[lldb][dap] Avoid concurrent HandleCommand calls (llvm#83162)

The `EventThreadFunction` can end up calling `HandleCommand`
concurrently with the main request processing thread. The underlying API
does not appear to be thread safe, so add a narrowly scoped mutex lock
to prevent calling it in this place from more than one thread.

Fixes llvm#81686. Prior to this, TestDAP_launch.py is 4% flaky. After, it
passes in 1000 runs.

Author: rupprecht

lldb/test/API/tools/lldb-dap/commands/TestDAP_commands.py

@@ -1,13 +1,11 @@
 import os
-import unittest
 
 import dap_server
 import lldbdap_testcase
 from lldbsuite.test import lldbtest, lldbutil
 from lldbsuite.test.decorators import *
 
 
-@unittest.skip("https://llvm.org/PR81686")
 class TestDAP_commands(lldbdap_testcase.DAPTestCaseBase):
     def test_command_directive_quiet_on_success(self):
         program = self.getBuildArtifact("a.out")

lldb/tools/lldb-dap/LLDBUtils.cpp

@@ -9,6 +9,8 @@
 #include "LLDBUtils.h"
 #include "DAP.h"
 
+#include <mutex>
+
 namespace lldb_dap {
 
 bool RunLLDBCommands(llvm::StringRef prefix,
@@ -37,7 +39,15 @@ bool RunLLDBCommands(llvm::StringRef prefix,
       }
     }
 
-    interp.HandleCommand(command.str().c_str(), result);
+    {
+      // Prevent simultaneous calls to HandleCommand, e.g. EventThreadFunction
+      // may asynchronously call RunExitCommands when we are already calling
+      // RunTerminateCommands.
+      static std::mutex handle_command_mutex;
+      std::lock_guard<std::mutex> locker(handle_command_mutex);
+      interp.HandleCommand(command.str().c_str(), result);
+    }
+
     const bool got_error = !result.Succeeded();
     // The if statement below is assuming we always print out `!` prefixed
     // lines. The only time we don't print is when we have `quiet_on_success ==