[1.5.0] Enable multithreading in lib build by default (#2584)

* Update lib Makefile to have new targets

* Update lib/README.md for mt

Makefile

@@ -57,8 +57,8 @@ all32:
 	$(MAKE) -C $(PRGDIR) zstd32
 	$(MAKE) -C $(TESTDIR) all32
 
-.PHONY: lib lib-release
+.PHONY: lib lib-release lib-mt lib-nomt
-lib lib-release :
+lib lib-release lib-mt lib-nomt:
 	$(Q)$(MAKE) -C $(ZSTDDIR) $@
 
 .PHONY: zstd zstd-release
@@ -151,7 +151,6 @@ clean:
 ifneq (,$(filter $(shell uname),Linux Darwin GNU/kFreeBSD GNU OpenBSD FreeBSD DragonFly NetBSD MSYS_NT Haiku))
 
 HOST_OS = POSIX
-CMAKE_PARAMS = -DZSTD_BUILD_CONTRIB:BOOL=ON -DZSTD_BUILD_STATIC:BOOL=ON -DZSTD_BUILD_TESTS:BOOL=ON -DZSTD_ZLIB_SUPPORT:BOOL=ON -DZSTD_LZMA_SUPPORT:BOOL=ON -DCMAKE_BUILD_TYPE=Release
 
 HAVE_COLORNEVER = $(shell echo a | egrep --color=never a > /dev/null 2> /dev/null && echo 1 || echo 0)
 EGREP_OPTIONS ?=
@@ -357,12 +356,13 @@ lz4install:
 endif
 
 
+CMAKE_PARAMS = -DZSTD_BUILD_CONTRIB:BOOL=ON -DZSTD_BUILD_STATIC:BOOL=ON -DZSTD_BUILD_TESTS:BOOL=ON -DZSTD_ZLIB_SUPPORT:BOOL=ON -DZSTD_LZMA_SUPPORT:BOOL=ON -DCMAKE_BUILD_TYPE=Release
+
 ifneq (,$(filter MSYS%,$(shell uname)))
 HOST_OS = MSYS
 CMAKE_PARAMS = -G"MSYS Makefiles" -DCMAKE_BUILD_TYPE=Debug -DZSTD_MULTITHREAD_SUPPORT:BOOL=OFF -DZSTD_BUILD_STATIC:BOOL=ON -DZSTD_BUILD_TESTS:BOOL=ON
 endif
 
-
 #------------------------------------------------------------------------
 # target specific tests
 #------------------------------------------------------------------------

lib/Makefile

@@ -8,6 +8,9 @@
 # You may select, at your option, one of the above-listed licenses.
 # ################################################################
 
+# Note: by default, the static library is built single-threaded and dynamic library is built
+# multi-threaded. It is possible to force multi or single threaded builds by appending
+# -mt or -nomt to the build target (like lib-mt for multi-threaded, lib-nomt for single-threaded).
 .PHONY: default
 default: lib-release
 
@@ -68,6 +71,10 @@ DEBUGFLAGS= -Wall -Wextra -Wcast-qual -Wcast-align -Wshadow \
 CFLAGS   += $(DEBUGFLAGS) $(MOREFLAGS)
 FLAGS     = $(CPPFLAGS) $(CFLAGS)
 
+CPPFLAGS_DYNLIB  = -DZSTD_MULTITHREAD # dynamic library build defaults to multi-threaded
+LDFLAGS_DYNLIB   = -pthread
+CPPFLAGS_STATLIB =                    # static library build defaults to single-threaded
+
 HAVE_COLORNEVER = $(shell echo a | grep --color=never a > /dev/null 2> /dev/null && echo 1 || echo 0)
 GREP_OPTIONS ?=
 ifeq ($HAVE_COLORNEVER, 1)
@@ -224,6 +231,7 @@ all: lib
 
