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<tr><td width=20><td><b>THREAD(3)</b><td align=right><b>THREAD(3)</b>
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    <br>
<p><font size=+1><b>NAME     </b></font><br>

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    alt, chancreate, chanfree, chaninit, chanprint, chansetname, mainstacksize,
    proccreate, procdata, recv, recvp, recvul, send, sendp, sendul,
    nbrecv, nbrecvp, nbrecvul, nbsend, nbsendp, nbsendul, threadcreate,
    threaddata, threadexec, threadexecl, threadexits, threadexitsall,
    threadgetgrp, threadgetname, threadint,
    threadintgrp, threadkill, threadkillgrp, threadmain, threadnotify,
    threadid, threadpid, threadsetgrp, threadsetname, threadsetstate,
    threadspawn, threadwaitchan, yield &ndash; thread and proc management<br>
    
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<p><font size=+1><b>SYNOPSIS     </b></font><br>

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    <tt><font size=+1>#include &lt;u.h&gt;<br>
    #include &lt;libc.h&gt;<br>
    #include &lt;thread.h&gt;<br>
    #define &nbsp;&nbsp;&nbsp;CHANEND  &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;0<br>
    #define &nbsp;&nbsp;&nbsp;CHANSND  &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;1<br>
    #define &nbsp;&nbsp;&nbsp;CHANRCV  &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;2<br>
    #define &nbsp;&nbsp;&nbsp;CHANNOP  &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;3<br>
    #define &nbsp;&nbsp;&nbsp;CHANNOBLK &nbsp;&nbsp;&nbsp;4<br>
    typedef struct Alt Alt;<br>
    struct Alt {<br>
    
    <table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>

        Channel *c;<br>
        void &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;*v;<br>
        int &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;op;<br>
        Channel **tag;<br>
        int &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;entryno;<br>
        char &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;*name;<br>
        
    </table>
    };<br>
    
    <table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
    
    void &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;threadmain(int argc, char *argv[])<br>
    int &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;mainstacksize<br>
    int &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;proccreate(void (*fn)(void*), void *arg, uint stacksize)<br>
    int &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;threadcreate(void (*fn)(void*), void *arg, uint stacksize)<br>
    void &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;threadexits(char *status)<br>
    void &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;threadexitsall(char *status)<br>
    void &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;yield(void)<br>
    int &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;threadid(void)<br>
    int &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;threadgrp(void)<br>
    int &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;threadsetgrp(int group)<br>
    int &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;threadpid(int id)<br>
    int &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;threadint(int id)<br>
    int &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;threadintgrp(int group)<br>
    int &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;threadkill(int id)<br>
    int &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;threadkillgrp(int group)<br>
    void &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;threadsetname(char *name)<br>
    char* &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;threadgetname(void)<br>
    void** &nbsp;&nbsp;&nbsp;&nbsp;threaddata(void)<br>
    void** &nbsp;&nbsp;&nbsp;&nbsp;procdata(void)<br>
    int &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;chaninit(Channel *c, int elsize, int nel)<br>
    Channel* chancreate(int elsize, int nel)<br>
    void &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;chanfree(Channel *c)<br>
    int &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;alt(Alt *alts)<br>
    int &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;recv(Channel *c, void *v)<br>
    void* &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;recvp(Channel *c)<br>
    ulong &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;recvul(Channel *c)<br>
    int &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;nbrecv(Channel *c, void *v)<br>
    void* &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;nbrecvp(Channel *c)<br>
    ulong &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;nbrecvul(Channel *c)<br>
    int &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;send(Channel *c, void *v)<br>
    int &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;sendp(Channel *c, void *v)<br>
    int &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;sendul(Channel *c, ulong v)<br>
    int &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;nbsend(Channel *c, void *v)<br>
    int &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;nbsendp(Channel *c, void *v)<br>
    int &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;nbsendul(Channel *c, ulong v)<br>
    int &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;chanprint(Channel *c, char *fmt, ...)<br>
    int &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;threadspawn(int fd[3], char *file, char *args[])<br>
    int &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;threadexecl(Channel *cpid, int fd[3], char *file, ...)<br>
    int &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;threadexec(Channel *cpid, int fd[3], char *file, char *args[])<br>
    Channel* threadwaitchan(void)<br>
    int &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;threadnotify(int (*f)(void*, char*), int in)<br>
    </font></tt>
</table>
<p><font size=+1><b>DESCRIPTION     </b></font><br>

