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| <!DOCTYPE html> | ||
| <html lang="en"> | ||
| <head> | ||
| <meta charset="utf-8"> | ||
| <title>Compiler Services: Notes on the FSharpChecker caches | ||
| </title> | ||
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| <meta name="description" content="F# compiler services for creating IDE tools, language extensions and for F# embedding"> | ||
| <meta name="author" content="Microsoft Corporation, Dave Thomas, Anh-Dung Phan, Tomas Petricek"> | ||
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| <h3 class="muted">F# Compiler Services</h3> | ||
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| <h1><a name="Compiler-Services-Notes-on-the-FSharpChecker-caches" class="anchor" href="#Compiler-Services-Notes-on-the-FSharpChecker-caches">Compiler Services: Notes on the FSharpChecker caches</a></h1> | ||
| <p>This is a design note on the FSharpChecker component and its caches. See also the notes on the <a href="queue.html">FSharpChecker operations queue</a></p> | ||
| <p>Each FSharpChecker object maintains a set of caches. These are</p> | ||
| <ul> | ||
| <li> | ||
| <p><code>scriptClosureCache</code> - an MRU cache of default size <code>projectCacheSize</code> that caches the | ||
| computation of GetProjectOptionsFromScript. This computation can be lengthy as it can involve processing the transative closure | ||
| of all <code>#load</code> directives, which in turn can mean parsing an unbounded number of script files</p> | ||
| </li> | ||
| <li> | ||
| <p><code>incrementalBuildersCache</code> - an MRU cache of projects where a handle is being kept to their incremental checking state, | ||
| of default size <code>projectCacheSize</code> (= 3 unless explicitly set as a parameter). | ||
| The "current background project" (see the <a href="queue.html">FSharpChecker operations queue</a>) | ||
| will be one of these projects. When analyzing large collections of projects, this cache usually occupies by far the most memory. | ||
| Increasing the size of this cache can dramatically decrease incremental computation of project-wide checking, or of checking | ||
| individual files within a project, but can very greatly increase memory usage.</p> | ||
| </li> | ||
| <li><p><code>braceMatchCache</code> - an MRU cache of size <code>braceMatchCacheSize</code> (default = 5) keeping the results of calls to MatchBraces, keyed by filename, source and project options.</p></li> | ||
| <li> | ||
| <p><code>parseFileInProjectCache</code> - an MRU cache of size <code>parseFileInProjectCacheSize</code> (default = 2) keeping the results of ParseFileInProject, | ||
| keyed by filename, source and project options.</p> | ||
| </li> | ||
| <li> | ||
| <p><code>parseAndCheckFileInProjectCache</code> - an MRU cache of size <code>incrementalTypeCheckCacheSize</code> (default = 5) keeping the results of | ||
| ParseAndCheckFileInProject, CheckFileInProject and/or CheckFileInProjectIfReady. This is keyed by filename, file source | ||
| and project options. The results held in this cache are only returned if they would reflect an accurate parse and check of the | ||
| file.</p> | ||
| </li> | ||
| <li> | ||
| <p><code>parseAndCheckFileInProjectCachePossiblyStale</code> - a somewhat peculiar MRU cache of size <code>incrementalTypeCheckCacheSize</code> (default = 5) | ||
| keeping the results of ParseAndCheckFileInProject, CheckFileInProject and CheckFileInProjectIfReady, | ||
| keyed by filename and project options. This cache is accessed by TryGetRecentTypeCheckResultsForFile. Because the results | ||
| are accessed regardless of the content of the file, the checking results returned may be "stale".</p> | ||
| </li> | ||
| <li><p><code>getToolTipTextCache</code> - an aged lookup cache of strong size <code>getToolTipTextSize</code> (default = 5) computing the results of GetToolTipText.</p></li> | ||
| <li> | ||
| <p><code>ilModuleReaderCache</code> - an aged lookup of weak references to "readers" for references .NET binaries. Because these | ||
| are all weak references, you can generally ignore this cache, since its entries will be automatically collected. | ||
| Strong references to binary readers will be kept by other FCS data structures, e.g. any project checkers, symbols or project checking results.</p> | ||
| <p>In more detail, the bytes for referenced .NET binaries are read into memory all at once, eagerly. Files are not left | ||
| open or memory-mapped when using FSharpChecker (as opposed to FsiEvaluationSession, which loads assemblies using reflection). | ||
| The purpose of this cache is mainly to ensure that while setting up compilation, the reads of mscorlib, FSharp.Core and so on | ||
| amortize cracking the DLLs.</p> | ||
| </li> | ||
| <li> | ||
| <p><code>frameworkTcImportsCache</code> - an aged lookup of strong size 8 which caches the process of setting up type checking against a set of system | ||
| components (e.g. a particular version of mscorlib, FSharp.Core and other system DLLs). These resources are automatically shared between multiple | ||
| project checkers which happen to reference the same set of system assemblies.</p> | ||
| </li> | ||
| </ul> | ||
| <p>Profiling the memory used by the various caches can be done by looking for the corresponding static roots in memory profiling traces.</p> | ||
| <p>The sizes of some of these caches can be adjusted by giving parameters to FSharpChecker. Unless otherwise noted, | ||
| the cache sizes above indicate the "strong" size of the cache, where memory is held regardless of the memory | ||
| pressure on the system. Some of the caches can also hold "weak" references which can be collected at will by the GC.</p> | ||
| <blockquote> | ||
| <p>Note: Because of these caches, uou should generally use one global, shared FSharpChecker for everything in an IDE application.</p> | ||
| </blockquote> | ||
| <h2><a name="Low-Memory-Condition" class="anchor" href="#Low-Memory-Condition">Low-Memory Condition</a></h2> | ||
| <p>Version 1.4.0.8 added a "maximum memory" limit specified by the <code>MaxMemory</code> property on FSharpChecker (in MB). If an FCS project operation | ||
| is performed (see <code>CheckMaxMemoryReached</code> in <code>service.fs</code>) and <code>System.GC.GetTotalMemory(false)</code> reports a figure greater than this, then | ||
| the strong sizes of all FCS caches are reduced to either 0 or 1. This happens for the remainder of the lifetime of the FSharpChecker object. | ||
| In practice this will still make tools like the Visual Studio F# Power Tools usable, but some operations like renaming across multiple | ||
| projects may take substantially longer.</p> | ||
| <p>By default the maximum memory trigger is disabled, see <code>maxMBDefault</code> in <code>service.fs</code>.</p> | ||
| <p>Reducing the FCS strong cache sizes does not guarantee there will be enough memory to continue operations - even holding one project | ||
| strongly may exceed a process memory budget. It just means FCS may hold less memory strongly.</p> | ||
| <p>If you do not want the maximum memory limit to apply then set MaxMemory to System.Int32.MaxValue.</p> | ||
| <h2><a name="Summary" class="anchor" href="#Summary">Summary</a></h2> | ||
| <p>In this design note, you learned that the FSharpChecker component keeps a set of caches in order to support common | ||
| incremental analysis scenarios reasonably efficiently. They correspond roughly to the original caches and sizes | ||
| used by the Visual F# Tools, from which the FSharpChecker component derives.</p> | ||
| <p>In long running, highly interactive, multi-project scenarios you should carefully | ||
| consider the cache sizes you are using and the tradeoffs involved between incremental multi-project checking and memory usage.</p> | ||
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| <li><a href="./queue.html">The FSharpChecker operations queue</a></li> | ||
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