 
 .PHONY: libzstd.a  # must be run every time
+libzstd.a: CPPFLAGS += $(CPPFLAGS_STATLIB)
 
 ifndef BUILD_DIR
 # determine BUILD_DIR from compilation flags
@@ -240,7 +248,10 @@ ZSTD_STATLIB_OBJ := $(addprefix $(ZSTD_STATLIB_DIR)/,$(ZSTD_LOCAL_OBJ))
 $(ZSTD_STATLIB): ARFLAGS = rcs
 $(ZSTD_STATLIB): | $(ZSTD_STATLIB_DIR)
 $(ZSTD_STATLIB): $(ZSTD_STATLIB_OBJ)
-	@echo compiling static library
+  # Check for multithread flag at target execution time
+	$(if $(filter -DZSTD_MULTITHREAD,$(CPPFLAGS)),\
+    @echo compiling multi-threaded static library $(LIBVER),\
+    @echo compiling single-threaded static library $(LIBVER))
 	$(AR) $(ARFLAGS) $@ $^
 
 libzstd.a: $(ZSTD_STATLIB)
@@ -259,8 +270,9 @@ else  # not Windows
 
 LIBZSTD = libzstd.$(SHARED_EXT_VER)
 .PHONY: $(LIBZSTD)  # must be run every time
-$(LIBZSTD): CFLAGS += -fPIC -fvisibility=hidden
+$(LIBZSTD): CPPFLAGS += $(CPPFLAGS_DYNLIB)
-$(LIBZSTD): LDFLAGS += -shared
+$(LIBZSTD): CFLAGS   += -fPIC -fvisibility=hidden
+$(LIBZSTD): LDFLAGS  += -shared $(LDFLAGS_DYNLIB)
 
 ifndef BUILD_DIR
 # determine BUILD_DIR from compilation flags
@@ -277,7 +289,10 @@ ZSTD_DYNLIB_OBJ := $(addprefix $(ZSTD_DYNLIB_DIR)/,$(ZSTD_LOCAL_OBJ))
 
 $(ZSTD_DYNLIB): | $(ZSTD_DYNLIB_DIR)
 $(ZSTD_DYNLIB): $(ZSTD_DYNLIB_OBJ)
-	@echo compiling dynamic library $(LIBVER)
+# Check for multithread flag at target execution time
+	$(if $(filter -DZSTD_MULTITHREAD,$(CPPFLAGS)),\
+    @echo compiling multi-threaded dynamic library $(LIBVER),\
+    @echo compiling single-threaded dynamic library $(LIBVER))
 	$(CC) $(FLAGS) $^ $(LDFLAGS) $(SONAME_FLAGS) -o $@
 	@echo creating versioned links
 	ln -sf $@ libzstd.$(SHARED_EXT_MAJOR)
@@ -299,10 +314,17 @@ lib : libzstd.a libzstd
 # note : do not define lib-mt or lib-release as .PHONY
 # make does not consider implicit pattern rule for .PHONY target
 
-%-mt : CPPFLAGS += -DZSTD_MULTITHREAD
+%-mt : CPPFLAGS_DYNLIB  := -DZSTD_MULTITHREAD
-%-mt : LDFLAGS  += -pthread
+%-mt : CPPFLAGS_STATLIB := -DZSTD_MULTITHREAD
+%-mt : LDFLAGS_DYNLIB   := -pthread
 %-mt : %
-	@echo multi-threading build completed
+	@echo multi-threaded build completed
+
+%-nomt : CPPFLAGS_DYNLIB  :=
+%-nomt : LDFLAGS_DYNLIB   :=
+%-nomt : CPPFLAGS_STATLIB :=
+%-nomt : %
+	@echo single-threaded build completed
 
 %-release : DEBUGFLAGS :=
 %-release : %

lib/README.md

@@ -19,12 +19,16 @@ The scope can be reduced on demand (see paragraph _modular build_).
 
 #### Multithreading support
 
-Multithreading is disabled by default when building with `make`.
+When building with `make`, by default the dynamic library is multithreaded and static library is single-threaded (for compatibility reasons).
+
 Enabling multithreading requires 2 conditions :
 - set build macro `ZSTD_MULTITHREAD` (`-DZSTD_MULTITHREAD` for `gcc`)
 - for POSIX systems : compile with pthread (`-pthread` compilation flag for `gcc`)
 
-Both conditions are automatically applied when invoking `make lib-mt` target.
+For convenience, we provide a build target to generate multi and single threaded libraries:
+- Force enable multithreading on both dynamic and static libraries by appending `-mt` to the target, e.g. `make lib-mt`.
+- Force disable multithreading on both dynamic and static libraries by appending `-nomt` to the target, e.g. `make lib-nomt`.
+- By default, as mentioned before, dynamic library is multithreaded, and static library is single-threaded, e.g. `make lib`.
 
 When linking a POSIX program with a multithreaded version of `libzstd`,
 note that it's necessary to invoke the `-pthread` flag during link stage.