mdbx: fix/rework cache-line alignment.

src/bits.h

@@ -55,6 +55,7 @@
 #pragma warning(disable : 4310) /* cast truncates constant value */
 #pragma warning(disable : 4820) /* bytes padding added after data member for aligment */
 #pragma warning(disable : 4548) /* expression before comma has no effect; expected expression with side - effect */
+#pragma warning(disable : 4366) /* the result of the unary '&' operator may be unaligned */
 #endif                          /* _MSC_VER (warnings) */
 
 #include "../mdbx.h"
@@ -252,7 +253,7 @@ typedef struct MDBX_reader {
   uint8_t pad[MDBX_CACHELINE_SIZE -
               (sizeof(txnid_t) + sizeof(mdbx_pid_t) + sizeof(mdbx_tid_t)) %
                   MDBX_CACHELINE_SIZE];
-} __cache_aligned MDBX_reader;
+} MDBX_reader;
 
 /* Information about a single database in the environment. */
 typedef struct MDBX_db {
@@ -410,42 +411,50 @@ typedef struct MDBX_lockinfo {
   /* Flags which environment was opened. */
   volatile uint32_t mti_envmode;
 
-  union {
 #ifdef MDBX_OSAL_LOCK
+  /* Mutex protecting write access to this table. */
+  union {
     MDBX_OSAL_LOCK mti_wmutex;
+    uint8_t pad_mti_wmutex[MDBX_OSAL_LOCK_SIZE % sizeof(size_t)];
+  };
 #endif
-    uint64_t align_wmutex;
-  };
+#define MDBX_lockinfo_SIZE_A                                                   \
+  (8 /* mti_magic_and_version */ + 4 /* mti_os_and_format */ +                 \
+   4 /* mti_envmode */ + MDBX_OSAL_LOCK_SIZE /* mti_wmutex */ +                \
+   MDBX_OSAL_LOCK_SIZE % sizeof(size_t) /* pad_mti_wmutex */)
 
-  union {
-    /* The number of slots that have been used in the reader table.
-     * This always records the maximum count, it is not decremented
-     * when readers release their slots. */
-    volatile unsigned __cache_aligned mti_numreaders;
-    uint64_t align_numreaders;
-  };
+  /* cache-line alignment */
+  uint8_t
+      pad_a[MDBX_CACHELINE_SIZE - MDBX_lockinfo_SIZE_A % MDBX_CACHELINE_SIZE];
+
+  /* The number of slots that have been used in the reader table.
+   * This always records the maximum count, it is not decremented
+   * when readers release their slots. */
+  volatile unsigned mti_numreaders;
 
-  union {
 #ifdef MDBX_OSAL_LOCK
-    /* Mutex protecting access to this table. */
+  /* Mutex protecting readers registration access to this table. */
+  union {
     MDBX_OSAL_LOCK mti_rmutex;
+    uint8_t pad_mti_rmutex[MDBX_OSAL_LOCK_SIZE % sizeof(size_t)];
+  };
 #endif
-    uint64_t align_rmutex;
-  };
 
-  union {
-    volatile txnid_t mti_oldest;
-    uint64_t align_oldest;
-  };
+  volatile txnid_t mti_oldest;
+  volatile uint32_t mti_readers_refresh_flag;
 
-  union {
-    volatile uint32_t mti_readers_refresh_flag;
-    uint64_t align_reader_finished_flag;
-  };
+#define MDBX_lockinfo_SIZE_B                                                   \
+  (sizeof(unsigned) /* mti_numreaders */ +                                     \
+   MDBX_OSAL_LOCK_SIZE /* mti_rmutex */ + sizeof(txnid_t) /* mti_oldest */ +   \
+   sizeof(uint32_t) /* mti_readers_refresh_flag */ +                           \
+   MDBX_OSAL_LOCK_SIZE % sizeof(size_t) /* pad_mti_rmutex */)
 
-  uint8_t pad_align[MDBX_CACHELINE_SIZE - sizeof(uint64_t) * 7];
+  /* cache-line alignment */
+  uint8_t
+      pad_b[MDBX_CACHELINE_SIZE - MDBX_lockinfo_SIZE_B % MDBX_CACHELINE_SIZE];
+
+  MDBX_reader mti_readers[1];
 
-  MDBX_reader __cache_aligned mti_readers[1];
 } MDBX_lockinfo;
 
 #pragma pack(pop)

src/defs.h

@@ -192,16 +192,6 @@
 #	endif
 #endif /* __prefetch */
 
-#ifndef __aligned
-#   if defined(__GNUC__) || __has_attribute(aligned)
-#       define __aligned(N) __attribute__((aligned(N)))
-#   elif defined(_MSC_VER)
-#       define __aligned(N) __declspec(align(N))
-#   else
-#       define __aligned(N)
-#   endif
-#endif /* __aligned */
-
 #ifndef __noreturn
 #   if defined(__GNUC__) || __has_attribute(noreturn)
 #       define __noreturn __attribute__((noreturn))

src/mdbx.c

@@ -2618,6 +2618,12 @@ static int mdbx_txn_renew0(MDBX_txn *txn, unsigned flags) {
     return MDBX_PANIC;
   }
 
+  STATIC_ASSERT(sizeof(MDBX_reader) == MDBX_CACHELINE_SIZE);
+  STATIC_ASSERT(offsetof(MDBX_lockinfo, mti_numreaders) % MDBX_CACHELINE_SIZE ==
+                0);
+  STATIC_ASSERT(offsetof(MDBX_lockinfo, mti_readers) % MDBX_CACHELINE_SIZE ==
+                0);
+
   pgno_t upper_pgno = 0;
   if (flags & MDBX_TXN_RDONLY) {
     txn->mt_flags = MDBX_TXN_RDONLY;
@@ -2673,9 +2679,6 @@ static int mdbx_txn_renew0(MDBX_txn *txn, unsigned flags) {
         }
       }
 
-      STATIC_ASSERT(sizeof(MDBX_reader) == MDBX_CACHELINE_SIZE);
-      STATIC_ASSERT(
-          offsetof(MDBX_lockinfo, mti_readers) % MDBX_CACHELINE_SIZE == 0);
       r = &env->me_lck->mti_readers[slot];
       /* Claim the reader slot, carefully since other code
        * uses the reader table un-mutexed: First reset the

src/osal.h

@@ -353,10 +353,6 @@ static __inline void mdbx_memory_barrier(void) {
 #endif
 #endif /* MDBX_CACHELINE_SIZE */
 
-#ifndef __cache_aligned
-#define __cache_aligned __aligned(MDBX_CACHELINE_SIZE)
-#endif
-
 #if MDBX_CACHE_IS_COHERENT
 #define mdbx_coherent_barrier() mdbx_compiler_barrier()
 #else
@@ -553,7 +549,13 @@ void mdbx_osal_jitter(bool tiny);
 #else
 #define MDBX_OSAL_LOCK pthread_mutex_t
 #define MDBX_OSAL_LOCK_SIGN UINT32_C(0x8017)
-#endif
+#endif /* MDBX_OSAL_LOCK */
+
+#ifdef MDBX_OSAL_LOCK
+#define MDBX_OSAL_LOCK_SIZE sizeof(MDBX_OSAL_LOCK)
+#else
+#define MDBX_OSAL_LOCK_SIZE 0
+#endif /* MDBX_OSAL_LOCK_SIZE */
 
 int mdbx_lck_init(MDBX_env *env);