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 * --------------------------------------------------------------------------*/
23 #ifndef __CAPABILITY_H__
24 #define __CAPABILITY_H__
26 // All the capabilities
27 extern Capability *capabilities;
29 // Initialised the available capabilities.
31 extern void initCapabilities( void );
33 // Releases a capability
35 extern void releaseCapability( Capability* cap );
37 // Signal that a thread has become runnable
39 extern void threadRunnable ( void );
41 // Return the capability that I own.
43 extern Capability *myCapability (void);
45 extern void prodWorker ( void );
47 #ifdef RTS_SUPPORTS_THREADS
48 // Gives up the current capability IFF there is a higher-priority
49 // thread waiting for it. This happens in one of two ways:
51 // (a) we are passing the capability to another OS thread, so
52 // that it can run a bound Haskell thread, or
54 // (b) there is an OS thread waiting to return from a foreign call
56 // On return: *pCap is NULL if the capability was released. The
57 // current worker thread should then re-acquire it using
58 // waitForCapability().
60 extern void yieldCapability( Capability **pCap );
62 // Acquires a capability for doing some work.
64 // If the current OS thread is bound to a particular Haskell thread,
65 // then pThreadCond points to a condition variable for waking up this
66 // OS thread when its Haskell thread is ready to run.
68 // On return: pCap points to the capability.
69 extern void waitForCapability( Mutex* pMutex, Capability** pCap,
70 Condition *pThreadCond );
72 // Acquires a capability at a return point.
74 // OS threads waiting in this function get priority over those waiting
75 // in waitForWorkCapability().
77 // On return: pCap points to the capability.
78 extern void waitForReturnCapability(Mutex* pMutex, Capability** pCap);
80 // Signals that the next time a capability becomes free, it should
81 // be transfered to a particular OS thread, identified by the
82 // condition variable pTargetThreadCond.
84 extern void passCapability(Condition *pTargetThreadCond);
86 // Signals that the next time a capability becomes free, it should
87 // be transfered to an ordinary worker thread.
89 extern void passCapabilityToWorker( void );
91 extern nat rts_n_free_capabilities;
93 extern Capability *free_capabilities;
95 /* number of worker threads waiting for a return capability
97 extern nat rts_n_waiting_workers;
99 static inline rtsBool needToYieldToReturningWorker(void)
101 return rts_n_waiting_workers > 0;
104 static inline nat getFreeCapabilities (void)
106 return rts_n_free_capabilities;
109 static inline rtsBool noCapabilities (void)
111 return (rts_n_free_capabilities == 0);
114 static inline rtsBool allFreeCapabilities (void)
117 return (rts_n_free_capabilities == RTS_DEREF(RtsFlags).ParFlags.nNodes);
119 return (rts_n_free_capabilities == 1);
123 #else // !RTS_SUPPORTS_THREADS
125 // Grab a capability. (Only in the non-threaded RTS; in the threaded
126 // RTS one of the waitFor*Capability() functions must be used).
128 extern void grabCapability( Capability **pCap );
130 #endif /* !RTS_SUPPORTS_THREADS */
132 #endif /* __CAPABILITY_H__ */