[Git][ghc/ghc][wip/ghc-debug] 8 commits: Add test for StgTSO decoding (#18405)

Sven Tennie gitlab at gitlab.haskell.org
Sun Jun 28 15:28:12 UTC 2020



Sven Tennie pushed to branch wip/ghc-debug at Glasgow Haskell Compiler / GHC


Commits:
595d363c by Sven Tennie at 2020-06-28T17:24:47+02:00
Add test for StgTSO decoding (#18405)

This makes sure ghc-heap decodes StgTSO and StgStack correctly.

To assert - otherwise dynamic - properties, a new, non-running TSO is
created in create_tso() (create_tso.c).

size is renamed to stack_size to use a dedicated type.

size was already defined as a HalfWord in GenClosure, which is
only equivalent to Word32 on 64bit architectures.

- - - - -
b09b0816 by Sven Tennie at 2020-06-28T17:27:15+02:00
Revert changes to TSO.h

The memory layout of StgTSO isn't significant anymore as we decode it
with hsc2hs.

(Of course the basic structure of a closure with an info table must be
still in place, but that's not touched by this commit.)

- - - - -
5d3904e2 by Sven Tennie at 2020-06-28T17:27:15+02:00
Add some documentation

- - - - -
dc93991c by Sven Tennie at 2020-06-28T17:27:15+02:00
Add/update documentation for FindPtrCb

- - - - -
109bdf57 by Sven Tennie at 2020-06-28T17:27:15+02:00
Adjust type of getClosureX to type of getClosureDataX (#18405)

After a rebase the compiler complained:

libraries/ghc-heap/GHC/Exts/Heap.hs:89:23: error:
    • Couldn't match type: a -> IO (Ptr StgInfoTable, [Word], [b])
                     with: forall c. c -> IO (Ptr StgInfoTable, [Word], [b])
      Expected: (forall c. c -> IO (Ptr StgInfoTable, [Word], [b]))
                -> a -> IO (GenClosure b)
        Actual: (a -> IO (Ptr StgInfoTable, [Word], [b]))
                -> a -> IO (GenClosure b)
    • In the expression: getClosureX
      In an equation for ‘getClosureDataX’: getClosureDataX = getClosureX
      In the instance declaration for ‘HasHeapRep a’
    • Relevant bindings include
        getClosureDataX :: (forall c.
                            c -> IO (Ptr StgInfoTable, [Word], [b]))
                           -> a -> IO (GenClosure b)
          (bound at libraries/ghc-heap/GHC/Exts/Heap.hs:89:5)
   |
89 |     getClosureDataX = getClosureX
   |                       ^^^^^^^^^^^
)

- - - - -
5f47e2ed by Sven Tennie at 2020-06-28T17:27:15+02:00
Add test for rts_pause and rts_unpause (#18405)

- - - - -
8d8410e9 by Sven Tennie at 2020-06-28T17:27:15+02:00
Add test list_threads_and_misc_roots (#18405)

It uses rts_listThreads() and rts_listMiscRoots().

- - - - -
32a06874 by Sven Tennie at 2020-06-28T17:27:15+02:00
Introduce rts_isPaused() (#18405)

Some operations are only save when the RTS is paused. This predicate
helps to make such checks.

- - - - -


19 changed files:

- includes/RtsAPI.h
- includes/rts/storage/TSO.h
- libraries/ghc-heap/GHC/Exts/Heap.hs
- libraries/ghc-heap/GHC/Exts/Heap/ClosureTypes.hs
- libraries/ghc-heap/GHC/Exts/Heap/Closures.hs
- libraries/ghc-heap/tests/all.T
- + libraries/ghc-heap/tests/create_tso.c
- + libraries/ghc-heap/tests/create_tso.h
- + libraries/ghc-heap/tests/list_threads_and_misc_roots.hs
- + libraries/ghc-heap/tests/list_threads_and_misc_roots_c.c
- + libraries/ghc-heap/tests/list_threads_and_misc_roots_c.h
- + libraries/ghc-heap/tests/tso_and_stack_closures.hs
- rts/Heap.c
- rts/Printer.c
- rts/RtsAPI.c
- + testsuite/tests/rts/ghc-debug/all.T
- + testsuite/tests/rts/ghc-debug/pause_and_unpause.hs
- + testsuite/tests/rts/ghc-debug/pause_and_unpause_thread.c
- + testsuite/tests/rts/ghc-debug/pause_and_unpause_thread.h


