+/* Equivalent to write_stream_list_serial(), except this takes a @num_threads
+ * parameter and will perform compression using that many threads. Falls
+ * back to write_stream_list_serial() on certain errors, such as a failure to
+ * create the number of threads requested.
+ *
+ * High level description of the algorithm for writing compressed streams in
+ * parallel: We perform compression on chunks of size WIM_CHUNK_SIZE bytes
+ * rather than on full files. The currently executing thread becomes the main
+ * thread and is entirely in charge of reading the data to compress (which may
+ * be in any location understood by the resource code--- such as in an external
+ * file being captured, or in another WIM file from which an image is being
+ * exported) and actually writing the compressed data to the output file.
+ * Additional threads are "compressor threads" and all execute the
+ * compressor_thread_proc, where they repeatedly retrieve buffers of data from
+ * the main thread, compress them, and hand them back to the main thread.
+ *
+ * Certain streams, such as streams that do not need to be compressed (e.g.
+ * input compression type same as output compression type) or streams of very
+ * small size are placed in a list (main_writer_thread_ctx.serial_list) and
+ * handled entirely by the main thread at an appropriate time.
+ *
+ * At any given point in time, multiple streams may be having chunks compressed
+ * concurrently. The stream that the main thread is currently *reading* may be
+ * later in the list that the stream that the main thread is currently
+ * *writing*.
+ */