<INTERFACE> The <CD/CML/ structure <SEEALSO> <PP> <SPEC> <TYPE><ID>thread_id <COMMENT> <PP> Thread IDs are the unique IDs associated with &CML; threads. These IDs are in an unspecified total order that can be used to break cyclic depedencies (see <VALREF/compareTid/). <SPEC> <TYPE><TYPARAM>'a<ID>chan <COMMENT> <PP> This is the type constructor for synchronous channels. <SPEC> <TYPE><TYPARAM>'a<ID>event <COMMENT> <PP> Event values are abstract representations of synchronous operations (so called first-class sychronous operations). <SPEC> <VAL>version<TY>{system : string, version_id : int list, date : string} <VAL>banner<TY>string <COMMENT> <PP> These specify the version of &CML; in the same format as &SMLNJ;. <SPEC> <VAL>spawnc<TY>('a -> unit) -> 'a -> thread_id <VAL>spawn<TY>(unit -> unit) -> thread_id <COMMENT> <PROTOTY> spawnc <ARG/f/ <ARG/x/ <PROTO> spawn <ARG/f/ </PROTOTY> creates a new thread of control to evaluate the body of <ARG/f/. A new unique ID for the thread is created and returned. <SPEC> <VAL>yield<TY>unit -> unit <COMMENT> <PP> This function can be used to implement an explicit context switch. Since CML is preemptively scheduled, it should never be necessary for user programs to call this function. It is mainly used for performance measurements. <SPEC> <VAL>exit<TY>unit -> 'a <COMMENT> <PROTOTY> exit () </PROTOTY> causes the calling thread to terminate. <SPEC> <VAL>getTid<TY>unit -> thread_id <COMMENT> <PROTOTY> getTid () </PROTOTY> returns the thread ID of the calling thread. <SPEC> <VAL>sameTid<TY>(thread_id * thread_id) -> bool <COMMENT> <PROTOTY> sameTid (<ARG/tid1/, <ARG/tid2/) </PROTOTY> returns <CD/true/, if the two thread IDs are the same ID. <SPEC> <VAL>compareTid<TY>(thread_id * thread_id) -> order <COMMENT> <PROTOTY> compareTid (<ARG/tid1/, <ARG/tid2/) </PROTOTY> compares the two thread IDs and returns their order in the total ordering of thread IDs. The precise semantics of this ordering is left unspecified, other than to say it is a total order. <SPEC> <VAL>hashTid<TY>thread_id -> word <COMMENT> <PROTOTY> hashTid <ARG/tid/ </PROTOTY> returns a hashing of the thread ID <ARG/tid/. <SPEC> <VAL>tidToString<TY>thread_id -> string <COMMENT> <PROTOTY> tidToString <ARG/tid/ </PROTOTY> returns a string representation of the thread ID <ARG/tid/. <SPEC> <VAL>joinEvt<TY>thread_id -> unit event <COMMENT> <PROTOTY> joinEvt <ARG/tid/ </PROTOTY> creates an event value for synchronizing on the termination of the thread with the ID <ARG/tid/. There are three ways that a thread may terminate: the function that was passed to <VALREF/spawn/ (or <VALREF/spawnc/) may return; it may call the <VALREF/exit/ function, or it may have an uncaught exception. Note that <VALREF NOLINK/joinEvt/ does not distinguish between these cases; it also does not become enabled if the named thread deadlocks (even if it is garbage collected). <SPEC> <VAL>channel<TY>unit -> 'a chan <COMMENT> <PROTOTY> channel () </PROTOTY> creates a new synchronous channel. <SPEC> <VAL>sameChannel<TY>('a chan * 'a chan) -> bool <COMMENT> <PROTOTY> sameChannel (<ARG/ch1/, <ARG/ch2/) </PROTOTY> returns <CD/true/, if the two channels are the same channel. <SPEC> <VAL>send<TY>('a chan * 'a) -> unit <COMMENT> <PROTOTY> send (<ARG/ch/, <ARG/msg/) </PROTOTY> sends the message <ARG/msg/ on the synchronous channel <ARG/ch/. This operation blocks the calling thread until there is another thread attempting to receive a message from the channel <ARG/ch/, at which point the receiving thread gets the message and both threads continue execution. <SPEC> <VAL>recv<TY>'a chan -> 'a <COMMENT> <PROTOTY> recv <ARG/ch/ </PROTOTY> receives a message from the channel <ARG/ch/. This operation blocks the calling thread until there is another thread attempting to send a message on the channel <ARG/ch/, at which point both threads continue execution. <SPEC> <VAL>sendEvt<TY>('a chan * 'a) -> unit event <VAL>recvEvt<TY>'a chan -> 'a event <COMMENT> <PP> These functions create event values to represent the <VALREF/send/ and <VALREF/recv/ operations. <SPEC> <VAL>sendPoll<TY>('a chan * 'a) -> bool <COMMENT> <PROTOTY> sendPoll (<ARG/ch/, <ARG/msg/) </PROTOTY> attempts to send the message <ARG/msg/ on the synchronous channel <ARG/ch/. If