3024359 Make sure that the per-thread cache of the list of file systems

currently registered is only updated at times when no active loops are
traversing it.  Also reduce the amount of epoch storing and checking to
where it can make a difference.

1 files changed, 45 insertions, 31 deletions

diff --git a/generic/tclIOUtil.c b/generic/tclIOUtil.c
index 9e36d64..dccbeb5 100644
--- a/generic/tclIOUtil.c
+++ b/generic/tclIOUtil.c
@@ -39,9 +39,10 @@ static void		FsAddMountsToGlobResult(Tcl_Obj *resultPtr,
 			    Tcl_GlobTypeData *types);
 static void		FsUpdateCwd(Tcl_Obj *cwdObj, ClientData clientData);
 
-#ifdef TCL_THREADS
 static void		FsRecacheFilesystemList(void);
-#endif
+static void		Claim(void);
+static void		Disclaim(void);
+
 
 /*
  * These form part of the native filesystem support. They are needed here
@@ -409,7 +410,7 @@ static FilesystemRecord nativeFilesystemRecord = {
  * trigger cache cleanup in all threads.
  */
 
-static int theFilesystemEpoch = 0;
+static int theFilesystemEpoch = 1;
 
 /*
  * Stores the linked list of filesystems. A 1:1 copy of this list is also
@@ -581,12 +582,11 @@ TclFSCwdPointerEquals(
     }
 }
 
-#ifdef TCL_THREADS
 static void
 FsRecacheFilesystemList(void)
 {
     ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&tclFsDataKey);
-    FilesystemRecord *fsRecPtr, *tmpFsRecPtr = NULL, *toFree = NULL;
+    FilesystemRecord *fsRecPtr, *tmpFsRecPtr = NULL, *toFree = NULL, *list;
 
     /*
      * Trash the current cache.
@@ -595,20 +595,16 @@ FsRecacheFilesystemList(void)
     fsRecPtr = tsdPtr->filesystemList;
     while (fsRecPtr != NULL) {
 	tmpFsRecPtr = fsRecPtr->nextPtr;
-	fsRecPtr->fsPtr = NULL;
 	fsRecPtr->nextPtr = toFree;
 	toFree = fsRecPtr;
 	fsRecPtr = tmpFsRecPtr;
     }
-    tsdPtr->filesystemList = NULL;
 
     /*
-     * Code below operates on shared data. We are already called under mutex
-     * lock so we can safely proceed.
-     *
      * Locate tail of the global filesystem list.
      */
 
+    Tcl_MutexLock(&filesystemMutex);
     fsRecPtr = filesystemList;
     while (fsRecPtr != NULL) {
 	tmpFsRecPtr = fsRecPtr;
@@ -619,21 +615,23 @@ FsRecacheFilesystemList(void)
      * Refill the cache honouring the order.
      */
 
+    list = NULL;
     fsRecPtr = tmpFsRecPtr;
     while (fsRecPtr != NULL) {
 	tmpFsRecPtr = (FilesystemRecord *) ckalloc(sizeof(FilesystemRecord));
 	*tmpFsRecPtr = *fsRecPtr;
-	tmpFsRecPtr->nextPtr = tsdPtr->filesystemList;
+	tmpFsRecPtr->nextPtr = list;
 	tmpFsRecPtr->prevPtr = NULL;
-	if (tsdPtr->filesystemList) {
-	    tsdPtr->filesystemList->prevPtr = tmpFsRecPtr;
-	}
-	tsdPtr->filesystemList = tmpFsRecPtr;
+	list = tmpFsRecPtr;
 	fsRecPtr = fsRecPtr->prevPtr;
     }
+    tsdPtr->filesystemList = list;
+    tsdPtr->filesystemEpoch = theFilesystemEpoch;
+    Tcl_MutexUnlock(&filesystemMutex);
 
     while (toFree) {
 	FilesystemRecord *next = toFree->nextPtr;
+	toFree->fsPtr = NULL;
 	ckfree((char *)toFree);
 	toFree = next;
     }
@@ -647,27 +645,16 @@ FsRecacheFilesystemList(void)
 	tsdPtr->initialized = 1;
     }
 }
-#endif /* TCL_THREADS */
 
 static FilesystemRecord *
 FsGetFirstFilesystem(void)
 {
     ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&tclFsDataKey);
-    FilesystemRecord *fsRecPtr;
-#ifndef TCL_THREADS
-    tsdPtr->filesystemEpoch = theFilesystemEpoch;
-    fsRecPtr = filesystemList;
-#else
-    Tcl_MutexLock(&filesystemMutex);
-    if (tsdPtr->filesystemList == NULL
-	    || (tsdPtr->filesystemEpoch != theFilesystemEpoch)) {
+    if (tsdPtr->filesystemList == NULL || ((tsdPtr->claims == 0)
+	    && (tsdPtr->filesystemEpoch != theFilesystemEpoch))) {
 	FsRecacheFilesystemList();
-	tsdPtr->filesystemEpoch = theFilesystemEpoch;
     }
-    Tcl_MutexUnlock(&filesystemMutex);
-    fsRecPtr = tsdPtr->filesystemList;
-#endif
-    return fsRecPtr;
+    return tsdPtr->filesystemList;
 }
 
