8320318: ObjectMonitor Responsible thread

src/hotspot/cpu/aarch64/c2_MacroAssembler_aarch64.cpp

@@ -150,10 +150,12 @@ void C2_MacroAssembler::fast_unlock(Register objectReg, Register boxReg, Registe
   Register oop = objectReg;
   Register box = boxReg;
   Register disp_hdr = tmpReg;
+  Register owner_addr = tmpReg;
   Register tmp = tmp2Reg;
   Label cont;
   Label object_has_monitor;
   Label count, no_count;
+  Label unlocked;
 
   assert(LockingMode != LM_LIGHTWEIGHT, "lightweight locking should use fast_unlock_lightweight");
   assert_different_registers(oop, box, tmp, disp_hdr);
@@ -204,14 +206,40 @@ void C2_MacroAssembler::fast_unlock(Register objectReg, Register boxReg, Registe
   b(cont);
 
   bind(notRecursive);
+
+  // Compute owner address.
+  lea(owner_addr, Address(tmp, ObjectMonitor::owner_offset()));
+
+  // Set owner to null.
+  // Release to satisfy the JMM
+  stlr(zr, owner_addr);
+  // We need a full fence after clearing owner to avoid stranding.
+  // StoreLoad achieves this.
+  membar(StoreLoad);
+
+  // Check if the entry lists are empty.
   ldr(rscratch1, Address(tmp, ObjectMonitor::EntryList_offset()));
-  ldr(disp_hdr, Address(tmp, ObjectMonitor::cxq_offset()));
-  orr(rscratch1, rscratch1, disp_hdr); // Will be 0 if both are 0.
-  cmp(rscratch1, zr); // Sets flags for result
-  cbnz(rscratch1, cont);
-  // need a release store here
-  lea(tmp, Address(tmp, ObjectMonitor::owner_offset()));
-  stlr(zr, tmp); // set unowned
+  ldr(tmpReg, Address(tmp, ObjectMonitor::cxq_offset()));
+  orr(rscratch1, rscratch1, tmpReg);
+  cmp(rscratch1, zr);
+  br(Assembler::EQ, cont);     // If so we are done.
+
+  // Check if there is a successor.
+  ldr(rscratch1, Address(tmp, ObjectMonitor::succ_offset()));
+  cmp(rscratch1, zr);
+  br(Assembler::NE, unlocked); // If so we are done.
+
+  // Save the monitor pointer in the current thread, so we can try to
+  // reacquire the lock in SharedRuntime::monitor_exit_helper().
+  str(tmp, Address(rthread, JavaThread::unlocked_inflated_monitor_offset()));
+
+  cmp(zr, rthread); // Set Flag to NE => slow path
+  b(cont);
+
+  bind(unlocked);
+  cmp(zr, zr); // Set Flag to EQ => fast path
+
+  // Intentional fall-through
 
   bind(cont);
   // flag == EQ indicates success
@@ -498,33 +526,41 @@ void C2_MacroAssembler::fast_unlock_lightweight(Register obj, Register box, Regi
 
     bind(not_recursive);
 
-    Label release;
     const Register t2_owner_addr = t2;
 
     // Compute owner address.
     lea(t2_owner_addr, Address(t1_monitor, ObjectMonitor::owner_offset()));
 
+    // Set owner to null.
+    // Release to satisfy the JMM
+    stlr(zr, t2_owner_addr);
+    // We need a full fence after clearing owner to avoid stranding.
+    // StoreLoad achieves this.
+    membar(StoreLoad);
+
     // Check if the entry lists are empty.
     ldr(rscratch1, Address(t1_monitor, ObjectMonitor::EntryList_offset()));
     ldr(t3_t, Address(t1_monitor, ObjectMonitor::cxq_offset()));
     orr(rscratch1, rscratch1, t3_t);
     cmp(rscratch1, zr);
-    br(Assembler::EQ, release);
+    br(Assembler::EQ, unlocked);  // If so we are done.
 
-    // The owner may be anonymous and we removed the last obj entry in
-    // the lock-stack. This loses the information about the owner.
-    // Write the thread to the owner field so the runtime knows the owner.
-    str(rthread, Address(t2_owner_addr));
-    b(slow_path);
+    // Check if there is a successor.
+    ldr(rscratch1, Address(t1_monitor, ObjectMonitor::succ_offset()));
+    cmp(rscratch1, zr);
+    br(Assembler::NE, unlocked);  // If so we are done.
 
