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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
using System;
using System.Collections.Generic;
using Microsoft.Build.Collections;
using Microsoft.Build.Evaluation;
using Microsoft.Build.Execution;
using Microsoft.Build.Shared;
using ElementLocation = Microsoft.Build.Construction.ElementLocation;
#nullable disable
namespace Microsoft.Build.BackEnd
{
/// <summary>
/// This class is used by objects in the build engine that have the ability to execute themselves in batches, to partition the
/// items they consume into "buckets", based on the values of select item metadata.
/// </summary>
/// <remarks>
/// What batching does
///
/// Batching partitions the items consumed by the batchable object into buckets, where each bucket
/// contains a set of items that have the same value set on all item metadata consumed by the object.
/// Metadata consumed may be unqualified, for example %(m), or qualified by the item list to which it
/// refers, for example %(a.m).
///
/// If metadata is qualified, for example %(a.m), then this is considered distinct to metadata with the
/// same name on a different item type. For example, %(a.m) is distinct to %(b.m), and items of type ‘b’
/// are considered to always have a blank value for %(a.m). This means items of type ‘b’ will only be
/// placed in buckets where %(a.m) is blank. However %(a.m) is equivalent to %(m) on items of type ‘a’.
///
/// There is an extra ambiguity rule: every items consumed by the object must have an explicit value for
/// every piece of unqualified metadata. For example, if @(a), %(m), and %(a.n) are consumed, every item
/// of type ‘a’ must have a value for the metadata ‘m’ but need not all necessarily have a value for the
/// metadata ‘n’. This rule eliminates ambiguity about whether items that do not define values for an
/// unqualified metadata should go in all buckets, or just into buckets with a blank value for
/// that metadata.
///
/// For example
///
/// <ItemGroup>
/// <a Include='a1;a2'>
/// <n>m0</n>
/// </a>
/// <a Include='a3'>
/// <n>m1</n>
/// </a>
/// <b Include='b1'>
/// <n>n0</n>
/// </b>
/// <b Include='b2;b3'>
/// <n>n1</n>
/// </b>
/// <b Include='b4'/>
/// </ItemGroup>
///
/// <Target Name="t" >
/// <Message Text="a={@(a).%(a.n)} b={@(b).%(b.n)}" />
/// </Target>
///
/// Will produce 5 buckets:
///
/// a={a1;a2.m0} b={.}
/// a={a3.m1} b={.}
/// a={.} b={b1.n0}
/// a={.} b={b2;b3.n1}
/// a={.} b={b4.}
///
/// </remarks>
internal static class BatchingEngine
{
#region Methods
/// <summary>
/// Determines how many times the batchable object needs to be executed (each execution is termed a "batch"), and prepares
/// buckets of items to pass to the object in each batch.
/// </summary>
/// <returns>List containing ItemBucket objects, each one representing an execution batch.</returns>
internal static List<ItemBucket> PrepareBatchingBuckets(
List<string> batchableObjectParameters,
Lookup lookup,
ElementLocation elementLocation)
{
return PrepareBatchingBuckets(batchableObjectParameters, lookup, null, elementLocation);
}
/// <summary>
/// Determines how many times the batchable object needs to be executed (each execution is termed a "batch"), and prepares
/// buckets of items to pass to the object in each batch.
/// </summary>
/// <param name="elementLocation"></param>
/// <param name="batchableObjectParameters"></param>
/// <param name="lookup"></param>
/// <param name="implicitBatchableItemType">Any item type that can be considered an implicit input to this batchable object.
/// This is useful for items inside targets, where the item name is plainly an item type that's an "input" to the object.</param>
/// <returns>List containing ItemBucket objects, each one representing an execution batch.</returns>
internal static List<ItemBucket> PrepareBatchingBuckets(
List<string> batchableObjectParameters,
Lookup lookup,
string implicitBatchableItemType,
ElementLocation elementLocation)
{
if (batchableObjectParameters == null)
{
ErrorUtilities.ThrowInternalError("Need the parameters of the batchable object to determine if it can be batched.");
}
if (lookup == null)
{
ErrorUtilities.ThrowInternalError("Need to specify the lookup.");
}
ItemsAndMetadataPair pair = ExpressionShredder.GetReferencedItemNamesAndMetadata(batchableObjectParameters);
// All the @(itemname) item list references in the tag, including transforms, etc.
