Stack allocation separated into separate functions

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

Makefile.am

@@ -39,6 +39,8 @@ libmill_la_SOURCES = \
     list.c\
     slist.h\
     slist.c\
+    stack.h\
+    stack.c\
     tcp.c\
     utils.h\
     utils.c

libmill.c

@@ -25,6 +25,7 @@
 #include "libmill.h"
 #include "list.h"
 #include "slist.h"
+#include "stack.h"
 #include "utils.h"
 
 #include <assert.h>
@@ -39,16 +40,10 @@
 /*  Coroutines                                                                */
 /******************************************************************************/
 
-/* Size of stack for new coroutines. In bytes. */
-#define MILL_STACK_SIZE 16384
-
 /* Maximum size of an item in a channel that we can handle without
    extra memory allocation. */
 #define MILL_MAXINLINECHVALSIZE 128
 
-/* Maximum number of unused cached stacks. */
-#define MILL_MAX_CACHED_STACKS 64
-
 volatile int mill_unoptimisable1 = 1;
 volatile void *mill_unoptimisable2 = NULL;
 
@@ -161,11 +156,6 @@ struct mill_fdwitem {
 };
 static struct mill_fdwitem *wait_items = NULL;
 
-/* A stack of unused coroutine stacks. This allows for extra-fast allocation
-   of a new stack. The FIFO nature of this structure minimises cache misses. */
-static int num_cached_crs = 0;
-static struct mill_cr *cached_crs = NULL;
-
 /* Removes current coroutine from the queue and returns it to the caller. */
 static struct mill_cr *mill_suspend() {
     struct mill_cr *cr = first_cr;
@@ -274,17 +264,7 @@ static void mill_ctxswitch(void) {
 void *mill_go_prologue(const char *created) {
     if(mill_setjmp(&first_cr->ctx))
         return NULL;
-    struct mill_cr *cr;
-    if(cached_crs) {
-        cr = cached_crs;
-        cached_crs = cached_crs->next;
-        --num_cached_crs;
-    }
-    else {
-        char *ptr = malloc(MILL_STACK_SIZE);
-        assert(ptr);
-        cr = (struct mill_cr*)(ptr + MILL_STACK_SIZE - sizeof(struct mill_cr));
-    }
+    struct mill_cr *cr = ((struct mill_cr*)mill_allocstack()) - 1;
     mill_list_insert(&all_crs, &cr->all_crs_item, NULL);
     cr->id = next_cr_id;
     cr->created = created;
@@ -310,15 +290,7 @@ void mill_go_epilogue(void) {
         cr->val.ptr = NULL;
     }
     mill_list_erase(&all_crs, &cr->all_crs_item);
-    if(num_cached_crs >= MILL_MAX_CACHED_STACKS) {
-        char *ptr = ((char*)(cr + 1)) - MILL_STACK_SIZE;
-        free(ptr);
-    }
-    else {
-        cr->next = cached_crs;
-        cached_crs = cr;
-        ++num_cached_crs;
-    }
+    mill_freestack(cr + 1);
     mill_ctxswitch();
 }
 

stack.c

@@ -0,0 +1,66 @@
+/*
+
+  Copyright (c) 2015 Martin Sustrik
+
+  Permission is hereby granted, free of charge, to any person obtaining a copy
+  of this software and associated documentation files (the "Software"),
+  to deal in the Software without restriction, including without limitation
+  the rights to use, copy, modify, merge, publish, distribute, sublicense,
+  and/or sell copies of the Software, and to permit persons to whom
+  the Software is furnished to do so, subject to the following conditions:
+
+  The above copyright notice and this permission notice shall be included
+  in all copies or substantial portions of the Software.
+
+  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+  THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+  FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+  IN THE SOFTWARE.
+
+*/
+
+#include "slist.h"
+#include "stack.h"
+
+#include <assert.h>
+#include <stdlib.h>
+
+/* Size of stack for new coroutines. In bytes. */
+#ifndef MILL_STACK_SIZE
+#define MILL_STACK_SIZE 16384
+#endif
+
+/* Maximum number of unused cached stacks. */
+#ifndef MILL_MAX_CACHED_STACKS
+#define MILL_MAX_CACHED_STACKS 64
+#endif
+
+/* A stack of unused coroutine stacks. This allows for extra-fast allocation
+   of a new stack. The FIFO nature of this structure minimises cache misses.
+   When the stack is cached its mill_slist_item is placed on its top rather
+   then on the bottom. That way we minimise page misses. */
+static int mill_num_cached_stacks = 0;
+static struct mill_slist mill_cached_stacks = {0};
+
+void *mill_allocstack(void) {
+    if(mill_slist_empty(&mill_cached_stacks))
+        return (void*)(mill_slist_pop(&mill_cached_stacks) + 1);
+    char *ptr = malloc(MILL_STACK_SIZE);
+    assert(ptr);
+    return ptr + MILL_STACK_SIZE; 
+}
+
+void mill_freestack(void *stack) {
+    if(mill_num_cached_stacks >= MILL_MAX_CACHED_STACKS) {
+        char *ptr = ((char*)stack) - MILL_STACK_SIZE;
+        free(ptr);
+        return;
+    }
+    struct mill_slist_item *item = ((struct mill_slist_item*)stack) - 1;
+    mill_slist_push(&mill_cached_stacks, item);
+    ++mill_num_cached_stacks;
+}
+

stack.h

@@ -0,0 +1,35 @@
+/*
+
+  Copyright (c) 2015 Martin Sustrik
+
+  Permission is hereby granted, free of charge, to any person obtaining a copy
+  of this software and associated documentation files (the "Software"),
+  to deal in the Software without restriction, including without limitation
+  the rights to use, copy, modify, merge, publish, distribute, sublicense,
+  and/or sell copies of the Software, and to permit persons to whom
+  the Software is furnished to do so, subject to the following conditions:
+
+  The above copyright notice and this permission notice shall be included
+  in all copies or substantial portions of the Software.
+
+  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+  THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+  FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+  IN THE SOFTWARE.
+
+*/
+
+#ifndef MILL_STACK_INCLUDED
+#define MILL_STACK_INCLUDED
+
+/* Allocates new stack. Returns pointer to the *top* of the stack.
+   For now we assume that the stack grows downwards. */
+void *mill_allocstack(void);
+
+/* Deallocates a stack. The argument is pointer to the top of the stack. */
+void mill_freestack(void *stack);
+
+#endif