-    bind(release);
-    // Set owner to null.
-    // Release to satisfy the JMM
-    stlr(zr, t2_owner_addr);
+    // Save the monitor pointer in the current thread, so we can try to
+    // reacquire the lock in SharedRuntime::monitor_exit_helper().
+    str(t1_monitor, Address(rthread, JavaThread::unlocked_inflated_monitor_offset()));
+
+    cmp(zr, rthread); // Set Flag to NE => slow path
+    b(slow_path);
   }
 
   bind(unlocked);
   decrement(Address(rthread, JavaThread::held_monitor_count_offset()));
+  cmp(zr, zr); // Set Flags to EQ => fast path
 
 #ifdef ASSERT
   // Check that unlocked label is reached with Flags == EQ.

src/hotspot/cpu/ppc/macroAssembler_ppc.cpp

@@ -2715,13 +2715,34 @@ void MacroAssembler::compiler_fast_unlock_object(ConditionRegister flag, Registe
   b(success);
 
   bind(notRecursive);
+
+  // Set owner to null.
+  // Release to satisfy the JMM
+  release();
+  li(temp, 0);
+  std(temp, in_bytes(ObjectMonitor::owner_offset()), current_header);
+  // We need a full fence after clearing owner to avoid stranding.
+  // StoreLoad achieves this.
+  membar(StoreLoad);
+
+  // Check if the entry lists are empty.
   ld(temp,             in_bytes(ObjectMonitor::EntryList_offset()), current_header);
   ld(displaced_header, in_bytes(ObjectMonitor::cxq_offset()), current_header);
   orr(temp, temp, displaced_header); // Will be 0 if both are 0.
   cmpdi(flag, temp, 0);
-  bne(flag, failure);
-  release();
-  std(temp, in_bytes(ObjectMonitor::owner_offset()), current_header);
+  beq(flag, success);  // If so we are done.
+
+  // Check if there is a successor.
+  ld(temp, in_bytes(ObjectMonitor::succ_offset()), current_header);
+  cmpdi(flag, temp, 0);
+  bne(flag, success);  // If so we are done.
+
+  // Save the monitor pointer in the current thread, so we can try
+  // to reacquire the lock in SharedRuntime::monitor_exit_helper().
+  std(current_header, in_bytes(JavaThread::unlocked_inflated_monitor_offset()), R16_thread);
+
+  crxor(flag, Assembler::equal, flag, Assembler::equal); // Set flag = NE => slow path
+  b(failure);
 
   // flag == EQ indicates success, decrement held monitor count
   // flag == NE indicates failure
@@ -3028,27 +3049,39 @@ void MacroAssembler::compiler_fast_unlock_lightweight_object(ConditionRegister f
 
     bind(not_recursive);
 
-    Label release_;
+    Label set_eq_unlocked;
     const Register t2 = tmp2;
 
+    // Set owner to null.
+    // Release to satisfy the JMM
+    release();
+    li(t, 0);
+    std(t, in_bytes(ObjectMonitor::owner_offset()), monitor);
+    // We need a full fence after clearing owner to avoid stranding.
+    // StoreLoad achieves this.
+    membar(StoreLoad);
+
     // Check if the entry lists are empty.
     ld(t, in_bytes(ObjectMonitor::EntryList_offset()), monitor);
     ld(t2, in_bytes(ObjectMonitor::cxq_offset()), monitor);
     orr(t, t, t2);
     cmpdi(CCR0, t, 0);
-    beq(CCR0, release_);
+    beq(CCR0, unlocked); // If so we are done.
 
-    // The owner may be anonymous and we removed the last obj entry in
-    // the lock-stack. This loses the information about the owner.
-    // Write the thread to the owner field so the runtime knows the owner.
-    std(R16_thread, in_bytes(ObjectMonitor::owner_offset()), monitor);
+    // Check if there is a successor.
+    ld(t, in_bytes(ObjectMonitor::succ_offset()), monitor);
+    cmpdi(CCR0, t, 0);
+    bne(CCR0, set_eq_unlocked); // If so we are done.
+
+    // Save the monitor pointer in the current thread, so we can try
+    // to reacquire the lock in SharedRuntime::monitor_exit_helper().
+    std(monitor, in_bytes(JavaThread::unlocked_inflated_monitor_offset()), R16_thread);
+
+    crxor(CCR0, Assembler::equal, CCR0, Assembler::equal); // Set flag = NE => slow path
     b(slow_path);
 