Changes:

=====================================
includes/RtsAPI.h
=====================================
@@ -492,14 +492,27 @@ typedef struct RtsPaused_ {
     Capability *capabilities;
 } RtsPaused;
 
+// Halt execution of all Haskell threads.
+// It is different to rts_lock because it pauses all capabilities. rts_lock
+// only pauses a single capability.
+// rts_pause() and rts_unpause() have to be executed from the same OS thread
+// (i.e. myTask() must stay the same).
 RtsPaused rts_pause (void);
+
+// Counterpart of rts_pause: Continue from a pause.
+// rts_pause() and rts_unpause() have to be executed from the same OS thread
+// (i.e. myTask() must stay the same).
 void rts_unpause (RtsPaused paused);
 
-// List all live threads. Must be done while RTS is paused.
+// Tells the current state of the RTS regarding rts_pause() and rts_unpause().
+bool rts_isPaused(void);
+
+// List all live threads. Must be done while RTS is paused (see rts_pause()).
 typedef void (*ListThreadsCb)(void *user, StgTSO *);
 void rts_listThreads(ListThreadsCb cb, void *user);
 
-// List all non-thread GC roots. Must be done while RTS is paused.
+// List all non-thread GC roots. Must be done while RTS is paused (see
+// rts_pause()).
 typedef void (*ListRootsCb)(void *user, StgClosure *);
 void rts_listMiscRoots(ListRootsCb cb, void *user);
 


=====================================
includes/rts/storage/TSO.h
=====================================
@@ -107,22 +107,6 @@ typedef struct StgTSO_ {
      */
     struct StgStack_       *stackobj;
 
-    struct InCall_ *bound;
-    struct Capability_ *cap;
-
-    struct StgTRecHeader_ *trec; /* STM transaction record */
-
-    /*
-     * A list of threads blocked on this TSO waiting to throw exceptions.
-     */
-    struct MessageThrowTo_ *blocked_exceptions;
-
-    /*
-     * A list of StgBlockingQueue objects, representing threads
-     * blocked on thunks that are under evaluation by this thread.
-     */
-    struct StgBlockingQueue_ *bq;
-
     /*
      * The tso->dirty flag indicates that this TSO's stack should be
      * scanned during garbage collection.  It also indicates that this
@@ -144,6 +128,21 @@ typedef struct StgTSO_ {
     StgThreadID             id;
     StgWord32               saved_errno;
     StgWord32               dirty;          /* non-zero => dirty */
+    struct InCall_*         bound;
+    struct Capability_*     cap;
+
+    struct StgTRecHeader_ * trec;       /* STM transaction record */
+
+    /*
+     * A list of threads blocked on this TSO waiting to throw exceptions.
+    */
+    struct MessageThrowTo_ * blocked_exceptions;
+
+    /*
+     * A list of StgBlockingQueue objects, representing threads
+     * blocked on thunks that are under evaluation by this thread.
+    */
+    struct StgBlockingQueue_ *bq;
 
