[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, 19 insertions, 16 deletions

diff --git a/lldb/source/Commands/CommandObjectTarget.cpp b/lldb/source/Commands/CommandObjectTarget.cpp
index 71ddc8d933e1..bd9470b80494 100644
--- a/lldb/source/Commands/CommandObjectTarget.cpp
+++ b/lldb/source/Commands/CommandObjectTarget.cpp
@@ -57,6 +57,7 @@
 #include "lldb/Utility/Timer.h"
 #include "lldb/ValueObject/ValueObjectVariable.h"
 #include "lldb/lldb-enumerations.h"
+#include "lldb/lldb-forward.h"
 #include "lldb/lldb-private-enumerations.h"
 
 #include "clang/Frontend/CompilerInstance.h"
@@ -4923,11 +4924,13 @@ Filter Options:
 
 protected:
   void IOHandlerActivated(IOHandler &io_handler, bool interactive) override {
-    StreamFileSP output_sp(io_handler.GetOutputStreamFileSP());
-    if (output_sp && interactive) {
-      output_sp->PutCString(
-          "Enter your stop hook command(s).  Type 'DONE' to end.\n");
-      output_sp->Flush();
+    if (interactive) {
+      if (lldb::LockableStreamFileSP output_sp =
+              io_handler.GetOutputStreamFileSP()) {
+        LockedStreamFile locked_stream = output_sp->Lock();
+        locked_stream.PutCString(
+            "Enter your stop hook command(s).  Type 'DONE' to end.\n");
+      }
     }
   }
 
@@ -4935,12 +4938,12 @@ protected:
                               std::string &line) override {
     if (m_stop_hook_sp) {
       if (line.empty()) {
-        StreamFileSP error_sp(io_handler.GetErrorStreamFileSP());
-        if (error_sp) {
-          error_sp->Printf("error: stop hook #%" PRIu64
-                           " aborted, no commands.\n",
-                           m_stop_hook_sp->GetID());
-          error_sp->Flush();
+        if (lldb::LockableStreamFileSP error_sp =
+                io_handler.GetErrorStreamFileSP()) {
+          LockedStreamFile locked_stream = error_sp->Lock();
+          locked_stream.Printf("error: stop hook #%" PRIu64
+                               " aborted, no commands.\n",
+                               m_stop_hook_sp->GetID());
         }
         GetTarget().UndoCreateStopHook(m_stop_hook_sp->GetID());
       } else {
@@ -4949,11 +4952,11 @@ protected:
             static_cast<Target::StopHookCommandLine *>(m_stop_hook_sp.get());
 
         hook_ptr->SetActionFromString(line);
-        StreamFileSP output_sp(io_handler.GetOutputStreamFileSP());
-        if (output_sp) {
-          output_sp->Printf("Stop hook #%" PRIu64 " added.\n",
-                            m_stop_hook_sp->GetID());
-          output_sp->Flush();
+        if (lldb::LockableStreamFileSP output_sp =
+                io_handler.GetOutputStreamFileSP()) {
+          LockedStreamFile locked_stream = output_sp->Lock();
+          locked_stream.Printf("Stop hook #%" PRIu64 " added.\n",
+                               m_stop_hook_sp->GetID());
         }
       }
       m_stop_hook_sp.reset();