diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index 377fa591a8b3abb2152f07352bbadc5317ac0e8f..a7e40cc4a5989953ecb6398f1265498ddf99e0eb 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -471,6 +471,9 @@ typedef struct
slock_t *ShmemLock;
VariableCache ShmemVariableCache;
Backend *ShmemBackendArray;
+#ifndef HAVE_SPINLOCKS
+ PGSemaphore SpinlockSemaArray;
+#endif
LWLock *LWLockArray;
slock_t *ProcStructLock;
PROC_HDR *ProcGlobal;
@@ -5626,6 +5629,9 @@ save_backend_variables(BackendParameters *param, Port *port,
param->ShmemVariableCache = ShmemVariableCache;
param->ShmemBackendArray = ShmemBackendArray;
+#ifndef HAVE_SPINLOCKS
+ param->SpinlockSemaArray = SpinlockSemaArray;
+#endif
param->LWLockArray = LWLockArray;
param->ProcStructLock = ProcStructLock;
param->ProcGlobal = ProcGlobal;
@@ -5854,6 +5860,9 @@ restore_backend_variables(BackendParameters *param, Port *port)
ShmemVariableCache = param->ShmemVariableCache;
ShmemBackendArray = param->ShmemBackendArray;
+#ifndef HAVE_SPINLOCKS
+ SpinlockSemaArray = param->SpinlockSemaArray;
+#endif
LWLockArray = param->LWLockArray;
ProcStructLock = param->ProcStructLock;
ProcGlobal = param->ProcGlobal;
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 1c8783f2c085e8151f5d46798d59c4ff871f0fa7..3c04fc31baed54f45ddbe852f901554e1b154ee3 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -105,6 +105,7 @@ CreateSharedMemoryAndSemaphores(bool makePrivate, int port)
* need to be so careful during the actual allocation phase.
*/
size = 100000;
+ size = add_size(size, SpinlockSemaSize());
size = add_size(size, hash_estimate_size(SHMEM_INDEX_SIZE,
sizeof(ShmemIndexEnt)));
size = add_size(size, BufferShmemSize());
diff --git a/src/backend/storage/ipc/shmem.c b/src/backend/storage/ipc/shmem.c
index e93b988ad743d49cbc284617e346bb2820468851..70b02ca8384b87354aebe96f59a36ebdd8d073e5 100644
--- a/src/backend/storage/ipc/shmem.c
+++ b/src/backend/storage/ipc/shmem.c
@@ -116,9 +116,24 @@ InitShmemAllocation(void)
Assert(shmhdr != NULL);
/*
- * Initialize the spinlock used by ShmemAlloc. We have to do the space
- * allocation the hard way, since obviously ShmemAlloc can't be called
- * yet.
+ * If spinlocks are disabled, initialize emulation layer. We have to do
+ * the space allocation the hard way, since obviously ShmemAlloc can't be
+ * called yet.
+ */
+#ifndef HAVE_SPINLOCKS
+ {
+ PGSemaphore spinsemas;
+
+ spinsemas = (PGSemaphore) (((char *) shmhdr) + shmhdr->freeoffset);
+ shmhdr->freeoffset += MAXALIGN(SpinlockSemaSize());
+ SpinlockSemaInit(spinsemas);
+ Assert(shmhdr->freeoffset <= shmhdr->totalsize);
+ }
+#endif
+
+ /*
+ * Initialize the spinlock used by ShmemAlloc; we have to do this the hard
+ * way, too, for the same reasons as above.
*/
ShmemLock = (slock_t *) (((char *) shmhdr) + shmhdr->freeoffset);
shmhdr->freeoffset += MAXALIGN(sizeof(slock_t));
diff --git a/src/backend/storage/lmgr/spin.c b/src/backend/storage/lmgr/spin.c
index 08782178de9d08d805505852bce1341a85be6c13..3d116bc7a2e4467184939216ed0100e1e8f7d5d4 100644
--- a/src/backend/storage/lmgr/spin.c
+++ b/src/backend/storage/lmgr/spin.c
@@ -29,6 +29,18 @@
#include "storage/spin.h"
+PGSemaphore SpinlockSemaArray;
+
+/*
+ * Report the amount of shared memory needed to store semaphores for spinlock
+ * support.
