From 4f60a817e3ea408a176c74ec0f0ea5e9f151dd61 Mon Sep 17 00:00:00 2001
From: Ben Adams <thundercat@illyriad.co.uk>
Date: Tue, 30 Aug 2016 03:23:53 +0100
Subject: [PATCH] Monitor.TryEnter asm timeout != 0 before spin (#6951)

* JIT_MonTryEnter_Slow timeout != 0 before spin
* JIT_MonTryEnter_InlineGetThread timeout != 0 before spin
---
 src/vm/amd64/JitHelpers_InlineGetThread.asm | 52 ++++++++++++++++-------------
 src/vm/amd64/JitHelpers_Slow.asm            | 20 ++++++-----
 2 files changed, 40 insertions(+), 32 deletions(-)

diff --git a/src/vm/amd64/JitHelpers_InlineGetThread.asm b/src/vm/amd64/JitHelpers_InlineGetThread.asm
index 2a5e3b9..700c3b3 100644
--- a/src/vm/amd64/JitHelpers_InlineGetThread.asm
+++ b/src/vm/amd64/JitHelpers_InlineGetThread.asm
@@ -960,6 +960,10 @@ endif
         ret
 
     PrepareToWaitThinLock:
+        ; Return failure if timeout is zero
+        cmp     dword ptr [rsp + 10h], 0
+        je      TimeoutZero
+ 
         ; If we are on an MP system, we try spinning for a certain number of iterations
         cmp     dword ptr [g_SystemInfo + OFFSETOF__g_SystemInfo__dwNumberOfProcessors], 1
         jle     FramedLockHelper
@@ -982,6 +986,16 @@ endif
     RetryHelperThinLock:
         jmp     RetryThinLock
 
+	TimeoutZero:
+        ; Did not acquire, return FALSE
+        mov     byte ptr [r8], 0
+ifdef MON_DEBUG
+ifdef TRACK_SYNC
+        add     rsp, MON_ENTER_STACK_SIZE_INLINEGETTHREAD
+endif
+endif
+        ret
+
     HaveHashOrSyncBlockIndex:
         ; If we have a hash code already, we need to create a sync block
         test    eax, BIT_SBLK_IS_HASHCODE
@@ -1067,9 +1081,21 @@ endif
         ret
 
     PrepareToWait:
+        ; Return failure if timeout is zero
+        cmp     dword ptr [rsp + 10h], 0
+ifdef MON_DEBUG
+ifdef TRACK_SYNC
+        ; if we are using the _DEBUG stuff then rsp has been adjusted
+        ; so compare the value at the adjusted position
+        ; there's really little harm in the extra stack read
+        cmp     dword ptr [rsp + MON_ENTER_STACK_SIZE_INLINEGETTHREAD + 10h]
+endif
+endif
+        je      TimeoutZero
+
         ; If we are on an MP system, we try spinning for a certain number of iterations
         cmp     dword ptr [g_SystemInfo + OFFSETOF__g_SystemInfo__dwNumberOfProcessors], 1
-        jle     WouldBlock
+        jle     Block
     
         ; Exponential backoff; delay by approximately 2*r10d clock cycles
         mov     eax, r10d
@@ -1084,29 +1110,7 @@ endif
         cmp     r10d, dword ptr [g_SpinConstants + OFFSETOF__g_SpinConstants__dwMaximumDuration]
         jle     RetrySyncBlock
 
-        ; We would need to block to enter the section. Return failure if
-        ; timeout is zero, else call the farmed helper to do the blocking
-        ; form of TryEnter.
-    WouldBlock:
-        mov     rdx, [rsp + 10h]
-        ; if we are using the _DEBUG stuff then rsp has been adjusted
-        ; just overwrite the wrong RDX value that we already retrieved
-        ; there's really little harm in the extra stack read
-ifdef MON_DEBUG
-ifdef TRACK_SYNC
-        mov     rdx, [rsp + MON_ENTER_STACK_SIZE_INLINEGETTHREAD + 10h]
-endif
-endif
-        test    rdx, rdx
-        jnz     Block
-        ; Return FALSE
-        mov		byte ptr [r8], 0
-ifdef MON_DEBUG
-ifdef TRACK_SYNC
-        add     rsp, MON_ENTER_STACK_SIZE_INLINEGETTHREAD
-endif
-endif
-        ret
+        jmp     Block
 
     RetryHelperSyncBlock:
         jmp     RetrySyncBlock
diff --git a/src/vm/amd64/JitHelpers_Slow.asm b/src/vm/amd64/JitHelpers_Slow.asm
index 66b0e90..7deed49 100644
--- a/src/vm/amd64/JitHelpers_Slow.asm
+++ b/src/vm/amd64/JitHelpers_Slow.asm
@@ -1452,6 +1452,10 @@ NESTED_ENTRY JIT_MonTryEnter_Slow, _TEXT
         ret
 
     PrepareToWaitThinLock:
+        ; Return failure if timeout is zero
+        test    rsi, rsi
+        jz     TimeoutZero
+
         ; If we are on an MP system, we try spinning for a certain number of iterations
         cmp     dword ptr [g_SystemInfo + OFFSETOF__g_SystemInfo__dwNumberOfProcessors], 1
         jle     FramedLockHelper
@@ -1553,9 +1557,13 @@ endif
         ret
 
     PrepareToWait:
+        ; Return failure if timeout is zero
+        test    rsi, rsi
+        jz      TimeoutZero
+
         ; If we are on an MP system, we try spinning for a certain number of iterations
         cmp     dword ptr [g_SystemInfo + OFFSETOF__g_SystemInfo__dwNumberOfProcessors], 1
-        jle     WouldBlock
+        jle     Block
     
         ; Exponential backoff; delay by approximately 2*r10d clock cycles
         mov     eax, r10d
@@ -1570,15 +1578,11 @@ endif
         cmp     r10d, dword ptr [g_SpinConstants + OFFSETOF__g_SpinConstants__dwMaximumDuration]
         jle     RetrySyncBlock
 
-        ; We would need to block to enter the section. Return failure if
-        ; timeout is zero, else call the farmed helper to do the blocking
-        ; form of TryEnter.
-    WouldBlock:
-        test    rsi, rsi
-        jnz     Block
+        jmp     Block
 
+    TimeoutZero:
         ; Return FALSE
-        mov		byte ptr [r8], 0
+        mov     byte ptr [r8], 0
         add     rsp, MON_ENTER_STACK_SIZE
         pop     rsi
         ret
-- 
2.7.4