lmdb: Make SysV semaphores robust. Cleanup MDB_ROBUST.

Backport from master: 66e3f5139105822196aea6a6e63596d25734222a.

Change-Id: Idda165be19ee95c2a0839a180a2ece395502ce26

lmdb.h

@@ -109,7 +109,9 @@
  *	  The transaction becomes "long-lived" as above until a check
  *	  for stale readers is performed or the lockfile is reset,
  *	  since the process may not remove it from the lockfile.
- *	  Except write-transactions on Unix with MDB_ROBUST or on Windows.
+ *
+ *	  This does not apply to write transactions if the system clears
+ *	  stale writers, see above.
  *
  *	- If you do that anyway, do a periodic check for stale readers. Or
  *	  close the environment once in a while, so the lockfile can get reset.

mdb.c

@@ -208,7 +208,7 @@ union semun {
 #define MDB_DEVEL 0
 #endif
 
-#if defined(_WIN32) || (defined(EOWNERDEAD) && !defined(MDB_USE_SYSV_SEM))
+#if defined(_WIN32) || defined(MDB_USE_SYSV_SEM) || defined(EOWNERDEAD)
 #define MDB_ROBUST_SUPPORTED	1
 #endif
 
@@ -222,6 +222,16 @@ union semun {
 # define mdb_func_	"<mdb_unknown>"
 #endif
 
+/* Internal error codes, not exposed outside liblmdb */
+#define	MDB_NO_ROOT		(MDB_LAST_ERRCODE + 10)
+#ifdef _WIN32
+#define MDB_OWNERDEAD	((int) WAIT_ABANDONED)
+#elif defined MDB_USE_SYSV_SEM
+#define MDB_OWNERDEAD	(MDB_LAST_ERRCODE + 11)
+#else
+#define MDB_OWNERDEAD	EOWNERDEAD
+#endif
+
 #ifdef _WIN32
 #define MDB_USE_HASH	1
 #define MDB_PIDLOCK	0
@@ -237,7 +247,6 @@ typedef HANDLE mdb_mutex_t;
 #define pthread_key_delete(x)	TlsFree(x)
 #define pthread_getspecific(x)	TlsGetValue(x)
 #define pthread_setspecific(x,y)	(TlsSetValue(x,y) ? 0 : ErrCode())
-#define pthread_mutex_consistent(mutex) 0
 #define pthread_mutex_unlock(x)	ReleaseMutex(*x)
 #define pthread_mutex_lock(x)	WaitForSingleObject(*x, INFINITE)
 #define pthread_cond_signal(x)	SetEvent(*x)
@@ -247,6 +256,7 @@ typedef HANDLE mdb_mutex_t;
 #define MDB_MUTEX(env, rw)		((env)->me_##rw##mutex)
 #define LOCK_MUTEX0(mutex)		WaitForSingleObject(mutex, INFINITE)
 #define UNLOCK_MUTEX(mutex)		ReleaseMutex(mutex)
+#define mdb_mutex_consistent(mutex)	0
 #define getpid()	GetCurrentProcessId()
 #define	MDB_FDATASYNC(fd)	(!FlushFileBuffers(fd))
 #define	MDB_MSYNC(addr,len,flags)	(!FlushViewOfFile(addr,len))
@@ -274,6 +284,7 @@ typedef HANDLE mdb_mutex_t;
 typedef struct mdb_mutex {
 	int semid;
 	int semnum;
+	int *locked;
 } mdb_mutex_t;
 
 #define MDB_MUTEX(env, rw)		(&(env)->me_##rw##mutex)
@@ -281,19 +292,28 @@ typedef struct mdb_mutex {
 #define UNLOCK_MUTEX(mutex)		do { \
 	struct sembuf sb = { 0, 1, SEM_UNDO }; \
 	sb.sem_num = (mutex)->semnum; \
+	*(mutex)->locked = 0; \
 	semop((mutex)->semid, &sb, 1); \
 } while(0)
 
 static int
 mdb_sem_wait(mdb_mutex_t *sem)
 {
-   int rc;
+	int rc, *locked = sem->locked;
-   struct sembuf sb = { 0, -1, SEM_UNDO };
+	struct sembuf sb = { 0, -1, SEM_UNDO };
-   sb.sem_num = sem->semnum;
+	sb.sem_num = sem->semnum;
-   while ((rc = semop(sem->semid, &sb, 1)) && (rc = errno) == EINTR) ;
+	do {
-   return rc;
+		if (!semop(sem->semid, &sb, 1)) {
+			rc = *locked ? MDB_OWNERDEAD : MDB_SUCCESS;
+			*locked = 1;
+			break;
+		}
+	} while ((rc = errno) == EINTR);
+	return rc;
 }
 
