source: libcfa/src/concurrency/channel.hfa@ 056bee8

#pragma once

#include <locks.hfa>

struct no_reacq_lock {
    inline exp_backoff_then_block_lock;
};

// have to override these by hand to get around plan 9 inheritance bug where resolver can't find the appropriate routine to call
static inline void   ?{}( no_reacq_lock & this ) { ((exp_backoff_then_block_lock &)this){}; }
static inline bool   try_lock(no_reacq_lock & this) { return try_lock(((exp_backoff_then_block_lock &)this)); }
static inline void   lock(no_reacq_lock & this) { lock(((exp_backoff_then_block_lock &)this)); }
static inline void   unlock(no_reacq_lock & this) { unlock(((exp_backoff_then_block_lock &)this)); }
static inline void   on_notify(no_reacq_lock & this, struct thread$ * t ) { on_notify(((exp_backoff_then_block_lock &)this), t); }
static inline size_t on_wait(no_reacq_lock & this) { return on_wait(((exp_backoff_then_block_lock &)this)); }
// override wakeup so that we don't reacquire the lock if using a condvar
static inline void   on_wakeup( no_reacq_lock & this, size_t recursion ) {}

#define __PREVENTION_CHANNEL
#ifdef __PREVENTION_CHANNEL
forall( T ) {
struct channel {
    size_t size;
    size_t front, back, count;
    T * buffer;
    thread$ * chair;
    T * chair_elem;
    exp_backoff_then_block_lock c_lock, p_lock;
    __spinlock_t mutex_lock;
    char __padding[64]; // avoid false sharing in arrays
};

static inline void ?{}( channel(T) &c, size_t _size ) with(c) {
    size = _size;
    front = back = count = 0;
    buffer = anew( size );
    chair = 0p;
    mutex_lock{};
    c_lock{};
    p_lock{};
}

static inline void ?{}( channel(T) &c ){ ((channel(T) &)c){ 0 }; }
static inline void ^?{}( channel(T) &c ) with(c) { delete( buffer ); }
static inline size_t get_count( channel(T) & chan ) with(chan) { return count; }
static inline size_t get_size( channel(T) & chan ) with(chan) { return size; }
static inline bool has_waiters( channel(T) & chan ) with(chan) { return chair != 0p; }

static inline void insert_( channel(T) & chan, T & elem ) with(chan) {
    memcpy((void *)&buffer[back], (void *)&elem, sizeof(T));
    count += 1;
    back++;
    if ( back == size ) back = 0;
}

static inline void insert( channel(T) & chan, T elem ) with( chan ) {
    lock( p_lock );
    lock( mutex_lock __cfaabi_dbg_ctx2 );

    // have to check for the zero size channel case
    if ( size == 0 && chair != 0p ) {
        memcpy((void *)chair_elem, (void *)&elem, sizeof(T));
        unpark( chair );
        chair = 0p;
        unlock( mutex_lock );
        unlock( p_lock );
        unlock( c_lock );
        return;
    }

    // wait if buffer is full, work will be completed by someone else
    if ( count == size ) {
        chair = active_thread();
        chair_elem = &elem;
        unlock( mutex_lock );
        park( );
        return;
    } // if

    if ( chair != 0p ) {
        memcpy((void *)chair_elem, (void *)&elem, sizeof(T));
        unpark( chair );
        chair = 0p;
        unlock( mutex_lock );
        unlock( p_lock );
        unlock( c_lock );
        return;
    }
    else insert_( chan, elem );

    unlock( mutex_lock );
    unlock( p_lock );
}

static inline T remove( channel(T) & chan ) with(chan) {
    lock( c_lock );
    lock( mutex_lock __cfaabi_dbg_ctx2 );
    T retval;

    // have to check for the zero size channel case
    if ( size == 0 && chair != 0p ) {
        memcpy((void *)&retval, (void *)chair_elem, sizeof(T));
        unpark( chair );
        chair = 0p;
        unlock( mutex_lock );
        unlock( p_lock );
        unlock( c_lock );
        return retval;
    }

