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/* ---------------------------------------------------------------------------
* (c) The GHC Team, 2001-2006
* Capabilities
* For details on the high-level design, see
* A Capability holds all the state an OS thread/task needs to run
* Haskell code: its STG registers, a pointer to its TSO, a nursery
* etc. During STG execution, a pointer to the Capabilitity is kept in
* a register (BaseReg).
* Only in a THREADED_RTS build will there be multiple capabilities,
* in the non-threaded RTS there is one global capability, called
* MainCapability.
* --------------------------------------------------------------------------*/
#include "sm/GC.h" // for evac_fn
#include "Task.h"
#include "Sparks.h"
#include "BeginPrivate.h"
struct Capability_ {
// State required by the STG virtual machine when running Haskell
// code. During STG execution, the BaseReg register always points
// to the StgRegTable of the current Capability (&cap->r).
StgFunTable f;
StgRegTable r;
nat no; // capability number.
// The Task currently holding this Capability. This task has
// exclusive access to the contents of this Capability (apart from
// returning_tasks_hd/returning_tasks_tl).
// Locks required: cap->lock.
Task *running_task;
// true if this Capability is running Haskell code, used for
// catching unsafe call-ins.
rtsBool in_haskell;
// The run queue. The Task owning this Capability has exclusive
// access to its run queue, so can wake up threads without
// taking a lock, and the common path through the scheduler is
// also lock-free.
StgTSO *run_queue_hd;
StgTSO *run_queue_tl;
// Tasks currently making safe foreign calls. Doubly-linked.
// When returning, a task first acquires the Capability before
// removing itself from this list, so that the GC can find all
// the suspended TSOs easily. Hence, when migrating a Task from
// the returning_tasks list, we must also migrate its entry from
// this list.
InCall *suspended_ccalls;
// One mutable list per generation, so we don't need to take any
// locks when updating an old-generation thunk. This also lets us
// keep track of which closures this CPU has been mutating, so we
// can traverse them using the right thread during GC and avoid
// unnecessarily moving the data from one cache to another.
bdescr **mut_lists;
bdescr **saved_mut_lists; // tmp use during GC
// block for allocating pinned objects into
bdescr *pinned_object_block;
// Context switch flag. We used to have one global flag, now one
// per capability. Locks required : none (conflicts are harmless)
int context_switch;
#if defined(THREADED_RTS)
// Worker Tasks waiting in the wings. Singly-linked.
Task *spare_workers;
nat n_spare_workers; // count of above
// This lock protects running_task, returning_tasks_{hd,tl}, wakeup_queue.
Mutex lock;
// Tasks waiting to return from a foreign call, or waiting to make
// a new call-in using this Capability (NULL if empty).
// NB. this field needs to be modified by tasks other than the
// running_task, so it requires cap->lock to modify. A task can
// check whether it is NULL without taking the lock, however.
Task *returning_tasks_hd; // Singly-linked, with head/tail
Task *returning_tasks_tl;
// Messages, or END_TSO_QUEUE.
Message *inbox;
SparkPool *sparks;
// Stats on spark creation/conversion
SparkCounters spark_stats;
// Per-capability STM-related data
StgTVarWatchQueue *free_tvar_watch_queues;
StgInvariantCheckQueue *free_invariant_check_queues;
StgTRecChunk *free_trec_chunks;
StgTRecHeader *free_trec_headers;
nat transaction_tokens;
} // typedef Capability is defined in RtsAPI.h
// Capabilities are stored in an array, so make sure that adjacent
// Capabilities don't share any cache-lines:
#ifndef mingw32_HOST_OS
#if defined(THREADED_RTS)
#define ASSERT_TASK_ID(task) ASSERT(task->id == osThreadId())
#define ASSERT_TASK_ID(task) /*empty*/
// These properties should be true when a Task is holding a Capability
ASSERT(cap->running_task != NULL && cap->running_task == task); \
ASSERT(task->cap == cap); \
// Sometimes a Task holds a Capability, but the Task is not associated
// with that Capability (ie. task->cap != cap). This happens when
// (a) a Task holds multiple Capabilities, and (b) when the current
// Task is bound, its thread has just blocked, and it may have been
// moved to another Capability.
ASSERT(cap->run_queue_hd == END_TSO_QUEUE ? \
cap->run_queue_tl == END_TSO_QUEUE : 1); \
ASSERT(myTask() == task); \
#if defined(THREADED_RTS)
rtsBool checkSparkCountInvariant (void);
// Converts a *StgRegTable into a *Capability.
INLINE_HEADER Capability *
regTableToCapability (StgRegTable *reg)
return (Capability *)((void *)((unsigned char*)reg - STG_FIELD_OFFSET(Capability,r)));
// Initialise the available capabilities.
void initCapabilities (void);
// Release a capability. This is called by a Task that is exiting
// Haskell to make a foreign call, or in various other cases when we
// want to relinquish a Capability that we currently hold.
// ASSUMES: cap->running_task is the current Task.
