CMake: Add support for building a thread-less library

Add support for building a thread-less Libiio.

This disables all current backends, but applications are still free to
provide their own external backend. This is especially useful on
embedded, where threads generally aren't a thing.

Signed-off-by: Paul Cercueil <[email protected]>

CMakeLists.txt

@@ -372,6 +372,10 @@ set(LIBIIO_VERSION ${VERSION}.g${LIBIIO_VERSION_GIT})
 file(WRITE ${CMAKE_BINARY_DIR}/.version ${LIBIIO_VERSION})
 
 if(WITH_LOCAL_BACKEND)
+	if (NO_THREADS)
+		message(SEND_ERROR "Local backend require threads.")
+	endif()
+
 	target_sources(iio PRIVATE local.c)
 
 	# Link with librt if present
@@ -576,7 +580,10 @@ elseif(NEED_LIBXML2)
 		"If you want to enable the XML backend, set WITH_XML_BACKEND=ON.")
 endif()
 
-if (WIN32)
+option(NO_THREADS "Build a thread-less Libiio library" OFF)
+if (NO_THREADS)
+	target_sources(iio PRIVATE lock-dummy.c)
+elseif (WIN32)
 	target_sources(iio PRIVATE lock-windows.c)
 else ()
 	if (NOT ANDROID)
@@ -606,6 +613,10 @@ if (IIOD_CLIENT OR WITH_IIOD)
 endif()
 
 if (IIOD_CLIENT)
+	if (NO_THREADS)
+		message(SEND_ERROR "Backends using iiod-client require threads.")
+	endif()
+
 	target_sources(iio PRIVATE iiod-client.c)
 	target_link_libraries(iio PRIVATE iiod-responder)
 endif()
@@ -625,6 +636,10 @@ if(WITH_EXAMPLES)
 	add_subdirectory(examples)
 endif()
 if (WITH_IIOD)
+	if (NO_THREADS)
+		message(SEND_ERROR "IIOD require threads.")
+	endif()
+
 	if (NOT PTHREAD_LIBRARIES)
 		message(SEND_ERROR "IIOD requires pthread support.\n"
 			"If you want to disable IIOD, set WITH_IIOD=OFF.")
@@ -672,6 +687,7 @@ string(REPLACE ";" "," LIBIIO_SCAN_BACKENDS "${LIBIIO_SCAN_BACKENDS}")
 
 configure_file(iio-config.h.cmakein ${CMAKE_CURRENT_BINARY_DIR}/iio-config.h @ONLY)
 
+toggle_iio_feature("${NO_THREADS}" threadless)
 toggle_iio_feature("${LIBIIO_COMPAT}" compat)
 toggle_iio_feature("${WITH_XML_BACKEND}" xml)
 toggle_iio_feature("${WITH_ZSTD}" zstd)

iio-config.h.cmakein

@@ -41,6 +41,7 @@
 #cmakedefine01 HAVE_DNS_SD
 #cmakedefine01 HAVE_AVAHI
 #cmakedefine01 WITH_ZSTD
+#cmakedefine01 NO_THREADS
 
 #cmakedefine HAS_PIPE2
 #cmakedefine HAS_STRDUP
@@ -50,7 +51,6 @@
 #cmakedefine HAS_NEWLOCALE
 #cmakedefine HAS_PTHREAD_SETNAME_NP
 #cmakedefine HAVE_IPV6
-#cmakedefine NO_THREADS
 
 #define IF_ENABLED(cfg, ptr) ((cfg) ? (ptr) : NULL)
 

lock-dummy.c

@@ -0,0 +1,80 @@
+// SPDX-License-Identifier: LGPL-2.1-or-later
+/*
+ * libiio - Library for interfacing industrial I/O (IIO) devices
+ *
+ * Copyright (C) 2024 Analog Devices, Inc.
+ * Author: Paul Cercueil <[email protected]>
+ */
+
+#include <iio/iio.h>
+#include <iio/iio-lock.h>
+
+#include <errno.h>
+#include <stdlib.h>
+
+struct iio_mutex {
+	int dummy; /* Flawfinder: ignore */
+};
+
+struct iio_cond {
+	int dummy; /* Flawfinder: ignore */
+};
+
+struct iio_mutex * iio_mutex_create(void)
+{
+	struct iio_mutex *lock = malloc(sizeof(*lock));
+
+	if (!lock)
+		return iio_ptr(-ENOMEM);
+
+	return lock;
+}
+
+void iio_mutex_destroy(struct iio_mutex *lock)
+{
+	free(lock);
+}
+
+void iio_mutex_lock(struct iio_mutex *lock)
+{
+}
+
+void iio_mutex_unlock(struct iio_mutex *lock)
+{
+}
+
+struct iio_cond * iio_cond_create(void)
+{
+	struct iio_cond *cond = malloc(sizeof(*cond));
+
+	if (!cond)
+		return iio_ptr(-ENOMEM);
+
+	return cond;
+}
+
+void iio_cond_destroy(struct iio_cond *cond)
+{
+	free(cond);
+}
+
+int iio_cond_wait(struct iio_cond *cond, struct iio_mutex *lock,
+		  unsigned int timeout_ms)
+{
+	return -ETIMEDOUT;
+}
+
+void iio_cond_signal(struct iio_cond *cond)
+{
+}
+
+struct iio_thrd * iio_thrd_create(int (*thrd)(void *),
+				  void *d, const char *name)
+{
+	return iio_ptr(-ENOSYS);
+}
+
+int iio_thrd_join_and_destroy(struct iio_thrd *thrd)
+{
+	return 0;
+}