Bug 691691: Add way of clearing cached objects out of the xref.

We add various facilities here, intended to allow us to efficiently
minimise the memory we use for holding cached pdf objects.

Firstly, we add the ability to 'mark' all the currently loaded objects.

Next we add the ability to 'clear the xref' - to drop all the currently
loaded objects that have no other references except the ones held by the
xref table itself.

Finally, we add the ability to 'clear the xref to the last mark' - to
drop all the currently loaded objects that have been created since the
last 'mark' operation and have no other references except the ones held
by the xref table.

We expose this to the user by adding a new device hint 'FZ_NO_CACHE'.
If set on the device, then the PDF interpreter will pdf_mark_xref before
starting and pdf_clear_xref_to_mark afterwards. Thus no additional
objects will be retained in memory after a given page is run, unless
someone else picks them up and takes a reference to them as part of
the run.

We amend our simple example app to set this device hint when loading
pages as part of a search.

1 files changed, 32 insertions, 30 deletions

diff --git a/platform/x11/pdfapp.c b/platform/x11/pdfapp.c
index cade7509..bb619614 100644
--- a/platform/x11/pdfapp.c
+++ b/platform/x11/pdfapp.c
@@ -26,7 +26,7 @@ enum
 	PDFAPP_OUTLINE_LOAD_NOW = 2
 };
 
-static void pdfapp_showpage(pdfapp_t *app, int loadpage, int drawpage, int repaint, int transition);
+static void pdfapp_showpage(pdfapp_t *app, int loadpage, int drawpage, int repaint, int transition, int searching);
 static void pdfapp_updatepage(pdfapp_t *app);
 
 static void pdfapp_warn(pdfapp_t *app, const char *fmt, ...)
@@ -330,7 +330,7 @@ void pdfapp_open_progressive(pdfapp_t *app, char *filename, int reload, int bps)
 		app->pany = 0;
 	}
 
-	pdfapp_showpage(app, 1, 1, 1, 0);
+	pdfapp_showpage(app, 1, 1, 1, 0, 0);
 }
 
 void pdfapp_close(pdfapp_t *app)
@@ -512,7 +512,7 @@ static void pdfapp_panview(pdfapp_t *app, int newx, int newy)
 	app->pany = newy;
 }
 
-static void pdfapp_loadpage(pdfapp_t *app)
+static void pdfapp_loadpage(pdfapp_t *app, int no_cache)
 {
 	fz_device *mdev = NULL;
 	int errored = 0;
@@ -561,6 +561,8 @@ static void pdfapp_loadpage(pdfapp_t *app)
 		/* Create display lists */
 		app->page_list = fz_new_display_list(app->ctx);
 		mdev = fz_new_list_device(app->ctx, app->page_list);
+		if (no_cache)
+			fz_enable_device_hints(mdev, FZ_NO_CACHE);
 		cookie.incomplete_ok = 1;
 		fz_run_page_contents(app->doc, app->page, mdev, &fz_identity, &cookie);
 		fz_free_device(mdev);
@@ -688,7 +690,7 @@ static void pdfapp_updatepage(pdfapp_t *app)
 		fz_free_device(idev);
 	}
 
-	pdfapp_showpage(app, 0, 0, 1, 0);
+	pdfapp_showpage(app, 0, 0, 1, 0, 0);
 }
 
 void pdfapp_reloadpage(pdfapp_t *app)
@@ -705,10 +707,10 @@ void pdfapp_reloadpage(pdfapp_t *app)
 		}
 		app->outline_deferred = 0;
 	}
-	pdfapp_showpage(app, 1, 1, 1, 0);
+	pdfapp_showpage(app, 1, 1, 1, 0, 0);
 }
 
-static void pdfapp_showpage(pdfapp_t *app, int loadpage, int drawpage, int repaint, int transition)
+static void pdfapp_showpage(pdfapp_t *app, int loadpage, int drawpage, int repaint, int transition, int searching)
 {
 	char buf[MAX_TITLE];
 	fz_device *idev;
@@ -733,7 +735,7 @@ static void pdfapp_showpage(pdfapp_t *app, int loadpage, int drawpage, int repai
 
 	if (loadpage)
 	{
-		pdfapp_loadpage(app);
+		pdfapp_loadpage(app, searching);
 