     /*
      * The allocation limit for this thread, which is updated as the


=====================================
libraries/ghc-heap/GHC/Exts/Heap.hs
=====================================
@@ -79,9 +79,11 @@ class HasHeapRep (a :: TYPE rep) where
     -- 'Word' for "raw" usage of pointers.
     getClosureDataX ::
         (forall c . c -> IO (Ptr StgInfoTable, [Word], [b]))
-        -- ^ Helper function to get info table, memory and pointers of the closure
+        -- ^ Helper function to get info table, memory and pointers of the
+        -- closure. The order of @[b]@ is significant and determined by
+        -- @collect_pointers()@ in @rts/Heap.c at .
         -> a -- ^ Closure to decode
-        -> IO (GenClosure b) -- Heap representation of the closure
+        -> IO (GenClosure b) -- ^ Heap representation of the closure
 
 instance HasHeapRep (a :: TYPE 'LiftedRep) where
     getClosureDataX = getClosureX
@@ -150,14 +152,28 @@ getClosureData :: forall rep (a :: TYPE rep) . HasHeapRep a => a -> IO Closure
 getClosureData = getClosureDataX getClosureRaw
 
 
--- | This function returns a parsed heap representation of the argument _at
--- this moment_, even if it is unevaluated or an indirection or other exotic
--- stuff.  Beware when passing something to this function, the same caveats as
--- for 'asBox' apply.
-getClosureX :: forall a b . (a -> IO (Ptr StgInfoTable, [Word], [b]))
-            -> a -> IO (GenClosure b)
+-- | This function returns a parsed heap representation ('GenClosure') of the
+-- closure _at this moment_, even if it is unevaluated or an indirection or
+-- other exotic stuff. Beware when passing something to this function, the same
+-- caveats as for 'asBox' apply.
+--
+-- Inside a GHC context 'b' is usually a 'GHC.Exts.Heap.Closures.Box'
+-- containing a thunk or an evaluated heap object. Outside it can be a
+-- 'Word' for "raw" usage of pointers.
+--
+-- 'get_closure_raw' should provide low level details of the closure's heap
+-- respresentation. The order of @[b]@ is significant and determined by
+-- @collect_pointers()@ in @rts/Heap.c at .
+--
+-- For most use cases 'getClosureData' is an easier to use alternative.
+getClosureX :: forall a b.
+            (forall c . c -> IO (Ptr StgInfoTable, [Word], [b]))
+            -- ^ Helper function to get info table, memory and pointers of the
+            -- closure
+            -> a -- ^ Closure to decode
+            -> IO (GenClosure b) -- ^ Heap representation of the closure
 getClosureX get_closure_raw x = do
-    (iptr, wds, pts) <- get_closure_raw x
+    (iptr, wds, pts) <- get_closure_raw (unsafeCoerce# x)
     itbl <- peekItbl iptr
     -- The remaining words after the header
     let rawWds = drop (closureTypeHeaderSize (tipe itbl)) wds
@@ -341,7 +357,7 @@ getClosureX get_closure_raw x = do
 
                 pure $ StackClosure
                     { info = itbl
-                    , size = FFIClosures.stack_size fields
+                    , stack_size = FFIClosures.stack_size fields
                     , stack_dirty = FFIClosures.stack_dirty fields
                     , stackPointer = (pts !! 0)
                     , stack  = FFIClosures.stack fields


=====================================
libraries/ghc-heap/GHC/Exts/Heap/ClosureTypes.hs
=====================================
@@ -81,7 +81,7 @@ data ClosureType
     | SMALL_MUT_ARR_PTRS_FROZEN_CLEAN
     | COMPACT_NFDATA
     | N_CLOSURE_TYPES
- deriving (Enum, Eq, Ord, Show, Generic)
+ deriving (Enum, Eq, Ord, Show, Generic, Bounded)
 
 -- | Return the size of the closures header in words
 closureTypeHeaderSize :: ClosureType -> Int


=====================================
libraries/ghc-heap/GHC/Exts/Heap/Closures.hs
=====================================
@@ -285,7 +285,7 @@ data GenClosure b
   -- Representation of StgStack: The 'tsoStack' of a 'TSOClosure'.
   | StackClosure
      { info :: !StgInfoTable
-     , size :: !Word32 -- ^ stack size in *words*
+     , stack_size :: !Word32 -- ^ stack size in *words*
      , stack_dirty :: !Word8 -- ^ non-zero => dirty
 #if __GLASGOW_HASKELL__ >= 811
      , stack_marking :: Word8


