From 08364ac773bdc95b9407974b5c761dbdab863f4d Mon Sep 17 00:00:00 2001
From: Loris Cro <kappaloris@gmail.com>
Date: Tue, 16 Jun 2020 23:14:05 +0200
Subject: [PATCH] read

Signed-off-by: Loris Cro <kappaloris@gmail.com>
---
 lib/std/event/loop.zig | 40 ++++++++++++++++++++++++++--------------
 lib/std/fs/file.zig    |  8 +++++---
 lib/std/os.zig         |  7 +------
 3 files changed, 32 insertions(+), 23 deletions(-)

diff --git a/lib/std/event/loop.zig b/lib/std/event/loop.zig
index 2dc1d5659e..7adc6e3a8f 100644
--- a/lib/std/event/loop.zig
+++ b/lib/std/event/loop.zig
@@ -822,23 +822,35 @@ pub const Loop = struct {
 
     /// Performs an async `os.read` using a separate thread.
     /// `fd` must block and not return EAGAIN.
-    pub fn read(self: *Loop, fd: os.fd_t, buf: []u8) os.ReadError!usize {
-        var req_node = Request.Node{
-            .data = .{
-                .msg = .{
-                    .read = .{
-                        .fd = fd,
-                        .buf = buf,
-                        .result = undefined,
+    pub fn read(self: *Loop, fd: os.fd_t, buf: []u8, simulate_evented: bool) os.ReadError!usize {
+        if (simulate_evented) {
+            var req_node = Request.Node{
+                .data = .{
+                    .msg = .{
+                        .read = .{
+                            .fd = fd,
+                            .buf = buf,
+                            .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.read.result;
+        } else {
+            while (true) {
+                return os.read(fd, buf) catch |err| switch (err) {
+                    error.WouldBlock => {
+                        self.waitUntilFdReadable(fd);
+                        continue;
+                    },
+                    else => return err,
+                };
+            }
         }
-        return req_node.data.msg.read.result;
     }
 
     /// Performs an async `os.readv` using a separate thread.
diff --git a/lib/std/fs/file.zig b/lib/std/fs/file.zig
index 73babf5fa2..bd0b8a2943 100644
--- a/lib/std/fs/file.zig
+++ b/lib/std/fs/file.zig
@@ -414,10 +414,12 @@ pub const File = struct {
     pub fn read(self: File, buffer: []u8) ReadError!usize {
         if (is_windows) {
             return windows.ReadFile(self.handle, buffer, null, self.intended_io_mode);
-        } else if (self.capable_io_mode != self.intended_io_mode) {
-            return std.event.Loop.instance.?.read(self.handle, buffer);
-        } else {
+        }
+
+        if (self.intended_io_mode == .blocking or !std.io.is_async) {
             return os.read(self.handle, buffer);
+        } else {
+            return std.event.Loop.instance.?.read(self.handle, buffer, self.capable_io_mode != self.intended_io_mode);
         }
     }
 
diff --git a/lib/std/os.zig b/lib/std/os.zig
index 023c1d5971..7db545a17c 100644
--- a/lib/std/os.zig
+++ b/lib/std/os.zig
@@ -366,12 +366,7 @@ pub fn read(fd: fd_t, buf: []u8) ReadError!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,