/**
 * io/protocol.ts
 *
 * Shared constants and message shapes for the I/O broker channel.
 *
 * Each decode worker gets one SharedArrayBuffer channel:
 *   [ 64-byte Int32 header | one block of data ]
 * Requests travel worker → broker as port messages; replies to a *blocked*
 * worker travel exclusively through the SAB (the worker cannot run its event
 * loop while parked in Atomics.wait). Async RPC replies (registration) use
 * normal port messages, which only happen while the worker is unblocked.
 */
export declare const CTRL_STATUS = 0;
export declare const CTRL_SEQ = 1;
export declare const CTRL_BYTES = 2;
export declare const CTRL_ERRNO = 3;
/** Header length in bytes; keeps the data region 64-byte aligned. */
export declare const HEADER_BYTES = 64;
export declare const STATUS_PENDING = 0;
export declare const STATUS_OK = 1;
export declare const STATUS_ERROR = 2;
/** errno values mirrored from Emscripten's wasi errno table. */
export declare const EINVAL = 28;
export declare const EIO = 29;
/** Resolved I/O tuning; user-facing knobs live on OpenSlideOptions.io. */
export interface IoConfig {
    /** Bytes per cached block / per range request. */
    blockSize: number;
    /** Byte budget of the broker's shared LRU block cache. */
    brokerCacheBytes: number;
    /** Blocks to prefetch ahead of a sequential read pattern. */
    readAhead: number;
    /** Max concurrent readRegion calls per decode worker. */
    maxConcurrentReads: number;
    /** How long a blocked read waits for the broker before failing with EIO. */
    readTimeoutMs: number;
}
export declare const DEFAULT_IO_CONFIG: IoConfig;
/** Worker → broker messages (over the per-worker MessagePort). */
export type IoRequest = {
    type: 'read';
    seq: number;
    fileKey: string;
    blockIndex: number;
} | {
    type: 'register-url';
    rpcId: number;
    fileKey: string;
    url: string;
} | {
    type: 'register-files';
    files: Array<{
        fileKey: string;
        file: File;
        size: number;
    }>;
} | {
    type: 'release';
    fileKeys: string[];
};
/** Broker → worker async RPC replies (only consumed while unblocked). */
export type IoReply = {
    type: 'rpc';
    rpcId: number;
    ok: true;
    size: number;
} | {
    type: 'rpc';
    rpcId: number;
    ok: false;
    error: string;
};
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