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sstables: replace potentially large for loop with do_until

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We are pushing ints here, so it shouldn't be that bad in practice.
But a potentially gigantic for loop is just asking for a stall since we won't
need_preempt() it.

Signed-off-by: Glauber Costa <glauber@scylladb.com>
This commit is contained in:
Glauber Costa
2018-03-14 11:58:03 -04:00
parent 091b0f9d41
commit 0d9488eae6
1 changed files with 12 additions and 11 deletions
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23
sstables/sstables.cc
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@@ -646,22 +646,23 @@ future<> parse(random_access_reader& in, summary& s) {
check_buf_size(buf, len);
s.entries.resize(s.header.size);
// Positions are encoded in little-endian.
auto b = buf.get();
s.positions = utils::chunked_vector<pos_type>();
for (size_t i = 0; i < s.header.size; ++i) {
return do_until([&s] { return s.positions.size() == s.header.size; }, [&s, b] () mutable {
s.positions.push_back(seastar::read_le<pos_type>(b));
b += sizeof(pos_type);
}
// Since the keys in the index are not sized, we need to calculate
// the start position of the index i+1 to determine the boundaries
// of index i. The "memory_size" field in the header determines the
// total memory used by the map, so if we push it to the vector, we
// can guarantee that no conditionals are used, and we can always
// query the position of the "next" index.
s.positions.push_back(s.header.memory_size);
return make_ready_future<>();
}).then([&s] {
// Since the keys in the index are not sized, we need to calculate
// the start position of the index i+1 to determine the boundaries
// of index i. The "memory_size" field in the header determines the
// total memory used by the map, so if we push it to the vector, we
// can guarantee that no conditionals are used, and we can always
// query the position of the "next" index.
s.positions.push_back(s.header.memory_size);
return make_ready_future<>();
});
}).then([&in, &s] {
in.seek(sizeof(summary::header) + s.header.memory_size);
return parse(in, s.first_key, s.last_key);