1 /* ---------------------------------------------------------------------------
3 * (c) The GHC Team, 2001-2003
7 * The notion of a capability is used when operating in multi-threaded
8 * environments (which the SMP and Threads builds of the RTS do), to
9 * hold all the state an OS thread/task needs to run Haskell code:
10 * its STG registers, a pointer to its TSO, a nursery etc. During
11 * STG execution, a pointer to the capabilitity is kept in a
14 * Only in an SMP build will there be multiple capabilities, the threaded
15 * RTS and other non-threaded builds, there is one global capability,
16 * namely MainRegTable.
18 * This header file contains the functions for working with capabilities.
19 * (the main, and only, consumer of this interface is the scheduler).
21 * --------------------------------------------------------------------------*/
30 // State required by the STG virtual machine when running Haskell
31 // code. During STG execution, the BaseReg register always points
32 // to the StgRegTable of the current Capability (&cap->r).
36 nat no; // capability number.
38 // The Task currently holding this Capability. This task has
39 // exclusive access to the contents of this Capability (apart from
40 // returning_tasks_hd/returning_tasks_tl).
41 // Locks required: cap->lock.
44 // true if this Capability is running Haskell code, used for
45 // catching unsafe call-ins.
48 // The run queue. The Task owning this Capability has exclusive
49 // access to its run queue, so can wake up threads without
50 // taking a lock, and the common path through the scheduler is
55 // Tasks currently making safe foreign calls. Doubly-linked.
56 // When returning, a task first acquires the Capability before
57 // removing itself from this list, so that the GC can find all
58 // the suspended TSOs easily. Hence, when migrating a Task from
59 // the returning_tasks list, we must also migrate its entry from
61 Task *suspended_ccalling_tasks;
63 #if defined(THREADED_RTS)
64 // Worker Tasks waiting in the wings. Singly-linked.
67 // This lock protects running_task and returning_tasks_{hd,tl}.
70 // Tasks waiting to return from a foreign call, or waiting to make
71 // a new call-in using this Capability (NULL if empty).
72 // NB. this field needs to be modified by tasks other than the
73 // running_task, so it requires cap->lock to modify. A task can
74 // check whether it is NULL without taking the lock, however.
75 Task *returning_tasks_hd; // Singly-linked, with head/tail
76 Task *returning_tasks_tl;
78 }; // typedef Capability, defined in RtsAPI.h
80 // Converts a *StgRegTable into a *Capability.
82 INLINE_HEADER Capability *
83 regTableToCapability (StgRegTable *reg)
85 return (Capability *)((void *)((unsigned char*)reg - sizeof(StgFunTable)));
88 // Initialise the available capabilities.
90 void initCapabilities (void);
92 // Release a capability. This is called by a Task that is exiting
93 // Haskell to make a foreign call, or in various other cases when we
94 // want to relinquish a Capability that we currently hold.
96 // ASSUMES: cap->running_task is the current Task.
98 #if defined(THREADED_RTS)
99 void releaseCapability (Capability* cap);
100 void releaseCapability_ (Capability* cap); // assumes cap->lock is held
102 // releaseCapability() is empty in non-threaded RTS
103 INLINE_HEADER void releaseCapability (Capability* cap STG_UNUSED) {};
104 INLINE_HEADER void releaseCapability_ (Capability* cap STG_UNUSED) {};
107 #if !IN_STG_CODE && !defined(SMP)
108 // for non-SMP, we have one global capability
109 extern Capability MainCapability;
112 // Array of all the capabilities
114 extern nat n_capabilities;
115 extern Capability *capabilities;
117 // The Capability that was last free. Used as a good guess for where
118 // to assign new threads.
120 extern Capability *last_free_capability;
122 // Acquires a capability at a return point. If *cap is non-NULL, then
123 // this is taken as a preference for the Capability we wish to
126 // OS threads waiting in this function get priority over those waiting
127 // in waitForCapability().
129 // On return, *cap is non-NULL, and points to the Capability acquired.
131 void waitForReturnCapability (Capability **cap/*in/out*/, Task *task);
133 #if defined(THREADED_RTS)
135 // Gives up the current capability IFF there is a higher-priority
136 // thread waiting for it. This happens in one of two ways:
138 // (a) we are passing the capability to another OS thread, so
139 // that it can run a bound Haskell thread, or
141 // (b) there is an OS thread waiting to return from a foreign call
143 // On return: *pCap is NULL if the capability was released. The
144 // current task should then re-acquire it using waitForCapability().
146 void yieldCapability (Capability** pCap, Task *task);
148 // Acquires a capability for doing some work.
150 // On return: pCap points to the capability.
152 void waitForCapability (Task *task, Mutex *mutex, Capability **pCap);
154 // Wakes up a worker thread on just one Capability, used when we
155 // need to service some global event.
157 void prodOneCapability (void);
159 // Similar to prodOneCapability(), but prods all of them.
161 void prodAllCapabilities (void);
163 // Waits for a capability to drain of runnable threads and workers,
164 // and then acquires it. Used at shutdown time.
166 void shutdownCapability (Capability *cap, Task *task);
168 #else // !THREADED_RTS
170 // Grab a capability. (Only in the non-threaded RTS; in the threaded
171 // RTS one of the waitFor*Capability() functions must be used).
173 extern void grabCapability (Capability **pCap);
175 #endif /* !THREADED_RTS */
177 #endif /* CAPABILITY_H */