HashSet<string> consumedItemReferences = pair.Items;
// All the %(itemname.metadataname) references in the tag (not counting those embedded
// inside item transforms), and note that the itemname portion is optional.
// The keys in the returned hash table are the qualified metadata names (e.g. "EmbeddedResource.Culture"
// or just "Culture"). The values are MetadataReference structs, which simply split out the item
// name (possibly null) and the actual metadata name.
Dictionary<string, MetadataReference> consumedMetadataReferences = pair.Metadata;
List<ItemBucket> buckets = null;
if (consumedMetadataReferences?.Count > 0)
{
// Add any item types that we were explicitly told to assume.
if (implicitBatchableItemType != null)
{
consumedItemReferences ??= new HashSet<string>(MSBuildNameIgnoreCaseComparer.Default);
consumedItemReferences.Add(implicitBatchableItemType);
}
// This method goes through all the item list references and figures out which ones
// will be participating in batching, and which ones won't. We get back a hashtable
// where the key is the item name that will be participating in batching. The values
// are all String.Empty (not used). This method may return additional item names
// that weren't represented in "consumedItemReferences"... this would happen if there
// were qualified metadata references in the consumedMetadataReferences table, such as
// %(EmbeddedResource.Culture).
Dictionary<string, ICollection<ProjectItemInstance>> itemListsToBeBatched = GetItemListsToBeBatched(consumedMetadataReferences, consumedItemReferences, lookup, elementLocation);
// At this point, if there were any metadata references in the tag, but no item
// references to batch on, we've got a problem because we can't figure out which
// item lists the user wants us to batch.
if (itemListsToBeBatched.Count == 0)
{
foreach (string unqualifiedMetadataName in consumedMetadataReferences.Keys)
{
// Of course, since this throws an exception, there's no way we're ever going
// to really loop here... it's just that the foreach is the only way I can
// figure out how to get data out of the hashtable without knowing any of the
// keys!
ProjectErrorUtilities.ThrowInvalidProject(elementLocation, "CannotReferenceItemMetadataWithoutItemName", unqualifiedMetadataName);
}
}
else
{
// If the batchable object consumes item metadata as well as items to be batched,
// we need to partition the items consumed by the object.
buckets = BucketConsumedItems(lookup, itemListsToBeBatched, consumedMetadataReferences, elementLocation);
}
}
// if the batchable object does not consume any item metadata or items, or if the item lists it consumes are all
// empty, then the object does not need to be batched
if ((buckets == null) || (buckets.Count == 0))
{
// create a default bucket that references the project items and properties -- this way we always have a bucket
buckets = new List<ItemBucket>(1);
buckets.Add(new ItemBucket(null, null, lookup, buckets.Count));
}
return buckets;
}
/// <summary>
/// Of all the item lists that are referenced in this batchable object, which ones should we
/// batch on, and which ones should we just pass in wholesale to every invocation of the
/// target/task?
///
/// Rule #1. If the user has referenced any *qualified* item metadata such as %(EmbeddedResource.Culture),
/// then that item list "EmbeddedResource" will definitely get batched.
///
/// Rule #2. For all the unqualified item metadata such as %(Culture), we make sure that
/// every single item in every single item list being passed into the task contains a value
/// for that metadata. If not, it's an error. If so, we batch all of those item lists.
///
/// All other item lists will not be batched, and instead will be passed in wholesale to all buckets.
/// </summary>
/// <returns>Dictionary containing the item names that should be batched. If the items match unqualified metadata,
/// the entire list of items will be returned in the Value. Otherwise, the Value will be empty, indicating only the
/// qualified item set (in the Key) should be batched.
/// </returns>
private static Dictionary<string, ICollection<ProjectItemInstance>> GetItemListsToBeBatched(
Dictionary<string, MetadataReference> consumedMetadataReferences, // Key is [string] potentially qualified metadata name
// Value is [struct MetadataReference]
HashSet<string> consumedItemReferenceNames,
Lookup lookup,
ElementLocation elementLocation)
{
// The keys in this hashtable are the names of the items that we will batch on.
