diff options
Diffstat (limited to 'generic/tclStringObj.c')
| -rw-r--r-- | generic/tclStringObj.c | 115 |
1 files changed, 90 insertions, 25 deletions
diff --git a/generic/tclStringObj.c b/generic/tclStringObj.c index ef85f9c..3bdefbd 100644 --- a/generic/tclStringObj.c +++ b/generic/tclStringObj.c @@ -33,7 +33,7 @@ * See the file "license.terms" for information on usage and redistribution * of this file, and for a DISCLAIMER OF ALL WARRANTIES. * - * RCS: @(#) $Id: tclStringObj.c,v 1.17 2000/05/26 08:52:17 hobbs Exp $ */ + * RCS: @(#) $Id: tclStringObj.c,v 1.18 2000/08/30 01:43:00 ericm Exp $ */ #include "tclInt.h" @@ -108,6 +108,51 @@ typedef struct String { #define SET_STRING(objPtr, stringPtr) \ (objPtr)->internalRep.otherValuePtr = (VOID *) (stringPtr) +/* + * TCL STRING GROWTH ALGORITHM + * + * When growing strings (during an append, for example), the following growth + * algorithm is used: + * if (oldSpace + appendLength < TCL_GROWTH_LARGE_STRING) { + * newSpace = 2 * (oldSpace + appendLength) + * } else { + * newSpace = (2 * appendLength) + TCL_GROWTH_MIN_ALLOC + oldSpace + * } + * + * This allows more efficient use of memory for large strings; if the + * doubling algorithm were used after TCL_GROWTH_LARGE_STRING, the + * maximum string size in Tcl would be about 1/2 the size of available + * memory. With this adaptive algorithm, effectively all of available memory + * can be allocated. + * + * The addition of TCL_GROWTH_MIN_ALLOC allows for efficient handling + * of very small appends. Without this extra slush factor, a sequence + * of several small appends would cause several memory allocations. + * As long as TCL_GROWTH_MIN_ALLOC is a reasonable size, we can + * avoid that behavior. + * + * We do NOT use TCL_GROWTH_MIN_ALLOC for strings smaller than + * TCL_GROWTH_LARGE_STRING simply because we want our small strings + * to stay small; an allocation of TCL_GROWTH_MIN_ALLOC for a string + * that is only a few bytes long is wasteful. + * + * The growth algorithm can be tuned by adjusting the following parameters: + * + * TCL_GROWTH_LARGE_STRING Cutoff point, in bytes, at which to switch + * from the doubling algorithm to the adaptive. + * algorithm. Default is 1048576 (1 megabyte) + * TCL_GROWTH_MIN_ALLOC Additional space, in bytes, to allocate with + * each allocation for strings larger than + * TCL_GROWTH_LARGE_STRING. + * Default is 1024 (1 kilobyte). + */ +#ifndef TCL_GROWTH_LARGE_STRING +#define TCL_GROWTH_LARGE_STRING 1048576 +#endif +#ifndef TCL_GROWTH_MIN_ALLOC +#define TCL_GROWTH_MIN_ALLOC 1024 +#endif + /* *---------------------------------------------------------------------- @@ -667,12 +712,19 @@ Tcl_SetObjLength(objPtr, length) * Not enough space in current string. Reallocate the string * space and free the old string. */ - - new = (char *) ckalloc((unsigned) (length+1)); - if (objPtr->bytes != NULL) { - memcpy((VOID *) new, (VOID *) objPtr->bytes, - (size_t) objPtr->length); - Tcl_InvalidateStringRep(objPtr); + if (objPtr->bytes != tclEmptyStringRep) { + new = (char *) ckrealloc((char *)objPtr->bytes, + (unsigned)(length+1)); + } else { + new = NULL; + } + if (new == NULL) { + new = (char *) ckalloc((unsigned) (length+1)); + if (objPtr->bytes != NULL && objPtr->length != 0) { + memcpy((VOID *) new, (VOID *) objPtr->bytes, + (size_t) objPtr->length); + Tcl_InvalidateStringRep(objPtr); + } } objPtr->bytes = new; stringPtr->allocated = length; @@ -982,15 +1034,17 @@ AppendUnicodeToUnicodeRep(objPtr, unicode, appendNumChars) /* * If not enough space has been allocated for the unicode rep, - * reallocate the internal rep object with double the amount of - * space needed, so the unicode string can grow without being - * reallocated. + * reallocate the internal rep object with additional space. See the + * "TCL STRING GROWTH ALGORITHM" comment at the top of this file for an + * explanation of the growth algorithm. */ numChars = stringPtr->numChars + appendNumChars; if (numChars >= stringPtr->uallocated) { - stringPtr->uallocated = numChars * 2; + stringPtr->uallocated = numChars + + (numChars >= TCL_GROWTH_LARGE_STRING ? + (2 * appendNumChars) + TCL_GROWTH_MIN_ALLOC : numChars); stringPtr = (String *) ckrealloc((char*)stringPtr, STRING_SIZE(stringPtr->uallocated)); SET_STRING(objPtr, stringPtr); @@ -1138,13 +1192,15 @@ AppendUtfToUtfRep(objPtr, bytes, numBytes) if (newLength > (int) stringPtr->allocated) { /* - * There isn't currently enough space in the string - * representation so allocate additional space. Overallocate the - * space by doubling it so that we won't have to do as much - * reallocation in the future. + * There isn't currently enough space in the string representation + * so allocate additional space. See the "TCL STRING GROWTH ALGORITHM" + * comment at the top of this file for an explanation of the growth + * algorithm. */ - Tcl_SetObjLength(objPtr, 2*newLength); + Tcl_SetObjLength(objPtr, newLength + + (newLength >= TCL_GROWTH_LARGE_STRING ? + (2 * numBytes) + TCL_GROWTH_MIN_ALLOC : newLength)); } else { /* @@ -1207,7 +1263,8 @@ Tcl_AppendStringsToObjVA (objPtr, argList) */ nargs = 0; - newLength = oldLength = objPtr->length; + newLength = 0; + oldLength = objPtr->length; while (1) { string = va_arg(argList, char *); if (string == NULL) { @@ -1231,23 +1288,31 @@ Tcl_AppendStringsToObjVA (objPtr, argList) newLength += strlen(string); args[nargs++] = string; } - if (newLength == oldLength) { + if (newLength == 0) { goto done; } stringPtr = GET_STRING(objPtr); - if (newLength > (int) stringPtr->allocated) { + if (oldLength + newLength > (int) stringPtr->allocated) { /* * There isn't currently enough space in the string - * representation so allocate additional space. If the current + * representation, so allocate additional space. If the current * string representation isn't empty (i.e. it looks like we're - * doing a series of appends) then overallocate the space so - * that we won't have to do as much reallocation in the future. + * doing a series of appends) then the growth algorithm described in + * the "TCL STRING GROWTH ALGORITHM" comment at the top of this file is + * used to determine how much memory to allocate. Otherwise, exactly + * enough memory is allocated. */ - Tcl_SetObjLength(objPtr, - (objPtr->length == 0) ? newLength : 2*newLength); + if (oldLength == 0) { + Tcl_SetObjLength(objPtr, newLength); + } else if (oldLength < TCL_GROWTH_LARGE_STRING) { + Tcl_SetObjLength(objPtr, 2 * (oldLength + newLength)); + } else { + Tcl_SetObjLength(objPtr, + oldLength + (2 * newLength) + TCL_GROWTH_MIN_ALLOC); + } } /* @@ -1278,7 +1343,7 @@ Tcl_AppendStringsToObjVA (objPtr, argList) if (dst != NULL) { *dst = 0; } - objPtr->length = newLength; + objPtr->length = oldLength + newLength; done: /* |