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From "William A. Rowe, Jr." <wr...@rowe-clan.net>
Subject sdbm locks, second try
Date Thu, 03 May 2001 02:42:10 GMT
I haven't thoroughly vetted it yet, but I'm not wasting the effort until
I have the feedback on what should/shouldn't be changed.

I explicitly decided not to do stacked locks/refcounting.  Win32 will not
allow you to 'promote' a sharelock into an exclusivelock.  Ergo, it's not
portable.

If folks would take a look at this, and comment;




Index: dbm/sdbm/sdbm.c
===================================================================
RCS file: /home/cvs/apr-util/dbm/sdbm/sdbm.c,v
retrieving revision 1.16
diff -u -r1.16 sdbm.c
--- dbm/sdbm/sdbm.c 2001/05/01 05:37:05 1.16
+++ dbm/sdbm/sdbm.c 2001/05/02 20:59:32
@@ -98,6 +98,7 @@
 #define OFF_PAG(off) (apr_off_t) (off) * PBLKSIZ
 #define OFF_DIR(off) (apr_off_t) (off) * DBLKSIZ
 
+
 static long masks[] = {
         000000000000, 000000000001, 000000000003, 000000000007,
         000000000017, 000000000037, 000000000077, 000000000177,
@@ -115,9 +116,9 @@
 {
     apr_sdbm_t *db = data;
 
+    if (db->flags & (SDBM_SHARED_LOCK | SDBM_EXCLUSIVE_LOCK))
+        (void) apr_sdbm_unlock(db);
     (void) apr_file_close(db->dirf);
-    if (!(db->flags & SDBM_SHARED))
-        (void) sdbm_unlock(db);
     (void) apr_file_close(db->pagf);
     free(db);
 
@@ -163,26 +164,21 @@
      * If we fail anywhere, undo everything, return NULL.
      */
 
-    if ((status = apr_file_open(&db->pagf, pagname, flags, perms, p))
+    if ((status = apr_file_open(&db->dirf, dirname, flags, perms, p))
                 != APR_SUCCESS)
         goto error;
 
-    if ((status = sdbm_lock(db, !(db->flags & SDBM_RDONLY)))
+    if ((status = apr_file_open(&db->pagf, pagname, flags, perms, p))
                 != APR_SUCCESS)
         goto error;
 
-    if ((status = apr_file_open(&db->dirf, dirname, flags, perms, p))
+    if ((status = apr_sdbm_lock(db, (db->flags & SDBM_RDONLY) 
+                                        ? APR_FLOCK_SHARED
+                                        : APR_FLOCK_EXCLUSIVE))
                 != APR_SUCCESS)
         goto error;
 
     /*
-     * if we are opened in SHARED mode, unlock ourself 
-     */
-    if (db->flags & SDBM_SHARED)
-        if ((status = sdbm_unlock(db)) != APR_SUCCESS)
-            goto error;
-
-    /*
      * need the dirfile size to establish max bit number.
      */
     if ((status = apr_file_info_get(&finfo, APR_FINFO_SIZE, db->dirf)) 
@@ -190,12 +186,17 @@
         goto error;
 
     /*
+     * if we are opened in SHARED mode, unlock ourself 
+     */
+    if (db->flags & SDBM_SHARED)
+        if ((status = apr_sdbm_unlock(db)) != APR_SUCCESS)
+            goto error;
+
+    /*
      * zero size: either a fresh database, or one with a single,
      * unsplit data page: dirpage is all zeros.
      */
-    db->dirbno = (!finfo.size) ? 0 : -1;
-    db->pagbno = -1;
-    db->maxbno = finfo.size * BYTESIZ;
+    SDBM_INVALIDATE_CACHE(db, finfo);
 
     /* (apr_pcalloc zeroed the buffers) */
 
@@ -207,10 +208,11 @@
     return APR_SUCCESS;
 
 error:
+    if (db->dirf && db->pagf)
+        (void) apr_sdbm_unlock(db);
     if (db->dirf != NULL)
         (void) apr_file_close(db->dirf);
     if (db->pagf != NULL) {
-        (void) sdbm_unlock(db);
         (void) apr_file_close(db->pagf);
     }
     free(db);
@@ -236,11 +238,13 @@
                             apr_sdbm_datum_t key)
 {
     apr_status_t status;
+    int impllock = !(db->flags & (SDBM_SHARED_LOCK | SDBM_EXCLUSIVE_LOCK));
+
     if (db == NULL || bad(key))
         return APR_EINVAL;
 
-    if (db->flags & SDBM_SHARED)
-        if ((status = sdbm_lock(db, 0)) != APR_SUCCESS)
+    if (impllock)
+        if ((status = apr_sdbm_lock(db, APR_FLOCK_SHARED)) != APR_SUCCESS)
             return ioerr(db, status);
 
     if ((status = getpage(db, exhash(key))) == APR_SUCCESS) {
@@ -250,9 +254,8 @@
     else
         ioerr(db, status);
 
