[stable] Revert "Fix dlang#22754 - Move Object.__monitor to druntime (dlang#22766)"

ibuclaw · ibuclaw · commit d35c399ab978 · 2026-03-27T07:51:07.000+01:00
This reverts commit b660a8d.
diff --git a/changelog/dmd.monitor-field.dd b/changelog/dmd.monitor-field.dd
diff --git a/compiler/src/dmd/dclass.d b/compiler/src/dmd/dclass.d
@@ -333,17 +333,11 @@ extern (C++) class ClassDeclaration : AggregateDeclaration
     }
 
     /**************
-     * Returns: true if there's a __monitor field, i.e. the druntime `Object` class declares it
+     * Returns: true if there's a __monitor field
      */
     final bool hasMonitor()
     {
-        if (classKind != ClassKind.d)
-            return false;
-        // Check if Object in druntime actually declares a __monitor field.
-        // Custom druntimes can omit it by not declaring it in Object.
-        if (!object || !object.symtab)
-            return true; // conservative: Object not yet loaded, assume monitor present
-        return object.symtab.lookup(Id.__monitor) !is null;
+        return classKind == ClassKind.d;
     }
 
     /****************************************
diff --git a/compiler/src/dmd/dinterpret.d b/compiler/src/dmd/dinterpret.d
@@ -2867,11 +2867,8 @@ public:
             size_t totalFieldCount = 0;
             for (ClassDeclaration c = cd; c; c = c.baseClass)
                 totalFieldCount += c.fields.length;
-
-            totalFieldCount -= cd.hasMonitor(); // skip __monitor field
-
             auto elems = new Expressions(totalFieldCount);
-            ptrdiff_t fieldsSoFar = totalFieldCount;
+            size_t fieldsSoFar = totalFieldCount;
             for (ClassDeclaration c = cd; c; c = c.baseClass)
             {
                 fieldsSoFar -= c.fields.length;
@@ -2883,9 +2880,6 @@ public:
                         result = CTFEExp.cantexp;
                         return;
                     }
-                    if (fieldsSoFar + ptrdiff_t(i) < 0) // field -1 = __monitor which we skip
-                        break;
-
                     Expression m;
                     if (v._init)
                     {
diff --git a/compiler/src/dmd/dsymbolsem.d b/compiler/src/dmd/dsymbolsem.d
@@ -9978,6 +9978,8 @@ private extern(C++) class FinalizeSizeVisitor : Visitor
         {
             outerCd.alignsize = target.ptrsize;
             outerCd.structsize = target.ptrsize;      // allow room for __vptr
+            if (outerCd.hasMonitor())
+                outerCd.structsize += target.ptrsize; // allow room for __monitor
         }
 
         //printf("finalizeSize() %s, sizeok = %d\n", toChars(), sizeok);
diff --git a/compiler/src/dmd/dtoh.d b/compiler/src/dmd/dtoh.d
@@ -1065,9 +1065,6 @@ public:
 
         if (adparent)
         {
-            if (vd.ident && vd.ident == Id.__monitor)
-                return;
-
             writeProtection(vd.visibility.kind);
             typeToBuffer(type, vd, true);
             buf.writestringln(";");
diff --git a/compiler/src/dmd/expressionsem.d b/compiler/src/dmd/expressionsem.d
@@ -9983,11 +9983,7 @@ private extern (C++) final class ExpressionSemanticVisitor : Visitor
             if (t1.ty == Tpointer)
                 t1 = t1.nextOf();
 
-            // __monitor is always void* regardless of shared - strip shared from the mod
-            auto t1mod = t1.mod;
-            if (exp.var.ident == Id.__monitor)
-                t1mod &= ~MODFlags.shared_;
-            exp.type = exp.type.addMod(t1mod);
+            exp.type = exp.type.addMod(t1.mod);
 
