Merge pull request #1000 from facebook/progressiveFlush

Progressive flush

doc/zstd_manual.html

@@ -926,7 +926,7 @@ size_t ZSTD_CCtx_refPrefix_advanced(ZSTD_CCtx* cctx, const void* prefix, size_t
 </p></pre><BR>
 
 <pre><b>typedef enum {
-    ZSTD_e_continue=0, </b>/* collect more data, encoder transparently decides when to output result, for optimal conditions */<b>
+    ZSTD_e_continue=0, </b>/* collect more data, encoder decides when to output compressed result, for optimal conditions */<b>
     ZSTD_e_flush,      </b>/* flush any data provided so far - frame will continue, future data can still reference previous data for better compression */<b>
     ZSTD_e_end         </b>/* flush any remaining data and close current frame. Any additional data starts a new frame. */<b>
 } ZSTD_EndDirective;
@@ -945,10 +945,11 @@ size_t ZSTD_CCtx_refPrefix_advanced(ZSTD_CCtx* cctx, const void* prefix, size_t
                                                      and then immediately returns, just indicating that there is some data remaining to be flushed.
                                                      The function nonetheless guarantees forward progress : it will return only after it reads or write at least 1+ byte.
   - Exception : in multi-threading mode, if the first call requests a ZSTD_e_end directive, it is blocking : it will complete compression before giving back control to caller.
-  - @return provides the minimum amount of data remaining to be flushed from internal buffers
+  - @return provides a minimum amount of data remaining to be flushed from internal buffers
             or an error code, which can be tested using ZSTD_isError().
             if @return != 0, flush is not fully completed, there is still some data left within internal buffers.
-            This is useful to determine if a ZSTD_e_flush or ZSTD_e_end directive is completed.
+            This is useful for ZSTD_e_flush, since in this case more flushes are necessary to empty all buffers.
+            For ZSTD_e_end, @return == 0 when internal buffers are fully flushed and frame is completed.
   - after a ZSTD_e_end directive, if internal buffer is not fully flushed (@return != 0),
             only ZSTD_e_end or ZSTD_e_flush operations are allowed.
             Before starting a new compression job, or changing compression parameters,