Add handle_eintr to wrap EINTR handling in syscalls

gdbsupport/ChangeLog:

	* eintr.h: New file.

gdbsupport/ChangeLog

@@ -1,3 +1,7 @@
+2020-09-10  Kamil Rytarowski  <n54@gmx.com>
+
+	* eintr.h: New file.
+
 2020-08-13  Simon Marchi  <simon.marchi@polymtl.ca>
 
 	* selftest.h (run_tests): Change parameter to array_view.

gdbsupport/eintr.h

@@ -0,0 +1,67 @@
+/* Utility for handling interrupted syscalls by signals.
+
+   Copyright (C) 2020 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#ifndef GDBSUPPORT_EINTR_H
+#define GDBSUPPORT_EINTR_H
+
+#include <cerrno>
+
+namespace gdb
+{
+/* Repeat a system call interrupted with a signal.
+
+   A utility for handling interrupted syscalls, which return with error
+   and set the errno to EINTR.  The interrupted syscalls can be repeated,
+   until successful completion.  This utility avoids wrapping code with
+   manual checks for such errors which are highly repetitive.
+
+   For example, with:
+
+   ssize_t ret;
+   do
+     {
+       errno = 0;
+       ret = ::write (pipe[1], "+", 1);
+     }
+   while (ret == -1 && errno == EINTR);
+
+   You could wrap it by writing the wrapped form:
+
+   ssize_t ret = gdb::handle_eintr<ssize_t> (-1, ::write, pipe[1], "+", 1);
+
+   The RET typename specifies the return type of the wrapped system call, which
+   is typically int or ssize_t.  The R argument specifies the failure value
+   indicating the interrupted syscall when calling the F function with
+   the A... arguments.  */
+
+template <typename Ret, typename Fun, typename... Args>
+inline Ret handle_eintr (const Ret &R, const Fun &F, const Args &... A)
+{
+  Ret ret;
+  do
+    {
+      errno = 0;
+      ret = F (A...);
+    }
+  while (ret == R && errno == EINTR);
+  return ret;
+}
+}
+
+#endif /* GDBSUPPORT_EINTR_H */