             // https://issues.dlang.org/show_bug.cgi?id=23109
             // Run semantic on the DotVarExp type
diff --git a/compiler/src/dmd/glue/todt.d b/compiler/src/dmd/glue/todt.d
@@ -37,7 +37,6 @@ import dmd.dsymbol;
 import dmd.dtemplate;
 import dmd.errors;
 import dmd.expression;
-import dmd.id;
 import dmd.expressionsem : toBool, toInteger;
 import dmd.func;
 import dmd.globals;
@@ -782,11 +781,6 @@ private void membersToDt(AggregateDeclaration ad, ref DtBuilder dtb,
             size_t index = 0;
             for (ClassDeclaration c = cdb.baseClass; c; c = c.baseClass)
                 index += c.fields.length;
-            // CTFE elements exclude __monitor (emitted separately).
-            // Subtract it from the index, but only when Object is actually
-            // in the base hierarchy (index > 0 means cdb is not itself Object).
-            if (index > 0)
-                index -= cdb.hasMonitor();
             membersToDt(cdb, dtb, elements, index, concreteType, null);
             offset = cdb.structsize;
         }
@@ -851,12 +845,9 @@ private void membersToDt(AggregateDeclaration ad, ref DtBuilder dtb,
         offset = 0;
     // `offset` now is where the fields start
 
-    // __monitor is emitted separately (not from CTFE elements), so exclude it from the count.
-    // This applies to Object itself (the root class with no base class), not to interfaces.
-    const size_t monitorExcluded = (cd && !cd.isInterfaceDeclaration() && !cd.baseClass && cd.hasMonitor()) ? 1 : 0;
     assert(!elements ||
            firstFieldIndex <= elements.length &&
-           firstFieldIndex + ad.fields.length - monitorExcluded <= elements.length);
+           firstFieldIndex + ad.fields.length <= elements.length);
 
     uint bitByteOffset = 0;     // byte offset of bit field
     uint bitOffset = 0;         // starting bit number
@@ -909,10 +900,6 @@ private void membersToDt(AggregateDeclaration ad, ref DtBuilder dtb,
 
     foreach (i, field; ad.fields)
     {
-        // __monitor is emitted separately (not from CTFE elements), skip it here
-        if (field.ident == Id.__monitor)
-            continue;
-
         // skip if no element for this field
         if (elements && !(*elements)[firstFieldIndex + i])
             continue;
@@ -1179,9 +1166,6 @@ void ClassReferenceExp_toInstanceDt(ClassReferenceExp ce, ref DtBuilder dtb)
     size_t firstFieldIndex = 0;
     for (ClassDeclaration c = cd.baseClass; c; c = c.baseClass)
         firstFieldIndex += c.fields.length;
-    // CTFE elements exclude __monitor (it is emitted separately by membersToDt),
-    // so adjust the index to match the elements array layout.
-    firstFieldIndex -= cd.hasMonitor();
     membersToDt(cd, dtb, ce.value.elements, firstFieldIndex, cd, null);
 }
 
diff --git a/compiler/src/dmd/glue/toobj.d b/compiler/src/dmd/glue/toobj.d
@@ -1253,8 +1253,7 @@ private void ClassInfoToDt(ref DtBuilder dtb, ClassDeclaration cd, Symbol* sinit
     }
 
     // m_init[]
-    // Class instances always have at least a vtable pointer
-    assert(cd.structsize >= target.ptrsize || (cd.classKind == ClassKind.cpp && cd.structsize >= 4));
+    assert(cd.structsize >= 8 || (cd.classKind == ClassKind.cpp && cd.structsize >= 4));
     dtb.size(cd.structsize);           // size
     dtb.xoff(sinit, 0, TYnptr);         // initializer
 
