zstdmt: added ability to change compression parameters during compression

lib/compress/zstd_compress.c

@@ -476,6 +476,9 @@ size_t ZSTD_CCtxParam_setParameter(
 /** ZSTD_CCtx_setParametersUsingCCtxParams() :
  *  just applies `params` into `cctx`
  *  no action is performed, parameters are merely stored.
+ *  If ZSTDMT is enabled, parameters are pushed to cctx->mtctx.
+ *    This is possible even if a compression is ongoing.
+ *    In which case, new parameters will be applied on the fly, starting with next compression job.
  */
 size_t ZSTD_CCtx_setParametersUsingCCtxParams(
         ZSTD_CCtx* cctx, const ZSTD_CCtx_params* params)
@@ -484,6 +487,10 @@ size_t ZSTD_CCtx_setParametersUsingCCtxParams(
     if (cctx->cdict) return ERROR(stage_wrong);
 
     cctx->requestedParams = *params;
+#ifdef ZSTD_MULTITHREAD
+    if (cctx->mtctx)
+        ZSTDMT_MTCtx_setParametersUsingCCtxParams(cctx->mtctx, params);
+#endif
 
     return 0;
 }

lib/compress/zstdmt_compress.c

@@ -664,6 +664,25 @@ static ZSTD_CCtx_params ZSTDMT_initJobCCtxParams(ZSTD_CCtx_params const params)
     return jobParams;
 }
 
+/*! ZSTDMT_MTCtx_setParametersUsingCCtxParams() :
+ *  Apply a ZSTD_CCtx_params to the compression context.
+ *  This entry point is accessed while compression is ongoing,
+ *  new parameters will be applied to next compression job.
+ *  However, following parameters are NOT updated :
+ *  - window size
+ *  - pledgedSrcSize
+ *  - nb threads
+ *  - job size
+ *  - overlap size
+ */
+void ZSTDMT_MTCtx_setParametersUsingCCtxParams(ZSTDMT_CCtx* mtctx, const ZSTD_CCtx_params* params)
+{
+    U32 const wlog = mtctx->params.cParams.windowLog;
+    mtctx->params = *params;
+    mtctx->params.cParams.windowLog = wlog;  /* Do not modify windowLog ! */
+    /* note : other parameters not updated are simply not used beyond initialization */
+}
+
 /* ZSTDMT_getNbThreads():
  * @return nb threads currently active in mtctx.
  * mtctx must be valid */
@@ -856,7 +875,7 @@ size_t ZSTDMT_compress_advanced(ZSTDMT_CCtx* mtctx,
                                void* dst, size_t dstCapacity,
                          const void* src, size_t srcSize,
                          const ZSTD_CDict* cdict,
-                               ZSTD_parameters const params,
+                               ZSTD_parameters params,
                                unsigned overlapLog)
 {
     ZSTD_CCtx_params cctxParams = mtctx->params;

lib/compress/zstdmt_compress.h

@@ -38,7 +38,7 @@ ZSTDLIB_API size_t ZSTDMT_freeCCtx(ZSTDMT_CCtx* mtctx);
 ZSTDLIB_API size_t ZSTDMT_sizeof_CCtx(ZSTDMT_CCtx* mtctx);
 
 
-/* ===   Simple buffer-to-butter one-pass function   === */
+/* ===   Simple one-pass compression function   === */
 
 ZSTDLIB_API size_t ZSTDMT_compressCCtx(ZSTDMT_CCtx* mtctx,
                                        void* dst, size_t dstCapacity,
@@ -50,7 +50,7 @@ ZSTDLIB_API size_t ZSTDMT_compressCCtx(ZSTDMT_CCtx* mtctx,
 /* ===   Streaming functions   === */
 
 ZSTDLIB_API size_t ZSTDMT_initCStream(ZSTDMT_CCtx* mtctx, int compressionLevel);
-ZSTDLIB_API size_t ZSTDMT_resetCStream(ZSTDMT_CCtx* mtctx, unsigned long long pledgedSrcSize);  /**< if srcSize is not known at reset time, use ZSTD_CONTENTSIZE_UNKNOWN. Note: for compatibility with older programs, 0 means the same as ZSTD_CONTENTSIZE_UNKNOWN, but it may change in the future, to mean "empty" */
+ZSTDLIB_API size_t ZSTDMT_resetCStream(ZSTDMT_CCtx* mtctx, unsigned long long pledgedSrcSize);  /**< if srcSize is not known at reset time, use ZSTD_CONTENTSIZE_UNKNOWN. Note: for compatibility with older programs, 0 means the same as ZSTD_CONTENTSIZE_UNKNOWN, but it will change in the future to mean "empty" */
 
 ZSTDLIB_API size_t ZSTDMT_compressStream(ZSTDMT_CCtx* mtctx, ZSTD_outBuffer* output, ZSTD_inBuffer* input);
 
@@ -68,7 +68,7 @@ ZSTDLIB_API size_t ZSTDMT_compress_advanced(ZSTDMT_CCtx* mtctx,
                                            void* dst, size_t dstCapacity,
                                      const void* src, size_t srcSize,
                                      const ZSTD_CDict* cdict,
-                                           ZSTD_parameters const params,
+                                           ZSTD_parameters params,
                                            unsigned overlapLog);
 
 ZSTDLIB_API size_t ZSTDMT_initCStream_advanced(ZSTDMT_CCtx* mtctx,
@@ -109,15 +109,30 @@ ZSTDLIB_API size_t ZSTDMT_compressStream_generic(ZSTDMT_CCtx* mtctx,
                                                 ZSTD_EndDirective endOp);
 
 
-/* ===   Private definitions; never ever use directly  === */
+/* ========================================================
+ * ===  Private interface, for use by ZSTD_compress.c   ===
+ * ===  Not exposed in libzstd. Never invoke directly   ===
+ * ======================================================== */
 
 size_t ZSTDMT_CCtxParam_setMTCtxParameter(ZSTD_CCtx_params* params, ZSTDMT_parameter parameter, unsigned value);
 
 /* ZSTDMT_CCtxParam_setNbThreads()
- * Set nbThreads, and clamp it correctly,
+ * Set nbThreads, and clamp it.
- * also reset jobSize and overlapLog */
+ * Also reset jobSize and overlapLog */
 size_t ZSTDMT_CCtxParam_setNbThreads(ZSTD_CCtx_params* params, unsigned nbThreads);
 
+/*! ZSTDMT_MTCtx_setParametersUsingCCtxParams() :
+ *  Apply a ZSTD_CCtx_params to the compression context.
+ *  This works even during compression, and will be applied to next compression job.
+ *  However, the following parameters will NOT be updated after compression has been started :
+ *  - window size
+ *  - pledgedSrcSize
+ *  - nb threads
+ *  - job size
+ *  - overlap size
+ */
+void ZSTDMT_MTCtx_setParametersUsingCCtxParams(ZSTDMT_CCtx* mtctx, const ZSTD_CCtx_params* params);
+
 /* ZSTDMT_getNbThreads():
  * @return nb threads currently active in mtctx.
  * mtctx must be valid */

lib/zstd.h

@@ -1198,7 +1198,7 @@ ZSTDLIB_API size_t ZSTD_compress_generic_simpleArgs (
 ZSTDLIB_API ZSTD_CCtx_params* ZSTD_createCCtxParams(void);
 
 /*! ZSTD_resetCCtxParams() :
- *  Reset params to default, with the default compression level.
+ *  Reset params to default values.
  */
 ZSTDLIB_API size_t ZSTD_resetCCtxParams(ZSTD_CCtx_params* params);