hss_thread_pthread.c

/*
#include "hss_thread.h"

#include <pthread.h>
#include <string.h>


 * This is an implementation of our threaded abstraction using the
 * POSIX pthread API
 *
 * C11 has a similar (but not precisely identical) API to the one that POSIX
 * defines (at least for what we do; all we need is thread create/join and
 * mutex's, which *any* thread library should provide).  I'd code up the
 * support for that API as well (using the same base logic, with typedef's and
 * helper inlines to isolate the differences), however I don't have a C11
 * implementation handy to test it


#define MAX_THREAD 16    Number try to create more than 16 threads, no
                         matter what the application tries to tell us
#define DEFAULT_THREAD 16  The number of threads to run if the
                         application doesn't tell us otherwise (e.g.
                         passes in 0)

#define MIN_DETAIL 16    So the alignment kludge we do doesn't waste space

 The information we track about a thread we may have launched
struct thread_state {
    pthread_t thread_id;
    enum { never_was, alive, dead } state;
};

struct work_item {
    struct work_item *link;     They're in a linked list

    void (*function)(const void *detail,    Function to call
                             struct thread_collection *col);

         These two items are used to pass the thread state to the thread
         if this is the first work item for the thread to process
    struct thread_collection *col;  The parent thread_collection
    struct thread_state *state;  The pointer into the thread collection
                                state for the state of this thread

        The detail structure that we pass to the function
        We'll malloc enough space to hold the entire structure
    union {                     union here so that the detail array is
        void *align1;           correctly aligned for various datatypes
        long long align2;
        void (*align3)(void);
        unsigned char detail[MIN_DETAIL];
    } x;
};

struct thread_collection {
    pthread_mutex_t lock;        Must be locked before this structure is
                                 accessed if there might be a thread
    pthread_mutex_t write_lock;  Must be locked before common user data is
                                 written

    unsigned num_thread;
    unsigned current_ptr;        There two are here to avoid O(N) table
    unsigned num_alive;          scanning in the most common scenarios

         Information about the worker threads we may have created
    struct thread_state threads[MAX_THREAD];


         * Queue (FIFO) of work items submitted, and which can't be processed
         * immedately.  We do a FIFO, rather than a stack, so that we perform
         * the requests in the order they were issued (which isn't something
         * the interface guarantees; however it doesn't interfere with the
         * request ordering we ask applications to make)

    struct work_item *top_work_queue;
    struct work_item *end_work_queue;
};


 * Allocate a thread control structure

struct thread_collection *hss_thread_init(int num_thread) {
    if (num_thread == 0) num_thread = DEFAULT_THREAD;
    if (num_thread <= 1) return 0;   Not an error: an indication to run
                                     single threaded
    if (num_thread > MAX_THREAD) num_thread = MAX_THREAD;

    struct thread_collection *col = malloc( sizeof *col );
    if (!col) return 0;   On malloc failure, run single threaded

    col->num_thread = num_thread;

    if (0 != pthread_mutex_init( &col->lock, 0 )) {
        free(col);
        return 0;
    }

    if (0 != pthread_mutex_init( &col->write_lock, 0 )) {
        pthread_mutex_destroy( &col->lock );
        free(col);
        return 0;
    }

    col->current_ptr = 0;
    col->num_alive = 0;
    unsigned i;
    for (i=0; i<num_thread; i++) {
        col->threads[i].state = never_was;
    }
    col->top_work_queue = 0;
    col->end_work_queue = 0;

    return col;
}


 * This is the base routine that a worker thread runs

static void *worker_thread( void *arg ) {
    struct work_item *w = arg;   The initial work item
    struct thread_collection *col = w->col;
    struct thread_state *state = w->state;

    for (;;) {
         Perform the work item in front of us
        (w->function)(w->x.detail, col);

         Ok, we did that
        free(w);

         Check if there's anything else to do
        pthread_mutex_lock( &col->lock );

        w = col->top_work_queue;
        if (w) {
             More work; pull it off the queue
            col->top_work_queue = w->link;
            if (w == col->end_work_queue) col->end_work_queue = 0;

             And go handle it
            pthread_mutex_unlock( &col->lock );
            continue;
        }

         No more work for us to do; post our obituary
        state->state = dead;
        col->num_alive -= 1;
        pthread_mutex_unlock( &col->lock );

