Only set EAGAIN when written == 0 and length > 0. Fixes #2957

Because we use NIO channels for all IO, but need to behave like POSIX IO functions, we emulate errno behavior for various cases. This particular issue is an edge case, when writing zero bytes to a stream marked as nonblocking (as happens after it is used in an IO.select operation); we see that it's nonblocking and nothing was written and unconditionally treat that as EAGAIN. Instead, we should only set EAGAIN when zero bytes are written and we actually did have bytes to write.
jruby · May 21, 2015 · f156123 · f156123
1 parent ae31756
commit f156123
Showing 1 changed file with 1 addition and 1 deletion.
diff --git a/core/src/main/java/org/jruby/util/io/PosixShim.java b/core/src/main/java/org/jruby/util/io/PosixShim.java
@@ -91,7 +91,7 @@ public int write(ChannelFD fd, byte[] bytes, int offset, int length, boolean non
 
             int written = fd.chWrite.write(tmp);
 
-            if (written == 0) {
+            if (written == 0 && length > 0) {
                 // if it's a nonblocking write against a file and we've hit EOF, do EAGAIN
                 if (nonblock) {
                     errno = Errno.EAGAIN;