=====================================
libraries/ghc-heap/tests/all.T
=====================================
@@ -36,3 +36,16 @@ test('closure_size_noopt',
      ],
      compile_and_run, [''])
 
+test('tso_and_stack_closures',
+     [extra_files(['create_tso.c','create_tso.h']),
+      ignore_stdout,
+      ignore_stderr
+     ],
+     multi_compile_and_run, ['tso_and_stack_closures', [('create_tso.c','')], ''])
+
+test('list_threads_and_misc_roots',
+     [extra_files(['list_threads_and_misc_roots_c.c','list_threads_and_misc_roots_c.h']),
+      ignore_stdout,
+      ignore_stderr
+     ],
+     multi_compile_and_run, ['list_threads_and_misc_roots', [('list_threads_and_misc_roots_c.c','')], '-threaded'])


=====================================
libraries/ghc-heap/tests/create_tso.c
=====================================
@@ -0,0 +1,10 @@
+#include "Rts.h"
+#include "RtsAPI.h"
+
+StgTSO* create_tso(){
+    HaskellObj trueClosure = rts_mkBool(&MainCapability, 1);
+
+    StgTSO * tso = createGenThread(&MainCapability, 500U, trueClosure);
+
+    return tso;
+}


=====================================
libraries/ghc-heap/tests/create_tso.h
=====================================
@@ -0,0 +1,3 @@
+#include "RtsAPI.h"
+
+StgTSO* create_tso();


=====================================
libraries/ghc-heap/tests/list_threads_and_misc_roots.hs
=====================================
@@ -0,0 +1,72 @@
+{-# LANGUAGE MagicHash #-}
+
+import Foreign.Ptr
+import Foreign.Marshal.Array
+import GHC.IORef
+import Control.Concurrent
+import GHC.Exts.Heap
+import GHC.Exts
+
+
+-- Invent a type to bypass the type constraints of getClosureData.
+-- Infact this will be a Word#, that is directly given to unpackClosure#
+-- (which is a primop that expects a pointer to a closure).
+data FoolClosure
+
+foreign import ccall safe "list_threads_and_misc_roots_c.h listThreadsAndMiscRoots"
+    listThreadsAndMiscRoots_c :: IO ()
+
+foreign import ccall safe "list_threads_and_misc_roots_c.h getTSOCount"
+    getTSOCount_c :: IO Int
+
+foreign import ccall safe "list_threads_and_misc_roots_c.h getTSOs"
+    getTSOs_c :: IO (Ptr Word)
+
+foreign import ccall safe "list_threads_and_misc_roots_c.h getMiscRootsCount"
+    getMiscRootsCount_c :: IO Int
+
+foreign import ccall safe "list_threads_and_misc_roots_c.h getMiscRoots"
+    getMiscRoots_c :: IO (Ptr Word)
+
+main :: IO ()
+main = do
+    listThreadsAndMiscRoots_c
+
+    tsoCount <- getTSOCount_c
+    tsos <- getTSOs_c
+    tsoList <- peekArray tsoCount tsos
+    tsoClosures <- mapM createClosure tsoList
+    assertEqual tsoCount $ length tsoClosures
+    mapM (assertEqual TSO) $ map (tipe . info) tsoClosures
+
+    miscRootsCount <- getMiscRootsCount_c
+    miscRoots <- getMiscRoots_c
+    miscRootsList <- peekArray miscRootsCount miscRoots
+    heapClosures <- mapM createClosure miscRootsList
+    assertEqual miscRootsCount $ length heapClosures
+    -- Regarding the type system, this always has to be True, but we want to
+    -- force evaluation / de-serialization with a simple check.
+    mapM assertIsClosureType $ map (tipe . info) heapClosures
+
+    return ()
+
+createClosure :: Word -> IO (GenClosure Box)
+createClosure tsoPtr = do
+    let wPtr = unpackWord# tsoPtr
+    getClosureData ((unsafeCoerce# wPtr) :: FoolClosure)
+
+unpackWord# :: Word -> Word#
+unpackWord# (W# w#) = w#
+
+assertEqual :: (Show a, Eq a) => a -> a -> IO ()
+assertEqual a b
+    | a /= b = error (show a ++ " /= " ++ show b)
+    | otherwise = return ()
+
+assertIsClosureType :: ClosureType -> IO ()
+assertIsClosureType t
+    | t `elem` enumerate = return ()
+    | otherwise = error (show t ++ " not in  " ++ show enumerate)
+    where
+        enumerate :: [ClosureType]
+        enumerate = [minBound..maxBound]


