1 /* -----------------------------------------------------------------------------
3 * (c) The GHC Team, 1998-2004
7 * This file is written in a subset of C--, extended with various
8 * features specific to GHC. It is compiled by GHC directly. For the
9 * syntax of .cmm files, see the parser in ghc/compiler/cmm/CmmParse.y.
11 * ---------------------------------------------------------------------------*/
14 #include "RaiseAsync.h"
16 import ghczmprim_GHCziBool_True_closure;
18 /* -----------------------------------------------------------------------------
21 A thread can request that asynchronous exceptions not be delivered
22 ("blocked") for the duration of an I/O computation. The primitive
24 blockAsyncExceptions# :: IO a -> IO a
26 is used for this purpose. During a blocked section, asynchronous
27 exceptions may be unblocked again temporarily:
29 unblockAsyncExceptions# :: IO a -> IO a
31 Furthermore, asynchronous exceptions are blocked automatically during
32 the execution of an exception handler. Both of these primitives
33 leave a continuation on the stack which reverts to the previous
34 state (blocked or unblocked) on exit.
36 A thread which wants to raise an exception in another thread (using
37 killThread#) must block until the target thread is ready to receive
38 it. The action of unblocking exceptions in a thread will release all
39 the threads waiting to deliver exceptions to that thread.
41 NB. there's a bug in here. If a thread is inside an
42 unsafePerformIO, and inside blockAsyncExceptions# (there is an
43 unblockAsyncExceptions_ret on the stack), and it is blocked in an
44 interruptible operation, and it receives an exception, then the
45 unsafePerformIO thunk will be updated with a stack object
46 containing the unblockAsyncExceptions_ret frame. Later, when
47 someone else evaluates this thunk, the blocked exception state is
50 -------------------------------------------------------------------------- */
52 INFO_TABLE_RET( stg_unblockAsyncExceptionszh_ret, RET_SMALL )
56 StgTSO_flags(CurrentTSO) = StgTSO_flags(CurrentTSO) &
57 ~(TSO_BLOCKEX::I32|TSO_INTERRUPTIBLE::I32);
59 /* Eagerly raise a blocked exception, if there is one */
60 if (StgTSO_blocked_exceptions(CurrentTSO) != END_TSO_QUEUE) {
62 * We have to be very careful here, as in killThread#, since
63 * we are about to raise an async exception in the current
64 * thread, which might result in the thread being killed.
67 STK_CHK_GEN( WDS(2), R1_PTR, stg_unblockAsyncExceptionszh_ret_info);
70 Sp(0) = stg_gc_unpt_r1_info;
72 (r) = foreign "C" maybePerformBlockedException (MyCapability() "ptr",
73 CurrentTSO "ptr") [R1];
76 if (StgTSO_what_next(CurrentTSO) == ThreadKilled::I16) {
77 jump stg_threadFinished;
80 ASSERT(StgTSO_what_next(CurrentTSO) == ThreadRunGHC::I16);
81 jump %ENTRY_CODE(Sp(0));
87 jump %ENTRY_CODE(Sp(0));
90 INFO_TABLE_RET( stg_blockAsyncExceptionszh_ret, RET_SMALL )
92 StgTSO_flags(CurrentTSO) =
93 StgTSO_flags(CurrentTSO) | TSO_BLOCKEX::I32 | TSO_INTERRUPTIBLE::I32;
96 jump %ENTRY_CODE(Sp(0));
99 blockAsyncExceptionszh_fast
101 /* Args: R1 :: IO a */
102 STK_CHK_GEN( WDS(2)/* worst case */, R1_PTR, blockAsyncExceptionszh_fast);
104 if ((TO_W_(StgTSO_flags(CurrentTSO)) & TSO_BLOCKEX) == 0) {
106 StgTSO_flags(CurrentTSO) =
107 StgTSO_flags(CurrentTSO) | TSO_BLOCKEX::I32 | TSO_INTERRUPTIBLE::I32;
109 /* avoid growing the stack unnecessarily */
110 if (Sp(0) == stg_blockAsyncExceptionszh_ret_info) {
114 Sp(0) = stg_unblockAsyncExceptionszh_ret_info;
122 unblockAsyncExceptionszh_fast
126 /* Args: R1 :: IO a */
127 STK_CHK_GEN( WDS(4), R1_PTR, unblockAsyncExceptionszh_fast);
128 /* 4 words: one for the unblock frame, 3 for setting up the
129 * stack to call maybePerformBlockedException() below.