@@ -1329,8 +1328,6 @@ Louter:
         foreach (vd; pc.fields)
         {
             //printf("vd = %s %s\n", vd.kind(), vd.toChars());
-            if (vd.ident == Id.__monitor)
-                continue;   // __monitor is not GC-managed
             if (vd.hasPointers())
             {
                 flags &= ~ClassFlags.noPointers;  // not no-how, not no-way
diff --git a/compiler/src/dmd/statementsem.d b/compiler/src/dmd/statementsem.d
@@ -3129,12 +3129,6 @@ Statement statementSemanticVisit(Statement s, Scope* sc)
                 ss.exp = new CastExp(ss.loc, ss.exp, t);
                 ss.exp = ss.exp.expressionSemantic(sc);
             }
-            if (!cd.hasMonitor())
-            {
-                error(ss.loc, "cannot `synchronize` on a `%s` because `object.Object` has no `__monitor` field",
-                      cd.toChars());
-                return setError();
-            }
             version (all)
             {
                 /* Rewrite as:
diff --git a/compiler/src/dmd/traits.d b/compiler/src/dmd/traits.d
@@ -267,8 +267,6 @@ ulong getTypePointerBitmap(Loc loc, Type t, ref Array!(ulong) data, ErrorSink eS
                 visitTopLevelClass(t.sym.baseClass.type.isTypeClass());
             foreach (v; t.sym.fields)
             {
-                if (v.ident == Id.__monitor)
-                    continue; // __monitor is not GC-managed
                 offset = classoff + v.offset;
                 visit(v.type);
             }
@@ -1788,7 +1786,6 @@ Expression semanticTraits(TraitsExp e, Scope* sc)
                 // Skip over internal members in __traits(allMembers)
                 if ((sm.isCtorDeclaration() && sm.ident != Id.ctor) ||
                     (sm.isDtorDeclaration() && sm.ident != Id.dtor) ||
-                    (sm.ident == Id.__monitor) ||
                     (sm.isPostBlitDeclaration() && sm.ident != Id.postblit) ||
                     sm.isInvariantDeclaration() ||
                     sm.isUnitTestDeclaration())
diff --git a/compiler/src/dmd/typesem.d b/compiler/src/dmd/typesem.d
@@ -7069,11 +7069,6 @@ Expression dotExp(Type mt, Scope* sc, Expression e, Identifier ident, DotExpFlag
                 // Don't include hidden 'this' pointer
                 if (v.isThisDeclaration())
                     continue;
-
-                // Don't include __monitor field
-                if (v.ident == Id.__monitor)
-                    continue;
-
                 Expression ex;
                 if (ev)
                     ex = new DotVarExp(e.loc, ev, v);
@@ -7187,6 +7182,17 @@ Expression dotExp(Type mt, Scope* sc, Expression e, Identifier ident, DotExpFlag
                 return e;
             }
 
+            if (ident == Id.__monitor && mt.sym.hasMonitor())
+            {
+                /* The handle to the monitor (call it a void*)
+                 * *(cast(void**)e + 1)
+                 */
+                e = e.castTo(sc, mt.tvoidptr.pointerTo());
+                e = new AddExp(e.loc, e, IntegerExp.literal!1);
+                e = new PtrExp(e.loc, e);
+                e = e.expressionSemantic(sc);
+                return e;
+            }
 
             if (ident == Id.outer && mt.sym.vthis)
             {
diff --git a/compiler/src/tests/cxxfrontend.cc b/compiler/src/tests/cxxfrontend.cc
@@ -269,7 +269,7 @@ void test_semantic()
     /* Mini object.d source. Module::parse will add internal members also. */
     const char *buf =
         "module object;\n"
-        "class Object { void* __monitor; }\n"
+        "class Object { }\n"
         "class Throwable { }\n"
         "class Error : Throwable { this(immutable(char)[]); }";
 
diff --git a/compiler/test/compilable/b18242.d b/compiler/test/compilable/b18242.d
@@ -7,7 +7,7 @@ class Object { }
 class TypeInfo { }
 class TypeInfo_Class : TypeInfo
 {
-    version(D_LP64) { ubyte[136+24] _x; } else { ubyte[68+20] _x; }
+    version(D_LP64) { ubyte[136+16] _x; } else { ubyte[68+16] _x; }
 }
 