=====================================
libraries/ghc-heap/tests/list_threads_and_misc_roots_c.c
=====================================
@@ -0,0 +1,54 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include "Rts.h"
+#include "RtsAPI.h"
+#include "list_threads_and_misc_roots_c.h"
+
+int tsoCount = 0;
+StgTSO** tsos;
+
+int miscRootsCount = 0;
+StgClosure** miscRoots;
+
+void collectTSOsCallback(void *user, StgTSO* tso){
+    tsoCount++;
+    tsos = realloc(tsos, sizeof(StgTSO*) * tsoCount);
+    tsos[tsoCount - 1] = tso;
+}
+
+void collectMiscRootsCallback(void *user, StgClosure* closure){
+    miscRootsCount++;
+    miscRoots = realloc(miscRoots, sizeof(StgClosure*) * miscRootsCount);
+    miscRoots[miscRootsCount - 1] = closure;
+}
+
+void* listThreads_thread(void* unused){
+    RtsPaused paused = rts_pause();
+    rts_listThreads(&collectTSOsCallback, NULL);
+    rts_listMiscRoots(&collectMiscRootsCallback, NULL);
+    rts_unpause(paused);
+
+    return NULL;
+}
+
+void listThreadsAndMiscRoots(void){
+    pthread_t threadId;
+    pthread_create(&threadId, NULL, &listThreads_thread, NULL);
+    pthread_join(threadId, NULL);
+}
+
+int getTSOCount(void){
+    return tsoCount;
+}
+
+StgTSO** getTSOs(void){
+    return tsos;
+}
+
+int getMiscRootsCount(void){
+    return miscRootsCount;
+}
+
+StgClosure** getMiscRoots(void){
+    return miscRoots;
+}


=====================================
libraries/ghc-heap/tests/list_threads_and_misc_roots_c.h
=====================================
@@ -0,0 +1,11 @@
+#include "Rts.h"
+
+void listThreadsAndMiscRoots(void);
+
+int getTSOCount(void);
+
+StgTSO** getTSOs(void);
+
+int getMiscRootsCount(void);
+
+StgClosure** getMiscRoots(void);


