Split out queue data structure

Makefile

@@ -1,5 +1,5 @@
 TARGET = cmsg
-OBJECTS = main.o harness.o net.o util.o relay.o
+OBJECTS = main.o harness.o net.o util.o relay.o dataq.o
 
 CFLAGS = -D_XOPEN_SOURCE=600 -Wall -O0 -g
 #CFLAGS = -D_XOPEN_SOURCE=600 -Wall -O3

dataq.c

@@ -0,0 +1,32 @@
+#include <stdlib.h>
+#include <string.h>
+#include <stdio.h>
+
+#include "dataq.h"
+
+#define QLINK(q,x)	(*((void **)(((char *) x) + (q)->link_offset)))
+
+void enqueue(queue_t *q, void *x) {
+  QLINK(q, x) = NULL;
+  if (q->head == NULL) {
+    q->head = x;
+  } else {
+    QLINK(q, q->tail) = x;
+  }
+  q->tail = x;
+  q->count++;
+}
+
+void *dequeue(queue_t *q) {
+  if (q->head == NULL) {
+    return NULL;
+  } else {
+    void *x = q->head;
+    q->head = QLINK(q, x);
+    if (q->head == NULL) {
+      q->tail = NULL;
+    }
+    q->count--;
+    return x;
+  }
+}

dataq.h

@@ -0,0 +1,14 @@
+#ifndef cmsg_dataq_h
+#define cmsg_dataq_h
+
+typedef struct queue_t_ {
+  size_t link_offset;
+  int count;
+  void *head;
+  void *tail;
+} queue_t;
+
+extern void enqueue(queue_t *q, void *x);
+extern void *dequeue(queue_t *q);
+
+#endif

harness.c

@@ -3,6 +3,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <stdio.h>
+#include <stddef.h>
 
 #include <sys/time.h>
 
@@ -13,6 +14,7 @@ typedef unsigned char u_char;
 
 #include "cmsg_private.h"
 #include "harness.h"
+#include "dataq.h"
 
 #include <assert.h>
 
@@ -33,40 +35,11 @@ typedef unsigned char u_char;
 
 Process *current_process = NULL;
 
+#define EMPTY_PROCESS_QUEUE ((queue_t) { offsetof(Process, link), 0, NULL, NULL })
+
 static ucontext_t scheduler;
-static ProcessQueue runlist = { 0, NULL, NULL };
-static ProcessQueue deadlist = { 0, NULL, NULL };
-
-static void zero_queue(ProcessQueue *pq) {
-  pq->count = 0;
-  pq->head = NULL;
-  pq->tail = NULL;
-}
-
-static void enqueue(ProcessQueue *pq, Process *p) {
-  p->link = NULL;
-  if (pq->head == NULL) {
-    pq->head = p;
-  } else {
-    pq->tail->link = p;
-  }
-  pq->tail = p;
-  pq->count++;
-}
-
-static Process *dequeue(ProcessQueue *pq) {
-  if (pq->head == NULL) {
-    return NULL;
-  } else {
-    Process *p = pq->head;
-    pq->head = p->link;
-    if (pq->head == NULL) {
-      pq->tail = NULL;
-    }
-    pq->count--;
-    return p;
-  }
-}
+static queue_t runlist = EMPTY_PROCESS_QUEUE;
+static queue_t deadlist = EMPTY_PROCESS_QUEUE;
 
 static void enqueue_runlist(Process *p) {
   p->state = PROCESS_RUNNING;
@@ -253,8 +226,8 @@ void boot_harness(void) {
   ICHECK(getcontext(&scheduler), "boot_harness getcontext");
   while (1) {
     while (runlist.count) {
-      ProcessQueue work = runlist;
-      zero_queue(&runlist);
+      queue_t work = runlist;
+      runlist = EMPTY_PROCESS_QUEUE;
       info("Processing %d jobs\n", work.count);
       while ((current_process = dequeue(&work)) != NULL) {
 	//info("entering %p\n", current_process);

harness.h

@@ -25,12 +25,6 @@ typedef struct IOHandle {
   short error_kind;
 } IOHandle;
 
-typedef struct ProcessQueue {
-  int count;
-  Process *head;
-  Process *tail;
-} ProcessQueue;
-
 extern Process *current_process;
 
 extern void yield(void);