+#define mdb_mutex_consistent(mutex)	0
+
 #else
 	/** Pointer/HANDLE type of shared mutex/semaphore.
 	 */
@@ -308,6 +328,9 @@ typedef pthread_mutex_t mdb_mutex_t;
 	/** Unlock the reader or writer mutex.
 	 */
 #define UNLOCK_MUTEX(mutex)	pthread_mutex_unlock(mutex)
+	/** Mark mutex-protected data as repaired, after death of previous owner.
+	 */
+#define mdb_mutex_consistent(mutex)	pthread_mutex_consistent(mutex)
 #endif	/* MDB_USE_SYSV_SEM */
 
 	/** Get the error code for the last failed system function.
@@ -336,11 +359,17 @@ typedef pthread_mutex_t mdb_mutex_t;
 #if defined(_WIN32)
 #define MNAME_LEN	32
 #elif defined(MDB_USE_SYSV_SEM)
-#define MNAME_LEN	0
+#define MNAME_LEN	(sizeof(int))
 #else
 #define MNAME_LEN	(sizeof(pthread_mutex_t))
 #endif
 
+#ifdef MDB_USE_SYSV_SEM
+#define SYSV_SEM_FLAG	1		/**< SysV sems in lockfile format */
+#else
+#define SYSV_SEM_FLAG	0
+#endif
+
 /** @} */
 
 #ifdef MDB_ROBUST_SUPPORTED
@@ -667,6 +696,7 @@ typedef struct MDB_txbody {
 	char	mtb_rmname[MNAME_LEN];
 #elif defined(MDB_USE_SYSV_SEM)
 	int 	mtb_semid;
+	int		mtb_rlocked;
 #else
 		/** Mutex protecting access to this table.
 		 *	This is the #MDB_MUTEX(env,r) reader table lock.
@@ -695,22 +725,25 @@ typedef struct MDB_txninfo {
 #define mti_rmname	mt1.mtb.mtb_rmname
 #define mti_txnid	mt1.mtb.mtb_txnid
 #define mti_numreaders	mt1.mtb.mtb_numreaders
-		char pad[(sizeof(MDB_txbody)+CACHELINE-1) & ~(CACHELINE-1)];
-	} mt1;
 #ifdef MDB_USE_SYSV_SEM
 #define	mti_semid	mt1.mtb.mtb_semid
-#else
+#define	mti_rlocked	mt1.mtb.mtb_rlocked
+#endif
+		char pad[(sizeof(MDB_txbody)+CACHELINE-1) & ~(CACHELINE-1)];
+	} mt1;
 	union {
 #if defined(_WIN32)
 		char mt2_wmname[MNAME_LEN];
 #define	mti_wmname	mt2.mt2_wmname
+#elif defined MDB_USE_SYSV_SEM
+		int mt2_wlocked;
+#define mti_wlocked	mt2.mt2_wlocked
 #else
 		pthread_mutex_t	mt2_wmutex;
 #define mti_wmutex	mt2.mt2_wmutex
 #endif
 		char pad[(MNAME_LEN+CACHELINE-1) & ~(CACHELINE-1)];
 	} mt2;
-#endif
 	MDB_reader	mti_readers[1];
 } MDB_txninfo;
 
@@ -719,7 +752,7 @@ typedef struct MDB_txninfo {
 	((uint32_t) \
 	 ((MDB_LOCK_VERSION) \
 	  /* Flags which describe functionality */ \
-	  + (((MNAME_LEN) == 0)   << 18) /* MDB_USE_SYSV_SEM */ \
+	  + (SYSV_SEM_FLAG << 18) \
 	  + (((MDB_PIDLOCK) != 0) << 16)))
 /** @} */
 