132 /* If exceptions are already unblocked, there's nothing to do */
133 if ((TO_W_(StgTSO_flags(CurrentTSO)) & TSO_BLOCKEX) != 0) {
135 StgTSO_flags(CurrentTSO) = StgTSO_flags(CurrentTSO) &
136 ~(TSO_BLOCKEX::I32|TSO_INTERRUPTIBLE::I32);
138 /* avoid growing the stack unnecessarily */
139 if (Sp(0) == stg_unblockAsyncExceptionszh_ret_info) {
143 Sp(0) = stg_blockAsyncExceptionszh_ret_info;
146 /* Eagerly raise a blocked exception, if there is one */
147 if (StgTSO_blocked_exceptions(CurrentTSO) != END_TSO_QUEUE) {
149 * We have to be very careful here, as in killThread#, since
150 * we are about to raise an async exception in the current
151 * thread, which might result in the thread being killed.
153 * Now, if we are to raise an exception in the current
154 * thread, there might be an update frame above us on the
155 * stack due to unsafePerformIO. Hence, the stack must
156 * make sense, because it is about to be snapshotted into
160 Sp(2) = stg_ap_v_info;
162 Sp(0) = stg_enter_info;
165 (r) = foreign "C" maybePerformBlockedException (MyCapability() "ptr",
166 CurrentTSO "ptr") [R1];
169 if (StgTSO_what_next(CurrentTSO) == ThreadKilled::I16) {
170 jump stg_threadFinished;
173 ASSERT(StgTSO_what_next(CurrentTSO) == ThreadRunGHC::I16);
174 jump %ENTRY_CODE(Sp(0));
177 /* we'll just call R1 directly, below */
188 asyncExceptionsBlockedzh_fast
191 if ((TO_W_(StgTSO_flags(CurrentTSO)) & TSO_BLOCKEX) != 0) {
200 /* args: R1 = TSO to kill, R2 = Exception */
209 /* Needs 3 words because throwToSingleThreaded uses some stack */
210 STK_CHK_GEN( WDS(3), R1_PTR & R2_PTR, killThreadzh_fast);
213 * We might have killed ourselves. In which case, better be *very*
214 * careful. If the exception killed us, then return to the scheduler.
215 * If the exception went to a catch frame, we'll just continue from
219 if (StgTSO_what_next(target) == ThreadRelocated::I16) {
220 target = StgTSO__link(target);
223 if (target == CurrentTSO) {
225 * So what should happen if a thread calls "throwTo self" inside
226 * unsafePerformIO, and later the closure is evaluated by another
227 * thread? Presumably it should behave as if throwTo just returned,
228 * and then continue from there. See #3279, #3288. This is what
229 * happens: on resumption, we will just jump to the next frame on
230 * the stack, which is the return point for killThreadzh_fast.
233 /* ToDo: what if the current thread is blocking exceptions? */
234 foreign "C" throwToSingleThreaded(MyCapability() "ptr",
235 target "ptr", exception "ptr")[R1,R2];
236 if (StgTSO_what_next(CurrentTSO) == ThreadKilled::I16) {
237 jump stg_threadFinished;
240 ASSERT(StgTSO_what_next(CurrentTSO) == ThreadRunGHC::I16);
241 jump %ENTRY_CODE(Sp(0));
246 out = Sp - WDS(1); /* ok to re-use stack space here */
248 (retcode) = foreign "C" throwTo(MyCapability() "ptr",
254 switch [THROWTO_SUCCESS .. THROWTO_BLOCKED] (retcode) {
256 case THROWTO_SUCCESS: {
257 jump %ENTRY_CODE(Sp(0));
260 case THROWTO_BLOCKED: {
262 // we must block, and call throwToReleaseTarget() before returning
263 jump stg_block_throwto;
269 /* -----------------------------------------------------------------------------
271 -------------------------------------------------------------------------- */
275 /* Catch frames are very similar to update frames, but when entering
276 * one we just pop the frame off the stack and perform the correct
277 * kind of return to the activation record underneath us on the stack.
