From 7d8a0a1cdd62112ccdae2a80bb55ec9cec99b978 Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Sun, 7 Jun 2009 17:01:57 +0100
Subject: [PATCH] [cairo] Keep a small stash of cairo contexts

A cairo context is meant to be extremely cheap to create such that it can
be used in transient expose events. Thus these are allocated reasonably
frequently and show up malloc profiles.
---
 src/cairo.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 49 insertions(+), 2 deletions(-)

diff --git a/src/cairo.c b/src/cairo.c
index 0c58cfecd..91b882883 100644
--- a/src/cairo.c
+++ b/src/cairo.c
@@ -117,6 +117,53 @@ _cairo_set_error (cairo_t *cr, cairo_status_t status)
     status = _cairo_error (status);
 }
 
+#if HAS_ATOMIC_OPS
+/* We keep a small stash of contexts to reduce malloc pressure */
+#define CAIRO_STASH_SIZE 4
+static struct {
+    cairo_t pool[CAIRO_STASH_SIZE];
+    int occupied;
+} _context_stash;
+
+static cairo_t *
+_context_get (void)
+{
+    int avail, old, new;
+
+    do {
+	old = _context_stash.occupied;
+	avail = ffs (~old) - 1;
+	if (avail >= CAIRO_STASH_SIZE)
+	    return malloc (sizeof (cairo_t));
+
+	new = old | (1 << avail);
+    } while (_cairo_atomic_int_cmpxchg (&_context_stash.occupied, old, new) != old);
+
+    return &_context_stash.pool[avail];
+}
+
+static void
+_context_put (cairo_t *cr)
+{
+    int old, new, avail;
+
+    if (cr < &_context_stash.pool[0] ||
+	cr >= &_context_stash.pool[CAIRO_STASH_SIZE])
+    {
+	return free (cr);
+    }
+
+    avail = ~(1 << (cr - &_context_stash.pool[0]));
+    do {
+	old = _context_stash.occupied;
+	new = old & avail;
+    } while (_cairo_atomic_int_cmpxchg (&_context_stash.occupied, old, new) != old);
+}
+#else
+#define _context_get() malloc (sizeof (cairo_t))
+#define _context_put(cr) free (cr)
+#endif
+
 /**
  * cairo_create:
  * @target: target surface for the context
@@ -150,7 +197,7 @@ cairo_create (cairo_surface_t *target)
     if (target && target->status == CAIRO_STATUS_NO_MEMORY)
 	return (cairo_t *) &_cairo_nil;
 
-    cr = malloc (sizeof (cairo_t));
+    cr = _context_get ();
     if (unlikely (cr == NULL)) {
 	status = _cairo_error (CAIRO_STATUS_NO_MEMORY);
 	return (cairo_t *) &_cairo_nil;
@@ -248,7 +295,7 @@ cairo_destroy (cairo_t *cr)
 
     _cairo_user_data_array_fini (&cr->user_data);
 
-    free (cr);
+    _context_put (cr);
 }
 slim_hidden_def (cairo_destroy);