Make the Windows Console work better

The stdio reader thread now appears to be working recursively along
cosmopolitan subprocesses. For example, it's now possible to launch
vim.com from the unbourne.com bestline repl, thanks to hacks plus a
bug fix to select() timeouts.

libc/calls/tcflush.c

@@ -23,10 +23,14 @@
 #include "libc/calls/syscall_support-nt.internal.h"
 #include "libc/calls/termios.h"
 #include "libc/dce.h"
+#include "libc/errno.h"
 #include "libc/fmt/itoa.h"
 #include "libc/intrin/strace.internal.h"
 #include "libc/mem/alloca.h"
 #include "libc/nt/comms.h"
+#include "libc/nt/console.h"
+#include "libc/sysv/consts/fileno.h"
+#include "libc/sysv/consts/o.h"
 #include "libc/sysv/consts/termios.h"
 #include "libc/sysv/errfuns.h"
 
@@ -45,18 +49,48 @@ static const char *DescribeFlush(char buf[12], int action) {
 }
 
 static dontinline textwindows int sys_tcflush_nt(int fd, int queue) {
-  bool32 ok;
-  int64_t h;
-  if (!__isfdopen(fd)) return ebadf();
-  ok = true;
-  h = g_fds.p[fd].handle;
-  if (queue == TCIFLUSH || queue == TCIOFLUSH) {
-    ok &= !!PurgeComm(h, kNtPurgeRxclear);
+  if (!__isfdopen(fd)) {
+    return ebadf();
   }
-  if (queue == TCOFLUSH || queue == TCIOFLUSH) {
-    ok &= !!PurgeComm(h, kNtPurgeTxclear);
+  int64_t hConin;
+  if (__isfdkind(fd, kFdConsole)) {
+    hConin = g_fds.p[fd].handle;
+  } else if (fd == 0 || fd == 1 || fd == 2) {
+    hConin = g_fds.p[(fd = 0)].handle;
+  } else {
+    return enotty();
   }
-  return ok ? 0 : __winerr();
+  uint32_t inmode;
+  if (!GetConsoleMode(hConin, &inmode)) {
+    return enotty();
+  }
+  if (queue == TCOFLUSH) {
+    return 0;  // windows console output is never buffered
+  }
+  FlushConsoleInputBuffer(hConin);
+  int rc = 0;
+  int e = errno;
+  int oldflags = g_fds.p[fd].flags;
+  g_fds.p[fd].flags |= O_NONBLOCK;
+  for (;;) {
+    char buf[512];
+    ssize_t got = sys_read_nt_impl(fd, buf, 512, -1);
+    if (!got) {
+      break;
+    } else if (got == -1) {
+      if (errno == EAGAIN) {
+        errno = e;
+      } else if (errno == EINTR) {
+        errno = e;
+        continue;
+      } else {
+        rc = -1;
+      }
+      break;
+    }
+  }
+  g_fds.p[fd].flags = oldflags;
+  return rc;
 }
 
 /**
@@ -77,7 +111,9 @@ static dontinline textwindows int sys_tcflush_nt(int fd, int queue) {
  */
 int tcflush(int fd, int queue) {
   int rc;
-  if (fd < g_fds.n && g_fds.p[fd].kind == kFdZip) {
+  if (queue != TCIFLUSH && queue != TCOFLUSH && queue != TCIOFLUSH) {
+    rc = einval();
+  } else if (fd < g_fds.n && g_fds.p[fd].kind == kFdZip) {
     rc = enotty();
   } else if (IsLinux()) {
     rc = sys_ioctl(fd, TCFLSH, queue);