#if defined(THREADED_RTS)
void releaseCapability (Capability* cap);
void releaseAndWakeupCapability (Capability* cap);
void releaseCapability_ (Capability* cap, rtsBool always_wakeup);
// assumes cap->lock is held
// releaseCapability() is empty in non-threaded RTS
INLINE_HEADER void releaseCapability (Capability* cap STG_UNUSED) {};
INLINE_HEADER void releaseAndWakeupCapability (Capability* cap STG_UNUSED) {};
INLINE_HEADER void releaseCapability_ (Capability* cap STG_UNUSED,
rtsBool always_wakeup STG_UNUSED) {};
// declared in includes/rts/Threads.h:
// extern Capability MainCapability;
// declared in includes/rts/Threads.h:
// extern nat n_capabilities;
// Array of all the capabilities
extern Capability *capabilities;
// The Capability that was last free. Used as a good guess for where
// to assign new threads.
extern Capability *last_free_capability;
// GC indicator, in scope for the scheduler
#define PENDING_GC_SEQ 1
#define PENDING_GC_PAR 2
extern volatile StgWord waiting_for_gc;
// Acquires a capability at a return point. If *cap is non-NULL, then
// this is taken as a preference for the Capability we wish to
// acquire.
// OS threads waiting in this function get priority over those waiting
// in waitForCapability().
// On return, *cap is non-NULL, and points to the Capability acquired.
void waitForReturnCapability (Capability **cap/*in/out*/, Task *task);
EXTERN_INLINE void recordMutableCap (StgClosure *p, Capability *cap, nat gen);
EXTERN_INLINE void recordClosureMutated (Capability *cap, StgClosure *p);
#if defined(THREADED_RTS)
// Gives up the current capability IFF there is a higher-priority
// thread waiting for it. This happens in one of two ways:
// (a) we are passing the capability to another OS thread, so
// that it can run a bound Haskell thread, or
// (b) there is an OS thread waiting to return from a foreign call
// On return: *pCap is NULL if the capability was released. The
// current task should then re-acquire it using waitForCapability().
void yieldCapability (Capability** pCap, Task *task);
// Acquires a capability for doing some work.
// On return: pCap points to the capability.
void waitForCapability (Task *task, Mutex *mutex, Capability **pCap);
// Wakes up a worker thread on just one Capability, used when we
// need to service some global event.
void prodOneCapability (void);
void prodCapability (Capability *cap, Task *task);
// Similar to prodOneCapability(), but prods all of them.
void prodAllCapabilities (void);
// Attempt to gain control of a Capability if it is free.
rtsBool tryGrabCapability (Capability *cap, Task *task);
// Try to find a spark to run
StgClosure *findSpark (Capability *cap);
// True if any capabilities have sparks
rtsBool anySparks (void);
INLINE_HEADER rtsBool emptySparkPoolCap (Capability *cap);
INLINE_HEADER nat sparkPoolSizeCap (Capability *cap);
INLINE_HEADER void discardSparksCap (Capability *cap);
#else // !THREADED_RTS
// Grab a capability. (Only in the non-threaded RTS; in the threaded
// RTS one of the waitFor*Capability() functions must be used).
extern void grabCapability (Capability **pCap);
#endif /* !THREADED_RTS */
// Waits for a capability to drain of runnable threads and workers,
// and then acquires it. Used at shutdown time.
void shutdownCapability (Capability *cap, Task *task, rtsBool wait_foreign);
// Shut down all capabilities.
void shutdownCapabilities(Task *task, rtsBool wait_foreign);
// cause all capabilities to context switch as soon as possible.
void setContextSwitches(void);
INLINE_HEADER void contextSwitchCapability(Capability *cap);
// Free all capabilities
void freeCapabilities (void);
// For the GC:
void markCapability (evac_fn evac, void *user, Capability *cap,
rtsBool no_mark_sparks USED_IF_THREADS);
void markCapabilities (evac_fn evac, void *user);
void traverseSparkQueues (evac_fn evac, void *user);
/* -----------------------------------------------------------------------------
-------------------------------------------------------------------------- */
INLINE_HEADER rtsBool emptyInbox(Capability *cap);;
#endif // THREADED_RTS
/* -----------------------------------------------------------------------------
* INLINE functions... private below here
* -------------------------------------------------------------------------- */
recordMutableCap (StgClosure *p, Capability *cap, nat gen)
bdescr *bd;
// We must own this Capability in order to modify its mutable list.
// ASSERT(cap->running_task == myTask());
// NO: assertion is violated by performPendingThrowTos()
bd = cap->mut_lists[gen];
if (bd->free >= bd->start + BLOCK_SIZE_W) {
bdescr *new_bd;
new_bd = allocBlock_lock();
new_bd->link = bd;
bd = new_bd;
cap->mut_lists[gen] = bd;
*bd->free++ = (StgWord)p;
recordClosureMutated (Capability *cap, StgClosure *p)
bdescr *bd;
bd = Bdescr((StgPtr)p);
if (bd->gen_no != 0) recordMutableCap(p,cap,bd->gen_no);
#if defined(THREADED_RTS)
emptySparkPoolCap (Capability *cap)
{ return looksEmpty(cap->sparks); }
sparkPoolSizeCap (Capability *cap)
{ return sparkPoolSize(cap->sparks); }
discardSparksCap (Capability *cap)
{ discardSparks(cap->sparks); }
contextSwitchCapability (Capability *cap)
// setting HpLim to NULL ensures that the next heap check will
// fail, and the thread will return to the scheduler.
cap->r.rHpLim = NULL;
// But just in case it didn't work (the target thread might be
// modifying HpLim at the same time), we set the end-of-block
// context-switch flag too:
cap->context_switch = 1;
INLINE_HEADER rtsBool emptyInbox(Capability *cap)
return (cap->inbox == (Message*)END_TSO_QUEUE);
#include "EndPrivate.h"
#endif /* CAPABILITY_H */
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