From 189c8967235e956afa8a1a921ddfcb0d48fca67f Mon Sep 17 00:00:00 2001
From: Andrew Binstock <920630+platypusguy@users.noreply.github.com>
Date: Mon, 13 Jan 2025 20:11:55 -0800
Subject: [PATCH] JACOBIN-575 Creation of new global method table (GMT), which
 will replace the present MTable, aka MT.

---
 src/classloader/gmt.go | 87 ++++++++++++++++++++++++++++++++++++++++++
 src/config/buildno.go  |  2 +-
 2 files changed, 88 insertions(+), 1 deletion(-)
 create mode 100644 src/classloader/gmt.go

diff --git a/src/classloader/gmt.go b/src/classloader/gmt.go
new file mode 100644
index 00000000..a2235984
--- /dev/null
+++ b/src/classloader/gmt.go
@@ -0,0 +1,87 @@
+/*
+ * Jacobin VM - A Java virtual machine
+ * Copyright (c) 2025 by  the Jacobin Authors. All rights reserved.
+ * Licensed under Mozilla Public License 2.0 (MPL 2.0)  Consult jacobin.org.
+ */
+
+package classloader
+
+import (
+	"fmt"
+	"os"
+	"sort"
+	"sync"
+)
+
+// GMT = global method table. It's a map of fully qualified method (FQN) name to
+// method data, called gmtEntry. The gmtEntry consists of a byte identifying whether
+// the method is a Java method ('J') or a golang-implemented native method ('G').
+// he other field is a pointer to the method data.
+//
+// When a function is invoked, the lookup mechanism checks the GMT for a pointer
+// to the method data. The method in the class is never called directly--only ever
+// through a GMT look-up. This allows for the method to be overridden in a subclass,
+// and for us to insert go methods in lieu of JDK native methods
+//
+// Entries are added to the GMT when a class is instantiated. In other words, it's
+// lazy loading.
+
+var GMT = make(gmt)
+
+type gmt map[string]gmtEntry
+type gmtEntry struct {
+	MethData interface{} // pointer to the method data
+	MType    byte        // method type, G = Go method, J = Java method
+}
+
+// // JmEntry is the entry in the Mtable for Java methods.
+// type JmEntry struct {
+// 	AccessFlags int
+// 	MaxStack    int
+// 	MaxLocals   int
+// 	Code        []byte
+// 	// Exceptions  []uint16 prior to JACOBIN-575
+// 	Exceptions []CodeException // the exception data stored in the code attribute.
+// 	Attribs    []Attr
+// 	params     []ParamAttrib
+// 	CodeAttr   CodeAttrib
+// 	deprecated bool
+// 	Cp         *CPool
+// }
+
+// Function is the generic-style function used for Go entries: a function that accepts a
+// slice of empty interfaces and returns an empty interface
+// type Function func([]interface{}) interface{}
+
+// MTmutex is used for updates to the MTable because multiple threads could be
+// updating it simultaneously.
+var GMTmutex sync.Mutex
+
+// adds an entry to the MTable, using a mutex
+func GmtAddEntry(key string, mte gmtEntry) {
+	// fmt.Printf("DEBUG gmt.go AddEntry key=%s, gmtEntry=%s\n", key, string(mte.MType))
+	GMTmutex.Lock()
+	GMT[key] = mte
+	GMTmutex.Unlock()
+}
+
+// DumpMTable dumps the contents of MTable in sorted order to stderr
+func DumpGmt() {
+	_, _ = fmt.Fprintln(os.Stderr, "\n===== DumpGMT BEGIN")
+	// Create an array of keys.
+	keys := make([]string, 0, len(GMT))
+	for key := range MTable {
+		keys = append(keys, key)
+	}
+
+	// Sort the keys (FQNs).
+	// All the upper case entries precede all the lower case entries.
+	sort.Strings(keys)
+
+	// In key sequence order, display the key and its value.
+	for _, key := range keys {
+		entry := MTable[key]
+		_, _ = fmt.Fprintf(os.Stderr, "%s   %s\n", string(entry.MType), key)
+	}
+	_, _ = fmt.Fprintln(os.Stderr, "===== DumpGMT END")
+}
diff --git a/src/config/buildno.go b/src/config/buildno.go
index 6fa3dad4..09ed37c1 100644
--- a/src/config/buildno.go
+++ b/src/config/buildno.go
@@ -8,4 +8,4 @@
 
 package config
 
-var BuildNo = 3415
\ No newline at end of file
+var BuildNo = 3416
\ No newline at end of file