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    The thread library provides parallel programming support similar
    to that of the languages Alef and Newsqueak. Threads and procs
    occupy a shared address space, communicating and synchronizing
    through <i>channels</i> and shared variables. 
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    A <i>proc</i> is a Plan 9 process that contains one or more cooperatively
    scheduled <i>threads</i>. Programs using threads must replace <i>main</i> by
    <i>threadmain</i>. The thread library provides a <i>main</i> function that sets
    up a proc with a single thread executing <i>threadmain</i> on a stack
    of size <i>mainstacksize</i> (default eight kilobytes). To set
    <i>mainstacksize</i>, declare a global variable initialized to the desired
    value (<i>e.g.</i>, <tt><font size=+1>int mainstacksize = 1024</font></tt>). 
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    <i>Threadcreate</i> creates a new thread in the calling proc, returning
    a unique integer identifying the thread; the thread executes <i>fn(arg)</i>
    on a stack of size <i>stacksize</i>. Thread stacks are allocated in shared
    memory, making it valid to pass pointers to stack variables between
    threads and procs. <i>Proccreate</i> creates a new proc,
    and inside that proc creates a single thread as <i>threadcreate</i> would,
    returning the id of the created thread. Be aware that the calling
    thread may continue execution before the newly created proc and
    thread are scheduled. Because of this, <i>arg</i> should not point to
    data on the stack of a function that could return before the
    new process is scheduled. 
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    <i>Threadexits</i> terminates the calling thread. If the thread is the
    last in its proc, <i>threadexits</i> also terminates the proc, using
    <i>status</i> as the exit status. <i>Threadexitsall</i> terminates all procs
    in the program, using <i>status</i> as the exit status. 
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    When the last thread in <i>threadmain</i>&#8217;s proc exits, the program will
    appear to its parent to have exited. The remaining procs will
    still run together, but as a background program. 
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    The threads in a proc are coroutines, scheduled nonpreemptively
    in a round-robin fashion. A thread must explicitly relinquish
    control of the processor before another thread in the same proc
    is run. Calls that do this are <i>yield</i>, <i>proccreate</i>, <i>threadexec</i>,
    <i>threadexecl</i>, <i>threadexits</i>, <i>threadspawn</i>, <i>alt</i>, <i>send</i>, and <i>recv</i> (and
    the
    calls related to <i>send</i> and <i>recv</i>--see their descriptions further on).
    Procs are scheduled by the operating system. Therefore, threads
    in different procs can preempt one another in arbitrary ways and
    should synchronize their actions using <tt><font size=+1>qlocks</font></tt> (see <a href="../man3/lock.html"><i>lock</i>(3)</a>) or
    channel communication. System calls such as <a href="../man3/read.html"><i>read</i>(3)</a>
    block the entire proc; all threads in a proc block until the system
    call finishes. 
    <table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
    
    As mentioned above, each thread has a unique integer thread id.
    Thread ids are not reused; they are unique across the life of
    the program. <i>Threadid</i> returns the id for the current thread. Each
    thread also has a thread group id. The initial thread has a group
    id of zero. Each new thread inherits the group id of the
    thread that created it. <i>Threadgrp</i> returns the group id for the
    current thread; <i>threadsetgrp</i> sets it. <i>Threadpid</i> returns the pid
    of the Plan 9 process containing the thread identified by <i>id</i>,
    or &ndash;1 if no such thread is found. 
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    <i>Threadint</i> interrupts a thread that is blocked in a channel operation
    or system call. <i>Threadintgrp</i> interrupts all threads with the given
    group id. <i>Threadkill</i> marks a thread to die when it next relinquishes
    the processor (via one of the calls listed above). If the thread
    is blocked in a channel operation or system call, it is
    also interrupted. <i>Threadkillgrp</i> kills all threads with the given
    group id. Note that <i>threadkill</i> and <i>threadkillgrp</i> will not terminate
    a thread that never relinquishes the processor. 
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    Primarily for debugging, threads can have string names associated
    with them. <i>Threadgetname</i> returns the current thread&#8217;s name; <i>threadsetname</i>
    sets it. The pointer returned by <i>threadgetname</i> is only valid until
    the next call to <i>threadsetname</i>. 
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    Also for debugging, threads have a string state associated with
    them. <i>Threadsetstate</i> sets the state string. There is no <i>threadgetstate</i>;
    since the thread scheduler resets the state to <tt><font size=+1>Running</font></tt> every time
    it runs the thread, it is only useful for debuggers to inspect
    the state. 
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    <i>Threaddata</i> returns a pointer to a per-thread pointer that may
    be modified by threaded programs for per-thread storage. Similarly,
    <i>procdata</i> returns a pointer to a per-proc pointer. 
    <table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
    