 class Throwable { }
diff --git a/compiler/test/fail_compilation/extra-files/no_monitor_synchronized/object.d b/compiler/test/fail_compilation/extra-files/no_monitor_synchronized/object.d
diff --git a/compiler/test/fail_compilation/fail_opover.d b/compiler/test/fail_compilation/fail_opover.d
@@ -4,7 +4,7 @@
 TEST_OUTPUT:
 ---
 fail_compilation/fail_opover.d(39): Error: no `[]` operator overload for type `object.Object`
-$p:object.d$($n$):        perhaps define `auto opIndex() {}` for `object.Object`
+$p:object.d$(111):        perhaps define `auto opIndex() {}` for `object.Object`
 fail_compilation/fail_opover.d(43): Error: no `[]` operator overload for type `TestS`
 fail_compilation/fail_opover.d(41):        perhaps define `auto opIndex() {}` for `fail_opover.test1.TestS`
 fail_compilation/fail_opover.d(55): Error: no `[]` operator overload for type `S`
diff --git a/compiler/test/fail_compilation/no_monitor_synchronized.d b/compiler/test/fail_compilation/no_monitor_synchronized.d
diff --git a/compiler/test/runnable/test42.d b/compiler/test/runnable/test42.d
@@ -1315,12 +1315,6 @@ void test79()
 //        writeln(c.__monitor);
         assert(c.__monitor !is null);
     }
-
-    // __monitor on a shared object is still void*, not shared(void*)
-    shared C79 sc = new shared C79();
-    void* p = cast(void*) 0x1;
-    sc.__monitor = p;
-    assert(sc.__monitor == p);
 }
 
 /***************************************************/
diff --git a/druntime/src/core/sync/mutex.d b/druntime/src/core/sync/mutex.d
@@ -102,7 +102,7 @@ class Mutex :
 
         auto self = cast(Mutex) this;
         self.m_proxy.link = self;
-        self.__monitor = cast(void*) &self.m_proxy;
+        this.__monitor = cast(void*) &m_proxy;
     }
 
 
diff --git a/druntime/src/core/sync/rwmutex.d b/druntime/src/core/sync/rwmutex.d
@@ -201,9 +201,8 @@ class ReadWriteMutex
         this(this Q)() @trusted nothrow
             if (is(Q == Reader) || is(Q == shared Reader))
         {
-            auto self = cast(Reader) this;
-            self.m_proxy.link = cast(typeof(self.m_proxy.link)) this;
-            self.__monitor = cast(void*) &self.m_proxy;
+            m_proxy.link = cast(typeof(m_proxy.link)) this;
+            this.__monitor = cast(void*) &m_proxy;
         }
 
         /**
@@ -373,9 +372,8 @@ class ReadWriteMutex
         this(this Q)() @trusted nothrow
             if (is(Q == Writer) || is(Q == shared Writer))
         {
-            auto self = cast(Writer) this;
-            self.m_proxy.link = cast(typeof(self.m_proxy.link)) this;
-            self.__monitor = cast(void*) &self.m_proxy;
+            m_proxy.link = cast(typeof(m_proxy.link)) this;
+            this.__monitor = cast(void*) &m_proxy;
         }
 
 
diff --git a/druntime/src/object.d b/druntime/src/object.d
@@ -105,17 +105,11 @@ else version (AArch64)
     else version = WithArgTypes;
 }
 
-static assert(Object.__monitor.offsetof == size_t.sizeof);
-
 /**
  * All D class objects inherit from Object.
  */
 class Object
 {
-    // This is an internal field that is omitted from .tupleof, __traits(allMembers), pointer bitmaps etc.
-    // It can be removed in a custom druntime, but if it's there it must remain the first field.
-    void* __monitor;
-
     /**
      * Convert Object to a human readable string.
      */
diff --git a/spec/class.dd b/spec/class.dd
@@ -232,9 +232,9 @@ void main()
 
 $(H3 $(LNAME2 hidden-fields, Accessing Hidden Fields))
 
-        $(P The property $(D .__vptr) gives access to the class object's vtbl[],
-        but should not be used in user code. The $(D .__monitor) field is defined
-        in druntime, but excluded from `.tupleof` and introspection from traits.
+        $(P The properties $(D .__vptr) and $(D .__monitor) give access
+        to the class object's vtbl[] and monitor, respectively, but
+        should not be used in user code.
         See $(DDSUBLINK spec/abi, classes, the ABI) for details.
         )
         $(P See also: $(RELATIVE_LINK2 nested-context, Context Pointer).)

