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authorJohannes Schindelin <johannes.schindelin@gmx.de>2017-09-25 18:06:24 +0200
committerJunio C Hamano <gitster@pobox.com>2017-09-26 11:02:49 +0900
commitdb2f7c48cb30f8fdcb2933aa7d9890b34e0c4e94 (patch)
tree10fafc47a8017524f7f106c176329b15598db2ae
parent94c9fd268d4287f6fbfef84793288479905a7e48 (diff)
downloadgit-js/win32-lazyload-dll.tar.gz
Win32: simplify loading of DLL functionsjs/win32-lazyload-dll
Dynamic loading of DLL functions is duplicated in several places in Git for Windows' source code. This patch adds a pair of macros to simplify the process: the DECLARE_PROC_ADDR(<dll>, <return-type>, <function-name>, ...<function-parameter-types>...) macro to be used at the beginning of a code block, and the INIT_PROC_ADDR(<function-name>) macro to call before using the declared function. The return value of the INIT_PROC_ADDR() call has to be checked; If it is NULL, the function was not found in the specified DLL. Example: DECLARE_PROC_ADDR(kernel32.dll, BOOL, CreateHardLinkW, LPCWSTR, LPCWSTR, LPSECURITY_ATTRIBUTES); if (!INIT_PROC_ADDR(CreateHardLinkW)) return error("Could not find CreateHardLinkW() function"; if (!CreateHardLinkW(source, target, NULL)) return error("could not create hardlink from %S to %S", source, target); return 0; Signed-off-by: Karsten Blees <blees@dcon.de> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Reviewed-by: Jonathan Nieder <jrnieder@gmail.com> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
-rw-r--r--compat/win32/lazyload.h57
1 files changed, 57 insertions, 0 deletions
diff --git a/compat/win32/lazyload.h b/compat/win32/lazyload.h
new file mode 100644
index 0000000000..9e631c8593
--- /dev/null
+++ b/compat/win32/lazyload.h
@@ -0,0 +1,57 @@
+#ifndef LAZYLOAD_H
+#define LAZYLOAD_H
+
+/*
+ * A pair of macros to simplify loading of DLL functions. Example:
+ *
+ * DECLARE_PROC_ADDR(kernel32.dll, BOOL, CreateHardLinkW,
+ * LPCWSTR, LPCWSTR, LPSECURITY_ATTRIBUTES);
+ *
+ * if (!INIT_PROC_ADDR(CreateHardLinkW))
+ * return error("Could not find CreateHardLinkW() function";
+ *
+ * if (!CreateHardLinkW(source, target, NULL))
+ * return error("could not create hardlink from %S to %S",
+ * source, target);
+ */
+
+struct proc_addr {
+ const char *const dll;
+ const char *const function;
+ FARPROC pfunction;
+ unsigned initialized : 1;
+};
+
+/* Declares a function to be loaded dynamically from a DLL. */
+#define DECLARE_PROC_ADDR(dll, rettype, function, ...) \
+ static struct proc_addr proc_addr_##function = \
+ { #dll, #function, NULL, 0 }; \
+ static rettype (WINAPI *function)(__VA_ARGS__)
+
+/*
+ * Loads a function from a DLL (once-only).
+ * Returns non-NULL function pointer on success.
+ * Returns NULL + errno == ENOSYS on failure.
+ * This function is not thread-safe.
+ */
+#define INIT_PROC_ADDR(function) \
+ (function = get_proc_addr(&proc_addr_##function))
+
+static inline void *get_proc_addr(struct proc_addr *proc)
+{
+ /* only do this once */
+ if (!proc->initialized) {
+ HANDLE hnd;
+ proc->initialized = 1;
+ hnd = LoadLibraryExA(proc->dll, NULL,
+ LOAD_LIBRARY_SEARCH_SYSTEM32);
+ if (hnd)
+ proc->pfunction = GetProcAddress(hnd, proc->function);
+ }
+ /* set ENOSYS if DLL or function was not found */
+ if (!proc->pfunction)
+ errno = ENOSYS;
+ return proc->pfunction;
+}
+
+#endif