=====================================
libraries/ghc-heap/tests/tso_and_stack_closures.hs
=====================================
@@ -0,0 +1,77 @@
+{-# LANGUAGE ForeignFunctionInterface, MagicHash, CPP, BangPatterns #-}
+
+import Foreign
+import Foreign.C.Types
+import GHC.Exts.Heap
+import GHC.Exts
+
+import GHC.Word
+
+#include "ghcconfig.h"
+#include "rts/Constants.h"
+
+foreign import ccall unsafe "create_tso.h create_tso"
+    c_create_tso:: IO Word
+
+-- Invent a type to bypass the type constraints of getClosureData.
+-- Infact this will be a Word#, that is directly given to unpackClosure#
+-- (which is a primop that expects a pointer to a closure).
+data FoolStgTSO
+
+-- We can make some assumptions about the - otherwise dynamic - properties of
+-- StgTSO and StgStack, because a new, non-running TSO is created with
+-- create_tso() (create_tso.c).create_tso
+main :: IO ()
+main = do
+    tso <- createTSOClosure
+    assertEqual (what_next tso) ThreadRunGHC
+    assertEqual (why_blocked tso) NotBlocked
+    assertEqual (saved_errno tso) 0
+
+    print $ "tso : "++ show tso
+
+    -- The newly created TSO should be on the end of the run queue.
+    let !_linkBox = _link tso
+    _linkClosure <- getBoxedClosureData _linkBox
+    assertEqual (name _linkClosure) "END_TSO_QUEUE"
+
+    let !global_linkBox = global_link tso
+    globalLinkClosure <- getBoxedClosureData global_linkBox
+    assertEqual (getClosureType globalLinkClosure) TSO
+
+    let !stackBox = tsoStack tso
+    stackClosure <- getBoxedClosureData stackBox
+    assertEqual (getClosureType stackClosure) STACK
+
+    let !stackPointerBox = stackPointer stackClosure
+    stackPointerClosure <- getBoxedClosureData stackPointerBox
+    assertEqual (getClosureType stackPointerClosure) RET_SMALL
+
+    let !trecBox = trec tso
+    trecClosure <- getBoxedClosureData trecBox
+    assertEqual (name trecClosure) "NO_TREC"
+
+    let !blockedExceptionsBox = blocked_exceptions tso
+    blockedExceptionsClosure <- getBoxedClosureData blockedExceptionsBox
+    assertEqual (name blockedExceptionsClosure) "END_TSO_QUEUE"
+
+    let !bqBox = bq tso
+    bqClosure <- getBoxedClosureData bqBox
+    assertEqual (name bqClosure) "END_TSO_QUEUE"
+
+createTSOClosure :: IO (GenClosure Box)
+createTSOClosure = do
+    ptr <- c_create_tso
+    let wPtr = unpackWord# ptr
+    getClosureData ((unsafeCoerce# wPtr) :: FoolStgTSO)
+
+unpackWord# :: Word -> Word#
+unpackWord# (W# w#) = w#
+
+assertEqual :: (Show a, Eq a) => a -> a -> IO ()
+assertEqual a b
+  | a /= b = error (show a ++ " /= " ++ show b)
+  | otherwise = return ()
+
+getClosureType :: GenClosure b -> ClosureType
+getClosureType = tipe . info


=====================================
rts/Heap.c
=====================================
@@ -247,6 +247,13 @@ static StgWord collect_pointers(StgClosure *closure, StgWord size, StgClosure *p
 }
 
 StgArrBytes *heap_view_closurePtrsAsWords(Capability *cap, StgClosure *closure) {
+    if(!rts_isPaused()){
+        errorBelch("Warning: "
+            "The RTS must be paused (see rts_pause()) to inspect it's heap!");
+
+        return NULL;
+    }
+
     ASSERT(LOOKS_LIKE_CLOSURE_PTR(closure));
 
     StgWord size = heap_view_closureSize(closure);


=====================================
rts/Printer.c
=====================================
@@ -852,10 +852,12 @@ extern void DEBUG_LoadSymbols( const char *name STG_UNUSED )
 
 #endif /* USING_LIBBFD */
 
-// findPtr takes a callback so external tools such as ghc-debug can invoke it
-// and intercept the intermediate results. When findPtr successfully finds
-// a closure containing an address then the callback is called on the address
-// of that closure. The `StgClosure` argument is an untagged closure pointer.
+// findPtrCb takes a callback of type FindPtrCb, so external tools (such as
+// ghc-debug) can invoke it and intercept the intermediate results.
+// When findPtrCb successfully finds a closure containing an address then the
+// callback is called on the address of that closure.
+// The `StgClosure` argument is an untagged closure pointer.
+// `user` points to any data provided by the caller. It's not used internally.
 typedef void (*FindPtrCb)(void *user, StgClosure *);
 
 void findPtr(P_ p, int);                /* keep gcc -Wall happy */
@@ -949,11 +951,14 @@ findPtr_gen(FindPtrCb cb, void *user, P_ p, int follow)
   }
 }
 