-    if (db->flags & SDBM_SHARED)
-        if ((status = sdbm_unlock(db)) != APR_SUCCESS)
-            ioerr(db, status);
+    if (impllock)
+        (void) apr_sdbm_unlock(db);
 
     return status;
 }
@@ -274,14 +277,16 @@
 apr_status_t apr_sdbm_delete(apr_sdbm_t *db, const apr_sdbm_datum_t key)
 {
     apr_status_t status;
-
+    int impllock = !(db->flags & SDBM_EXCLUSIVE_LOCK);
+    
     if (db == NULL || bad(key))
         return APR_EINVAL;
     if (apr_sdbm_rdonly(db))
         return APR_EINVAL;
-
-    if (db->flags & SDBM_SHARED)
-        if ((status = sdbm_lock(db, 1)) != APR_SUCCESS)
+    if (db->flags & SDBM_SHARED_LOCK)
+        return APR_EINVAL;
+    if (impllock)
+        if ((status = apr_sdbm_lock(db, APR_FLOCK_EXCLUSIVE)) != APR_SUCCESS)
             return ioerr(db, status);
 
     if ((status = getpage(db, exhash(key))) == APR_SUCCESS) {
@@ -297,9 +302,8 @@
     else
         ioerr(db, status);
 
-    if (db->flags & SDBM_SHARED)
-        if ((status = sdbm_unlock(db)) != APR_SUCCESS)
-            return ioerr(db, status);
+    if (impllock)
+        (void) apr_sdbm_unlock(db);
 
     return status;
 }
@@ -310,12 +314,12 @@
     int need;
     register long hash;
     apr_status_t status;
+    int impllock = !(db->flags & SDBM_EXCLUSIVE_LOCK);
 
     if (db == NULL || bad(key))
         return APR_EINVAL;
     if (apr_sdbm_rdonly(db))
         return APR_EINVAL;
-
     need = key.dsize + val.dsize;
     /*
      * is the pair too big (or too small) for this database ??
@@ -323,8 +327,10 @@
     if (need < 0 || need > PAIRMAX)
         return APR_EINVAL;
 
-    if (db->flags & SDBM_SHARED)
-        if ((status = sdbm_lock(db, 1)) != APR_SUCCESS)
+    if (db->flags & SDBM_SHARED_LOCK)
+        return APR_EINVAL;
+    if (impllock)
+        if ((status = apr_sdbm_lock(db, APR_FLOCK_EXCLUSIVE)) != APR_SUCCESS)
             return ioerr(db, status);
 
     if ((status = getpage(db, (hash = exhash(key)))) == APR_SUCCESS) {
@@ -357,9 +363,8 @@
     }
 
 error:
-    if (db->flags & SDBM_SHARED)
-        if ((status = sdbm_unlock(db)) != APR_SUCCESS)
-            ioerr(db, status);
+    if (impllock)
+        (void) apr_sdbm_unlock(db);
 
     return status;
 }
@@ -473,9 +478,10 @@
 apr_status_t apr_sdbm_firstkey(apr_sdbm_t *db, apr_sdbm_datum_t *key)
 {
     apr_status_t status;
+    int impllock = !(db->flags & (SDBM_SHARED_LOCK | SDBM_EXCLUSIVE_LOCK));
 
-    if (db->flags & SDBM_SHARED)
-        if ((status = sdbm_lock(db, 0)) != APR_SUCCESS)
+    if (impllock)
+        if ((status = apr_sdbm_lock(db, APR_FLOCK_SHARED)) != APR_SUCCESS)
             return ioerr(db, status);
 
     /*
@@ -492,9 +498,8 @@
         status = getnext(key, db);
     }
 
-    if (db->flags & SDBM_SHARED)
-        if ((status = sdbm_unlock(db)) != APR_SUCCESS)
-            ioerr(db, status);
+    if (impllock)
+        (void) apr_sdbm_unlock(db);
 
     return status;
 }
@@ -502,16 +507,16 @@
 apr_status_t apr_sdbm_nextkey(apr_sdbm_t *db, apr_sdbm_datum_t *key)
 {
     apr_status_t status;
+    int impllock = !(db->flags & (SDBM_SHARED_LOCK | SDBM_EXCLUSIVE_LOCK));
 
-    if (db->flags & SDBM_SHARED)
-        if ((status = sdbm_lock(db, 0)) != APR_SUCCESS)
+    if (impllock)
+        if ((status = apr_sdbm_lock(db, APR_FLOCK_SHARED)) != APR_SUCCESS)
             return ioerr(db, status);
 
     status = getnext(key, db);
 
-    if (db->flags & SDBM_SHARED)
-        if ((status = sdbm_unlock(db)) != APR_SUCCESS)
-            ioerr(db, status);
+    if (impllock)
+        (void) apr_sdbm_unlock(db);
 
     return status;
 }
Index: dbm/sdbm/sdbm_lock.c
===================================================================
RCS file: /home/cvs/apr-util/dbm/sdbm/sdbm_lock.c,v
retrieving revision 1.6
diff -u -r1.6 sdbm_lock.c
--- dbm/sdbm/sdbm_lock.c 2001/04/30 17:16:19 1.6
+++ dbm/sdbm/sdbm_lock.c 2001/05/02 20:59:32
@@ -52,25 +52,47 @@
  * <http://www.apache.org/>.
  */
 
