source: libcfa/src/concurrency/ready_subqueue.hfa@ dcad80a

#pragma once

#define __CFA_NO_SCHED_STATS__

#include "containers/queueLockFree.hfa"

// Intrusives lanes which are used by the relaxed ready queue
struct __attribute__((aligned(128))) __intrusive_lane_t {
        struct $thread * prev;

        // spin lock protecting the queue
        volatile bool lock;

        __thread_desc_link anchor;

        #if !defined(__CFA_NO_STATISTICS__)
                unsigned cnt;
        #endif
};

// Get the head pointer (one before the first element) from the anchor
static inline $thread * mock_head(const __intrusive_lane_t & this) {
        $thread * rhead = ($thread *)(
                (uintptr_t)( &this.anchor ) - __builtin_offsetof( $thread, link )
        );
        return rhead;
}

// Ctor
void ?{}( __intrusive_lane_t & this ) {
        this.lock = false;
        this.prev = mock_head(this);
        this.anchor.next = 0p;
        this.anchor.ts   = -1llu;
        #if !defined(__CFA_NO_STATISTICS__)
                this.cnt  = 0;
        #endif

        // We add a boat-load of assertions here because the anchor code is very fragile
        /* paranoid */ _Static_assert( offsetof( $thread, link ) == offsetof(__intrusive_lane_t, anchor) );
        /* paranoid */ verify( offsetof( $thread, link ) == offsetof(__intrusive_lane_t, anchor) );
        /* paranoid */ verify( ((uintptr_t)( mock_head(this) ) + offsetof( $thread, link )) == (uintptr_t)(&this.anchor) );
        /* paranoid */ verify( &mock_head(this)->link.next == &this.anchor.next );
        /* paranoid */ verify( &mock_head(this)->link.ts   == &this.anchor.ts   );
        /* paranoid */ verify( mock_head(this)->link.next == 0p );
        /* paranoid */ verify( mock_head(this)->link.ts   == -1llu  );
        /* paranoid */ verify( mock_head(this) == this.prev );
        /* paranoid */ verify( __alignof__(__intrusive_lane_t) == 128 );
        /* paranoid */ verify( __alignof__(this) == 128 );
        /* paranoid */ verifyf( ((intptr_t)(&this) % 128) == 0, "Expected address to be aligned %p %% 128 == %zd", &this, ((intptr_t)(&this) % 128) );
}

// Dtor is trivial
void ^?{}( __intrusive_lane_t & this ) {
        // Make sure the list is empty
        /* paranoid */ verify( this.anchor.next == 0p );
        /* paranoid */ verify( this.anchor.ts   == -1llu );
        /* paranoid */ verify( mock_head(this)  == this.prev );
}

// Push a thread onto this lane
// returns true of lane was empty before push, false otherwise
static inline void push( __intrusive_lane_t & this, $thread * node ) {
        /* paranoid */ verify( this.lock );
        /* paranoid */ verify( node->link.next == 0p );
        /* paranoid */ verify( node->link.ts   == -1llu  );
        /* paranoid */ verify( this.prev->link.next == 0p );
        /* paranoid */ verify( this.prev->link.ts   == -1llu  );
        if( this.anchor.next == 0p ) {
                /* paranoid */ verify( this.anchor.next == 0p );
                /* paranoid */ verify( this.anchor.ts   == -1llu );
                /* paranoid */ verify( this.anchor.ts   != 0  );
                /* paranoid */ verify( this.prev == mock_head( this ) );
        } else {
                /* paranoid */ verify( this.anchor.next != 0p );
                /* paranoid */ verify( this.anchor.ts   != -1llu );
                /* paranoid */ verify( this.anchor.ts   != 0  );
                /* paranoid */ verify( this.prev != mock_head( this ) );
        }

        // Get the relevant nodes locally
        this.prev->link.next = node;
        this.prev->link.ts   = rdtscl();
        this.prev = node;
        #if !defined(__CFA_NO_STATISTICS__)
                this.cnt++;
        #endif
}

// Pop a thread from this lane (must be non-empty)
// returns popped
// returns true of lane was empty before push, false otherwise
static inline [* $thread, unsigned long long] pop( __intrusive_lane_t & this ) {
        /* paranoid */ verify( this.lock );
        /* paranoid */ verify( this.anchor.next != 0p );
        /* paranoid */ verify( this.anchor.ts   != -1llu );
        /* paranoid */ verify( this.anchor.ts   != 0  );

        // Get the relevant nodes locally
        unsigned long long ts = this.anchor.ts;
        $thread * node = this.anchor.next;
        this.anchor.next = node->link.next;
        this.anchor.ts   = node->link.ts;
        bool is_empty = this.anchor.next == 0p;
        node->link.next = 0p;
        node->link.ts   = -1llu;
        #if !defined(__CFA_NO_STATISTICS__)
                this.cnt--;
        #endif

        // Update head time stamp
        if(is_empty) this.prev = mock_head( this );

        /* paranoid */ verify( node->link.next == 0p );
        /* paranoid */ verify( node->link.ts   == -1llu  );
        /* paranoid */ verify( node->link.ts   != 0  );
        /* paranoid */ verify( this.anchor.ts  != 0  );
        return [node, ts];
}

// Check whether or not list is empty
static inline bool is_empty(__intrusive_lane_t & this) {
        return this.anchor.next == 0p;
}

// Return the timestamp
static inline unsigned long long ts(__intrusive_lane_t & this) {
        // Cannot verify here since it may not be locked
        /* paranoid */ verify(this.anchor.ts != 0);
        return this.anchor.ts;
}