// The values are always String.Empty (not used).
var itemListsToBeBatched = new Dictionary<string, ICollection<ProjectItemInstance>>(MSBuildNameIgnoreCaseComparer.Default);
// Loop through all the metadata references and find the ones that are qualified
// with an item name.
foreach (MetadataReference consumedMetadataReference in consumedMetadataReferences.Values)
{
if (consumedMetadataReference.ItemName != null)
{
// Rule #1. Qualified metadata reference.
// For metadata references that are qualified with an item name
// (e.g., %(EmbeddedResource.Culture) ), we add that item name to the list of
// consumed item names, even if the item name wasn't otherwise referenced via
// @(...) syntax, and even if every item in the list doesn't necessary contain
// a value for this metadata. This is the special power that you get by qualifying
// the metadata reference with an item name.
itemListsToBeBatched[consumedMetadataReference.ItemName] = null;
// Also add this qualified item to the consumed item references list, because
// %(EmbeddedResource.Culture) effectively means that @(EmbeddedResource) is
// being consumed, even though we may not see literally "@(EmbeddedResource)"
// in the tag anywhere. Adding it to this list allows us (down below in this
// method) to check that every item in this list has a value for each
// unqualified metadata reference.
consumedItemReferenceNames ??= new HashSet<string>(MSBuildNameIgnoreCaseComparer.Default);
consumedItemReferenceNames.Add(consumedMetadataReference.ItemName);
}
}
// Loop through all the metadata references and find the ones that are unqualified.
foreach (MetadataReference consumedMetadataReference in consumedMetadataReferences.Values)
{
if (consumedMetadataReference.ItemName == null)
{
// Rule #2. Unqualified metadata reference.
// For metadata references that are unqualified, every single consumed item
// must contain a value for that metadata. If any item doesn't, it's an error
// to use unqualified metadata.
if (consumedItemReferenceNames != null)
{
foreach (string consumedItemName in consumedItemReferenceNames)
{
// Loop through all the items in the item list.
ICollection<ProjectItemInstance> items = lookup.GetItems(consumedItemName);
if (items != null)
{
// Loop through all the items in the BuildItemGroup.
foreach (ProjectItemInstance item in items)
{
ProjectErrorUtilities.VerifyThrowInvalidProject(
item.HasMetadata(consumedMetadataReference.MetadataName),
elementLocation, "ItemDoesNotContainValueForUnqualifiedMetadata",
item.EvaluatedInclude, consumedItemName, consumedMetadataReference.MetadataName);
}
}
// This item list passes the test of having every single item containing
// a value for this metadata. Therefore, add this item list to the batching list.
// Also, to save doing lookup.GetItems again, put the items in the table as the value.
itemListsToBeBatched[consumedItemName] = items;
}
}
}
}
return itemListsToBeBatched;
}
/// <summary>
/// Partitions the items consumed by the batchable object into buckets, where each bucket contains a set of items that
/// have the same value set on all item metadata consumed by the object.
/// </summary>
/// <remarks>
/// PERF NOTE: Given n items and m batching metadata that produce l buckets, it is usually the case that n > l > m,
/// because a batchable object typically uses one or two item metadata to control batching, and only has a handful of
/// buckets. The number of buckets is typically only large if a batchable object is using single-item batching
/// (where l == n). Any algorithm devised for bucketing therefore, should try to minimize n and l in its complexity
/// equation. The algorithm below has a complexity of O(n*lg(l)*m/2) in its comparisons, and is effectively O(n) when
/// l is small, and O(n*lg(n)) in the worst case as l -> n. However, note that the comparison complexity is not the
/// same as the operational complexity for this algorithm. The operational complexity of this algorithm is actually
/// O(n*m + n*lg(l)*m/2 + n*l/2 + n + l), which is effectively O(n^2) in the worst case. The additional complexity comes
/// from the array and metadata operations that are performed. However, those operations are extremely cheap compared
/// to the comparison operations, which dominate the time spent in this method.
