medfall

commit 61b316d77f70af04e534a2a1340d1d16941fb97b
parent afc16da0d6d3fc9562e6c6f858dc140fcc4b33ea
Author: Michael Savage <mikejsavage@gmail.com>
Date:   Mon Aug 10 22:24:26 +0200

Add untested/preliminary background work queue implementation

Diffstat:
Makefile
 | 
2
+-
work_queue.cc
 | 
95
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
work_queue.h
 | 
11
+++++++++++
3 files changed, 107 insertions(+), 1 deletion(-)
diff --git a/Makefile b/Makefile
@@ -1,6 +1,6 @@
 all: medfall hm.so pp
 
-OBJS = main.o gl.o
+OBJS = main.o gl.o work_queue.o
 BSPOBJS = bsp.o bsp_renderer.o gl.o
 HMOBJS = hm.o heightmap.o terrain_manager.o stb_image.o stb_perlin.o
 PPOBJS = pp.o stb_image.o stb_image_write.o
diff --git a/work_queue.cc b/work_queue.cc
@@ -0,0 +1,95 @@
+#include <pthread.h>
+#include <semaphore.h>
+
+#include "int.h"
+#include "work_queue.h"
+
+// TODO: move me somewhere else
+#define assert( predicate ) { if( !( predicate ) ) { __builtin_trap(); } }
+#define array_len( x ) ( sizeof( x ) / sizeof( ( x )[ 0 ] ) )
+
+#define read_barrier() asm volatile ( "" ::: "memory" )
+#define write_barrier() asm volatile ( "" ::: "memory" )
+
+struct Job {
+	WorkQueueCallback * callback;
+	void * data;
+};
+
+struct WorkQueue {
+	Job jobs[ 256 ];
+
+	sem_t * sem;
+
+	// using head/length means we need to an atomic pair which is a pain
+	volatile u16 head;
+	volatile u16 tail;
+
+	volatile u16 jobs_queued;
+	volatile u16 jobs_completed;
+};
+
+static bool workqueue_step( WorkQueue * const queue ) {
+	const u16 current_head = queue->head;
+	const u16 new_head = ( current_head + 1 ) % array_len( queue->jobs );
+
+	if( queue->jobs_completed < queue->jobs_queued ) {
+		if( __sync_bool_compare_and_swap( &queue->head, current_head, new_head ) ) {
+			Job & job = queue->jobs[ current_head ];
+
+			job.callback( job.data );
+
+			__sync_fetch_and_add( &queue->jobs_completed, 1 );
+		}
+
+		return true;
+	}
+
+	return false;
+}
+
+static void * workqueue_worker( void * data ) {
+	WorkQueue * queue = ( WorkQueue * ) data;
+
+	for( ;; ) {
+		if( !workqueue_step( queue ) ) {
+			sem_wait( queue->sem );
+		}
+	}
+
+	return nullptr;
+}
+
+void workqueue_init( WorkQueue * const queue, const u32 num_threads ) {
+	*queue = { };
+
+	sem_init( queue->sem, 0, 0 );
+
+	for( u32 i = 0; i < num_threads; i++ ) {
+		pthread_t thread;
+		pthread_create( &thread, nullptr, workqueue_worker, queue );
+	}
+}
+
+void workqueue_enqueue( WorkQueue * const queue, WorkQueueCallback * const callback, void * const data ) {
+	assert( queue->jobs_queued < array_len( queue->jobs ) );
+
+	const Job job = { callback, data };
+
+	queue->jobs[ queue->tail ] = job;
+	queue->jobs_queued++;
+
+	write_barrier();
+	queue->tail = ( queue->tail + 1 ) % array_len( queue->jobs );
+
+	sem_post( queue->sem );
+}
+
+void workqueue_exhaust( WorkQueue * const queue ) {
+	while( queue->jobs_completed < queue->jobs_queued ) {
+		workqueue_step( queue );
+	}
+
+	queue->jobs_queued = 0;
+	queue->jobs_completed = 0;
+}
diff --git a/work_queue.h b/work_queue.h
@@ -0,0 +1,11 @@
+#ifndef _WORK_QUEUE_H_
+#define _WORK_QUEUE_H_
+
+#include "int.h"
+
+struct WorkQueue;
+
+#define WORK_QUEUE_CALLBACK( name ) void name( void * const data )
+typedef WORK_QUEUE_CALLBACK( WorkQueueCallback );
+
+#endif // _WORK_QUEUE_H_