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ProcessList: fix quadratic process removal when scanning

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This commit changes ProcessList_scan to lazily remove Processes by
index, which is known, instead of performing a brute-force search by
pid and immediately reclaiming the lost vector space via compaction.

Searching by pid is potentially quadratic in ProcessList_scan because
the process we are searching for is always at the back of the vector
(the scan starts from the back of the vector). Additionally, removal
via Vector_remove immediately reclaims space (by sliding elements
down).

With these changes process removal in ProcessList_scan is now linear.

Changes:
  * ProcessList: add new ProcessList_removeIndex function to remove
    by index
  * Vector: add Vector_softRemove and Vector_compact functions to
    support lazy removal/deletion of entries Vector_softRemove
    Vector_compact
  * Vector: replace Vector_count with Vector_countEquals since it only
    used for consistency assertions.
This commit is contained in:
Charlie Vieth
2022-02-05 18:47:43 -05:00
committed by BenBE
parent c7413fd677
commit 08166b27b1
5 changed files with 127 additions and 35 deletions
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20
Vector.h
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@ -22,6 +22,11 @@ typedef struct Vector_ {
int arraySize;
int growthRate;
int items;
/* lowest index of a pending soft remove/delete operation,
used to speed up compaction */
int dirty_index;
/* count of soft deletes, required for Vector_count to work in debug mode */
int dirty_count;
bool owner;
} Vector;
@ -44,6 +49,15 @@ Object* Vector_take(Vector* this, int idx);
Object* Vector_remove(Vector* this, int idx);
/* Vector_softRemove marks the item at index idx for deletion without
reclaiming any space. If owned, the item is immediately freed.
Vector_compact must be called to reclaim space.*/
Object* Vector_softRemove(Vector* this, int idx);
/* Vector_compact reclaims space free'd up by Vector_softRemove, if any. */
void Vector_compact(Vector* this);
void Vector_moveUp(Vector* this, int idx);
void Vector_moveDown(Vector* this, int idx);
@ -54,7 +68,11 @@ void Vector_set(Vector* this, int idx, void* data_);
Object* Vector_get(const Vector* this, int idx);
int Vector_size(const Vector* this);
unsigned int Vector_count(const Vector* this);
/* Vector_countEquals returns true if the number of non-NULL items
in the Vector is equal to expectedCount. This is only for debugging
and consistency checks. */
bool Vector_countEquals(const Vector* this, unsigned int expectedCount);
#else /* NDEBUG */