/*------------------------------------------------------------------------- * * lwlock.h * Lightweight lock manager * * * Portions Copyright (c) 1996-2016, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * * src/include/storage/lwlock.h * *------------------------------------------------------------------------- */ #ifndef LWLOCK_H #define LWLOCK_H #ifdef FRONTEND #error "lwlock.h may not be included from frontend code" #endif #include "lib/ilist.h" #include "storage/s_lock.h" #include "port/atomics.h" struct PGPROC; /* * Prior to PostgreSQL 9.4, every lightweight lock in the system was stored * in a single array. For convenience and for compatibility with past * releases, we still have a main array, but it's now also permissible to * store LWLocks elsewhere in the main shared memory segment or in a dynamic * shared memory segment. Each array of lwlocks forms a separate "tranche". * * It's occasionally necessary to identify a particular LWLock "by name"; e.g. * because we wish to report the lock to dtrace. We could store a name or * other identifying information in the lock itself, but since it's common * to have many nearly-identical locks (e.g. one per buffer) this would end * up wasting significant amounts of memory. Instead, each lwlock stores a * tranche ID which tells us which array it's part of. Based on that, we can * figure out where the lwlock lies within the array using the data structure * shown below; the lock is then identified based on the tranche name and * computed array index. We need the array stride because the array might not * be an array of lwlocks, but rather some larger data structure that includes * one or more lwlocks per element. */ typedef struct LWLockTranche { const char *name; void *array_base; Size array_stride; } LWLockTranche; /* * Code outside of lwlock.c should not manipulate the contents of this * structure directly, but we have to declare it here to allow LWLocks to be * incorporated into other data structures. */ typedef struct LWLock { slock_t mutex; /* Protects LWLock and queue of PGPROCs */ uint16 tranche; /* tranche ID */ pg_atomic_uint32 state; /* state of exclusive/nonexclusive lockers */ #ifdef LOCK_DEBUG pg_atomic_uint32 nwaiters; /* number of waiters */ #endif dlist_head waiters; /* list of waiting PGPROCs */ #ifdef LOCK_DEBUG struct PGPROC *owner; /* last exclusive owner of the lock */ #endif } LWLock; /* * In most cases, it's desirable to force each tranche of LWLocks to be aligned * on a cache line boundary and make the array stride a power of 2. This saves * a few cycles in indexing, but more importantly ensures that individual * LWLocks don't cross cache line boundaries. This reduces cache contention * problems, especially on AMD Opterons. In some cases, it's useful to add * even more padding so that each LWLock takes up an entire cache line; this is * useful, for example, in the main LWLock array, where the overall number of * locks is small but some are heavily contended. * * When allocating a tranche that contains data other than LWLocks, it is * probably best to include a bare LWLock and then pad the resulting structure * as necessary for performance. For an array that contains only LWLocks, * LWLockMinimallyPadded can be used for cases where we just want to ensure * that we don't cross cache line boundaries within a single lock, while * LWLockPadded can be used for cases where we want each lock to be an entire * cache line. * * On 32-bit platforms, an LWLockMinimallyPadded might actually contain more * than the absolute minimum amount of padding required to keep a lock from * crossing a cache line boundary, because an unpadded LWLock might fit into * 16 bytes. We ignore that possibility when determining the minimal amount * of padding. Older releases had larger LWLocks, so 32 really was the * minimum, and packing them in tighter might hurt performance. * * LWLOCK_MINIMAL_SIZE should be 32 on basically all common platforms, but * because slock_t is more than 2 bytes on some obscure platforms, we allow * for the possibility that it might be 64. */ #define LWLOCK_PADDED_SIZE PG_CACHE_LINE_SIZE #define LWLOCK_MINIMAL_SIZE (sizeof(LWLock) <= 32 ? 