Change the way that LWLocks for extensions are allocated.

The previous RequestAddinLWLocks() method had several disadvantages.
First, the locks would be in the main tranche; we've recently decided
that it's useful for LWLocks used for separate purposes to have
separate tranche IDs.  Second, there wasn't any correlation between
what code called RequestAddinLWLocks() and what code called
LWLockAssign(); when multiple modules are in use, it could become
quite difficult to troubleshoot problems where LWLockAssign() ran out
of locks.  To fix, create a concept of named LWLock tranches which
can be used either by extension or by core code.

Amit Kapila and Robert Haas

2 files changed, 17 insertions, 10 deletions

diff --git a/src/include/pg_config_manual.h b/src/include/pg_config_manual.h
index 383809bf5d8..ef895211da5 100644
--- a/src/include/pg_config_manual.h
+++ b/src/include/pg_config_manual.h
@@ -52,11 +52,6 @@
 #define SEQ_MINVALUE	(-SEQ_MAXVALUE)
 
 /*
- * Number of spare LWLocks to allocate for user-defined add-on code.
- */
-#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
diff --git a/src/include/storage/lwlock.h b/src/include/storage/lwlock.h
index 613df19ad64..b2bdbbaf1b9 100644
--- a/src/include/storage/lwlock.h
+++ b/src/include/storage/lwlock.h
@@ -119,6 +119,16 @@ typedef union 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"
 
@@ -178,12 +188,14 @@ extern void CreateLWLocks(void);
 extern void InitLWLockAccess(void);
 
 /*
- * The traditional method for obtaining an lwlock for use by an extension is
- * to call RequestAddinLWLocks() during postmaster startup; this will reserve
- * space for the indicated number of locks in MainLWLockArray.  Subsequently,
- * a lock can be allocated using LWLockAssign.
+ * Extensions (or core code) can obtain an LWLocks by calling
+ * RequestNamedLWLockTranche() during postmaster startup.  Subsequently,
+ * call GetNamedLWLockTranche() and to obtain a pointer to an array
+ * containing the number of LWLocks requested.
  */
-extern void RequestAddinLWLocks(int n);
+extern void RequestNamedLWLockTranche(const char *tranche_name, int num_lwlocks);
+extern LWLockPadded *GetNamedLWLockTranche(const char *tranche_name);
+
 extern LWLock *LWLockAssign(void);
 
 /*