         And that's all folks
        return 0;
    }
}


 * This adds function/details to the list of things that need to be done
 * It either creates a thread to do it, or (if we're maxed out) add it to
 * our honey-do list (or, as last resort, just does it itself)

void hss_thread_issue_work(struct thread_collection *col,
            void (*function)(const void *detail,
                             struct thread_collection *col),
            const void *detail, size_t size_detail_structure) {

     If we're running in single-threaded mode
    if (!col) {
        function( detail, col );
        return;
    }

     Allocate a work structure to hold this request
    size_t extra_space;
    if (size_detail_structure < MIN_DETAIL) extra_space = 0;
    else extra_space = size_detail_structure - MIN_DETAIL;
    struct work_item *w = malloc(sizeof *w + extra_space);

    if (!w) {
         Can't allocate the work structure; fall back to single-threaded
        function( detail, col );
        return;
    }
    w->col = col;
    w->function = function;
    memcpy( w->x.detail, detail, size_detail_structure );

    unsigned num_thread = col->num_thread;

    pthread_mutex_lock( &col->lock );

     Check if we can spawn a new thread
    if (col->num_alive < num_thread) {
         There's supposed to be room for another
         Look for the empty slot
        unsigned i, j;
        j = col->current_ptr;   Do round-robin (so we don't bang on
                                slot 0 whenever we try to start a thread)
        for (i=0; i<num_thread; i++, j = (j+1) % num_thread) {
            struct thread_state *p = &col->threads[j];
            switch (p->state) {
            case alive: continue;  This one's busy
            case dead:
                {
                 This one just died; grab its status (not that we care,
                 however that'll tell the thread library it can clean up)
                pthread_t thread_id = p->thread_id;
                void *status;    Ignored, but we need to place thread
                                 status somewhere
                pthread_mutex_unlock( &col->lock );
                pthread_join( thread_id, &status );
                pthread_mutex_lock( &col->lock );
                p->state = never_was;
                }
                 FALL THROUGH
            case never_was:
                 Now, we can spawn a new thread
                w->state = p;
                if (0 != pthread_create( &p->thread_id,
                                         NULL, worker_thread, w )) {
                     Hmmm, couldn't spawn it; fall back
                    default:  On error condition
                    pthread_mutex_unlock( &col->lock );
                    free(w);
                    function( detail, col );
                    return;
                }

                 We've kicked off the thread
                p->state = alive;
                col->num_alive += 1;
                     For the next request, start scanning at the next
                     thread object
                col->current_ptr = (j+1) % num_thread;
                pthread_mutex_unlock( &col->lock );
                return;
            }
        }
        col->num_alive = num_thread;  Hmmmm, everything was alive???
    }

     We can't create any more threads; enqueue this (and someone will get
     to it)
    w->link = 0;
    if (col->end_work_queue) {
        col->end_work_queue->link = w;
    }
    col->end_work_queue = w;
    if (!col->top_work_queue) col->top_work_queue = w;

    pthread_mutex_unlock( &col->lock );
}


 * This will wait for all the work items we'e issued to complete

void hss_thread_done(struct thread_collection *col) {
    if (!col) return;

    unsigned i;
    pthread_mutex_lock( &col->lock );
    for (i=0; i<col->num_thread; i++) {

         * Wait for each thread that we have spawned.
         * We're the only one that will spawn them, and so we don't have to
         * worry about any new ones appearing while we scan through the list

        if (col->threads[i].state != never_was) {
            void *status;
            pthread_t thread_id = col->threads[i].thread_id;
            pthread_mutex_unlock( &col->lock );
            pthread_join( thread_id, &status );
            pthread_mutex_lock( &col->lock );
        }
    }
    pthread_mutex_unlock( &col->lock );

     Ok, all the threads have finished; tear things down

    pthread_mutex_destroy( &col->lock );
    pthread_mutex_destroy( &col->write_lock );
    free(col);
}

void hss_thread_before_write(struct thread_collection *col) {
    if (!col) return;
    pthread_mutex_lock( &col->write_lock );
}

void hss_thread_after_write(struct thread_collection *col) {
    if (!col) return;
    pthread_mutex_unlock( &col->write_lock );
}
    

unsigned hss_thread_num_tracks(int num_thread) {
    if (num_thread == 0) num_thread = DEFAULT_THREAD;
    if (num_thread <= 1) return 1;
    if (num_thread >= MAX_THREAD) return MAX_THREAD;
    return num_thread;
}
*/