Windows: Manage thread local storage manually in dlfcn_w32

lib/roken/dlfcn_w32.c

@@ -36,17 +36,75 @@
 
 #define ERR_STR_LEN 256
 
-__declspec(thread) static char err_str[ERR_STR_LEN];
+static volatile DWORD dlfcn_tls = TLS_OUT_OF_INDEXES;
 
-static void set_error(const char * e) {
-    StringCbCopy(err_str, sizeof(err_str), e);
+static DWORD get_tl_error_slot(void)
+{
+    if (dlfcn_tls == TLS_OUT_OF_INDEXES) {
+        DWORD slot = TlsAlloc();
+        DWORD old_slot;
+
+        if (slot == TLS_OUT_OF_INDEXES)
+            return dlfcn_tls;
+
+        if ((old_slot = InterlockedCompareExchange(&dlfcn_tls, slot,
+                                                   TLS_OUT_OF_INDEXES)) !=
+            TLS_OUT_OF_INDEXES) {
+
+            /* Lost a race */
+            TlsFree(slot);
+            return old_slot;
+        } else {
+            return slot;
+        }
+    }
+
+    return dlfcn_tls;
+}
+
+static void set_error(const char * e)
+{
+    char * s;
+    char * old_s;
+    size_t len;
+
+    DWORD slot = get_tl_error_slot();
+
+    if (slot == TLS_OUT_OF_INDEXES)
+        return;
+
+    len = strlen(e) * sizeof(char) + sizeof(char);
+    s = LocalAlloc(LMEM_FIXED, len);
+    if (s == NULL)
+        return;
+
+    old_s = (char *) TlsGetValue(slot);
+    TlsSetValue(slot, (LPVOID) s);
+
+    if (old_s != NULL)
+        LocalFree(old_s);
 }
 
 static void set_error_from_last(void) {
-    FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM,
+    DWORD slot = get_tl_error_slot();
+    char * s = NULL;
+    char * old_s;
+
+    if (slot == TLS_OUT_OF_INDEXES)
+        return;
+
+    FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_ALLOCATE_BUFFER,
 		  0, GetLastError(), 0,
-		  err_str, sizeof(err_str)/sizeof(err_str[0]),
+		  (LPTSTR) &s, 0,
 		  NULL);
+    if (s == NULL)
+        return;
+
+    old_s = (char *) TlsGetValue(slot);
+    TlsSetValue(slot, (LPVOID) s);
+
+    if (old_s != NULL)
+        LocalFree(old_s);
 }
 
 ROKEN_LIB_FUNCTION int ROKEN_LIB_CALL
@@ -64,7 +122,12 @@ dlclose(void * vhm)
 ROKEN_LIB_FUNCTION char  * ROKEN_LIB_CALL
 dlerror(void)
 {
-    return err_str;
+    DWORD slot = get_tl_error_slot();
+
+    if (slot == TLS_OUT_OF_INDEXES)
+        return NULL;
+
+    return (char *) TlsGetValue(slot);
 }
 
 ROKEN_LIB_FUNCTION void  * ROKEN_LIB_CALL