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 struct Capability_ *next;
65 struct Capability_ *prev;
67 // Worker Tasks waiting in the wings. Singly-linked.
70 // This lock protects running_task and returning_tasks_{hd,tl}.
73 // Tasks waiting to return from a foreign call, or waiting to make
74 // a new call-in using this Capability (NULL if empty).
75 // NB. this field needs to be modified by tasks other than the
76 // running_task, so it requires cap->lock to modify. A task can
77 // check whether it is NULL without taking the lock, however.
78 Task *returning_tasks_hd; // Singly-linked, with head/tail
79 Task *returning_tasks_tl;
81 }; // typedef Capability, defined in RtsAPI.h
83 // Converts a *StgRegTable into a *Capability.
85 INLINE_HEADER Capability *
86 regTableToCapability (StgRegTable *reg)
88 return (Capability *)((void *)((unsigned char*)reg - sizeof(StgFunTable)));
91 // Initialise the available capabilities.
93 void initCapabilities (void);
95 // Release a capability. This is called by a Task that is exiting
96 // Haskell to make a foreign call, or in various other cases when we
97 // want to relinquish a Capability that we currently hold.
99 // ASSUMES: cap->running_task is the current Task.
101 #if defined(THREADED_RTS)
102 void releaseCapability (Capability* cap);
103 void releaseCapability_ (Capability* cap); // assumes cap->lock is held
105 // releaseCapability() is empty in non-threaded RTS
106 INLINE_HEADER void releaseCapability (Capability* cap STG_UNUSED) {};
107 INLINE_HEADER void releaseCapability_ (Capability* cap STG_UNUSED) {};
110 #if !IN_STG_CODE && !defined(SMP)
111 // for non-SMP, we have one global capability
112 extern Capability MainCapability;
115 // Array of all the capabilities
117 extern nat n_capabilities;
118 extern Capability *capabilities;
120 // The Capability that was last free. Used as a good guess for where
121 // to assign new threads.
123 extern Capability *last_free_capability;
125 // Acquires a capability at a return point. If *cap is non-NULL, then
126 // this is taken as a preference for the Capability we wish to
129 // OS threads waiting in this function get priority over those waiting
130 // in waitForCapability().
132 // On return, *cap is non-NULL, and points to the Capability acquired.
134 void waitForReturnCapability (Capability **cap/*in/out*/, Task *task);
136 #if defined(THREADED_RTS)
138 // Gives up the current capability IFF there is a higher-priority
139 // thread waiting for it. This happens in one of two ways:
141 // (a) we are passing the capability to another OS thread, so
142 // that it can run a bound Haskell thread, or
144 // (b) there is an OS thread waiting to return from a foreign call
146 // On return: *pCap is NULL if the capability was released. The
147 // current task should then re-acquire it using waitForCapability().
149 void yieldCapability (Capability** pCap, Task *task);
151 // Acquires a capability for doing some work.
153 // On return: pCap points to the capability.
155 void waitForCapability (Task *task, Mutex *mutex, Capability **pCap);
157 // Wakes up a worker thread on just one Capability, used when we
158 // need to service some global event.
160 void prodOneCapability (void);
162 // Similar to prodOneCapability(), but prods all of them.
164 void prodAllCapabilities (void);
166 // Waits for a capability to drain of runnable threads and workers,
167 // and then acquires it. Used at shutdown time.
169 void shutdownCapability (Capability *cap, Task *task);
171 #else // !THREADED_RTS
173 // Grab a capability. (Only in the non-threaded RTS; in the threaded
174 // RTS one of the waitFor*Capability() functions must be used).
176 extern void grabCapability (Capability **pCap);
178 #endif /* !THREADED_RTS */
180 #endif /* CAPABILITY_H */