/// </remarks>
/// <returns>List containing ItemBucket objects (can be empty), each one representing an execution batch.</returns>
private static List<ItemBucket> BucketConsumedItems(
Lookup lookup,
Dictionary<string, ICollection<ProjectItemInstance>> itemListsToBeBatched,
Dictionary<string, MetadataReference> consumedMetadataReferences,
ElementLocation elementLocation)
{
ErrorUtilities.VerifyThrow(itemListsToBeBatched.Count > 0, "Need item types consumed by the batchable object.");
ErrorUtilities.VerifyThrow(consumedMetadataReferences.Count > 0, "Need item metadata consumed by the batchable object.");
var buckets = new List<ItemBucket>();
// Get and iterate through the list of item names that we're supposed to batch on.
foreach (KeyValuePair<string, ICollection<ProjectItemInstance>> entry in itemListsToBeBatched)
{
string itemName = entry.Key;
// Use the previously-fetched items, if possible
ICollection<ProjectItemInstance> items = entry.Value ?? lookup.GetItems(itemName);
if (items != null)
{
foreach (ProjectItemInstance item in items)
{
// Get this item's values for all the metadata consumed by the batchable object.
Dictionary<string, string> itemMetadataValues = GetItemMetadataValues(item, consumedMetadataReferences, elementLocation);
// put the metadata into a dummy bucket we can use for searching
ItemBucket dummyBucket = ItemBucket.GetDummyBucketForComparisons(itemMetadataValues);
// look through all previously created buckets to find a bucket whose items have the same values as
// this item for all metadata consumed by the batchable object
int matchingBucketIndex = buckets.BinarySearch(dummyBucket);
ItemBucket matchingBucket = (matchingBucketIndex >= 0)
? buckets[matchingBucketIndex]
: null;
// If we didn't find a bucket that matches this item, create a new one, adding
// this item to the bucket.
if (matchingBucket == null)
{
matchingBucket = new ItemBucket(itemListsToBeBatched.Keys, itemMetadataValues, lookup, buckets.Count);
// make sure to put the new bucket into the appropriate location
// in the sorted list as indicated by the binary search
// NOTE: observe the ~ operator (bitwise complement) in front of
// the index -- see MSDN for more information on the return value
// from the List.BinarySearch() method
buckets.Insert(~matchingBucketIndex, matchingBucket);
}
// We already have a bucket for this type of item, so add this item to
// the bucket.
matchingBucket.AddItem(item);
}
}
}
// Put the buckets back in the order in which they were discovered, so that the first
// item declared in the project file ends up in the first batch passed into the target/task.
var orderedBuckets = new List<ItemBucket>(buckets.Count);
for (int i = 0; i < buckets.Count; ++i)
{
orderedBuckets.Add(null);
}
foreach (ItemBucket bucket in buckets)
{
orderedBuckets[bucket.BucketSequenceNumber] = bucket;
}
return orderedBuckets;
}
/// <summary>
/// Gets the values of the specified metadata for the given item.
/// The keys in the dictionary returned may be qualified and/or unqualified, exactly
/// as they are found in the metadata reference.
/// For example if %(x) is found, the key is "x", if %(z.x) is found, the key is "z.x".
/// This dictionary in each bucket is used by Expander to expand exactly the same metadata references, so
/// %(x) is expanded using the key "x", and %(z.x) is expanded using the key "z.x".
/// </summary>
/// <returns>the metadata values</returns>
private static Dictionary<string, string> GetItemMetadataValues(
ProjectItemInstance item,
Dictionary<string, MetadataReference> consumedMetadataReferences,
ElementLocation elementLocation)
{
var itemMetadataValues = new Dictionary<string, string>(consumedMetadataReferences.Count, MSBuildNameIgnoreCaseComparer.Default);
foreach (KeyValuePair<string, MetadataReference> consumedMetadataReference in consumedMetadataReferences)
{
string metadataQualifiedName = consumedMetadataReference.Key;
string metadataItemName = consumedMetadataReference.Value.ItemName;
string metadataName = consumedMetadataReference.Value.MetadataName;
if (
(metadataItemName != null) &&
(!String.Equals(item.ItemType, metadataItemName, StringComparison.OrdinalIgnoreCase)))
{
itemMetadataValues[metadataQualifiedName] = String.Empty;
}
else
{
try
{
// This returns String.Empty for both metadata that is undefined and metadata that has
// an empty value; they are treated the same.
itemMetadataValues[metadataQualifiedName] = ((IItem)item).GetMetadataValueEscaped(metadataName);
}
catch (InvalidOperationException e)
{
ProjectErrorUtilities.ThrowInvalidProject(elementLocation,
"CannotEvaluateItemMetadata", metadataName, e.Message);
}
}
}
return itemMetadataValues;
}
#endregion
}
}
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