+#include "apr_file_info.h"
 #include "apr_file_io.h"
 #include "apr_sdbm.h"
 
 #include "sdbm_private.h"
+#include "sdbm_tune.h"
 
 /* NOTE: this function blocks until it acquires the lock */
-apr_status_t sdbm_lock(apr_sdbm_t *db, int exclusive)
+apr_status_t apr_sdbm_lock(apr_sdbm_t *db, int type)
 {
-    int type;
+    apr_status_t status;
 
-    if (exclusive)
-        type = APR_FLOCK_EXCLUSIVE;
-    else
-        type = APR_FLOCK_SHARED;
+    if (db->flags & (SDBM_SHARED_LOCK | SDBM_EXCLUSIVE_LOCK))
+        return APR_EINVAL;
+    /*
+     * zero size: either a fresh database, or one with a single,
+     * unsplit data page: dirpage is all zeros.
+     */
+    if ((status = apr_file_lock(db->dirf, type)) == APR_SUCCESS) 
+    {
+        apr_finfo_t finfo;
+        if ((status = apr_file_info_get(&finfo, APR_FINFO_SIZE, db->dirf))
+                != APR_SUCCESS) {
+            (void) apr_file_unlock(db->dirf);
+            return status;
+        }
 
-    return apr_file_lock(db->pagf, type);
+        SDBM_INVALIDATE_CACHE(db, finfo);
+
+        if (type == APR_FLOCK_SHARED)
+            db->flags |= SDBM_SHARED_LOCK;
+        else if (type == APR_FLOCK_EXCLUSIVE)
+            db->flags |= SDBM_EXCLUSIVE_LOCK;
+    }
+    return status;
 }
 
-apr_status_t sdbm_unlock(apr_sdbm_t *db)
+apr_status_t apr_sdbm_unlock(apr_sdbm_t *db)
 {
-    return apr_file_unlock(db->pagf);
+    if (!(db->flags & (SDBM_SHARED_LOCK | SDBM_EXCLUSIVE_LOCK)))
+        return APR_EINVAL;
+    db->flags &= ~(SDBM_SHARED_LOCK | SDBM_EXCLUSIVE_LOCK);
+    return apr_file_unlock(db->dirf);
 }
Index: dbm/sdbm/sdbm_private.h
===================================================================
RCS file: /home/cvs/apr-util/dbm/sdbm/sdbm_private.h,v
retrieving revision 1.5
diff -u -r1.5 sdbm_private.h
--- dbm/sdbm/sdbm_private.h 2001/04/30 17:16:23 1.5
+++ dbm/sdbm/sdbm_private.h 2001/05/02 20:59:33
@@ -79,8 +79,10 @@
 #define SPLTMAX 10   /* maximum allowed splits */
 
 /* for apr_sdbm_t.flags */
-#define SDBM_RDONLY 0x1        /* data base open read-only */
-#define SDBM_SHARED 0x4        /* data base locks for shared write */
+#define SDBM_RDONLY         0x1    /* data base open read-only */
+#define SDBM_SHARED         0x2    /* data base open for sharing */
+#define SDBM_SHARED_LOCK 0x4    /* data base locks for shared write */
+#define SDBM_EXCLUSIVE_LOCK 0x8    /* data base locks for shared write */
 
 struct apr_sdbm_t {
     apr_pool_t *pool;
@@ -100,11 +102,17 @@
     apr_status_t status;               /* track the specific last error */
 };
 
-apr_status_t sdbm_lock(apr_sdbm_t *db, int exclusive);
-apr_status_t sdbm_unlock(apr_sdbm_t *db);
-
 extern const apr_sdbm_datum_t sdbm_nullitem;
 
 long sdbm_hash(const char *str, int len);
+
+/*
+ * zero the cache
+ */
+#define SDBM_INVALIDATE_CACHE(db, finfo) \
+    do { db->dirbno = (!finfo.size) ? 0 : -1; \
+         db->pagbno = -1; \
+         db->maxbno = finfo.size * BYTESIZ; \
+    } while (0);
 
 #endif /* SDBM_PRIVATE_H */
Index: include/apr_sdbm.h
===================================================================
RCS file: /home/cvs/apr-util/include/apr_sdbm.h,v
retrieving revision 1.5
diff -u -r1.5 apr_sdbm.h
--- include/apr_sdbm.h 2001/05/01 05:37:43 1.5
+++ include/apr_sdbm.h 2001/05/02 20:59:45
@@ -88,6 +88,8 @@
                            apr_pool_t *p);
 
 apr_status_t apr_sdbm_close(apr_sdbm_t *db);
+apr_status_t apr_sdbm_lock(apr_sdbm_t *db, int type);
+apr_status_t apr_sdbm_unlock(apr_sdbm_t *db);
 
 apr_status_t apr_sdbm_fetch(apr_sdbm_t *db, apr_sdbm_datum_t *val, apr_sdbm_datum_t key);
 apr_status_t apr_sdbm_delete(apr_sdbm_t *db, const apr_sdbm_datum_t key);



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