diff options
Diffstat (limited to 'rts/RtsAPI.c')
| -rw-r--r-- | rts/RtsAPI.c | 184 |
1 files changed, 177 insertions, 7 deletions
diff --git a/rts/RtsAPI.c b/rts/RtsAPI.c index 1d8e0bc1c8..bf58f53735 100644 --- a/rts/RtsAPI.c +++ b/rts/RtsAPI.c @@ -423,6 +423,10 @@ createStrictIOThread(Capability *cap, W_ stack_size, StgClosure *closure) /* ---------------------------------------------------------------------------- Evaluating Haskell expressions + + The running task (capability->running_task) must be bounded i.e. you must + call newBoundTask() before calling these functions. Note that rts_lock() and + rts_pause() both call newBoundTask(). ------------------------------------------------------------------------- */ void rts_eval (/* inout */ Capability **cap, @@ -597,12 +601,23 @@ rts_getSchedStatus (Capability *cap) return cap->running_task->incall->rstat; } +#if defined(THREADED_RTS) +// The task that paused the RTS. The rts_pausing_task variable is owned by the +// task that owns all capabilities (there is at most one such task). +// +// It's possible to remove this and instead define the pausing task as whichever +// task owns all capabilities, but using `rts_pausing_task` leads to marginally +// cleaner code/API and better error messages. +Task * rts_pausing_task = NULL; +#endif + Capability * rts_lock (void) { Capability *cap; Task *task; + // Bound the current task. This is necessary to support rts_eval* functions. task = newBoundTask(); if (task->running_finalizers) { @@ -613,6 +628,14 @@ rts_lock (void) stg_exit(EXIT_FAILURE); } +#if defined(THREADED_RTS) + if (rts_pausing_task == task) { + errorBelch("error: rts_lock: The RTS is already paused by this thread.\n" + " There is no need to call rts_lock if you have already called rts_pause."); + stg_exit(EXIT_FAILURE); + } +#endif + cap = NULL; waitForCapability(&cap, task); @@ -640,21 +663,21 @@ rts_unlock (Capability *cap) task = cap->running_task; ASSERT_FULL_CAPABILITY_INVARIANTS(cap,task); - // Now release the Capability. With the capability released, GC - // may happen. NB. does not try to put the current Task on the + // Now release the Capability. With the capability released, GC + // may happen. NB. does not try to put the current Task on the // worker queue. - // NB. keep cap->lock held while we call boundTaskExiting(). This + // NB. keep cap->lock held while we call exitMyTask(). This // is necessary during shutdown, where we want the invariant that // after shutdownCapability(), all the Tasks associated with the - // Capability have completed their shutdown too. Otherwise we - // could have boundTaskExiting()/workerTaskStop() running at some + // Capability have completed their shutdown too. Otherwise we + // could have exitMyTask()/workerTaskStop() running at some // random point in the future, which causes problems for // freeTaskManager(). ACQUIRE_LOCK(&cap->lock); releaseCapability_(cap,false); // Finally, we can release the Task to the free list. - boundTaskExiting(task); + exitMyTask(); RELEASE_LOCK(&cap->lock); if (task->incall == NULL) { @@ -665,6 +688,153 @@ rts_unlock (Capability *cap) } } +struct PauseToken_ { + Capability *capability; +}; + +Capability *pauseTokenCapability(PauseToken *pauseToken) { + return pauseToken->capability; +} + +#if defined(THREADED_RTS) + +// See Note [Locking and Pausing the RTS] +PauseToken *rts_pause (void) +{ + // It is an error if this thread already paused the RTS. If another + // thread has paused the RTS, then rts_pause will block until rts_resume is + // called (and compete with other threads calling rts_pause). The blocking + // behavior is implied by the use of `stopAllCapabilities`. + Task * task = getMyTask(); + if (rts_pausing_task == task) + { + // This task already pased the RTS. + errorBelch("error: rts_pause: This thread has already paused the RTS."); + stg_exit(EXIT_FAILURE); + } + + // The current task must not own a capability. This is true for non-worker + // threads e.g. when making a safe FFI call. We allow pausing when + // `task->cap->running_task != task` because the capability can be taken by + // other capabilities. Doing this check is justified because rts_pause is a + // user facing function and we want good error reporting. We also don't + // expect rts_pause to be performance critical. + if (task->cap && task->cap->running_task == task) + { + // This task owns a capability (and it can't be taken by other capabilities). + errorBelch(task->cap->in_haskell + ? ("error: rts_pause: attempting to pause via an unsafe FFI call.