Add IO#pread and IO#pwrite methods

These methods are useful for safe/concurrent file I/O in
multi-thread/process environments and also fairly standard
nowadays especially in systems supporting pthreads.

Based on patches by Avseyev <sergey.avseyev@gmail.com> at
[ruby-core:79290].  [Feature #4532]

* configure.in: check for pwrite(2).  pread() is already used
  internally for IO.copy_stream.

* io.c: implement wrappers for pread(2) and pwrite(2) and expose
  them in IO.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58240 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 21 insertions, 0 deletions

diff --git a/test/ruby/test_io.rb b/test/ruby/test_io.rb
index ca3f1e2d3b..d6cbf205e9 100644
--- a/test/ruby/test_io.rb
+++ b/test/ruby/test_io.rb
@@ -3525,5 +3525,26 @@ __END__
         end
       end
     end
+
+    def test_pread
+      make_tempfile { |t|
+        open(t.path) do |f|
+          assert_equal("bar", f.pread(3, 4))
+          buf = "asdf"
+          assert_equal("bar", f.pread(3, 4, buf))
+          assert_equal("bar", buf)
+          assert_raise(EOFError) { f.pread(1, f.size) }
+        end
+      }
+    end if IO.method_defined?(:pread)
+
+    def test_pwrite
+      make_tempfile { |t|
+        open(t.path, IO::RDWR) do |f|
+          assert_equal(3, f.pwrite(4, "ooo"))
+          assert_equal("ooo", f.pread(3, 4))
+        end
+      }
+    end if IO.method_defined?(:pread) and IO.method_defined?(:pwrite)
   end
 end