Multi-threaded support

[Michael Lui]

Is there any effort to create a thread-safe version?

From a cursory glance, it looks like it would require some thread_local specifiers and locking the error stream.

EDIT: My cursory glance was too cursory. I thought I spotted some namespace scoped variables.

[David Peter]

There is no effort so far, but I'd certainly be in favor of adding support (unless this would somehow require an insane amount of code). Thank you for the feedback!

[Henri Menke]

The dbg macro and the associated structs and functions have no shared state, so they can't race. The std::cerr stream is also thread-safe, so in principle it should suffice to chain all writes to std::cerr together.

diff --git a/dbg.h b/dbg.h
index da26989..55d243e 100644
--- a/dbg.h
+++ b/dbg.h
@@ -319,17 +319,19 @@ class DebugOutput {
     std::stringstream stream_value;
     const bool print_expr_and_type = pretty_print(stream_value, ref);
 
-    std::cerr << ansi(ANSI_DEBUG) << "[" << m_filepath << ":" << m_line << " ("
+    std::stringstream output;
+    output << ansi(ANSI_DEBUG) << "[" << m_filepath << ":" << m_line << " ("
               << m_function_name << ")] " << ansi(ANSI_RESET);
     if (print_expr_and_type) {
-      std::cerr << ansi(ANSI_EXPRESSION) << m_expression << ansi(ANSI_RESET)
+      output << ansi(ANSI_EXPRESSION) << m_expression << ansi(ANSI_RESET)
                 << " = ";
     }
-    std::cerr << ansi(ANSI_VALUE) << stream_value.str() << ansi(ANSI_RESET);
+    output << ansi(ANSI_VALUE) << stream_value.str() << ansi(ANSI_RESET);
     if (print_expr_and_type) {
-      std::cerr << " (" << ansi(ANSI_TYPE) << type << ansi(ANSI_RESET) << ")";
+      output << " (" << ansi(ANSI_TYPE) << type << ansi(ANSI_RESET) << ")";
     }
-    std::cerr << std::endl;
+    output << std::endl;
+    std::cerr << output.str();
 
     return std::forward<T>(value);
   }

Of course the << ostream operator must be thread-safe for the value to be streamed, but that is the user's responsibility. A well-behaved << operators should be const anyway.

[David Peter]

Thank you for the analysis! I think it is spot on. Let's implement the change with the additional stringstream 👍

[Henri Menke]

If the master branch hasn't diverged too far since my comment, you can just git apply the patch.

[David Peter]

Thank you.