Original file line number	Diff line number	Diff line change
`@@ -333,17 +333,11 @@ extern (C++) class ClassDeclaration : AggregateDeclaration`
`333`	`333`	`}`
`334`	`334`
`335`	`335`	`/**************`
`336`		- * Returns: true if there's a __monitor field, i.e. the druntime `Object` class declares it
	`336`	`+ * Returns: true if there's a __monitor field`
`337`	`337`	`*/`
`338`	`338`	`final bool hasMonitor()`
`339`	`339`	`{`
`340`		`- if (classKind != ClassKind.d)`
`341`		`- return false;`
`342`		`- // Check if Object in druntime actually declares a __monitor field.`
`343`		`- // Custom druntimes can omit it by not declaring it in Object.`
`344`		`- if (!object \|\| !object.symtab)`
`345`		`- return true; // conservative: Object not yet loaded, assume monitor present`
`346`		`- return object.symtab.lookup(Id.__monitor) !is null;`
	`340`	`+ return classKind == ClassKind.d;`
`347`	`341`	`}`
`348`	`342`
`349`	`343`	`/****************************************`
Original file line number	Diff line number	Diff line change
`@@ -9978,6 +9978,8 @@ private extern(C++) class FinalizeSizeVisitor : Visitor`
`9978`	`9978`	`{`
`9979`	`9979`	`outerCd.alignsize = target.ptrsize;`
`9980`	`9980`	`outerCd.structsize = target.ptrsize; // allow room for __vptr`
	`9981`	`+ if (outerCd.hasMonitor())`
	`9982`	`+ outerCd.structsize += target.ptrsize; // allow room for __monitor`
`9981`	`9983`	`}`
`9982`	`9984`
`9983`	`9985`	`//printf("finalizeSize() %s, sizeok = %d\n", toChars(), sizeok);`
Original file line number	Diff line number	Diff line change
`@@ -1065,9 +1065,6 @@ public:`
`1065`	`1065`
`1066`	`1066`	`if (adparent)`
`1067`	`1067`	`{`
`1068`		`- if (vd.ident && vd.ident == Id.__monitor)`
`1069`		`- return;`
`1070`		`-`
`1071`	`1068`	`writeProtection(vd.visibility.kind);`
`1072`	`1069`	`typeToBuffer(type, vd, true);`
`1073`	`1070`	`buf.writestringln(";");`
Original file line number	Diff line number	Diff line change
`@@ -1253,8 +1253,7 @@ private void ClassInfoToDt(ref DtBuilder dtb, ClassDeclaration cd, Symbol* sinit`
`1253`	`1253`	`}`
`1254`	`1254`
`1255`	`1255`	`// m_init[]`
`1256`		`- // Class instances always have at least a vtable pointer`
`1257`		`- assert(cd.structsize >= target.ptrsize \|\| (cd.classKind == ClassKind.cpp && cd.structsize >= 4));`
	`1256`	`+ assert(cd.structsize >= 8 \|\| (cd.classKind == ClassKind.cpp && cd.structsize >= 4));`
`1258`	`1257`	`dtb.size(cd.structsize); // size`
`1259`	`1258`	`dtb.xoff(sinit, 0, TYnptr); // initializer`
`1260`	`1259`
`@@ -1329,8 +1328,6 @@ Louter:`
`1329`	`1328`	`foreach (vd; pc.fields)`
`1330`	`1329`	`{`
`1331`	`1330`	`//printf("vd = %s %s\n", vd.kind(), vd.toChars());`
`1332`		`- if (vd.ident == Id.__monitor)`
`1333`		`- continue; // __monitor is not GC-managed`
`1334`	`1331`	`if (vd.hasPointers())`
`1335`	`1332`	`{`
`1336`	`1333`	`flags &= ~ClassFlags.noPointers; // not no-how, not no-way`
Original file line number	Diff line number	Diff line change
`@@ -3129,12 +3129,6 @@ Statement statementSemanticVisit(Statement s, Scope* sc)`
`3129`	`3129`	`ss.exp = new CastExp(ss.loc, ss.exp, t);`
`3130`	`3130`	`ss.exp = ss.exp.expressionSemantic(sc);`
`3131`	`3131`	`}`
`3132`		`- if (!cd.hasMonitor())`
`3133`		`- {`
`3134`		- error(ss.loc, "cannot `synchronize` on a `%s` because `object.Object` has no `__monitor` field",
`3135`		`- cd.toChars());`
`3136`		`- return setError();`
`3137`		`- }`
`3138`	`3132`	`version (all)`
`3139`	`3133`	`{`
`3140`	`3134`	`/* Rewrite as:`