Expose rcl default logging output handler (#660)

Signed-off-by: Ivan Santiago Paunovic <ivanpauno@ekumenlabs.com>

rcl/include/rcl/logging.h

@@ -21,11 +21,14 @@
 #include "rcl/types.h"
 #include "rcl/visibility_control.h"
 
+#include "rcutils/logging.h"
+
 #ifdef __cplusplus
 extern "C"
 {
 #endif
 
+typedef rcutils_logging_output_handler_t rcl_logging_output_handler_t;
 
 /// Configure the logging system.
 /**
@@ -53,6 +56,34 @@ rcl_logging_configure(
   const rcl_arguments_t * global_args,
   const rcl_allocator_t * allocator);
 
+/// Configure the logging system with the provided output handler.
+/**
+ * Similar to rcl_logging_configure, but it uses the provided output handler.
+ * \sa rcl_logging_configure
+ *
+ * <hr>
+ * Attribute          | Adherence
+ * ------------------ | -------------
+ * Allocates Memory   | Yes
+ * Thread-Safe        | No
+ * Uses Atomics       | No
+ * Lock-Free          | Yes
+ *
+ * \param global_args The global arguments for the system
+ * \param allocator Used to allocate memory used by the logging system
+ * \param output_handler Output handler to be installed
+ * \return `RCL_RET_OK` if successful, or
+ * \return `RCL_RET_BAD_ALLOC` if allocating memory failed, or
+ * \return `RCL_RET_ERR` if a general error occurs
+ */
+RCL_PUBLIC
+RCL_WARN_UNUSED
+rcl_ret_t
+rcl_logging_configure_with_output_handler(
+  const rcl_arguments_t * global_args,
+  const rcl_allocator_t * allocator,
+  rcl_logging_output_handler_t output_handler);
+
 /**
  * This function should be called to tear down the logging setup by the configure function.
  *
@@ -90,6 +121,28 @@ RCL_PUBLIC
 RCL_WARN_UNUSED
 bool rcl_logging_rosout_enabled();
 
+/// Default output handler used by rcl.
+/**
+ * This function can be wrapped in a language specific client library,
+ * adding the necessary mutual exclusion protection there, and then use
+ * `rcl_logging_configure_with_output_handler` instead of
+ * `rcl_logging_configure`.
+ *
+ * <hr>
+ * Attribute          | Adherence
+ * ------------------ | -------------
+ * Allocates Memory   | No
+ * Thread-Safe        | Yes
+ * Uses Atomics       | No
+ * Lock-Free          | Yes
+ */
+RCL_PUBLIC
+void
+rcl_logging_multiple_output_handler(
+  const rcutils_log_location_t * location,
+  int severity, const char * name, rcutils_time_point_value_t timestamp,
+  const char * format, va_list * args);
+
 #ifdef __cplusplus
 }
 #endif

rcl/src/rcl/logging.c

@@ -43,16 +43,6 @@ static bool g_rcl_logging_stdout_enabled = false;
 static bool g_rcl_logging_rosout_enabled = false;
 static bool g_rcl_logging_ext_lib_enabled = false;
 
-/**
- * An output function that sends to multiple output appenders.
- */
-static
-void
-rcl_logging_multiple_output_handler(
-  const rcutils_log_location_t * location,
-  int severity, const char * name, rcutils_time_point_value_t timestamp,
-  const char * format, va_list * args);
-
 /**
  * An output function that sends to the external logger library.
  */
@@ -64,7 +54,10 @@ rcl_logging_ext_lib_output_handler(
   const char * format, va_list * args);
 
 rcl_ret_t
-rcl_logging_configure(const rcl_arguments_t * global_args, const rcl_allocator_t * allocator)
+rcl_logging_configure_with_output_handler(
+  const rcl_arguments_t * global_args,
+  const rcl_allocator_t * allocator,
+  rcl_logging_output_handler_t output_handler)
 {
   RCL_CHECK_ARGUMENT_FOR_NULL(global_args, RCL_RET_INVALID_ARGUMENT);
   RCL_CHECK_ARGUMENT_FOR_NULL(allocator, RCL_RET_INVALID_ARGUMENT);
@@ -106,10 +99,17 @@ rcl_logging_configure(const rcl_arguments_t * global_args, const rcl_allocator_t
         rcl_logging_ext_lib_output_handler;
     }
   }
-  rcutils_logging_set_output_handler(rcl_logging_multiple_output_handler);
+  rcutils_logging_set_output_handler(output_handler);
   return status;
 }
 
+rcl_ret_t
+rcl_logging_configure(const rcl_arguments_t * global_args, const rcl_allocator_t * allocator)
+{
+  return rcl_logging_configure_with_output_handler(
+    global_args, allocator, &rcl_logging_multiple_output_handler);
+}
+
 rcl_ret_t rcl_logging_fini()
 {
   rcl_ret_t status = RCL_RET_OK;
@@ -130,7 +130,6 @@ bool rcl_logging_rosout_enabled()
   return g_rcl_logging_rosout_enabled;
 }
 
-static
 void
 rcl_logging_multiple_output_handler(
   const rcutils_log_location_t * location,