    // wait if buffer is empty, work will be completed by someone else
    if ( count == 0 ) { 
        chair = active_thread();
        chair_elem = &retval;
        unlock( mutex_lock );
        park( );
        return retval;
    }

    // Remove from buffer
    memcpy((void *)&retval, (void *)&buffer[front], sizeof(T));
    count -= 1;
    front = (front + 1) % size;

    if ( chair != 0p ) {
        insert_( chan, *chair_elem );  // do waiting producer work
        unpark( chair );
        chair = 0p;
        unlock( mutex_lock );
        unlock( p_lock );
        unlock( c_lock );
        return retval;
    }

    unlock( mutex_lock );
    unlock( c_lock );
    return retval;
}

} // forall( T )
#endif

#ifndef __PREVENTION_CHANNEL
forall( T ) {
struct channel {
    size_t size;
    size_t front, back, count;
    T * buffer;
    fast_cond_var( no_reacq_lock ) prods, cons;
    no_reacq_lock mutex_lock;
};

static inline void ?{}( channel(T) &c, size_t _size ) with(c) {
    size = _size;
    front = back = count = 0;
    buffer = anew( size );
    prods{};
    cons{};
    mutex_lock{};
}

static inline void ?{}( channel(T) &c ){ ((channel(T) &)c){ 0 }; }
static inline void ^?{}( channel(T) &c ) with(c) { delete( buffer ); }
static inline size_t get_count( channel(T) & chan ) with(chan) { return count; }
static inline size_t get_size( channel(T) & chan ) with(chan) { return size; }
static inline bool has_waiters( channel(T) & chan ) with(chan) { return !empty( cons ) || !empty( prods ); }
static inline bool has_waiting_consumers( channel(T) & chan ) with(chan) { return !empty( cons ); }
static inline bool has_waiting_producers( channel(T) & chan ) with(chan) { return !empty( prods ); }

static inline void insert_( channel(T) & chan, T & elem ) with(chan) {
    memcpy((void *)&buffer[back], (void *)&elem, sizeof(T));
    count += 1;
    back++;
    if ( back == size ) back = 0;
}


static inline void insert( channel(T) & chan, T elem ) with(chan) {
    lock( mutex_lock );

    // have to check for the zero size channel case
    if ( size == 0 && !empty( cons ) ) {
        memcpy((void *)front( cons ), (void *)&elem, sizeof(T));
        notify_one( cons );
        unlock( mutex_lock );
        return;
    }

    // wait if buffer is full, work will be completed by someone else
    if ( count == size ) { 
        wait( prods, mutex_lock, (uintptr_t)&elem );
        return;
    } // if

    if ( count == 0 && !empty( cons ) )
        // do waiting consumer work
        memcpy((void *)front( cons ), (void *)&elem, sizeof(T)); 
    else insert_( chan, elem );
    
    notify_one( cons );
    unlock( mutex_lock );
}

static inline T remove( channel(T) & chan ) with(chan) {
    lock( mutex_lock );
    T retval;

    // have to check for the zero size channel case
    if ( size == 0 && !empty( prods ) ) {
        memcpy((void *)&retval, (void *)front( prods ), sizeof(T));
        notify_one( prods );
        unlock( mutex_lock );
        return retval;
    }

    // wait if buffer is empty, work will be completed by someone else
    if (count == 0) { 
        wait( cons, mutex_lock, (uintptr_t)&retval );
        return retval;
    }

    // Remove from buffer
    memcpy((void *)&retval, (void *)&buffer[front], sizeof(T));
    count -= 1;
    front = (front + 1) % size;

    if (count == size - 1 && !empty( prods ) ) 
        insert_( chan, *((T *)front( prods )) );  // do waiting producer work

    notify_one( prods );
    unlock( mutex_lock );
    return retval;
}

} // forall( T )
#endif