try-compact-in-generation generation-number time-threshold &optional fraction-threshold => result
0 for the most recent generation, 1 for the most recent two generations, and so on up to a maximum (usually 3). Numbers outside this range signal an error.
A real number.
A real number between 0 and 1, defining the minimum fragmentation to actually compact. The default is 0.25.
try-compact-in-generation finds the most fragmented segment in the generation specified. If time-threshold is positive, it compacts this segment, and repeats this operation until time-threshold seconds have elapsed. At this point try-compact-in-generation returns, with value t if at least one segment was compacted and value nil otherwise. Because the operation cannot be stopped in the middle, the actual time taken will always be larger than time-threshold.
If fraction-threshold is 1, try-compact-in-generation does nothing. If fraction-threshold is 0, try-compact-in-generation will compact all uncompacted segments (unless it runs out of time). With the default (0.25) try-compact-in-generation compacts only moderately fragmented segments.
If time-threshold is negative, then try-compact-in-generation does not actually compact any segments. result is a boolean indicating whether try-compact-in-generation would actually try to compact a segment if it were to be called with a positive time-threshold and the other arguments unchanged.
This function is typically used after a call to check-fragmentation. For more information, see Controlling Fragmentation.
try-compact-in-generation is implemented only in 32-bit LispWorks. It is not relevant to the Memory Management API in 64-bit implementations, where marking-gc with the what-to-copy argument offers similar functionality ( although set-blocking-gen-num is intended to solve the problem of fragmentation automatically).
LispWorks User Guide and Reference Manual - 13 Feb 2015