void IOUringEngine::submit_read(int fd, size_t len, off_t offset, function<void(string)> cb)
  25 {
  26         if (!using_uring) {
  27                 // Synchronous read.
  28                 string s;
  29                 s.resize(len);
  30                 complete_pread(fd, &s[0], len, offset);
  31                 cb(move(s));
  32                 return;
  33         }
  34
  35 #ifndef WITHOUT_URING
  36         if (pending_reads < queue_depth) {
  37                 io_uring_sqe *sqe = io_uring_get_sqe(&ring);
  38                 if (sqe == nullptr) {
  39                         fprintf(stderr, "io_uring_get_sqe: %s\n", strerror(errno));
  40                         exit(1);
  41                 }
  42                 submit_read_internal(sqe, fd, len, offset, move(cb));
  43         } else {
  44                 queued_reads.push(QueuedRead{ fd, len, offset, move(cb) });
  45         }
  46 #endif
  47 }
  48
  49 #ifndef WITHOUT_URING
  50 void IOUringEngine::submit_read_internal(io_uring_sqe *sqe, int fd, size_t len, off_t offset, function<void(string)> cb)
  51 {
  52         void *buf;
  53         if (posix_memalign(&buf, /*alignment=*/4096, len)) {
  54                 fprintf(stderr, "Couldn't allocate %zu bytes: %s\n", len, strerror(errno));
  55                 exit(1);
  56         }
  57         PendingRead *pending = new PendingRead{ buf, len, move(cb), fd, offset, { buf, len } };
  58
  59         io_uring_prep_readv(sqe, fd, &pending->iov, 1, offset);
  60         io_uring_sqe_set_data(sqe, pending);
  61         ++pending_reads;
  62 }
  63 #endif
  64
  65 void IOUringEngine::finish()
  66 {
  67         if (!using_uring) {
  68                 return;
  69         }
  70
  71 #ifndef WITHOUT_URING
  72         bool anything_to_submit = true;
  73         while (pending_reads > 0) {
  74                 io_uring_cqe *cqe;
  75                 if (io_uring_peek_cqe(&ring, &cqe) != 0) {
  76                         if (anything_to_submit) {
  77                                 // Nothing ready, so submit whatever is pending and then do a blocking wait.
  78                                 int ret = io_uring_submit_and_wait(&ring, 1);
  79                                 if (ret < 0) {
  80                                         fprintf(stderr, "io_uring_submit(queued): %s\n", strerror(-ret));
  81                                         exit(1);
  82                                 }
  83                                 anything_to_submit = false;
  84                         } else {
  85                                 int ret = io_uring_wait_cqe(&ring, &cqe);
  86                                 if (ret < 0) {
  87                                         fprintf(stderr, "io_uring_wait_cqe: %s\n", strerror(-ret));
  88                                         exit(1);
  89                                 }
  90                         }
  91                 }
  92
  93                 unsigned head;
  94                 io_uring_for_each_cqe(&ring, head, cqe) {
  95                         PendingRead *pending = reinterpret_cast<PendingRead *>(cqe->user_data);
  96                         if (cqe->res <= 0) {
  97                                 fprintf(stderr, "async read failed: %s\n", strerror(-cqe->res));
  98                                 exit(1);
  99                         }
 100
 101                         if (size_t(cqe->res) < pending->iov.iov_len) {
 102                                 // Incomplete read, so resubmit it.
 103                                 pending->iov.iov_base = (char *)pending->iov.iov_base + cqe->res;
 104                                 pending->iov.iov_len -= cqe->res;
 105                                 pending->offset += cqe->res;
 106                                 io_uring_cqe_seen(&ring, cqe);
 107
 108                                 io_uring_sqe *sqe = io_uring_get_sqe(&ring);
 109                                 if (sqe == nullptr) {
 110                                         fprintf(stderr, "No free SQE for resubmit; this shouldn't happen.\n");
 111                                         exit(1);
 112                                 }
 113                                 io_uring_prep_readv(sqe, pending->fd, &pending->iov, 1, pending->offset);
 114                                 io_uring_sqe_set_data(sqe, pending);
 115                                 anything_to_submit = true;
 116                         } else {
 117                                 io_uring_cqe_seen(&ring, cqe);
 118                                 --pending_reads;
 119
 120                                 size_t old_pending_reads = pending_reads;
 121                                 pending->cb(string(reinterpret_cast<char *>(pending->buf), pending->len));
 122                                 free(pending->buf);
 123                                 delete pending;
 124
 125                                 if (pending_reads != old_pending_reads) {
 126                                         // A new read was made in the callback (and not queued),
 127                                         // so we need to re-submit.
 128                                         anything_to_submit = true;
 129                                 }
 130                         }
 131                 }
 132
 133                 // See if there are any queued reads we can submit now.
 134                 while (!queued_reads.empty() && pending_reads < queue_depth) {
 135                         io_uring_sqe *sqe = io_uring_get_sqe(&ring);
 136                         if (sqe == nullptr) {
 137                                 fprintf(stderr, "io_uring_get_sqe: %s\n", strerror(errno));
 138                                 exit(1);
 139                         }
 140                         QueuedRead &qr = queued_reads.front();
 141                         submit_read_internal(sqe, qr.fd, qr.len, qr.offset, move(qr.cb));
 142                         queued_reads.pop();
 143                         anything_to_submit = true;
 144                 }
 145         }
 146 #endif
 147 }
 148
 149 void complete_pread(int fd, void *ptr, size_t len, off_t offset)
 150 {
 151         while (len > 0) {
 152                 ssize_t ret = pread(fd, ptr, len, offset);
 153                 if (ret == -1 && errno == EINTR) {
 154                         continue;
 155                 }
 156                 if (ret <= 0) {
 157                         perror("pread");
 158                         exit(1);
 159                 }
 160                 ptr = reinterpret_cast<char *>(ptr) + ret;
 161                 len -= ret;
 162                 offset -= ret;
 163         }
 164 }