this operation can complete without blocking the calling thread, then the message is sent and <CD/true/ is returned. Otherwise, no communication is preformed and <CD/false/ is returned. This function is not recommended for general use; it is provided as an efficiency aid for certain kinds of protocols. <SPEC> <VAL>recvPoll<TY>'a chan -> 'a option <COMMENT> <PROTOTY> recvPoll <ARG/ch/ </PROTOTY> attempts to receive a message from the channel <ARG/ch/. If there is no other thread offering to <VALREF/send/ a message on <ARG/ch/, then this returns <VAL>wrap<TY>('a event * ('a -> 'b)) -> 'b event <COMMENT> <PROTOTY> wrap (<ARG/ev/, <ARG/f/) </PROTOTY> wraps the post-synchronization action <ARG/f/ around the event value <ARG/ev/. <SPEC> <VAL>wrapHandler<TY>('a event * (exn -> 'a event)) -> 'a event <COMMENT> <PROTOTY> wrapHandler (<ARG/ev/, <ARG/h/) </PROTOTY> wraps the exception handler function <ARG/h/ around the event value <ARG/ev/. If, during execution of some post-synchronization action in <ARG/ev/, an exception is raised, it will be caught and passed to <ARG/h/. Nesting of handlers works as would be expected: the innermost handler is the first one invoked. Note that exceptions raised in the pre-synchronization actions in <ARG/ev/ (i.e., actions defined by <VALREF/guard/ and <VALREF/withNack/) are not handled by <ARG/h/. <SPEC> <VAL>guard<TY>(unit -> 'a event) -> 'a event <COMMENT> <PROTOTY> guard <ARG/g/ </PROTOTY> creates a <IT>delayed</IT> event value from the function <ARG/g/. When the resulting event value is synchronized on, the function <ARG/g/ will be evaluated and the resulting event value will be used in its place in the synchronization. This provides a mechanism for implementing pre-synchronization actions, such as sending a request to a server. <SPEC> <VAL>withNack<TY>(unit event -> 'a event) -> 'a event <COMMENT> <PROTOTY> withNack <ARG/g/ </PROTOTY> creates a <IT>delayed</IT> event value from the function <ARG/g/. As in the case of <VALREF/guard/, the function <ARG/g/ will be evaluated at synchronization time and the resulting event value will be used in its place in the synchronization. Furthermore, when <ARG/g/ is evaluated, it is passed a <IT>negative acknowledgement</IT> event as an argument. This negative acknowledgement event is enabled in the case where some other event involved in the synchronization is chosen instead of the one produced by <ARG/g/. The <VALREF NOLINK/withNack/ combinator provides a mechanism for informing servers that a client has aborted a transaction. <SPEC> <VAL>choose<TY>'a event list -> 'a event <COMMENT> <PROTOTY> choose <ARG/evs/ </PROTOTY> constructs an event value that represents the non-deterministic choice of the events in the list <ARG/evs/. <SPEC> <VAL>sync<TY>'a event -> 'a <COMMENT> <PROTOTY> sync <ARG/ev/ </PROTOTY> synchronizes the calling thread on the event <ARG/ev/. <SPEC> <VAL>select<TY>'a event list -> 'a <COMMENT> <PROTOTY> select <ARG/evs/ </PROTOTY> synchronizes on the non-deterministic choice of the events in the list <ARG/evs/. It is semantically equivalant to: `<VALREF/sync/ (<VALREF/choose/ <ARG/evs/)` but is more efficient. <SPEC> <VAL>never<TY>'a event <COMMENT> <PROTOTY> never </PROTOTY> is an event value that is never enabled for synchronization. It is semantically equivalant to the expression: `<VALREF/choose/ []` <SPEC> <VAL>alwaysEvt<TY>'a -> 'a event <COMMENT> <PROTOTY> alwaysEvt <ARG/x/ </PROTOTY> creates an event value that is always enabled, and that returns the value <ARG/x/ upon synchronization. <SPEC> <VAL>timeOutEvt<TY>Time.time -> unit event <COMMENT> <PROTOTY> timeOutEvt <ARG/t/ </PROTOTY> creates an event value that becomes enabled at the time interval <ARG/t/ after synchronization. For example, the expression: `<VALREF/sync/ (timeOutEvt ( will delay the calling thread for one second. Note that the specified time interval is actually a minimum waiting time, and the delay may be longer. <SPEC> <VAL>atTimeEvt<TY>Time.time -> unit event <COMMENT> <PROTOTY> atTimeEvt <ARG/t/ </PROTOTY> creates an event value that becomes enabled at the specified time <ARG/t/. For example, the expression: `<VALREF/sync/ (atTimeEvt ( blocks the calling thread until the beginning of the year 2000.`` </INTERFACE>