Update list of wishes

TODO.md

@@ -36,6 +36,30 @@
 * See https://www.drdobbs.com/soft-real-time-programming-with-linux/184402031
   for soft-real-time programming hints.
 
+## Errors
+
+Simplify and speed-up error management.  Error stack almost never has a depth
+greater than one which means that each thread only has to memorize the last
+error.  The information about the last error can be stored in a per-thread
+static data of small size with qualifier `static _Thread_local` (or `static
+thread_local` with `<threads.h>`).  This data may have a small buffer of given
+size to store all needed information (perhaps with a flag indicating whether
+error message and/or function name are given by static strings).
+
+Simplifications:
+
+- No needs to perform any cleanup on exit and no risk or memory
+  leaks.
+
+- Bindings will be much easier to write.
+
+Expected speed-up:
+
+- Only 3ns to retrieve the per-thread data instead of 13ns in actual code.
+
+- No needs to allocate and free memory for each error.  At most, spend some
+  time to copy the error message and the function name.
+
 
 ## Things to do