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layout.go
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layout.go
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// Licensed to Elasticsearch B.V. under one or more contributor
// license agreements. See the NOTICE file distributed with
// this work for additional information regarding copyright
// ownership. Elasticsearch B.V. licenses this file to you under
// the Apache License, Version 2.0 (the "License"); you may
// not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied. See the License for the
// specific language governing permissions and limitations
// under the License.
package pq
import (
"unsafe"
bin "github.com/urso/go-bin"
"github.com/elastic/go-txfile"
)
// primitive types
type (
u32 = bin.U32le
u64 = bin.U64le
)
// queuePage is the root structure into a persisted Queue instance.
type queuePage struct {
version u32
// start/end of single linked events list and event ids
head pos // head points to first event in list
tail pos // tail points to next event to be written
// read points to next event to continue reading from
// if read == tail, all events have been read
read pos
inuse u64 // number of actively used data pages
}
type pos struct {
offset u64 // file offset of event
id u64 // id of event
}
// eventPage create a single list of event pages, storing a number
// of events per page.
// If off == 0, the page does contain data only.
type eventPage struct {
next u64 // PageID of next eventPage
first u64 // event id of first event in current page
last u64 // event id of last even in current page
off u32 // offset of first event in current page
}
// eventHeader is keeps track of the event size in bytes.
// The event ID can be 'computed' by iterating the events in a page.
type eventHeader struct {
sz u32
}
const (
queueVersion = 1
// SzRoot is the size of the queue header in bytes.
SzRoot = int(unsafe.Sizeof(queuePage{}))
szEventPageHeader = int(unsafe.Sizeof(eventPage{}))
szEventHeader = int(unsafe.Sizeof(eventHeader{}))
)
func castQueueRootPage(b []byte) (hdr *queuePage) { bin.UnsafeCastStruct(&hdr, b); return }
func castEventPageHeader(b []byte) (hdr *eventPage) { bin.UnsafeCastStruct(&hdr, b); return }
func castEventHeader(b []byte) (hdr *eventHeader) { bin.UnsafeCastStruct(&hdr, b); return }
func traceQueueHeader(hdr *queuePage) {
traceln("queue header:")
traceln(" version:", hdr.version.Get())
tracef(" head(%v, %v)\n", hdr.head.id.Get(), hdr.head.offset.Get())
tracef(" tail(%v, %v)\n", hdr.tail.id.Get(), hdr.tail.offset.Get())
tracef(" read(%v, %v)\n", hdr.read.id.Get(), hdr.read.offset.Get())
traceln(" data pages", hdr.inuse.Get())
}
func tracePageHeader(id txfile.PageID, hdr *eventPage) {
tracef("event page %v (next=%v, first=%v, last=%v, off=%v)\n",
id, hdr.next.Get(), hdr.first.Get(), hdr.last.Get(), hdr.off.Get())
}