Create a logger running in a separate thread to offload the work of writing a log to disc (or do anything else that can safely be done asynchronously).
Call aslog_init(size_t buffer_size, bool (*logger)(void *)) to set up aslog. buffer_size is the number of log items that can be buffered. If the buffer is full, aslog_log_enqueue will block until that is no longer the case. logger is a function that will be called by aslog to do the actual logging or whatever it is you want to do. logger will be called with a pointer to some data that has been previously enqueued by you and should return true for a successful log and false if something goes wrong. This function will return an opaque aslog_Logger_t struct that is NULL if something goes wrong.
Call aslog_log_enqueue(aslog_Logger_t log, void *data, bool final) to add a piece of data (pointed to by data) to the log buffer. Pass final = true if the item is the last one you want to log, so aslog does not keep waiting for data that is never going to come. aslog will not do anything with *data except pass the pointer back to your configured callback function. You are responsible for memory management. aslog is not your dad.
Call aslog_shutdown(aslog_Logger_t log) to clean up all memory used by aslog and join() the logger thread. Do this only after you have enqueued your last log item (as indicated by the final flag).