[lldb] Synchronize the debuggers output & error streams

This patch improves the synchronization of the debugger's output and error
streams using two new abstractions: `LockableStreamFile` and
`LockedStreamFile`.

 - `LockableStreamFile` is a wrapper around a `StreamFile` and a mutex. Client
   cannot use the `StreamFile` without calling `Lock`, which returns a
   `LockedStreamFile`.

 - `LockedStreamFile` is an RAII object that locks the stream for the duration
   of its existence.  As long as you hold on to the returned object you are
   permitted to write to the stream. The destruction of the object
   automatically flush the output stream.

1 files changed, 5 insertions, 4 deletions

diff --git a/lldb/source/Commands/CommandObjectExpression.cpp b/lldb/source/Commands/CommandObjectExpression.cpp
index 18526c4..a95dea6 100644
--- a/lldb/source/Commands/CommandObjectExpression.cpp
+++ b/lldb/source/Commands/CommandObjectExpression.cpp
@@ -12,6 +12,7 @@
 #include "lldb/Expression/REPL.h"
 #include "lldb/Expression/UserExpression.h"
 #include "lldb/Host/OptionParser.h"
+#include "lldb/Host/StreamFile.h"
 #include "lldb/Interpreter/CommandInterpreter.h"
 #include "lldb/Interpreter/CommandOptionArgumentTable.h"
 #include "lldb/Interpreter/CommandReturnObject.h"
@@ -22,6 +23,7 @@
 #include "lldb/Target/Target.h"
 #include "lldb/Utility/DiagnosticsRendering.h"
 #include "lldb/lldb-enumerations.h"
+#include "lldb/lldb-forward.h"
 #include "lldb/lldb-private-enumerations.h"
 
 using namespace lldb;
@@ -544,11 +546,10 @@ void CommandObjectExpression::GetMultilineExpression() {
                             1, // Show line numbers starting at 1
                             *this));
 
-  StreamFileSP output_sp = io_handler_sp->GetOutputStreamFileSP();
-  if (output_sp) {
-    output_sp->PutCString(
+  if (LockableStreamFileSP output_sp = io_handler_sp->GetOutputStreamFileSP()) {
+    LockedStreamFile locked_stream = output_sp->Lock();
+    locked_stream.PutCString(
         "Enter expressions, then terminate with an empty line to evaluate:\n");
-    output_sp->Flush();
   }
   debugger.RunIOHandlerAsync(io_handler_sp);
 }