deps.labjack: support building for windows

The only pthread functionality this seems to use is mutexes, which are
(fortunately) theoretically trivial to wrap for windows. This
compiles, though it is not clear if it actually works correctly.

deps/labjack/ljacklm/build.zig

@@ -17,6 +17,10 @@ pub fn build(b: *std.Build) !void {
         .link_libc = true,
     });
 
+    if (target.result.os.tag == .windows) {
+        libljacklm.defineCMacro("LJACKLM_USE_WINDOWS_MUTEX_SHIM", "1");
+    }
+
     libljacklm.addCSourceFile(.{ .file = b.path("libljacklm/ljacklm.c") });
     libljacklm.installHeader(b.path("libljacklm/ljacklm.h"), "ljacklm.h");
 

deps/labjack/ljacklm/libljacklm/ljacklm.c

@@ -23,7 +23,14 @@
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
-#include <pthread.h>
+
+#if defined(LJACKLM_USE_WINDOWS_MUTEX_SHIM)
+	#include <windows.h>
+	#include "windows_mutex_shim.h"
+#else
+	#include <pthread.h>
+#endif // LJACKLM_USE_WINDOWS_MUTEX_SHIM
+
 #include "labjackusb.h"
 
 
@@ -286,7 +293,9 @@ long GetU12Information( HANDLE hDevice,
 					    long *fcddMaxSize,
 					    long *hvcMaxSize);
 
+#if !defined(LJACKLM_USE_WINDOWS_MUTEX_SHIM)
 unsigned long GetTickCount( void);
+#endif
 
 
 __attribute__((constructor))
@@ -7266,6 +7275,7 @@ long GetU12Information( HANDLE hDevice,
 }
 
 
+#if !defined(LJACKLM_USE_WINDOWS_MUTEX_SHIM)
 //======================================================================
 //GetTickCount:	Implementation of GetTickCount() for Unix.  Returns the
 //				current time, expressed as millisconds since the Epoch 
@@ -7276,3 +7286,4 @@ unsigned long GetTickCount( void)
 	gettimeofday(&tv, NULL);
 	return (tv.tv_sec * 1000) + (tv.tv_usec / 1000);
 }
+#endif

deps/labjack/ljacklm/libljacklm/windows_mutex_shim.h

@@ -0,0 +1,28 @@
+#ifndef LJACKLM_WIN_MUTEX
+#define LJACKLM_WIN_MUTEX
+
+typedef CRITICAL_SECTION pthread_mutex_t;
+
+static inline int pthread_mutex_init(pthread_mutex_t *mutex, void *attr) {
+    InitializeCriticalSection(mutex);
+    return 0;
+}
+
+static inline void pthread_mutex_lock(pthread_mutex_t *mutex) {
+    EnterCriticalSection(mutex);
+}
+
+static inline int pthread_mutex_unlock(pthread_mutex_t *mutex) {
+    LeaveCriticalSection(mutex);
+    return 0;
+}
+
+static inline int pthread_mutex_trylock(pthread_mutex_t *mutex) {
+    return TryEnterCriticalSection(mutex) != 0;
+}
+
+static inline void pthread_mutex_destroy(pthread_mutex_t *mutex) {
+    DeleteCriticalSection(mutex);
+}
+
+#endif // LJACKLM_WIN_MUTEX