PHP マニュアル: Adjusts read and/or write watermarks

public void EventBufferEvent::setWatermark( int $events , int $lowmark , int $highmark )

Adjusts the read watermarks, the write watermarks , or both, of a single buffer event.

A buffer event watermark is an edge, a value specifying number of bytes to be read or written before callback is invoked. By default every read/write event triggers a callback invokation. See » Fast portable non-blocking network programming with Libevent: Callbacks and watermarks

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