\n" + " Perhaps a 'foreign import unsafe' should be 'safe'?") + : ("error: rts_pause: attempting to pause from a Task that owns a capability.\n" + " Have you already acquired a capability e.g. with rts_lock?")); + stg_exit(EXIT_FAILURE); + } + + // Bound the current task. This is necessary to support rts_eval* functions. + task = newBoundTask(); + stopAllCapabilities(NULL, task); + + // Now we own all capabilities so we own rts_pausing_task and may set it. + rts_pausing_task = task; + + PauseToken *token = malloc(sizeof(PauseToken)); + token->capability = task->cap; + return token; +} + +static void assert_isPausedOnMyTask(const char *functionName); + +// See Note [Locking and Pausing the RTS]. The pauseToken argument is here just +// for symmetry with rts_pause and to match the pattern of rts_lock/rts_unlock. +void rts_resume (PauseToken *pauseToken) +{ + assert_isPausedOnMyTask("rts_resume"); + Task * task = getMyTask(); + + // Now we own all capabilities so we own rts_pausing_task and may write to + // it. + rts_pausing_task = NULL; + + // releaseAllCapabilities will not block because the current task owns all + // capabilities. + releaseAllCapabilities(n_capabilities, NULL, task); + exitMyTask(); + free(pauseToken); +} + +// See RtsAPI.h +bool rts_isPaused(void) +{ + return rts_pausing_task != NULL; +} + +// Check that the rts_pause was called on this thread/task and this thread owns +// all capabilities. If not, outputs an error and exits with EXIT_FAILURE. +static void assert_isPausedOnMyTask(const char *functionName) +{ + Task * task = getMyTask(); + if (rts_pausing_task == NULL) + { + errorBelch ( + "error: %s: the rts is not paused. Did you forget to call rts_pause?", + functionName); + stg_exit(EXIT_FAILURE); + } + + if (task != rts_pausing_task) + { + // We don't have ownership of rts_pausing_task, so it may have changed + // just after the above read. Still, we are garanteed that + // rts_pausing_task won't be set to the current task (because the + // current task is here now!), so the error messages are still correct. + errorBelch ( + "error: %s: called from a different OS thread than rts_pause.", + functionName); + + stg_exit(EXIT_FAILURE); + } + + // Check that we own all capabilities. + for (unsigned int i = 0; i < n_capabilities; i++) + { + Capability *cap = capabilities[i]; + if (cap->running_task != task) + { + errorBelch ( + "error: %s: the pausing thread does not own all capabilities.\n" + " Have you manually released a capability after calling rts_pause?", + functionName); + stg_exit(EXIT_FAILURE); + } + } +} + + +#else +PauseToken GNU_ATTRIBUTE(__noreturn__) +*rts_pause (void) +{ + errorBelch("Warning: Pausing the RTS is only possible for " + "multithreaded RTS."); + stg_exit(EXIT_FAILURE); +} + +void GNU_ATTRIBUTE(__noreturn__) +rts_resume (PauseToken *pauseToken STG_UNUSED) +{ + errorBelch("Warning: Resuming the RTS is only possible for " + "multithreaded RTS."); + stg_exit(EXIT_FAILURE); +} + +bool rts_isPaused() +{ + errorBelch("Warning: Pausing/Resuming the RTS is only possible for " + "multithreaded RTS."); + return false; +} +#endif + void rts_done (void) { freeMyTask(); @@ -700,7 +870,7 @@ void rts_done (void) void hs_try_putmvar (/* in */ int capability, /* in */ HsStablePtr mvar) { - Task *task = getTask(); + Task *task = getMyTask(); Capability *cap; Capability *task_old_cap USED_IF_THREADS; |