280 INFO_TABLE_RET(stg_catch_frame, CATCH_FRAME,
281 #if defined(PROFILING)
282 W_ unused1, W_ unused2,
284 W_ unused3, P_ unused4)
286 Sp = Sp + SIZEOF_StgCatchFrame;
287 jump %ENTRY_CODE(Sp(SP_OFF));
290 /* -----------------------------------------------------------------------------
291 * The catch infotable
293 * This should be exactly the same as would be generated by this STG code
295 * catch = {x,h} \n {} -> catch#{x,h}
297 * It is used in deleteThread when reverting blackholes.
298 * -------------------------------------------------------------------------- */
300 INFO_TABLE(stg_catch,2,0,FUN,"catch","catch")
302 R2 = StgClosure_payload(R1,1); /* h */
303 R1 = StgClosure_payload(R1,0); /* x */
309 /* args: R1 = m :: IO a, R2 = handler :: Exception -> IO a */
310 STK_CHK_GEN(SIZEOF_StgCatchFrame + WDS(1), R1_PTR & R2_PTR, catchzh_fast);
312 /* Set up the catch frame */
313 Sp = Sp - SIZEOF_StgCatchFrame;
314 SET_HDR(Sp,stg_catch_frame_info,W_[CCCS]);
316 StgCatchFrame_handler(Sp) = R2;
317 StgCatchFrame_exceptions_blocked(Sp) = TO_W_(StgTSO_flags(CurrentTSO)) & TSO_BLOCKEX;
318 TICK_CATCHF_PUSHED();
320 /* Apply R1 to the realworld token */
326 /* -----------------------------------------------------------------------------
327 * The raise infotable
329 * This should be exactly the same as would be generated by this STG code
331 * raise = {err} \n {} -> raise#{err}
333 * It is used in raisezh_fast to update thunks on the update list
334 * -------------------------------------------------------------------------- */
336 INFO_TABLE(stg_raise,1,0,THUNK_1_0,"raise","raise")
338 R1 = StgThunk_payload(R1,0);
343 no_break_on_exception: W_[1];
346 INFO_TABLE_RET(stg_raise_ret, RET_SMALL, P_ arg1)
350 W_[no_break_on_exception] = 1;
359 /* args : R1 :: Exception */
363 #if defined(PROFILING)
364 /* Debugging tool: on raising an exception, show where we are. */
366 /* ToDo: currently this is a hack. Would be much better if
367 * the info was only displayed for an *uncaught* exception.
369 if (RtsFlags_ProfFlags_showCCSOnException(RtsFlags) != 0::I32) {
370 foreign "C" fprintCCS_stderr(W_[CCCS] "ptr") [];
375 StgTSO_sp(CurrentTSO) = Sp;
376 (frame_type) = foreign "C" raiseExceptionHelper(BaseReg "ptr", CurrentTSO "ptr", exception "ptr") [];
377 Sp = StgTSO_sp(CurrentTSO);
378 if (frame_type == ATOMICALLY_FRAME) {
379 /* The exception has reached the edge of a memory transaction. Check that
380 * the transaction is valid. If not then perhaps the exception should
381 * not have been thrown: re-run the transaction. "trec" will either be
382 * a top-level transaction running the atomic block, or a nested
383 * transaction running an invariant check. In the latter case we
384 * abort and de-allocate the top-level transaction that encloses it
385 * as well (we could just abandon its transaction record, but this makes
386 * sure it's marked as aborted and available for re-use). */
389 trec = StgTSO_trec(CurrentTSO);
390 (r) = foreign "C" stmValidateNestOfTransactions(trec "ptr") [];
391 ("ptr" outer) = foreign "C" stmGetEnclosingTRec(trec "ptr") [];
392 foreign "C" stmAbortTransaction(MyCapability() "ptr", trec "ptr") [];
393 foreign "C" stmFreeAbortedTRec(MyCapability() "ptr", trec "ptr") [];
395 if (outer != NO_TREC) {
396 foreign "C" stmAbortTransaction(MyCapability() "ptr", outer "ptr") [];
397 foreign "C" stmFreeAbortedTRec(MyCapability() "ptr", outer "ptr") [];
400 StgTSO_trec(CurrentTSO) = NO_TREC;
402 // Transaction was valid: continue searching for a catch frame
