Convert archiver's force_dir_scan variable to an atomic variable.

Commit bd5132db55 introduced new atomic read/write functions with
full barrier semantics, which are intended to simplify converting
non-performance-critical code to use atomic variables.  This commit
demonstrates one such conversion.

Reviewed-by: Yong Li
Discussion: https://postgr.es/m/20231110205128.GB1315705%40nathanxps13

diff --git a/src/backend/postmaster/pgarch.c b/src/backend/postmaster/pgarch.c
index 9c18e4b3efbc698b71925d474e14adbc75e1d00c..04fedfae2fa6791d28d01ac5442e90965d7814c2 100644 (file)
--- a/src/backend/postmaster/pgarch.c
+++ b/src/backend/postmaster/pgarch.c
@@ -45,7 +45,6 @@
 #include "storage/proc.h"
 #include "storage/procsignal.h"
 #include "storage/shmem.h"
-#include "storage/spin.h"
 #include "utils/guc.h"
 #include "utils/memutils.h"
 #include "utils/ps_status.h"
@@ -83,11 +82,9 @@ typedef struct PgArchData
    int         pgprocno;       /* pgprocno of archiver process */
 
    /*
-    * Forces a directory scan in pgarch_readyXlog().  Protected by arch_lck.
+    * Forces a directory scan in pgarch_readyXlog().
     */
-   bool        force_dir_scan;
-
-   slock_t     arch_lck;
+   pg_atomic_uint32 force_dir_scan;
 } PgArchData;
 
 char      *XLogArchiveLibrary = "";
@@ -174,7 +171,7 @@ PgArchShmemInit(void)
        /* First time through, so initialize */
        MemSet(PgArch, 0, PgArchShmemSize());
        PgArch->pgprocno = INVALID_PGPROCNO;
-       SpinLockInit(&PgArch->arch_lck);
+       pg_atomic_init_u32(&PgArch->force_dir_scan, 0);
    }
 }
 
@@ -545,18 +542,12 @@ pgarch_readyXlog(char *xlog)
    char        XLogArchiveStatusDir[MAXPGPATH];
    DIR        *rldir;
    struct dirent *rlde;
-   bool        force_dir_scan;
 
    /*
     * If a directory scan was requested, clear the stored file names and
     * proceed.
     */
-   SpinLockAcquire(&PgArch->arch_lck);
-   force_dir_scan = PgArch->force_dir_scan;
-   PgArch->force_dir_scan = false;
-   SpinLockRelease(&PgArch->arch_lck);
-
-   if (force_dir_scan)
+   if (pg_atomic_exchange_u32(&PgArch->force_dir_scan, 0) == 1)
        arch_files->arch_files_size = 0;
 
    /*
@@ -707,9 +698,7 @@ ready_file_comparator(Datum a, Datum b, void *arg)
 void
 PgArchForceDirScan(void)
 {
-   SpinLockAcquire(&PgArch->arch_lck);
-   PgArch->force_dir_scan = true;
-   SpinLockRelease(&PgArch->arch_lck);
+   pg_atomic_write_membarrier_u32(&PgArch->force_dir_scan, 1);
 }
 
 /*