-void
-findPtr(P_ p, int follow){
+// Special case of findPtrCb: Uses a default callback, that prints the closure
+// pointed to by p.
+void findPtr(P_ p, int follow){
   findPtr_gen(&findPtr_default_callback, NULL, p, follow);
 }
 
+// Call cb on the closure pointed to by p.
+// FindPtrCb is documented where it's defined.
 void findPtrCb(FindPtrCb cb, void* user, P_ p){
   findPtr_gen(cb, user, p, 0);
 }


=====================================
rts/RtsAPI.c
=====================================
@@ -651,6 +651,8 @@ static bool rts_paused = false;
 // Halt execution of all Haskell threads.
 // It is different to rts_lock because it pauses all capabilities. rts_lock
 // only pauses a single capability.
+// rts_pause() and rts_unpause() have to be executed from the same OS thread
+// (i.e. myTask() must stay the same).
 RtsPaused rts_pause (void)
 {
     struct RtsPaused_ paused;
@@ -661,6 +663,8 @@ RtsPaused rts_pause (void)
 }
 
 // Counterpart of rts_pause: Continue from a pause.
+// rts_pause() and rts_unpause() have to be executed from the same OS thread
+// (i.e. myTask() must stay the same).
 void rts_unpause (RtsPaused paused)
 {
     rts_paused = false;
@@ -668,6 +672,12 @@ void rts_unpause (RtsPaused paused)
     freeTask(paused.pausing_task);
 }
 
+// Tells the current state of the RTS regarding rts_pause() and rts_unpause().
+bool rts_isPaused(void)
+{
+    return rts_paused;
+}
+
 // Call cb for all StgTSOs. *user is a user defined payload to cb. It's not
 // used by the RTS.
 // rts_listThreads should only be called when the RTS is paused, i.e. rts_pause
@@ -728,6 +738,13 @@ void rts_unpause (RtsPaused paused STG_UNUSED)
                "multithreaded RTS.");
 }
 
+bool rts_isPaused(void)
+{
+    errorBelch("Warning: (Un-) Pausing the RTS is only possible for "
+               "multithreaded RTS.");
+    return false;
+}
+
 
 void rts_listThreads(ListThreadsCb cb STG_UNUSED, void *user STG_UNUSED)
 {


=====================================
testsuite/tests/rts/ghc-debug/all.T
=====================================
@@ -0,0 +1,6 @@
+test('pause_and_unpause',
+     [ extra_files(['pause_and_unpause_thread.c','pause_and_unpause_thread.h']),
+      ignore_stdout,
+      ignore_stderr
+     ],
+     multi_compile_and_run, ['pause_and_unpause', [('pause_and_unpause_thread.c','')], '-threaded'])


