[Webkit-unassigned] [Bug 227229] New: [GPU Process] RELEASE_ASSERT in RemoteResourceCacheProxy::didFinalizeRenderingUpdate() may fire if GPUP is relaunched

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=227229

            Bug ID: 227229
           Summary: [GPU Process] RELEASE_ASSERT in
                    RemoteResourceCacheProxy::didFinalizeRenderingUpdate()
                    may fire if GPUP is relaunched
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Canvas
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: sabouhallawa at apple.com
                CC: dino at apple.com

The member RemoteResourceCacheProxy::m_numberOfFontsUsedInCurrentRenderingUpdate is used to keep track the number of fonts which are used in the current RenderingUpdate. We keep a HashMap for all fonts in m_fontIdentifierToLastRenderingUpdateVersionMap. This HashMap contains the used fonts, whose count is represented by m_numberOfFontsUsedInCurrentRenderingUpdate, and other unused fonts. The goal of RemoteResourceCacheProxy::didFinalizeRenderingUpdate() is to remove some of the unused fonts if they are really old and if they take more than 25% of m_fontIdentifierToLastRenderingUpdateVersionMap.

There are two bugs in the font caching scenario:
1. When relaunching then GPUP process, RemoteResourceCacheProxy::remoteResourceCacheWasDestroyed() gets called. In this function we clear m_fontIdentifierToLastRenderingUpdateVersionMap but we do not set m_numberOfFontsUsedInCurrentRenderingUpdate to zero. This will make us hit the RELEASE_ASSERT RemoteResourceCacheProxy::didFinalizeRenderingUpdate() once we keep incrementing m_numberOfFontsUsedInCurrentRenderingUpdate.
2. When removing a font from GPUP process by calling RemoteRenderingBackendProxy::releaseRemoteResource(), we do not remove the corresponding entry from m_fontIdentifierToLastRenderingUpdateVersionMap. RemoteResourceCacheProxy::cacheFont() makes the assumption: if the font is found in m_fontIdentifierToLastRenderingUpdateVersionMap, it is also cached in GPUP.

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