feat(journal): add casInt for ptr

.gitignore

@@ -26,3 +26,6 @@ dist-newstyle/
 cabal.project.local*
 bench-*
 bench.*
+# C
+a.out
+core

src/journal/cbits/atomic.c

@@ -0,0 +1,21 @@
+#include <stdatomic.h>
+
+_Bool
+c_atomic_compare_exchange_strong(_Atomic(int) *object, int expected, int desired) {
+  return atomic_compare_exchange_strong(object, &expected, desired);
+}
+
+// #include <stdio.h> // XXX: remove
+// int
+// main(void) {
+// 	atomic_int acnt = 3;
+//   int res;
+// 	printf("acnt = %u\n", acnt);
+// 	res = c_atomic_compare_exchange_strong(&acnt, 3, 4);
+// 	printf("cas(3, 4) = %d\n", res);
+// 	res = c_atomic_compare_exchange_strong(&acnt, 2, 5);
+// 	printf("cas(2, 5) = %d\n", res);
+// 	res = c_atomic_compare_exchange_strong(&acnt, 4, 5);
+// 	printf("cas(4, 5) = %d\n", res);
+// 	printf("acnt = %u\n", acnt);
+// }

src/journal/journal.cabal

@@ -22,6 +22,7 @@ extra-source-files:
   CHANGELOG.md
   LICENSE
   README.md
+  cbits/atomic.c
 
 library
   hs-source-dirs:   src/
@@ -60,6 +61,7 @@ library
   ghc-options:      -O2
   if os(linux)
     extra-libraries: atomic
+  c-sources:        cbits/atomic.c
   default-language: Haskell2010
 
 test-suite test

src/journal/src/Journal/Internal/Atomics.hs

@@ -3,6 +3,7 @@
 module Journal.Internal.Atomics where
 
 import Foreign
+import Foreign.C.Types
 
 ------------------------------------------------------------------------
 
@@ -55,3 +56,17 @@ fetchAddInt32Ptr = c_atomic_fetch_add_int_4
 
 fetchAddInt64Ptr :: Ptr Int64 -> Int64 -> IO Int64
 fetchAddInt64Ptr = c_atomic_fetch_add_int_8
+
+------------------------------------------------------------------------
+
+foreign import ccall unsafe "c_atomic_compare_exchange_strong"
+  c_atomic_compare_exchange_strong :: Ptr Int -> Int -> Int -> IO CBool
+
+casIntPtr :: Ptr Int -> Int -> Int -> IO Bool
+casIntPtr ptr expected desired = do
+  result <- c_atomic_compare_exchange_strong ptr expected desired
+  case result of
+    0 -> return False
+    1 -> return True
+    _ ->
+      error "casIntAddr: impossible, c_atomic_compare_exchange_strong should return a _Bool"

src/journal/src/Journal/Internal/ByteBufferPtr.hs

@@ -455,16 +455,10 @@ writeWord32OffAddr bb offset@(I# offset#) value = do
 -- indicating whether the compare and swap succeded or not. Implies a full
 -- memory barrier.
 casIntAddr :: ByteBuffer -> Int -> Int -> Int -> IO Bool
-casIntAddr bb offset@(I# offset#) (I# old#) (I# new#) = do
+casIntAddr bb offset expected desired = do
   boundCheck bb offset
-  withForeignPtr (bbData bb) $ \(Ptr addr#) ->
-    IO $ \s ->
-      case casIntAddr# addr# offset# old# new# s of
-        (# s', before# #) -> case before# ==# old# of
-          1# -> (# s', True #)
-          0# -> (# s', False #)
-
-casIntAddr# = undefined
+  withForeignPtr (bbData bb) $ \ptr ->
+    casIntPtr (ptr `plusPtr` offset) expected desired
 
 -- | Given a bytebuffer, and offset in machine words, and a value to add,
 -- atomically add the value to the element. Returns the value of the element