cgi/Address: cache the GetChildId() value

This again eliminates a good amount of per-request overhead.

src/ResourceAddress.cxx

@@ -238,6 +238,27 @@ ResourceAddress::SaveBase(AllocatorPtr alloc,
 	gcc_unreachable();
 }
 
+inline void
+ResourceAddress::PostCacheStore(AllocatorPtr alloc) noexcept
+{
+	switch (type) {
+	case Type::NONE:
+	case Type::PIPE:
+		break;
+
+	case Type::CGI:
+	case Type::FASTCGI:
+	case Type::WAS:
+		GetCgi().PostCacheStore(alloc);
+		break;
+
+	case Type::LOCAL:
+	case Type::HTTP:
+	case Type::LHTTP:
+		break;
+	}
+}
+
 void
 ResourceAddress::CacheStore(AllocatorPtr alloc,
 			    const ResourceAddress &src,
@@ -246,6 +267,7 @@ ResourceAddress::CacheStore(AllocatorPtr alloc,
 {
 	if (base == nullptr) {
 		CopyFrom(alloc, src);
+		PostCacheStore(alloc);
 		return;
 	} else if (const char *tail = base_tail(uri, base)) {
 		/* we received a valid BASE packet - store only the base
@@ -255,6 +277,7 @@ ResourceAddress::CacheStore(AllocatorPtr alloc,
 			/* when the response is expandable, skip appending the
 			   tail URI, don't call SaveBase() */
 			CopyFrom(alloc, src);
+			PostCacheStore(alloc);
 			return;
 		}
 
@@ -267,8 +290,10 @@ ResourceAddress::CacheStore(AllocatorPtr alloc,
 		}
 
 		*this = src.SaveBase(alloc, tail);
-		if (IsDefined())
+		if (IsDefined()) {
+			PostCacheStore(alloc);
 			return;
+		}
 
 		/* the tail could not be applied to the address, so this is a
 		   base mismatch */

src/ResourceAddress.hxx

@@ -335,4 +335,7 @@ public:
 	 * Throws std::runtime_error on error.
 	 */
 	void Expand(AllocatorPtr alloc, const MatchData &match_data);
+
+private:
+	void PostCacheStore(AllocatorPtr alloc) noexcept;
 };

src/cgi/Address.cxx

@@ -38,6 +38,7 @@ CgiAddress::CgiAddress(AllocatorPtr alloc, const CgiAddress &src) noexcept
 	 query_string(alloc.CheckDup(src.query_string)),
 	 document_root(alloc.CheckDup(src.document_root)),
 	 address_list(alloc, src.address_list),
+	 cached_child_id(alloc.Dup(src.cached_child_id)),
 	 parallelism(src.parallelism),
 	 concurrency(src.concurrency),
 	 disposable(src.disposable),
@@ -50,6 +51,16 @@ CgiAddress::CgiAddress(AllocatorPtr alloc, const CgiAddress &src) noexcept
 {
 }
 
+void
+CgiAddress::PostCacheStore(AllocatorPtr alloc) noexcept
+{
+	/* cache the GetChildId() call only if we expect future calls
+           to have the same result, i.e. none of the relevant fields
+           are "expandable" */
+	if ((action != nullptr || !expand_path) && !IsChildExpandable())
+		cached_child_id = GetChildId(alloc);
+}
+
 [[gnu::pure]]
 static bool
 HasTrailingSlash(const char *p) noexcept
@@ -93,6 +104,9 @@ CgiAddress::GetURI(AllocatorPtr alloc) const noexcept
 StringWithHash
 CgiAddress::GetChildId(AllocatorPtr alloc) const noexcept
 {
+	if (!cached_child_id.IsNull())
+		return cached_child_id;
+
 	std::size_t hash = options.GetHash();
 
 	PoolStringBuilder<256> b;

src/cgi/Address.hxx

@@ -7,6 +7,7 @@
 #include "spawn/ChildOptions.hxx"
 #include "cluster/AddressList.hxx"
 #include "adata/ExpandableStringList.hxx"
+#include "util/StringWithHash.hxx"
 
 #include <string_view>
 
@@ -48,6 +49,8 @@ struct CgiAddress {
 	 */
 	AddressList address_list;
 
+	StringWithHash cached_child_id{nullptr};
+
 	/**
 	 * The maximum number of parallel child processes of this
 	 * kind.
@@ -93,6 +96,7 @@ struct CgiAddress {
 		 uri(src.uri), script_name(src.script_name), path_info(src.path_info),
 		 query_string(src.query_string), document_root(src.document_root),
 		 address_list(shallow_copy, src.address_list),
+		 cached_child_id(src.cached_child_id),
 		 concurrency(src.concurrency),
 		 disposable(src.disposable),
 		 request_uri_verbatim(src.request_uri_verbatim),
@@ -111,6 +115,8 @@ struct CgiAddress {
 
 	CgiAddress &operator=(const CgiAddress &) = delete;
 
+	void PostCacheStore(AllocatorPtr alloc) noexcept;
+
 	[[gnu::pure]]
 	const char *GetURI(AllocatorPtr alloc) const noexcept;
 
@@ -215,6 +221,12 @@ struct CgiAddress {
 			params.IsExpandable();
 	}
 
+	[[gnu::pure]]
+	bool IsChildExpandable() const noexcept {
+		return options.IsExpandable() ||
+			args.IsExpandable();
+	}
+
 	/**
 	 * Throws std::runtime_error on error.
 	 */