    <i>Threadexecl</i> and <i>threadexec</i> are threaded analogues of <i>exec</i> and
    <i>execl</i> (see <a href="../man3/exec.html"><i>exec</i>(3)</a>); on success, they replace the calling thread
    and invoke the external program, never returning. (Unlike on Plan
    9, the calling thread need not be the only thread in its proc--the
    other threads will continue executing.) On error, they return
    &ndash;1. If <i>cpid</i> is not null, the pid of the invoked program will be
    sent along <i>cpid</i> (using <i>sendul</i>) once the program has been started,
    or &ndash;1 will be sent if an error occurs. <i>Threadexec</i> and <i>threadexecl</i>
    will not access their arguments after sending a result along <i>cpid</i>.
    Thus, programs that malloc the <i>argv</i> passed to <i>threadexec
    </i>can safely free it once they have received the <i>cpid</i> response.
    
    <table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
    
    <i>Threadexecl</i> and <i>threadexec</i> will duplicate (see <a href="../man3/dup.html"><i>dup</i>(3)</a>) the three
    file descriptors in <i>fd</i> onto standard input, output, and error
    for the external program and then close them in the calling thread.
    Beware of code that sets<br>
    
    <table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>

        <tt><font size=+1>fd[0] = 0;<br>
        fd[1] = 1;<br>
        fd[2] = 2;<br>
        
        <table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
        </font></tt>
        
    </table>
    to use the current standard files. The correct code is<br>
    
    <table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>

        <tt><font size=+1>fd[0] = dup(0, &#8722;1);<br>
        fd[1] = dup(1, &#8722;1);<br>
        fd[2] = dup(2, &#8722;1);<br>
        
        <table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
        </font></tt>
        
    </table>
    <i>Threadspawn</i> is like <i>threadexec</i> but does not replace the current
    thread. It returns the pid of the invoked program on success,
    or &ndash;1 on error. 
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    <i>Threadwaitchan</i> returns a channel of pointers to <tt><font size=+1>Waitmsg</font></tt> structures
    (see <a href="../man3/wait.html"><i>wait</i>(3)</a>). When an exec&#8217;ed process exits, a pointer to a <tt><font size=+1>Waitmsg</font></tt>
    is sent to this channel. These <tt><font size=+1>Waitmsg</font></tt> structures have been allocated
    with <a href="../man3/malloc.html"><i>malloc</i>(3)</a> and should be freed after use. 
    <table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
    
    A <tt><font size=+1>Channel</font></tt> is a buffered or unbuffered queue for fixed-size messages.
    Procs and threads <i>send</i> messages into the channel and <i>recv</i> messages
    from the channel. If the channel is unbuffered, a <i>send</i> operation
    blocks until the corresponding <i>recv</i> operation occurs and <i>vice
    versa</i>. <i>Chaninit</i> initializes a <tt><font size=+1>Channel</font></tt> for
    messages of size <i>elsize</i> and with a buffer holding <i>nel</i> messages.
    If <i>nel</i> is zero, the channel is unbuffered. <i>Chancreate</i> allocates
    a new channel and initializes it. <i>Chanfree</i> frees a channel that
    is no longer used. <i>Chanfree</i> can be called by either sender or
    receiver after the last item has been sent or received. Freeing
    the
    channel will be delayed if there is a thread blocked on it until
    that thread unblocks (but <i>chanfree</i> returns immediately). 
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    The <tt><font size=+1>name</font></tt> element in the <tt><font size=+1>Channel</font></tt> structure is a description intended
    for use in debugging. <i>Chansetname</i> sets the name. 
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    <i>Send</i> sends the element pointed at by <i>v</i> to the channel <i>c</i>. If <i>v</i>
    is null, zeros are sent. <i>Recv</i> receives an element from <i>c</i> and stores
    it in <i>v</i>. If <i>v</i> is null, the received value is discarded. <i>Send</i> and
    <i>recv</i> return 1 on success, &ndash;1 if interrupted. <i>Nbsend</i> and <i>nbrecv</i>
    behave similarly, but return 0 rather than blocking. 
    <table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
    