@@ -2824,17 +2857,8 @@ mdb_txn_renew0(MDB_txn *txn)
 		if (ti) {
 			if (LOCK_MUTEX(rc, env, MDB_MUTEX(env, w)))
 				return rc;
-#ifdef MDB_USE_SYSV_SEM
-			meta = env->me_metas[ mdb_env_pick_meta(env) ];
-			txn->mt_txnid = meta->mm_txnid;
-			/* Update mti_txnid like mdb_mutex_failed() would,
-			 * in case last writer crashed before updating it.
-			 */
-			ti->mti_txnid = txn->mt_txnid;
-#else
 			txn->mt_txnid = ti->mti_txnid;
 			meta = env->me_metas[txn->mt_txnid & 1];
-#endif
 		} else {
 			meta = env->me_metas[ mdb_env_pick_meta(env) ];
 			txn->mt_txnid = meta->mm_txnid;
@@ -4790,6 +4814,10 @@ mdb_env_setup_locks(MDB_env *env, char *lpath, int mode, int *excl)
 	int fdflags;
 #	define MDB_CLOEXEC		0
 #endif
+#endif
+#ifdef MDB_USE_SYSV_SEM
+	int semid;
+	union semun semu;
 #endif
 	int rc;
 	off_t size, rsize;
@@ -4904,17 +4932,10 @@ mdb_env_setup_locks(MDB_env *env, char *lpath, int mode, int *excl)
 		env->me_wmutex = CreateMutex(&mdb_all_sa, FALSE, env->me_txns->mti_wmname);
 		if (!env->me_wmutex) goto fail_errno;
 #elif defined(MDB_USE_SYSV_SEM)
-		union semun semu;
 		unsigned short vals[2] = {1, 1};
-		int semid = semget(IPC_PRIVATE, 2, mode);
+		semid = semget(IPC_PRIVATE, 2, mode);
 		if (semid < 0)
 			goto fail_errno;
-
-		env->me_rmutex.semid = semid;
-		env->me_wmutex.semid = semid;
-		env->me_rmutex.semnum = 0;
-		env->me_wmutex.semnum = 1;
-
 		semu.array = vals;
 		if (semctl(semid, 0, SETALL, semu) < 0)
 			goto fail_errno;
@@ -4941,8 +4962,6 @@ mdb_env_setup_locks(MDB_env *env, char *lpath, int mode, int *excl)
 	} else {
 #ifdef MDB_USE_SYSV_SEM
 		struct semid_ds buf;
-		union semun semu;
-		int semid;
 #endif
 		if (env->me_txns->mti_magic != MDB_MAGIC) {
 			DPUTS("lock region has invalid magic");
@@ -4967,20 +4986,23 @@ mdb_env_setup_locks(MDB_env *env, char *lpath, int mode, int *excl)
 #elif defined(MDB_USE_SYSV_SEM)
 		semid = env->me_txns->mti_semid;
 		semu.buf = &buf;
-
 		/* check for read access */
 		if (semctl(semid, 0, IPC_STAT, semu) < 0)
 			goto fail_errno;
 		/* check for write access */
 		if (semctl(semid, 0, IPC_SET, semu) < 0)
 			goto fail_errno;
-
-		env->me_rmutex.semid = semid;
-		env->me_wmutex.semid = semid;
-		env->me_rmutex.semnum = 0;
-		env->me_wmutex.semnum = 1;
 #endif
 	}
+#ifdef MDB_USE_SYSV_SEM
+	env->me_rmutex.semid = semid;
+	env->me_wmutex.semid = semid;
+	env->me_rmutex.semnum = 0;
+	env->me_wmutex.semnum = 1;
+	env->me_rmutex.locked = &env->me_txns->mti_rlocked;
+	env->me_wmutex.locked = &env->me_txns->mti_wlocked;
+#endif
+
 	return MDB_SUCCESS;
 
 fail_errno:
@@ -6575,7 +6597,6 @@ int
 mdb_cursor_put(MDB_cursor *mc, MDB_val *key, MDB_val *data,
     unsigned int flags)
 {
-	enum { MDB_NO_ROOT = MDB_LAST_ERRCODE+10 }; /* internal code */
 	MDB_env		*env;
 	MDB_node	*leaf = NULL;
 	MDB_page	*fp, *mp;
@@ -10044,7 +10065,7 @@ static int mdb_reader_check0(MDB_env *env, int rlocked, int *dead)
 
 #ifdef MDB_ROBUST_SUPPORTED
 /** Handle #LOCK_MUTEX0() failure.
- * With #MDB_ROBUST, try to repair the lock file if the mutex owner died.
+ * Try to repair the lock file if the mutex owner died.
  * @param[in] env	the environment handle
  * @param[in] mutex	LOCK_MUTEX0() mutex
  * @param[in] rc	LOCK_MUTEX0() error (nonzero)
@@ -10053,11 +10074,8 @@ static int mdb_reader_check0(MDB_env *env, int rlocked, int *dead)
 static int mdb_mutex_failed(MDB_env *env, mdb_mutex_t *mutex, int rc)
 {
 	int toggle, rlocked, rc2;
-#ifndef _WIN32
-	enum { WAIT_ABANDONED = EOWNERDEAD };
-#endif
 
-	if (rc == (int) WAIT_ABANDONED) {
+	if (rc == MDB_OWNERDEAD) {
 		/* We own the mutex. Clean up after dead previous owner. */
 		rc = MDB_SUCCESS;
 		rlocked = (mutex == MDB_MUTEX(env, r));
@@ -10078,7 +10096,7 @@ static int mdb_mutex_failed(MDB_env *env, mdb_mutex_t *mutex, int rc)
 			(rc ? "this process' env is hosed" : "recovering")));
 		rc2 = mdb_reader_check0(env, rlocked, NULL);
 		if (rc2 == 0)
-			rc2 = pthread_mutex_consistent(mutex);
+			rc2 = mdb_mutex_consistent(mutex);
 		if (rc || (rc = rc2)) {
 			DPRINTF(("LOCK_MUTEX recovery failed, %s", mdb_strerror(rc)));
 			UNLOCK_MUTEX(mutex);