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strv: when growing strv arrays piecemeal actually allocate memory in exponential steps

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Let's improve memory allocation for call such as strv_extend() that just
one item to an strv: these are often called in a loop, where they used
to be very ineffecient, since we'd allocate byte-exact space. With this
change let's improve on that, by allocating exponentially by rounding up
to the next exponent of 2. This way we get GREEDY_REALLOC()-like
behaviour without passing around state.

In fact this should be good enough so that we could replace existing
loops around GREEDY_REALLOC() for strv build-up with plain strv_extend()
and get similar behaviour.
This commit is contained in:
Lennart Poettering
2019-12-09 18:30:00 +01:00
parent 47ac31f792
commit 6047637645
1 changed files with 16 additions and 12 deletions
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28
src/basic/strv.c
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@@ -193,7 +193,10 @@ int strv_extend_strv(char ***a, char **b, bool filter_duplicates) {
p = strv_length(*a);
q = strv_length(b);
t = reallocarray(*a, p + q + 1, sizeof(char *));
if (p >= SIZE_MAX - q)
return -ENOMEM;
t = reallocarray(*a, GREEDY_ALLOC_ROUND_UP(p + q + 1), sizeof(char *));
if (!t)
return -ENOMEM;
@@ -383,19 +386,18 @@ char *strv_join_prefix(char **l, const char *separator, const char *prefix) {
int strv_push(char ***l, char *value) {
char **c;
size_t n, m;
size_t n;
if (!value)
return 0;
n = strv_length(*l);
/* Increase and check for overflow */
m = n + 2;
if (m < n)
/* Check for overflow */
if (n > SIZE_MAX-2)
return -ENOMEM;
c = reallocarray(*l, m, sizeof(char*));
c = reallocarray(*l, GREEDY_ALLOC_ROUND_UP(n + 2), sizeof(char*));
if (!c)
return -ENOMEM;
@@ -408,19 +410,19 @@ int strv_push(char ***l, char *value) {
int strv_push_pair(char ***l, char *a, char *b) {
char **c;
size_t n, m;
size_t n;
if (!a && !b)
return 0;
n = strv_length(*l);
/* increase and check for overflow */
m = n + !!a + !!b + 1;
if (m < n)
/* Check for overflow */
if (n > SIZE_MAX-3)
return -ENOMEM;
c = reallocarray(*l, m, sizeof(char*));
/* increase and check for overflow */
c = reallocarray(*l, GREEDY_ALLOC_ROUND_UP(n + !!a + !!b + 1), sizeof(char*));
if (!c)
return -ENOMEM;
@@ -846,8 +848,10 @@ int strv_extend_n(char ***l, const char *value, size_t n) {
/* Adds the value n times to l */
k = strv_length(*l);
if (n >= SIZE_MAX - k)
return -ENOMEM;
nl = reallocarray(*l, k + n + 1, sizeof(char *));
nl = reallocarray(*l, GREEDY_ALLOC_ROUND_UP(k + n + 1), sizeof(char *));
if (!nl)
return -ENOMEM;