=====================================
testsuite/tests/rts/ghc-debug/pause_and_unpause.hs
=====================================
@@ -0,0 +1,73 @@
+{-# LANGUAGE ForeignFunctionInterface #-}
+
+import Data.Word
+import Data.IORef
+import GHC.Clock
+import Control.Concurrent
+import Foreign.C.Types
+import System.Mem
+import Control.Monad
+
+foreign import ccall safe "pause_and_unpause_thread.h pauseAndUnpause"
+    pauseAndUnpause_c :: IO ()
+
+foreign import ccall safe "pause_and_unpause_thread.h getUnixTime"
+    getUnixTime_c :: IO CTime
+
+foreign import ccall safe "pause_and_unpause_thread.h getPauseBegin"
+    getPauseBegin_c :: IO CTime
+
+foreign import ccall safe "pause_and_unpause_thread.h getPauseEnd"
+    getPauseEnd_c :: IO CTime
+
+clockEachSecond :: IORef [CTime] -> IO ()
+clockEachSecond ref = forever $ do
+  time <- getUnixTime_c
+  timesList <- readIORef ref
+  writeIORef ref $ time : timesList
+
+  sleepSeconds 1
+
+{- To show that rts_pause() and rts_unpause() work, clockEachSecond adds the
+current unix time to a list (once per Second). pauseAndUnpause_c stops the RTS
+for 5 Seconds. Thus there's an invariant that there should be no timestamp in
+the list that is in this 5 Seconds wide timeframe, which is defined by
+getPauseBegin_c and getPauseEnd_c. -}
+main :: IO ()
+main = do
+    ref <- newIORef []
+    forkIO $ clockEachSecond ref
+
+    sleepSeconds 3
+
+    pauseAndUnpause_c
+
+    -- This seems to sleep for 8 - 5 Seconds. That's strange, but should be
+    -- good enough for this test.
+    -- 5 Seconds is the time the whole RTS is paused. But I (Sven) don't
+    -- understand how this relates.
+    sleepSeconds 8
+
+    times <- readIORef ref
+
+    pauseBegin <- getPauseBegin_c
+    pauseEnd <- getPauseEnd_c
+    filter (\t -> pauseBegin < t && t < pauseEnd) times `shouldBe` []
+    filter (\t -> t <= pauseBegin) times `shouldNotBe` []
+    filter (\t -> t >= pauseEnd) times `shouldNotBe` []
+
+    return ()
+
+sleepSeconds :: Int -> IO ()
+sleepSeconds t = threadDelay $ oneSecondInMicroSeconds * t
+
+oneSecondInMicroSeconds :: Int
+oneSecondInMicroSeconds = 1000000
+
+shouldBe :: (Eq a, Show a) => a -> a -> IO ()
+shouldBe x y =
+  unless (x == y) $ fail $ show x ++ " is not equal to " ++ show y
+
+shouldNotBe :: (Eq a, Show a) => a -> a -> IO ()
+shouldNotBe x y =
+  unless (x /= y) $ fail $ show x ++ " is equal to " ++ show y


=====================================
testsuite/tests/rts/ghc-debug/pause_and_unpause_thread.c
=====================================
@@ -0,0 +1,45 @@
+#include <pthread.h>
+#include <time.h>
+#include <unistd.h>
+#include "pause_and_unpause_thread.h"
+#include "Rts.h"
+#include "RtsAPI.h"
+
+#include <stdio.h>
+
+struct PauseTimestamps timestamps = {0, 0};
+
+void* pauseAndUnpause_thread(void* unused){
+    RtsPaused r_paused = rts_pause();
+
+    if(!rts_isPaused()) {
+        errorBelch("Expected the RTS to be paused.");
+        exit(1);
+    }
+
+    timestamps.begin = time(NULL);
+    sleep(5);
+    timestamps.end = time(NULL);
+
+    rts_unpause(r_paused);
+
+    return NULL;
+}
+
+void pauseAndUnpause(void){
+    pthread_t threadId;
+    pthread_create(&threadId, NULL, &pauseAndUnpause_thread, NULL);
+    pthread_detach(threadId);
+}
+
+time_t getPauseBegin(void) {
+    return timestamps.begin;
+}
+
+time_t getPauseEnd(void) {
+    return timestamps.end;
+}
+
+time_t getUnixTime(void){
+    return time(NULL);
+}


=====================================
testsuite/tests/rts/ghc-debug/pause_and_unpause_thread.h
=====================================
@@ -0,0 +1,11 @@
+#include <time.h>
+
+struct PauseTimestamps{
+    time_t begin;
+    time_t end;
+};
+
+void pauseAndUnpause(void);
+time_t getPauseBegin(void);
+time_t getPauseEnd(void);
+time_t getUnixTime(void);



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/f1b38f6ba2124210127b2629fdc08a27ddc313ad...32a068747a3b45564259a9151d7c6f3398b548cc

-- 
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/f1b38f6ba2124210127b2629fdc08a27ddc313ad...32a068747a3b45564259a9151d7c6f3398b548cc
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