Handle write() returning EAGAIN by sleeping and retrying.

[buftee] / buftee.c

diff --git a/buftee.c b/buftee.c
index 77cba3a..feb213b 100644 (file)
--- a/buftee.c
+++ b/buftee.c
@@ -215,31 +215,54 @@ static int xread(const int fd, char* const restrict buf, const int count) {
   return (int)read_ret;
 }
 
+static void wait_until_writable(const int fd) {
+  fd_set write_fds;
+  FD_ZERO(&write_fds);
+  FD_SET(fd, &write_fds);
+  int select_ret = select(fd + 1, NULL, &write_fds, NULL, NULL);
+  if (select_ret == -1) {
+    if (errno == EINTR) {
+      assert(stopping);  // that should have been SIGTERM
+      return;
+    }
+    err(1, "select(write fd = %d) failed", fd);
+  }
+  if (!FD_ISSET(fd, &write_fds))
+    errx(1, "select() did not return writable fd = %d", fd);
+}
+
 static int xwrite(const int fd, struct buf* const buf) {
   ssize_t write_ret;
   int saved_errno;
   struct timespec t0;
   struct timespec t1;
 
-  get_mono_time(&t0);
-  write_ret = write(fd, buf->data, (size_t)buf->len);
-  saved_errno = errno;
-  get_mono_time(&t1);
-  warn_time("write()", &t0, &t1);
-
-  errno = saved_errno;
-  if (write_ret == -1)
-    err(1, "write(fd = %d, count = %d) failed", fd, buf->len);
-  //FIXME: EAGAIN?
-  if (write_ret == 0)
-    return 0;
-  assert(write_ret >= 0);
-  if (write_ret < buf->len)
-    err(1, "write(fd = %d, count = %d) stopped short (returned %d)",
-        fd, buf->len, (int)write_ret);
-    // FIXME: handle this
-  assert(write_ret == buf->len);
-  return (int)write_ret;
+  for (;;) {
+    get_mono_time(&t0);
+    write_ret = write(fd, buf->data, (size_t)buf->len);
+    saved_errno = errno;
+    get_mono_time(&t1);
+    warn_time("write()", &t0, &t1);
+
+    errno = saved_errno;
+    if (write_ret == -1) {
+      if (errno == EAGAIN) {
+        warn("write(fd = %d) got EAGAIN, sleeping and retrying", fd);
+        wait_until_writable(fd);
+        continue;
+      }
+      err(1, "write(fd = %d, count = %d) failed", fd, buf->len);
+    }
+    if (write_ret == 0)
+      return 0;  // EOF
+    assert(write_ret >= 0);
+    if (write_ret < buf->len)
+      err(1, "write(fd = %d, count = %d) stopped short (returned %d)",
+          fd, buf->len, (int)write_ret);
+      // FIXME: handle this
+    assert(write_ret == buf->len);
+    return (int)write_ret;
+  }
 }
 
 static void wait_until_readable(const int fd) {
@@ -252,7 +275,7 @@ static void wait_until_readable(const int fd) {
       assert(stopping);  // that should have been SIGTERM
       return;
     }
-    err(1, "select() failed");
+    err(1, "select(read fd = %d) failed", fd);
   }
   if (!FD_ISSET(fd, &read_fds))
     errx(1, "select() did not return readable fd = %d", fd);