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[Rust] Make find_duplicate_stored_vtable_revloc more efficient #5580

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[Rust] Make find_duplicate_stored_vtable_revloc more efficient #5580

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54 changes: 37 additions & 17 deletions rust/flatbuffers/src/builder.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -24,6 +24,7 @@ use std::slice::from_raw_parts;
use endian_scalar::{emplace_scalar, read_scalar_at};
use primitives::*;
use push::{Push, PushAlignment};
use std::collections::BTreeMap;
use table::Table;
use vector::{SafeSliceAccess, Vector};
use vtable::{field_index_to_field_offset, VTable};
Expand All @@ -46,7 +47,7 @@ pub struct FlatBufferBuilder<'fbb> {
head: usize,

field_locs: Vec<FieldLoc>,
written_vtable_revpos: Vec<UOffsetT>,
written_vtable_revpos: BTreeMap<(VOffsetT, VOffsetT), Vec<UOffsetT>>,

nested: bool,
finished: bool,
Expand Down Expand Up @@ -79,7 +80,7 @@ impl<'fbb> FlatBufferBuilder<'fbb> {
head: size,

field_locs: Vec::new(),
written_vtable_revpos: Vec::new(),
written_vtable_revpos: BTreeMap::new(),

nested: false,
finished: false,
Expand Down Expand Up @@ -112,7 +113,9 @@ impl<'fbb> FlatBufferBuilder<'fbb> {
}

self.head = self.owned_buf.len();
self.written_vtable_revpos.clear();
for table in self.written_vtable_revpos.values_mut() {
table.clear();
}

self.nested = false;
self.finished = false;
Expand Down Expand Up @@ -167,7 +170,7 @@ impl<'fbb> FlatBufferBuilder<'fbb> {
/// FlatBuffer. This is primarily used to check vtable deduplication.
#[inline]
pub fn num_written_vtables(&self) -> usize {
self.written_vtable_revpos.len()
self.written_vtable_revpos.values().map(|v| v.len()).sum()
}

/// Start a Table write.
Expand Down Expand Up @@ -455,11 +458,15 @@ impl<'fbb> FlatBufferBuilder<'fbb> {
// Write the VTable (we may delete it afterwards, if it is a duplicate):
let vt_start_pos = self.head;
let vt_end_pos = self.head + vtable_byte_len;

let vtable_byte_len = vtable_byte_len as VOffsetT;
let table_object_size = table_object_size as VOffsetT;

{
// write the vtable header:
let vtfw = &mut VTableWriter::init(&mut self.owned_buf[vt_start_pos..vt_end_pos]);
vtfw.write_vtable_byte_length(vtable_byte_len as VOffsetT);
vtfw.write_object_inline_size(table_object_size as VOffsetT);
vtfw.write_vtable_byte_length(vtable_byte_len);
vtfw.write_object_inline_size(table_object_size);

// serialize every FieldLoc to the vtable:
for &fl in self.field_locs.iter() {
Expand All @@ -474,18 +481,21 @@ impl<'fbb> FlatBufferBuilder<'fbb> {
}
let dup_vt_use = {
let this_vt = VTable::init(&self.owned_buf[..], self.head);
self.find_duplicate_stored_vtable_revloc(this_vt)
self.find_duplicate_stored_vtable_revloc(vtable_byte_len, table_object_size, this_vt)
};

let vt_use = match dup_vt_use {
Some(n) => {
VTableWriter::init(&mut self.owned_buf[vt_start_pos..vt_end_pos]).clear();
self.head += vtable_byte_len;
self.head += vtable_byte_len as usize;
n
}
None => {
let new_vt_use = self.used_space() as UOffsetT;
self.written_vtable_revpos.push(new_vt_use);
self.written_vtable_revpos
.entry((vtable_byte_len, table_object_size))
.or_default()
.push(new_vt_use);
new_vt_use
}
};
Expand All @@ -506,14 +516,24 @@ impl<'fbb> FlatBufferBuilder<'fbb> {
}

#[inline]
fn find_duplicate_stored_vtable_revloc(&self, needle: VTable) -> Option<UOffsetT> {
for &revloc in self.written_vtable_revpos.iter().rev() {
let o = VTable::init(
&self.owned_buf[..],
self.head + self.used_space() - revloc as usize,
);
if needle == o {
return Some(revloc);
fn find_duplicate_stored_vtable_revloc(
&self,
vtable_byte_len: VOffsetT,
table_object_size: VOffsetT,
needle: VTable,
) -> Option<UOffsetT> {
if let Some(tables) = self
.written_vtable_revpos
.get(&(vtable_byte_len, table_object_size))
{
for &revloc in tables.iter().rev() {
let o = VTable::init(
&self.owned_buf[..],
self.head + self.used_space() - revloc as usize,
);
if needle == o {
return Some(revloc);
}
}
}
None
Expand Down