-    bind(release_);
-    // Set owner to null.
-    release();
-    // t contains 0
-    std(t, in_bytes(ObjectMonitor::owner_offset()), monitor);
+    bind(set_eq_unlocked);
+    crorc(CCR0, Assembler::equal, CCR0, Assembler::equal); // Set flag = EQ => fast path
   }
 
   bind(unlocked);

src/hotspot/cpu/riscv/c2_MacroAssembler_riscv.cpp

@@ -165,6 +165,7 @@ void C2_MacroAssembler::fast_unlock(Register objectReg, Register boxReg,
   Register oop = objectReg;
   Register box = boxReg;
   Register disp_hdr = tmp1Reg;
+  Register owner_addr = tmp1Reg;
   Register tmp = tmp2Reg;
   Label object_has_monitor;
   // Finish fast lock successfully. MUST branch to with flag == 0
@@ -222,15 +223,33 @@ void C2_MacroAssembler::fast_unlock(Register objectReg, Register boxReg,
   j(unlocked);
 
   bind(notRecursive);
-  ld(t0, Address(tmp, ObjectMonitor::EntryList_offset()));
-  ld(disp_hdr, Address(tmp, ObjectMonitor::cxq_offset()));
-  orr(t0, t0, disp_hdr); // Will be 0 if both are 0.
-  bnez(t0, slow_path);
+  // Compute owner address.
+  la(owner_addr, Address(tmp, ObjectMonitor::owner_offset()));
 
-  // need a release store here
-  la(tmp, Address(tmp, ObjectMonitor::owner_offset()));
+  // Set owner to null.
+  // Release to satisfy the JMM
   membar(MacroAssembler::LoadStore | MacroAssembler::StoreStore);
-  sd(zr, Address(tmp)); // set unowned
+  sd(zr, Address(owner_addr));
+  // We need a full fence after clearing owner to avoid stranding.
+  // StoreLoad achieves this.
+  membar(StoreLoad);
+
+  // Check if the entry lists are empty.
+  ld(t0, Address(tmp, ObjectMonitor::EntryList_offset()));
+  ld(tmp1Reg, Address(tmp, ObjectMonitor::cxq_offset()));
+  orr(t0, t0, tmp1Reg);
+  beqz(t0, unlocked); // If so we are done.
+
+  // Check if there is a successor.
+  ld(t0, Address(tmp, ObjectMonitor::succ_offset()));
+  bnez(t0, unlocked); // If so we are done.
+
+  // Save the monitor pointer in the current thread, so we can try to
+  // reacquire the lock in SharedRuntime::monitor_exit_helper().
+  sd(tmp, Address(xthread, JavaThread::unlocked_inflated_monitor_offset()));
+
+  mv(flag, 1);
+  j(slow_path);
 
   bind(unlocked);
   mv(flag, zr);
@@ -534,28 +553,35 @@ void C2_MacroAssembler::fast_unlock_lightweight(Register obj, Register box,
 
     bind(not_recursive);
 
-    Label release;
     const Register tmp2_owner_addr = tmp2;
 
     // Compute owner address.
     la(tmp2_owner_addr, Address(tmp1_monitor, ObjectMonitor::owner_offset()));
 
+    // Set owner to null.
+    // Release to satisfy the JMM
+    membar(MacroAssembler::LoadStore | MacroAssembler::StoreStore);
+    sd(zr, Address(tmp2_owner_addr));
+    // We need a full fence after clearing owner to avoid stranding.
+    // StoreLoad achieves this.
+    membar(StoreLoad);
+
     // Check if the entry lists are empty.
     ld(t0, Address(tmp1_monitor, ObjectMonitor::EntryList_offset()));
     ld(tmp3_t, Address(tmp1_monitor, ObjectMonitor::cxq_offset()));
     orr(t0, t0, tmp3_t);
-    beqz(t0, release);
+    beqz(t0, unlocked); // If so we are done.
 
-    // The owner may be anonymous and we removed the last obj entry in
-    // the lock-stack. This loses the information about the owner.
-    // Write the thread to the owner field so the runtime knows the owner.
-    sd(xthread, Address(tmp2_owner_addr));
-    j(slow_path);
+    // Check if there is a successor.
+    ld(tmp3_t, Address(tmp1_monitor, ObjectMonitor::succ_offset()));
+    bnez(tmp3_t, unlocked); // If so we are done.
 
-    bind(release);
-    // Set owner to null.
-    membar(MacroAssembler::LoadStore | MacroAssembler::StoreStore);
-    sd(zr, Address(tmp2_owner_addr));
+    // Save the monitor pointer in the current thread, so we can try
+    // to reacquire the lock in SharedRuntime::monitor_exit_helper().
+    sd(tmp1_monitor, Address(xthread, JavaThread::unlocked_inflated_monitor_offset()));
+
+    mv(flag, 1);
+    j(slow_path);
   }
 
   bind(unlocked);