On 02/01/2017 05:36 PM, Luis Machado wrote:
+typedef std::unique_ptr<stdio_file> stdio_file_up;
+
+/* Like stdio_file, but specifically for stderr.
+
+ This exists because there is no real line-buffering on Windows, see
+ <http://msdn.microsoft.com/en-us/library/86cebhfs%28v=vs.71%29.aspx>
+ so the stdout is either fully-buffered or non-buffered. We can't
+ make stdout non-buffered, because of two concerns:
+
+ 1. Non-buffering hurts performance.
+ 2. Non-buffering may change GDB's behavior when it is interacting
+ with a front-end, such as Emacs.
+
+ We leave stdout as fully buffered, but flush it first when
+ something is written to stderr.
+
+ Note the the 'write_async_safe' method is not overwritten, because
Extra "the".
Did you mean overridden instead of overwritten?
Right, fixed.
The existing comment this is being moved from says "overwritten",
and I missed updating it. ("overwritten" made some sense
in current master, I guess, since to "override" a method
currently you "overwrite" a function pointer.)
+class stderr_file : public stdio_file
+{
+public:
+ explicit stderr_file (FILE *stream);
-/* Create/open a memory based file. Can be used as a scratch buffer
- for collecting output. */
-extern struct ui_file *mem_fileopen (void);
+ /* Flushes gdb_stdout before writing to the underlying stream. */
+ void write (const char *buf, long length_buf) override;
I noticed the above declaration and ...
+ /* Flushes gdb_stdout before writing to the underlying stream. */
+ void puts (const char *linebuffer) override;
... the above declaration both have the same documentation. Do they
accomplish the same?
They both flush gdb_stdout before deferring to the stdio_file
(the superclass) for the actual writing/outputting. "puts" exists as
a separate method because for some ui_file types it's more efficient to
call some available puts-like function (e.g. tui_puts), than
having the puts method always always call the write method, which
requires a strlen call.
Would this help?
gdb/ui-file.h | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/gdb/ui-file.h b/gdb/ui-file.h
index fc70417..d64cdce 100644
--- a/gdb/ui-file.h
+++ b/gdb/ui-file.h
@@ -58,6 +58,8 @@ public:
virtual void write_async_safe (const char *buf, long length_buf)
{ gdb_assert_not_reached ("write_async_safe"); }
+ /* Some ui_files override this to provide a efficient implementation
+ that avoids the strlen. */
virtual void puts (const char *str)
{ this->write (str, strlen (str)); }
@@ -227,10 +229,9 @@ class stderr_file : public stdio_file
public:
explicit stderr_file (FILE *stream);
- /* Flushes gdb_stdout before writing to the underlying stream. */
+ /* Override the output routines to flush gdb_stdout before deferring
+ to stdio_file for the actual outputting. */
void write (const char *buf, long length_buf) override;
-
- /* Flushes gdb_stdout before writing to the underlying stream. */
void puts (const char *linebuffer) override;
};