403 Sp = Sp + SIZEOF_StgAtomicallyFrame;
404 goto retry_pop_stack;
406 // Transaction was not valid: we retry the exception (otherwise continue
407 // with a further call to raiseExceptionHelper)
408 ("ptr" trec) = foreign "C" stmStartTransaction(MyCapability() "ptr", NO_TREC "ptr") [];
409 StgTSO_trec(CurrentTSO) = trec;
410 R1 = StgAtomicallyFrame_code(Sp);
415 // After stripping the stack, see whether we should break here for
416 // GHCi (c.f. the -fbreak-on-exception flag). We do this after
417 // stripping the stack for a reason: we'll be inspecting values in
418 // GHCi, and it helps if all the thunks under evaluation have
419 // already been updated with the exception, rather than being left
421 if (W_[no_break_on_exception] != 0) {
422 W_[no_break_on_exception] = 0;
424 if (TO_W_(CInt[rts_stop_on_exception]) != 0) {
426 // we don't want any further exceptions to be caught,
427 // until GHCi is ready to handle them. This prevents
428 // deadlock if an exception is raised in InteractiveUI,
429 // for exmplae. Perhaps the stop_on_exception flag should
431 W_[rts_stop_on_exception] = 0;
432 ("ptr" ioAction) = foreign "C" deRefStablePtr (W_[rts_breakpoint_io_action] "ptr") [];
435 Sp(5) = stg_raise_ret_info;
436 Sp(4) = stg_noforceIO_info; // required for unregisterised
437 Sp(3) = exception; // the AP_STACK
438 Sp(2) = ghczmprim_GHCziBool_True_closure; // dummy breakpoint info
439 Sp(1) = ghczmprim_GHCziBool_True_closure; // True <=> a breakpoint
441 jump RET_LBL(stg_ap_pppv);
445 if (frame_type == STOP_FRAME) {
447 * We've stripped the entire stack, the thread is now dead.
448 * We will leave the stack in a GC'able state, see the stg_stop_thread
449 * entry code in StgStartup.cmm.
451 Sp = CurrentTSO + TSO_OFFSET_StgTSO_stack
452 + WDS(TO_W_(StgTSO_stack_size(CurrentTSO))) - WDS(2);
453 Sp(1) = exception; /* save the exception */
454 Sp(0) = stg_enter_info; /* so that GC can traverse this stack */
455 StgTSO_what_next(CurrentTSO) = ThreadKilled::I16;
456 SAVE_THREAD_STATE(); /* inline! */
458 jump stg_threadFinished;
461 /* Ok, Sp points to the enclosing CATCH_FRAME or CATCH_STM_FRAME. Pop everything
462 * down to and including this frame, update Su, push R1, and enter the handler.
464 if (frame_type == CATCH_FRAME) {
465 handler = StgCatchFrame_handler(Sp);
467 handler = StgCatchSTMFrame_handler(Sp);
470 /* Restore the blocked/unblocked state for asynchronous exceptions
471 * at the CATCH_FRAME.
473 * If exceptions were unblocked, arrange that they are unblocked
474 * again after executing the handler by pushing an
475 * unblockAsyncExceptions_ret stack frame.
477 * If we've reached an STM catch frame then roll back the nested
478 * transaction we were using.
482 if (frame_type == CATCH_FRAME) {
483 Sp = Sp + SIZEOF_StgCatchFrame;
484 if (StgCatchFrame_exceptions_blocked(frame) == 0) {
486 Sp(0) = stg_unblockAsyncExceptionszh_ret_info;
490 trec = StgTSO_trec(CurrentTSO);
491 ("ptr" outer) = foreign "C" stmGetEnclosingTRec(trec "ptr") [];
492 foreign "C" stmAbortTransaction(MyCapability() "ptr", trec "ptr") [];
493 foreign "C" stmFreeAbortedTRec(MyCapability() "ptr", trec "ptr") [];
494 StgTSO_trec(CurrentTSO) = outer;
495 Sp = Sp + SIZEOF_StgCatchSTMFrame;
498 /* Ensure that async excpetions are blocked when running the handler.
500 StgTSO_flags(CurrentTSO) =
501 StgTSO_flags(CurrentTSO) | TSO_BLOCKEX::I32 | TSO_INTERRUPTIBLE::I32;
503 /* Call the handler, passing the exception value and a realworld
504 * token as arguments.
512 jump RET_LBL(stg_ap_pv);
517 /* Args :: R1 :: Exception */