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[RFC] include/interval_set: iterate until p->first < start #53063

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[RFC] include/interval_set: iterate until p->first < start #53063

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32 changes: 22 additions & 10 deletions src/include/interval_set.h
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Original file line number Diff line number Diff line change
Expand Up @@ -249,22 +249,34 @@ class interval_set {
private:
auto find_inc(T start) const {
auto p = m.lower_bound(start); // p->first >= start
if (p != m.begin() &&
(p == m.end() || p->first > start)) {
--p; // might overlap?
if (p->first + p->second <= start)
++p; // it doesn't.
if (p != m.end()) {
while (p != m.begin()) {
if (p->first <= start) {
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This is buggy. Old code will make sure that the p won't be .end(), but yours seems will crash ?

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so if we dont hit this if {} then it assume either p->first > start or p==m.end(), so in this case we decrement --p

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i.e. it wont hit end() here either

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Won't the m.lower_bound() return .end() if it couldn't find any item ?

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okay so you're implying that we should just return directly in case we dont find anything in the map, right? you're correct, i need to handle this edge case. decrementing in case there is nothing would be disastrous

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Yeah, the corner edge case.

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check now

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In erase() it will check ceph_assert(p != m.end()); . Your above change could return .end().

break;
} else {
--p; // might overlap?
}
}
if (p->first + p->second <= start) {
++p; // it doesn't.
}
}
return p;
}

auto find_inc_m(T start) {
auto p = m.lower_bound(start);
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if (p != m.begin() &&
(p == m.end() || p->first > start)) {
--p; // might overlap?
if (p->first + p->second <= start)
++p; // it doesn't.
if (p != m.end()) {
while (p != m.begin()) {
if (p->first <= start) {
break;
} else {
--p; // might overlap?
}
}
if (p->first + p->second <= start) {
++p; // it doesn't.
}
}
return p;
}
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