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RegionLoader: avoid hitting the disk twice during chunk reads

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this provides some performance improvement (although it's difficult to measure because of cache).
this does mean that we read some garbage data during chunk reads, but it's less costly than hitting the disk twice.
This commit is contained in:
Dylan K. Taylor 2021-01-20 21:05:44 +00:00
parent ecc1e1f698
commit e8ffab1787
1 changed files with 24 additions and 22 deletions
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46
src/pocketmine/level/format/io/region/RegionLoader.php
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@ -27,6 +27,8 @@ use pocketmine\level\format\ChunkException;
use pocketmine\level\format\io\exception\CorruptedChunkException;
use pocketmine\utils\AssumptionFailedError;
use pocketmine\utils\Binary;
use pocketmine\utils\BinaryDataException;
use pocketmine\utils\BinaryStream;
use function assert;
use function ceil;
use function chr;
@ -145,34 +147,34 @@ class RegionLoader{
fseek($this->filePointer, $this->locationTable[$index]->getFirstSector() << 12);
$prefix = fread($this->filePointer, 4);
if($prefix === false or strlen($prefix) !== 4){
throw new CorruptedChunkException("Corrupted chunk header detected (unexpected end of file reading length prefix)");
}
$length = Binary::readInt($prefix);
/*
* this might cause us to read some junk, but under normal circumstances it won't be any more than 4096 bytes wasted.
* doing this in a single call is faster than making two seeks and reads to fetch the chunk.
* this relies on the assumption that the end of the file is always padded to a multiple of 4096 bytes.
*/
$bytesToRead = $this->locationTable[$index]->getSectorCount() << 12;
$payload = fread($this->filePointer, $bytesToRead);
if($length <= 0){ //TODO: if we reached here, the locationTable probably needs updating
return null;
}
if($length > self::MAX_SECTOR_LENGTH){ //corrupted
throw new CorruptedChunkException("Length for chunk x=$x,z=$z ($length) is larger than maximum " . self::MAX_SECTOR_LENGTH);
if($payload === false || strlen($payload) !== $bytesToRead){
throw new CorruptedChunkException("Corrupted chunk detected (unexpected EOF, truncated or non-padded chunk found)");
}
$stream = new BinaryStream($payload);
if($length > ($this->locationTable[$index]->getSectorCount() << 12)){ //Invalid chunk, bigger than defined number of sectors
throw new CorruptedChunkException("Chunk length mismatch (expected " . ($this->locationTable[$index]->getSectorCount() << 12) . " sectors, got $length sectors)");
}
try{
$length = $stream->getInt();
if($length <= 0){ //TODO: if we reached here, the locationTable probably needs updating
return null;
}
$chunkData = fread($this->filePointer, $length);
if($chunkData === false or strlen($chunkData) !== $length){
throw new CorruptedChunkException("Corrupted chunk detected (unexpected end of file reading chunk data)");
}
$compression = $stream->getByte();
if($compression !== self::COMPRESSION_ZLIB and $compression !== self::COMPRESSION_GZIP){
throw new CorruptedChunkException("Invalid compression type (got $compression, expected " . self::COMPRESSION_ZLIB . " or " . self::COMPRESSION_GZIP . ")");
}
$compression = ord($chunkData[0]);
if($compression !== self::COMPRESSION_ZLIB and $compression !== self::COMPRESSION_GZIP){
throw new CorruptedChunkException("Invalid compression type (got $compression, expected " . self::COMPRESSION_ZLIB . " or " . self::COMPRESSION_GZIP . ")");
return $stream->get($length - 1); //length prefix includes the compression byte
}catch(BinaryDataException $e){
throw new CorruptedChunkException("Corrupted chunk detected: " . $e->getMessage(), 0, $e);
}
return substr($chunkData, 1);
}
/**