    <i>Sendp</i>, <i>nbsendp</i>, <i>sendul</i>, and <i>nbsendul</i> send a pointer or an unsigned
    long; the channel must have been initialized with the appropriate
    <i>elsize</i>. <i>Recvp</i>, <i>nbrecvp</i>, <i>recvul</i>, and <i>nbrecvul</i> receive a pointer
    or an unsigned long; they return zero when a zero is received,
    when interrupted, or (for <i>nbrecvp</i> and <i>nbrecvul</i>) when the
    operation would have blocked. To distinguish between these three
    cases, use <i>recv</i> or <i>nbrecv</i>. 
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    <i>Alt</i> can be used to recv from or send to one of a number of channels,
    as directed by an array of <tt><font size=+1>Alt</font></tt> structures, each of which describes
    a potential send or receive operation. In an <tt><font size=+1>Alt</font></tt> structure, <tt><font size=+1>c</font></tt>
    is the channel; <tt><font size=+1>v</font></tt> the value pointer (which may be null); and <tt><font size=+1>op</font></tt>
    the operation: <tt><font size=+1>CHANSND</font></tt> for a send operation,
    <tt><font size=+1>CHANRECV</font></tt> for a recv operation; <tt><font size=+1>CHANNOP</font></tt> for no operation (useful
    when <i>alt</i> is called with a varying set of operations). The array
    of <tt><font size=+1>Alt</font></tt> structures is terminated by an entry with <i>op</i> <tt><font size=+1>CHANEND</font></tt> or
    <tt><font size=+1>CHANNOBLK</font></tt>. If at least one <tt><font size=+1>Alt</font></tt> structure can proceed, one of them
    is chosen at random to be executed. <i>Alt</i> returns the
    index of the chosen structure. If no operations can proceed and
    the list is terminated with <tt><font size=+1>CHANNOBLK</font></tt>, <i>alt</i> returns the index of
    the terminating <tt><font size=+1>CHANNOBLK</font></tt> structure. Otherwise, <i>alt</i> blocks until
    one of the operations can proceed, eventually returning the index
    of the structure executes. <i>Alt</i> returns &ndash;1 when
    interrupted. The <tt><font size=+1>tag</font></tt> and <tt><font size=+1>entryno</font></tt> fields in the <tt><font size=+1>Alt</font></tt> structure are
    used internally by <i>alt</i> and need not be initialized. They are not
    used between <i>alt</i> calls. 
    <table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
    
    <i>Chanprint</i> formats its arguments in the manner of <a href="../man3/print.html"><i>print</i>(3)</a> and
    sends the result to the channel <i>c.</i> The string delivered by <i>chanprint</i>
    is allocated with <a href="../man3/malloc.html"><i>malloc</i>(3)</a> and should be freed upon receipt.
    
    <table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
    
    Thread library functions do not return on failure; if errors occur,
    the entire program is aborted. 
    <table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
    
    Threaded programs should use <i>threadnotify</i> in place of <i>atnotify</i>
    (see <a href="../man3/notify.html"><i>notify</i>(3)</a>). 
    <table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
    
    It is safe to use <a href="../man3/sysfatal.html"><i>sysfatal</i>(3)</a> in threaded programs. <i>Sysfatal</i> will
    print the error string and call <i>threadexitsall</i>. 
    <table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
    
    It is not safe to call <i>rfork</i> in a threaded program, except to
    call <tt><font size=+1>rfork(RFNOTEG)</font></tt> from the main proc before any other procs
    have been created. To create new processes, use <i>proccreate</i>.<br>
    
</table>
<p><font size=+1><b>FILES     </b></font><br>

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    <tt><font size=+1>/usr/local/plan9/acid/thread</font></tt> contains useful <a href="../man1/acid.html"><i>acid</i>(1)</a> functions
    for debugging threaded programs. 
    <table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
    
    <tt><font size=+1>/usr/local/plan9/src/libthread/test</font></tt> contains some example programs.<br>
    
</table>
<p><font size=+1><b>SOURCE     </b></font><br>

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    <tt><font size=+1>/usr/local/plan9/src/libthread<br>
    </font></tt>
</table>
<p><font size=+1><b>SEE ALSO    </b></font><br>

<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>

    <a href="../man3/intro.html"><i>intro</i>(3)</a>, <a href="../man3/ioproc.html"><i>ioproc</i>(3)</a><br>
    
</table>
<p><font size=+1><b>BUGS     </b></font><br>

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    To avoid name conflicts, <i>alt</i>, <i>nbrecv</i>, <i>nbrecvp</i>, <i>nbrecvul</i>, <i>nbsend</i>,
    <i>nbsendp</i>, <i>nbsendul</i>, <i>recv</i>, <i>recvp</i>, <i>recvul</i>, <i>send</i>, <i>sendp</i>, and <i>sendul</i>
    are defined as macros that expand to <i>chanalt</i>, <i>channbrecv</i>, and
    so on. <i>Yield</i> is defined as a macro that expands to <i>threadyield</i>.
    See <a href="../man3/intro.html"><i>intro</i>(3)</a>. 
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    The implementation of <i>threadnotify</i> may not be correct.<br>
    
</table>

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