Add a table of shared-memory lock offsets in a comment in the os_unix.c code.

Include some assert()s to help verify the numbers.

FossilOrigin-Name: b480aacb3430a789d98ffd81a1886bbbc3cda5b0e736ec9a3e2b463db2a3b3ad

1 files changed, 15 insertions, 0 deletions

diff --git a/src/os_unix.c b/src/os_unix.c
index adc89f5a7..76b4497a6 100644
--- a/src/os_unix.c
+++ b/src/os_unix.c
@@ -8067,6 +8067,21 @@ int sqlite3_os_init(void){
     sqlite3_vfs_register(&aVfs[i], i==0);
   }
   unixBigLock = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_VFS1);
+
+  /* Validate lock assumptions */
+  assert( SQLITE_SHM_NLOCK==8 );  /* Number of available locks */
+  assert( UNIX_SHM_BASE==120  );  /* Start of locking area */
+  /* Locks:
+  /*    WRITE       UNIX_SHM_BASE      120  */
+  /*    CKPT        UNIX_SHM_BASE+1    121  */
+  /*    RECOVER     UNIX_SHM_BASE+2    122  */
+  /*    READ-0      UNIX_SHM_BASE+3    123  */
+  /*    READ-1      UNIX_SHM_BASE+4    124  */
+  /*    READ-2      UNIX_SHM_BASE+5    125  */
+  /*    READ-3      UNIX_SHM_BASE+6    126  */
+  /*    READ-4      UNIX_SHM_BASE+7    127  */
+  /*    DMS         UNIX_SHM_BASE+8    128  */
+  assert( UNIX_SHM_DMS==128   );  /* Byte offset of the deadman-switch */
   return SQLITE_OK; 
 }