From 6c632f490f82d39a8c29ee378c8cf8c36624d626 Mon Sep 17 00:00:00 2001
From: Sasha Krassovsky <krassovskysasha@gmail.com>
Date: Thu, 30 Nov 2023 14:16:23 -0800
Subject: [PATCH] Switch lwlock to pthread_rwlock_t

---
 pgxn/neon/libpagestore.c | 22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/pgxn/neon/libpagestore.c b/pgxn/neon/libpagestore.c
index 8839dcf7ab..90d81679bd 100644
--- a/pgxn/neon/libpagestore.c
+++ b/pgxn/neon/libpagestore.c
@@ -19,7 +19,6 @@
 #include "access/xlog.h"
 #include "access/xlogutils.h"
 #include "storage/buf_internals.h"
-#include "storage/lwlock.h"
 #include "storage/ipc.h"
 #include "storage/pg_shmem.h"
 #include "c.h"
@@ -37,6 +36,8 @@
 #include "walproposer.h"
 #include "neon_utils.h"
 
+#include <pthread.h>
+
 #define PageStoreTrace DEBUG5
 
 #define RECONNECT_INTERVAL_USEC 1000000
@@ -69,7 +70,7 @@ int			max_reconnect_attempts = 60;
 
 typedef struct
 {
-    LWLockId lock;
+    pthread_rwlock_t lock;
     pg_atomic_uint64 update_counter;
     char pageserver_connstring[MAX_PAGESERVER_CONNSTRING_SIZE];
 } PagestoreShmemState;
@@ -105,10 +106,10 @@ AssignPageserverConnstring(const char *newval, void *extra)
 {
     if(!PagestoreShmemIsValid())
         return;
-    LWLockAcquire(pagestore_shared->lock, LW_EXCLUSIVE);
+    pthread_rwlock_wrlock(&pagestore_shared->lock);
     strlcpy(pagestore_shared->pageserver_connstring, newval, MAX_PAGESERVER_CONNSTRING_SIZE);
     pg_atomic_fetch_add_u64(&pagestore_shared->update_counter, 1);
-    LWLockRelease(pagestore_shared->lock);
+    pthread_rwlock_unlock(&pagestore_shared->lock);
 }
 
 static bool
@@ -125,17 +126,17 @@ ReloadConnstring()
 {
     if(!PagestoreShmemIsValid())
         return false;
-    LWLockAcquire(pagestore_shared->lock, LW_SHARED);
+    pthread_rwlock_rdlock(&pagestore_shared->lock);
 
     if(strcmp(local_pageserver_connstring, pagestore_shared->pageserver_connstring) == 0)
     {
-        LWLockRelease(pagestore_shared->lock);
+        pthread_rwlock_unlock(&pagestore_shared->lock);
         return false;
     }
 
     strlcpy(local_pageserver_connstring, pagestore_shared->pageserver_connstring, sizeof(local_pageserver_connstring));
     pagestore_local_counter = pg_atomic_read_u64(&pagestore_shared->update_counter);
-    LWLockRelease(pagestore_shared->lock);
+    pthread_rwlock_unlock(&pagestore_shared->lock);
     return true;
 }
 
@@ -496,7 +497,12 @@ PagestoreShmemInit(void)
                                        &found);
     if(!found)
     {
-        pagestore_shared->lock = &(GetNamedLWLockTranche("neon_libpagestore")->lock);
+        pthread_rwlockattr_t attr;
+        pthread_rwlockattr_init(&attr);
+        pthread_rwlockattr_setpshared(&attr, PTHREAD_PROCESS_SHARED); 
+        pthread_rwlock_init(&pagestore_shared->lock, &attr);
+        pthread_rwlockattr_destroy(&attr);
+
         pg_atomic_init_u64(&pagestore_shared->update_counter, 0);
         AssignPageserverConnstring(page_server_connstring, NULL);
     }