Commit 59ecdaea12

@@ -922,24 +922,36 @@ pub const Loop = struct {
 
     /// Performs an async `os.preadv` using a separate thread.
     /// `fd` must block and not return EAGAIN.
-    pub fn preadv(self: *Loop, fd: os.fd_t, iov: []const os.iovec, offset: u64) os.ReadError!usize {
-        var req_node = Request.Node{
-            .data = .{
-                .msg = .{
-                    .preadv = .{
-                        .fd = fd,
-                        .iov = iov,
-                        .offset = offset,
-                        .result = undefined,
+    pub fn preadv(self: *Loop, fd: os.fd_t, iov: []const os.iovec, offset: u64, simulate_evented: bool) os.ReadError!usize {
+        if (simulate_evented) {
+            var req_node = Request.Node{
+                .data = .{
+                    .msg = .{
+                        .preadv = .{
+                            .fd = fd,
+                            .iov = iov,
+                            .offset = offset,
+                            .result = undefined,
+                        },
                     },
+                    .finish = .{ .TickNode = .{ .data = @frame() } },
                 },
-                .finish = .{ .TickNode = .{ .data = @frame() } },
-            },
-        };
-        suspend {
-            self.posixFsRequest(&req_node);
+            };
+            suspend {
+                self.posixFsRequest(&req_node);
+            }
+            return req_node.data.msg.preadv.result;
+        } else {
+            while (true) {
+                return os.preadv(fd, iov, offset) catch |err| switch (err) {
+                    error.WouldBlock => {
+                        self.waitUntilFdReadable(fd);
+                        continue;
+                    },
+                    else => return err,
+                };
+            }
         }
-        return req_node.data.msg.preadv.result;
     }
 
     /// Performs an async `os.write` using a separate thread.

@@ -506,10 +506,12 @@ pub const File = struct {
             if (iovecs.len == 0) return @as(usize, 0);
             const first = iovecs[0];
             return windows.ReadFile(self.handle, first.iov_base[0..first.iov_len], offset, self.intended_io_mode);
-        } else if (self.capable_io_mode != self.intended_io_mode) {
-            return std.event.Loop.instance.?.preadv(self.handle, iovecs, offset);
-        } else {
+        }
+
+        if (self.intended_io_mode == .blocking) {
             return os.preadv(self.handle, iovecs, offset);
+        } else {
+            return std.event.Loop.instance.?.preadv(self.handle, iovecs, offset, self.capable_io_mode != self.intended_io_mode);
         }
     }
 

@@ -622,12 +622,7 @@ pub fn preadv(fd: fd_t, iov: []const iovec, offset: u64) PReadError!usize {
             EINTR => continue,
             EINVAL => unreachable,
             EFAULT => unreachable,
-            EAGAIN => if (std.event.Loop.instance) |loop| {
-                loop.waitUntilFdReadable(fd);
-                continue;
-            } else {
-                return error.WouldBlock;
-            },
+            EAGAIN => return error.WouldBlock,
             EBADF => return error.NotOpenForReading, // can be a race condition
             EIO => return error.InputOutput,
             EISDIR => return error.IsDir,