Changeset 3381 in kBuild for trunk/src

Timestamp:

Jun 12, 2020 11:36:10 AM (5 years ago)

Author:

bird

Message:

kFsCache: Account of race between us reading a directory and someone changing it, requiring re-reading the directory till at least 10ms has passed since the last direction change.

Location:

trunk/src/lib/nt

Files:

• kFsCache.c (modified) (7 diffs)
• kFsCache.h (modified) (1 diff)
• tstkFsCache.c (modified) (2 diffs)

trunk/src/lib/nt/kFsCache.c

@@ -64 +64 @@
 # define KFSCACHE_LOG2(a) do { } while (0)
 #endif
+
+/** The minimum time between a directory last populated time and its
+ * modification time for the cache to consider it up-to-date.
+ *
+ * This helps work around races between us reading a directory and someone else
+ * adding / removing files and directories to /from it.  Given that the
+ * effective time resolution typically is around 2000Hz these days, unless you
+ * use the new *TimePrecise API variants, there is plenty of room for a race
+ * here.
+ *
+ * The current value is 20ms in NT time units (100ns each), which translates
+ * to a 50Hz time update frequency. */
+#define KFSCACHE_MIN_LAST_POPULATED_VS_WRITE (20*1000*10)
 
 
@@ -662 +675 @@
             pDirObj->uDevNo             = pParent->uDevNo;
             pDirObj->iLastWrite         = 0;
+            pDirObj->iLastPopulated     = 0;
             pDirObj->fPopulated         = K_FALSE;
         }
@@ -1316 +1330 @@
     KFSDIRREPOP                 DirRePop    = { NULL, 0, 0, 0, NULL };
     MY_UNICODE_STRING           UniStrStar  = { 1 * sizeof(wchar_t), 2 * sizeof(wchar_t), L"*" };
+    FILETIME                    Now;
 
     /** @todo May have to make this more flexible wrt information classes since
@@ -1437 +1452 @@
      *       restart that single file name query.
      */
+    GetSystemTimeAsFileTime(&Now);
+    pDir->iLastPopulated = ((KI64)Now.dwHighDateTime << 32) | Now.dwLowDateTime;
     Ios.Information = -1;
     Ios.u.Status    = -1;
@@ -1526 +1543 @@
                                 if (   !pCurDir->fPopulated
                                     ||  (   pCurDir->iLastWrite == uPtr.pWithId->LastWriteTime.QuadPart
-                                         && (pCur->fFlags & KFSOBJ_F_WORKING_DIR_MTIME) ) )
+                                         && (pCur->fFlags & KFSOBJ_F_WORKING_DIR_MTIME)
+                                         &&    pCurDir->iLastPopulated - pCurDir->iLastWrite
+                                            >= KFSCACHE_MIN_LAST_POPULATED_VS_WRITE ))
                                 { /* kind of likely */ }
                                 else
@@ -1775 +1794 @@
             if (MY_NT_SUCCESS(rcNt))
             {
-                if (BasicInfo.LastWriteTime.QuadPart != pDir->iLastWrite)
+                if (   BasicInfo.LastWriteTime.QuadPart != pDir->iLastWrite
+                    || pDir->iLastPopulated - pDir->iLastWrite < KFSCACHE_MIN_LAST_POPULATED_VS_WRITE)
                 {
                     pDir->fNeedRePopulating = K_TRUE;
@@ -2059 +2079 @@
 
                 if (   pDir->iLastWrite == uBuf.FullInfo.LastWriteTime.QuadPart
-                    && (pObj->fFlags & KFSOBJ_F_WORKING_DIR_MTIME) )
+                    && (pObj->fFlags & KFSOBJ_F_WORKING_DIR_MTIME)
+                    && pDir->iLastPopulated - pDir->iLastWrite >= KFSCACHE_MIN_LAST_POPULATED_VS_WRITE)
                     KFSCACHE_LOG(("Refreshing %s/%s/ - no re-populating necessary.\n",
                                   pObj->pParent->Obj.pszName, pObj->pszName));

trunk/src/lib/nt/kFsCache.h

@@ -275 +275 @@
      *          parent directory is refreshed. */
     KI64                iLastWrite;
+    /** The time that iLastWrite was read. */
+    KI64                iLastPopulated;
 
     /** Set if populated. */

trunk/src/lib/nt/tstkFsCache.c

@@ -138 +138 @@
     /*
      * Try emulate the temp issue above.  Seem to require several files.
+     * (The problem was related to long/short filename updating.)
      */
     szPath[cchWorkDir++] = '\\';
@@ -165 +166 @@
     CHECK(pFsObj && pFsObj->bObjType == KFSOBJ_TYPE_MISSING);
 
-Sleep(100);
     sprintf(&szPath[cchWorkDir], "longfilename3.txt");
     CHECK(myCreateFile(szPath) == 0);