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MediaGallery: add back the "substantial requests only" check

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This avoids repeated database accesses for ranges that are mostly
loaded already.

Also, don't rebuild items that are already loaded, since overlapping
ranges are still expected in this design.
This commit is contained in:
Jordan Rose 2021-03-03 12:52:00 -08:00
parent 4e2fe8ca69
commit c81ceaaeeb
1 changed files with 117 additions and 32 deletions
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149
Signal/src/ViewControllers/MediaGallery/MediaGallery.swift
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@ -395,45 +395,124 @@ class MediaGallery {
return
}
let anchorItem: MediaGalleryItem? = sections[sectionIndex].value[safe: itemIndex] ?? nil
// May include a negative start location.
let naiveRequestRange: Range<Int> = {
let range: Range<Int> = {
switch direction {
case .around:
// To keep it simple, this isn't exactly *amount* sized if `message` window overlaps the end or
// beginning of the view. Still, we have sufficient buffer to fetch more as the user swipes.
let start: Int = itemIndex - Int(amount) / 2
let end: Int = itemIndex + Int(amount) / 2
return start..<end
case .before:
let start: Int = itemIndex + 1 - Int(amount)
let end: Int = itemIndex + 1
return start..<end
case .after:
let start: Int = itemIndex
let end: Int = itemIndex + Int(amount)
return start..<end
}
}()
if shouldLoadAlbumRemainder, let item = anchorItem {
let albumStart = (itemIndex - item.albumIndex)
let albumEnd = albumStart + item.message.attachmentIds.count
return (min(range.lowerBound, albumStart)..<max(range.upperBound, albumEnd))
}
return range
}()
func isSubstantialRequest() -> Bool {
// If we have not loaded the item at the given path yet, it's substantial.
guard let item = anchorItem else {
return true
}
let sectionItems = sections[sectionIndex].value
// If we're loading the remainder of an album, check to see if any items in the album are not loaded yet.
if shouldLoadAlbumRemainder {
let albumStart = itemIndex - item.albumIndex
let albumEnd = albumStart + item.message.attachmentIds.count
if sectionItems[albumStart..<albumEnd].contains(nil) {
return true
}
}
// Count unfetched items forward and backward.
func countUnfetched(in slice: ArraySlice<MediaGalleryItem?>) -> Int {
return slice.lazy.filter { $0 == nil }.count
}
let sectionSlice = sectionItems[max(0, naiveRequestRange.lowerBound) ..<
min(sectionItems.count, naiveRequestRange.upperBound)]
var unfetchedCount = countUnfetched(in: sectionSlice)
if naiveRequestRange.upperBound > sectionItems.count {
var currentSectionIndex = sectionIndex + 1
var remainingForward = naiveRequestRange.upperBound - sectionItems.count
repeat {
guard let currentSectionItems = sections[safe: currentSectionIndex]?.value else {
// We've reached the end of the fetched sections. If there are more sections, or the last item
// isn't fetched yet, assume it's substantial.
if !hasFetchedMostRecent || (sections.last?.value.last ?? nil) == nil {
return true
}
break
}
unfetchedCount += countUnfetched(in: currentSectionItems.prefix(remainingForward))
if remainingForward <= currentSectionItems.count {
break
}
remainingForward -= currentSectionItems.count
currentSectionIndex += 1
} while true
}
if naiveRequestRange.lowerBound < 0 {
var currentSectionIndex = sectionIndex - 1
var remainingBackward = -naiveRequestRange.lowerBound - sectionItems.count
repeat {
guard let currentSectionItems = sections[safe: currentSectionIndex]?.value else {
// We've reached the start of the fetched sections. If there are more sections, or the first
// item isn't fetched yet, assume it's substantial.
if !hasFetchedOldest || (sections.first?.value.first ?? nil) == nil {
return true
}
break
}
unfetchedCount += countUnfetched(in: currentSectionItems.suffix(remainingBackward))
if remainingBackward <= currentSectionItems.count {
break
}
remainingBackward -= currentSectionItems.count
currentSectionIndex -= 1
} while true
}
// If we haven't hit the start or end, and more than half the items are unfetched, it's substantial.
return unfetchedCount > (naiveRequestRange.count / 2)
}
if !isSubstantialRequest() {
return
}
var numNewlyLoadedEarlierSections: Int = 0
var numNewlyLoadedLaterSections: Int = 0
Bench(title: "fetching gallery items") {
self.databaseStorage.uiRead { transaction in
var requestRange: NSRange = {
var range: Range<Int> = {
switch direction {
case .around:
// To keep it simple, this isn't exactly *amount* sized if `message` window overlaps the end or
// beginning of the view. Still, we have sufficient buffer to fetch more as the user swipes.
let start: Int = itemIndex - Int(amount) / 2
let end: Int = itemIndex + Int(amount) / 2
return start..<end
case .before:
let start: Int = itemIndex + 1 - Int(amount)
let end: Int = itemIndex + 1
return start..<end
case .after:
let start: Int = itemIndex
let end: Int = itemIndex + Int(amount)
return start..<end
}
}()
if shouldLoadAlbumRemainder, let item = sections[sectionIndex].value[safe: itemIndex] ?? nil {
let albumStart = (itemIndex - item.albumIndex)
let albumEnd = albumStart + item.message.attachmentIds.count
range = (min(range.lowerBound, albumStart)..<max(range.upperBound, albumEnd))
}
return NSRange(range)
}()
// Figure out the earliest section this request will cross.
var currentSectionIndex = sectionIndex
var requestRange = NSRange(naiveRequestRange)
while requestRange.location < 0 {
if currentSectionIndex == 0 {
let newlyLoadedCount = loadEarlierSections(transaction: transaction)
@ -451,6 +530,7 @@ class MediaGallery {
let items = sections[currentSectionIndex].value
requestRange.location += items.count
}
let interval = DateInterval(start: sections.orderedKeys[currentSectionIndex].date,
end: .distantFutureForMillisecondTimestamp)
@ -491,6 +571,11 @@ class MediaGallery {
return
}
if let loadedItem = items[itemIndex] {
owsAssert(loadedItem.attachmentStream.uniqueId == attachment.uniqueId)
return
}
guard let item: MediaGalleryItem = self.buildGalleryItem(attachment: attachment,
transaction: transaction) else {
owsFailDebug("unexpectedly failed to buildGalleryItem")