refs #5730, make cachefiles list a doubly linked list for more efficient close, helps shutdown

git-svn-id: file:///svn/toku/tokudb@50881 c7de825b-a66e-492c-adef-691d508d4ae1

ft/cachetable-internal.h

@@ -94,6 +94,7 @@ class pair_list;
 //
 struct cachefile {
     CACHEFILE next;
+    CACHEFILE prev;
     bool for_checkpoint; //True if part of the in-progress checkpoint
 
     // If set and the cachefile closes, the file will be removed.

ft/cachetable.cc

@@ -353,6 +353,10 @@ int toku_cachetable_openfd_with_filenum (CACHEFILE *cfptr, CACHETABLE ct, int fd
     newcf->filenum = filenum;
     cachefile_init_filenum(newcf, fd, fname_in_env, fileid);
     newcf->next = ct->cf_list.m_head;
+    newcf->prev = NULL;
+    if (ct->cf_list.m_head) {
+        ct->cf_list.m_head->prev = newcf;
+    }
     ct->cf_list.m_head = newcf;
 
     bjm_init(&newcf->bjm);
@@ -425,17 +429,16 @@ static void remove_cf_from_cachefiles_list (CACHEFILE cf) {
     CACHETABLE ct = cf->cachetable;
     ct->cf_list.write_lock();
     invariant(ct->cf_list.m_head != NULL);
+    if (cf->next) {
+        cf->next->prev = cf->prev;
+    }
+    if (cf->prev) {
+        cf->prev->next = cf->next;
+    }
     if (cf == ct->cf_list.m_head) {
+        invariant(cf->prev == NULL);
         ct->cf_list.m_head = cf->next;
     }
-    else {
-        CACHEFILE curr_cf = ct->cf_list.m_head;
-        while (curr_cf->next != cf) {
-            curr_cf = curr_cf->next;
-        }
-        // at this point, curr_cf->next is pointing to cf
-        curr_cf->next = cf->next;
-    }
     ct->cf_list.write_unlock();
 }