+ */
+Size
+SpinlockSemaSize(void)
+{
+ return SpinlockSemas() * sizeof(PGSemaphoreData);
+}
+
#ifdef HAVE_SPINLOCKS
/*
@@ -52,22 +64,20 @@ SpinlockSemas(void)
int
SpinlockSemas(void)
{
- int nsemas;
-
- /*
- * It would be cleaner to distribute this logic into the affected modules,
- * similar to the way shmem space estimation is handled.
- *
- * For now, though, there are few enough users of spinlocks that we just
- * keep the knowledge here.
- */
- nsemas = NumLWLocks(); /* one for each lwlock */
- nsemas += NBuffers; /* one for each buffer header */
- nsemas += max_wal_senders; /* one for each wal sender process */
- nsemas += num_xloginsert_slots; /* one for each WAL insertion slot */
- nsemas += 30; /* plus a bunch for other small-scale use */
-
- return nsemas;
+ return NUM_SPINLOCK_SEMAPHORES;
+}
+
+/*
+ * Initialize semaphores.
+ */
+extern void
+SpinlockSemaInit(PGSemaphore spinsemas)
+{
+ int i;
+
+ for (i = 0; i < NUM_SPINLOCK_SEMAPHORES; ++i)
+ PGSemaphoreCreate(&spinsemas[i]);
+ SpinlockSemaArray = spinsemas;
}
/*
@@ -77,13 +87,15 @@ SpinlockSemas(void)
void
s_init_lock_sema(volatile slock_t *lock)
{
- PGSemaphoreCreate((PGSemaphore) lock);
+ static int counter = 0;
+
+ *lock = (++counter) % NUM_SPINLOCK_SEMAPHORES;
}
void
s_unlock_sema(volatile slock_t *lock)
{
- PGSemaphoreUnlock((PGSemaphore) lock);
+ PGSemaphoreUnlock(&SpinlockSemaArray[*lock]);
}
bool
@@ -98,7 +110,7 @@ int
tas_sema(volatile slock_t *lock)
{
/* Note that TAS macros return 0 if *success* */
- return !PGSemaphoreTryLock((PGSemaphore) lock);
+ return !PGSemaphoreTryLock(&SpinlockSemaArray[*lock]);
}
#endif /* !HAVE_SPINLOCKS */
diff --git a/src/include/pg_config_manual.h b/src/include/pg_config_manual.h
index 2387a434aa45ead4b1c8b14f86c94cf53d804b72..20c5ff0e90298f04e4ef4dbacf159d7593cfb9c0 100644
--- a/src/include/pg_config_manual.h
+++ b/src/include/pg_config_manual.h
@@ -56,6 +56,14 @@
*/
#define NUM_USER_DEFINED_LWLOCKS 4
+/*
+ * When we don't have native spinlocks, we use semaphores to simulate them.
+ * Decreasing this value reduces consumption of OS resources; increasing it
+ * may improve performance, but supplying a real spinlock implementation is
+ * probably far better.
+ */
+#define NUM_SPINLOCK_SEMAPHORES 1024
+
/*
* Define this if you want to allow the lo_import and lo_export SQL
* functions to be executed by ordinary users. By default these
diff --git a/src/include/storage/s_lock.h b/src/include/storage/s_lock.h
index b52f0e7f8523ba5586e6cdb0af38dfa11707fe80..2297f772805d8d17e19e3735005b6d27cf4626fd 100644
--- a/src/include/storage/s_lock.h
+++ b/src/include/storage/s_lock.h
@@ -915,7 +915,7 @@ spin_delay(void)
* to fall foul of kernel limits on number of semaphores, so don't use this
* unless you must! The subroutines appear in spin.c.
*/
-typedef PGSemaphoreData slock_t;
+typedef int slock_t;
extern bool s_lock_free_sema(volatile slock_t *lock);
extern void s_unlock_sema(volatile slock_t *lock);
diff --git a/src/include/storage/spin.h b/src/include/storage/spin.h
index e7201652499735595bcdd5021cb6c1e633fa71e3..2ac510db7a036931d6b24f723467fd936aaa3aa3 100644
--- a/src/include/storage/spin.h
+++ b/src/include/storage/spin.h
@@ -69,5 +69,11 @@
extern int SpinlockSemas(void);
+extern Size SpinlockSemaSize(void);
+
+#ifndef HAVE_SPINLOCKS
+extern void SpinlockSemaInit(PGSemaphore);
+extern PGSemaphore SpinlockSemaArray;
+#endif
#endif /* SPIN_H */