+#define EXPECT_TRUE(x) __builtin_expect(!!(x), 1)
+#define EXPECT_FALSE(x) __builtin_expect(!!(x), 0)
+
+#ifndef NBD_SINGLE_THREADED
+
+#define MAX_NUM_THREADS 32 // make this whatever you want, but make it a power of 2
+
+#define SYNC_SWAP(addr,x) __sync_lock_test_and_set(addr,x)
+#define SYNC_CAS(addr,old,x) __sync_val_compare_and_swap(addr,old,x)
+#define SYNC_ADD(addr,n) __sync_add_and_fetch(addr,n)
+#define SYNC_FETCH_AND_OR(addr,x) __sync_fetch_and_or(addr,x)
+#else// NBD_SINGLE_THREADED
+
+#define MAX_NUM_THREADS 1
+
+#define SYNC_SWAP(addr,x) ({ typeof(*(addr)) _old = *(addr); *(addr) = (x); _old; })
+#define SYNC_CAS(addr,old,x) ({ typeof(*(addr)) _old = *(addr); *(addr) = (x); _old; })
+//#define SYNC_CAS(addr,old,x) ({ typeof(*(addr)) _old = *(addr); if ((old) == _old) { *(addr) = (x); } _old; })
+#define SYNC_ADD(addr,n) ({ typeof(*(addr)) _old = *(addr); *(addr) += (n); _old; })
+#define SYNC_FETCH_AND_OR(addr,x) ({ typeof(*(addr)) _old = *(addr); *(addr) |= (x); _old; })
+
+#endif//NBD_SINGLE_THREADED