32 : 64) /* LWLock, padded to a full cache line size */ typedef union LWLockPadded { LWLock lock; char pad[LWLOCK_PADDED_SIZE]; } LWLockPadded; /* LWLock, minimally padded */ typedef union LWLockMinimallyPadded { LWLock lock; char pad[LWLOCK_MINIMAL_SIZE]; } LWLockMinimallyPadded; extern PGDLLIMPORT LWLockPadded *MainLWLockArray; extern char *MainLWLockNames[]; /* struct for storing named tranche information */ typedef struct NamedLWLockTranche { LWLockTranche lwLockTranche; int trancheId; } NamedLWLockTranche; extern PGDLLIMPORT NamedLWLockTranche *NamedLWLockTrancheArray; extern PGDLLIMPORT int NamedLWLockTrancheRequests; /* Names for fixed lwlocks */ #include "storage/lwlocknames.h" /* * It's a bit odd to declare NUM_BUFFER_PARTITIONS and NUM_LOCK_PARTITIONS * here, but we need them to figure out offsets within MainLWLockArray, and * having this file include lock.h or bufmgr.h would be backwards. */ /* Number of partitions of the shared buffer mapping hashtable */ #define NUM_BUFFER_PARTITIONS 128 /* Number of partitions the shared lock tables are divided into */ #define LOG2_NUM_LOCK_PARTITIONS 4 #define NUM_LOCK_PARTITIONS (1 << LOG2_NUM_LOCK_PARTITIONS) /* Number of partitions the shared predicate lock tables are divided into */ #define LOG2_NUM_PREDICATELOCK_PARTITIONS 4 #define NUM_PREDICATELOCK_PARTITIONS (1 << LOG2_NUM_PREDICATELOCK_PARTITIONS) /* Offsets for various chunks of preallocated lwlocks. */ #define BUFFER_MAPPING_LWLOCK_OFFSET NUM_INDIVIDUAL_LWLOCKS #define LOCK_MANAGER_LWLOCK_OFFSET \ (BUFFER_MAPPING_LWLOCK_OFFSET + NUM_BUFFER_PARTITIONS) #define PREDICATELOCK_MANAGER_LWLOCK_OFFSET \ (LOCK_MANAGER_LWLOCK_OFFSET + NUM_LOCK_PARTITIONS) #define NUM_FIXED_LWLOCKS \ (PREDICATELOCK_MANAGER_LWLOCK_OFFSET + NUM_PREDICATELOCK_PARTITIONS) typedef enum LWLockMode { LW_EXCLUSIVE, LW_SHARED, LW_WAIT_UNTIL_FREE /* A special mode used in PGPROC->lwlockMode, * when waiting for lock to become free. Not * to be used as LWLockAcquire argument */ } LWLockMode; #ifdef LOCK_DEBUG extern bool Trace_lwlocks; #endif extern bool LWLockAcquire(LWLock *lock, LWLockMode mode); extern bool LWLockConditionalAcquire(LWLock *lock, LWLockMode mode); extern bool LWLockAcquireOrWait(LWLock *lock, LWLockMode mode); extern void LWLockRelease(LWLock *lock); extern void LWLockReleaseClearVar(LWLock *lock, uint64 *valptr, uint64 val); extern void LWLockReleaseAll(void); extern bool LWLockHeldByMe(LWLock *lock); extern bool LWLockWaitForVar(LWLock *lock, uint64 *valptr, uint64 oldval, uint64 *newval); extern void LWLockUpdateVar(LWLock *lock, uint64 *valptr, uint64 value); extern Size LWLockShmemSize(void); extern void CreateLWLocks(void); extern void InitLWLockAccess(void); /* * Extensions (or core code) can obtain an LWLocks by calling * RequestNamedLWLockTranche() during postmaster startup. Subsequently, * call GetNamedLWLockTranche() to obtain a pointer to an array containing * the number of LWLocks requested. */ extern void RequestNamedLWLockTranche(const char *tranche_name, int num_lwlocks); extern LWLockPadded *GetNamedLWLockTranche(const char *tranche_name); /* * There is another, more flexible method of obtaining lwlocks. First, call * LWLockNewTrancheId just once to obtain a tranche ID; this allocates from * a shared counter. Next, each individual process using the tranche should * call LWLockRegisterTranche() to associate that tranche ID with appropriate * metadata. Finally, LWLockInitialize should be called just once per lwlock, * passing the tranche ID as an argument. * * It may seem strange that each process using the tranche must register it * separately, but dynamic shared memory segments aren't guaranteed to be * mapped at the same address in all coordinating backends, so storing the * registration in the main shared memory segment wouldn't work for that case. */ extern int LWLockNewTrancheId(void); extern void LWLockRegisterTranche(int tranche_id, LWLockTranche *tranche); extern void LWLockInitialize(LWLock *lock, int tranche_id); /* * We reserve a few predefined tranche IDs. A call to LWLockNewTrancheId * will never return a value less than LWTRANCHE_FIRST_USER_DEFINED. */ typedef enum BuiltinTrancheIds { LWTRANCHE_MAIN, LWTRANCHE_CLOG_BUFFERS, LWTRANCHE_COMMITTS_BUFFERS, LWTRANCHE_SUBTRANS_BUFFERS, LWTRANCHE_MXACTOFFSET_BUFFERS, LWTRANCHE_MXACTMEMBER_BUFFERS, LWTRANCHE_ASYNC_BUFFERS, LWTRANCHE_OLDSERXID_BUFFERS, LWTRANCHE_WAL_INSERT, LWTRANCHE_BUFFER_CONTENT, LWTRANCHE_BUFFER_IO_IN_PROGRESS, LWTRANCHE_REPLICATION_ORIGIN, LWTRANCHE_REPLICATION_SLOT_IO_IN_PROGRESS, LWTRANCHE_PROC, LWTRANCHE_FIRST_USER_DEFINED } BuiltinTrancheIds; /* * Prior to PostgreSQL 9.4, we used an enum type called LWLockId to refer * to LWLocks. New code should instead use LWLock *. However, for the * convenience of third-party code, we include the following typedef. */ typedef LWLock *LWLockId; #endif /* LWLOCK_H */