 /*
@@ -679,9 +666,21 @@ int
 TclFSEpochOk(
     int filesystemEpoch)
 {
+    return (filesystemEpoch == 0 || filesystemEpoch == theFilesystemEpoch);
+}
+
+static void
+Claim()
+{
     ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&tclFsDataKey);
-    (void) FsGetFirstFilesystem();
-    return (filesystemEpoch == tsdPtr->filesystemEpoch);
+    tsdPtr->claims++;
+}
+
+static void
+Disclaim()
+{
+    ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&tclFsDataKey);
+    tsdPtr->claims--;
 }
 
 /*
@@ -799,6 +798,7 @@ TclFinalizeFilesystem(void)
 	}
 	fsRecPtr = tmpFsRecPtr;
     }
+    theFilesystemEpoch++;
     filesystemList = NULL;
 
     /*
@@ -836,6 +836,7 @@ void
 TclResetFilesystem(void)
 {
     filesystemList = &nativeFilesystemRecord;
+    theFilesystemEpoch++;
 
 #ifdef __WIN32__
     /*
@@ -1408,6 +1409,7 @@ TclFSNormalizeToUniquePath(
 
     firstFsRecPtr = FsGetFirstFilesystem();
 
+    Claim();
     fsRecPtr = firstFsRecPtr;
     while (fsRecPtr != NULL) {
 	if (fsRecPtr->fsPtr == &tclNativeFilesystem) {
@@ -1440,6 +1442,7 @@ TclFSNormalizeToUniquePath(
 	}
 	fsRecPtr = fsRecPtr->nextPtr;
     }
+    Disclaim();
 
     return startAt;
 }
@@ -2634,6 +2637,7 @@ Tcl_FSGetCwd(
 	 */
 
 	fsRecPtr = FsGetFirstFilesystem();
+	Claim();
 	while ((retVal == NULL) && (fsRecPtr != NULL)) {
 	    Tcl_FSGetCwdProc *proc = fsRecPtr->fsPtr->getCwdProc;
 	    if (proc != NULL) {
@@ -2671,6 +2675,7 @@ Tcl_FSGetCwd(
 			}
 			Tcl_DecrRefCount(retVal);
 			retVal = NULL;
+			Disclaim();
 			goto cdDidNotChange;
 		    } else if (interp != NULL) {
 			Tcl_AppendResult(interp,
@@ -2683,6 +2688,7 @@ Tcl_FSGetCwd(
 	    }
 	    fsRecPtr = fsRecPtr->nextPtr;
 	}
+	Disclaim();
 
 	/*
 	 * Now the 'cwd' may NOT be normalized, at least on some platforms.
@@ -3628,6 +3634,7 @@ Tcl_FSListVolumes(void)
      */
 
     fsRecPtr = FsGetFirstFilesystem();
+    Claim();
     while (fsRecPtr != NULL) {
 	Tcl_FSListVolumesProc *proc = fsRecPtr->fsPtr->listVolumesProc;
 	if (proc != NULL) {
@@ -3639,6 +3646,7 @@ Tcl_FSListVolumes(void)
 	}
 	fsRecPtr = fsRecPtr->nextPtr;
     }
+    Disclaim();
 
     return resultPtr;
 }
@@ -3678,6 +3686,7 @@ FsListMounts(
      */
 
     fsRecPtr = FsGetFirstFilesystem();
+    Claim();
     while (fsRecPtr != NULL) {
 	if (fsRecPtr->fsPtr != &tclNativeFilesystem) {
 	    Tcl_FSMatchInDirectoryProc *proc =
@@ -3691,6 +3700,7 @@ FsListMounts(
 	}
 	fsRecPtr = fsRecPtr->nextPtr;
     }
+    Disclaim();
 
     return resultPtr;
 }
@@ -3903,6 +3913,7 @@ TclFSNonnativePathType(
      */
 
     fsRecPtr = FsGetFirstFilesystem();
+    Claim();
     while (fsRecPtr != NULL) {
 	Tcl_FSListVolumesProc *proc = fsRecPtr->fsPtr->listVolumesProc;
 
@@ -3981,6 +3992,7 @@ TclFSNonnativePathType(
 	}
 	fsRecPtr = fsRecPtr->nextPtr;
     }
+    Disclaim();
     return type;
 }
 
@@ -4375,6 +4387,7 @@ Tcl_FSGetFileSystemForPath(
      */
 
     fsRecPtr = FsGetFirstFilesystem();
+    Claim();
 
     if (TclFSEnsureEpochOk(pathPtr, &retVal) != TCL_OK) {
 	return NULL;
@@ -4403,6 +4416,7 @@ Tcl_FSGetFileSystemForPath(
 	}
 	fsRecPtr = fsRecPtr->nextPtr;
     }
+    Disclaim();
 
     return retVal;
 }