 		/* Zero search hit position */
 		app->hit_count = 0;
@@ -878,7 +880,7 @@ void pdfapp_gotopage(pdfapp_t *app, int number)
 	}
 	app->hist[app->histlen++] = app->pageno;
 	app->pageno = number + 1;
-	pdfapp_showpage(app, 1, 1, 1, 0);
+	pdfapp_showpage(app, 1, 1, 1, 0, 0);
 }
 
 void pdfapp_inverthit(pdfapp_t *app)
@@ -916,7 +918,7 @@ static void pdfapp_search_in_direction(pdfapp_t *app, enum panning *panto, int d
 		if (page != app->pageno)
 		{
 			app->pageno = page;
-			pdfapp_showpage(app, 1, 0, 0, 0);
+			pdfapp_showpage(app, 1, 0, 0, 0, 1);
 		}
 
 		app->hit_count = fz_search_text_page(app->ctx, app->page_text, app->search, app->hit_bbox, nelem(app->hit_bbox));
@@ -937,7 +939,7 @@ static void pdfapp_search_in_direction(pdfapp_t *app, enum panning *panto, int d
 	pdfapp_warn(app, "String '%s' not found.", app->search);
 
 	app->pageno = firstpage;
-	pdfapp_showpage(app, 1, 0, 0, 0);
+	pdfapp_showpage(app, 1, 0, 0, 0, 0);
 	wincursor(app, HAND);
 	winrepaint(app);
 }
@@ -982,7 +984,7 @@ void pdfapp_onkey(pdfapp_t *app, int c)
 							app->pageno = app->pagecount;
 						else
 							app->pageno--;
-						pdfapp_showpage(app, 1, 1, 0, 0);
+						pdfapp_showpage(app, 1, 1, 0, 0, 1);
 					}
 
 					pdfapp_onkey(app, 'n');
@@ -1034,13 +1036,13 @@ void pdfapp_onkey(pdfapp_t *app, int c)
 		app->resolution *= ZOOMSTEP;
 		if (app->resolution > MAXRES)
 			app->resolution = MAXRES;
-		pdfapp_showpage(app, 0, 1, 1, 0);
+		pdfapp_showpage(app, 0, 1, 1, 0, 0);
 		break;
 	case '-':
 		app->resolution /= ZOOMSTEP;
 		if (app->resolution < MINRES)
 			app->resolution = MINRES;
-		pdfapp_showpage(app, 0, 1, 1, 0);
+		pdfapp_showpage(app, 0, 1, 1, 0, 0);
 		break;
 
 	case 'W':
@@ -1049,7 +1051,7 @@ void pdfapp_onkey(pdfapp_t *app, int c)
 			app->resolution = MAXRES;
 		else if (app->resolution < MINRES)
 			app->resolution = MINRES;
-		pdfapp_showpage(app, 0, 1, 1, 0);
+		pdfapp_showpage(app, 0, 1, 1, 0, 0);
 		break;
 	case 'H':
 		app->resolution *= (double) app->winh / (double) fz_pixmap_height(app->ctx, app->image);
@@ -1057,36 +1059,36 @@ void pdfapp_onkey(pdfapp_t *app, int c)
 			app->resolution = MAXRES;
 		else if (app->resolution < MINRES)
 			app->resolution = MINRES;
-		pdfapp_showpage(app, 0, 1, 1, 0);
+		pdfapp_showpage(app, 0, 1, 1, 0, 0);
 		break;
 
 	case 'L':
 		app->rotate -= 90;
-		pdfapp_showpage(app, 0, 1, 1, 0);
+		pdfapp_showpage(app, 0, 1, 1, 0, 0);
 		break;
 	case 'R':
 		app->rotate += 90;
-		pdfapp_showpage(app, 0, 1, 1, 0);
+		pdfapp_showpage(app, 0, 1, 1, 0, 0);
 		break;
 
 	case 'c':
 		app->grayscale ^= 1;
-		pdfapp_showpage(app, 0, 1, 1, 0);
+		pdfapp_showpage(app, 0, 1, 1, 0, 0);
 		break;
 
 	case 'i':
 		app->invert ^= 1;
-		pdfapp_showpage(app, 0, 1, 1, 0);
+		pdfapp_showpage(app, 0, 1, 1, 0, 0);
 		break;
 
 #ifndef NDEBUG
 	case 'a':
 		app->rotate -= 15;
-		pdfapp_showpage(app, 0, 1, 1, 0);
+		pdfapp_showpage(app, 0, 1, 1, 0, 0);
 		break;
 	case 's':
 		app->rotate += 15;
-		pdfapp_showpage(app, 0, 1, 1, 0);
+		pdfapp_showpage(app, 0, 1, 1, 0, 0);
 		break;
 #endif
 
@@ -1108,27 +1110,27 @@ void pdfapp_onkey(pdfapp_t *app, int c)
 		}
 		app->shrinkwrap = 1;
 		app->panx = app->pany = 0;
-		pdfapp_showpage(app, 0, 0, 1, 0);
+		pdfapp_showpage(app, 0, 0, 1, 0, 0);
 		break;
 
 	case 'h':
 		app->panx += fz_pixmap_width(app->ctx, app->image) / 10;
-		pdfapp_showpage(app, 0, 0, 1, 0);
+		pdfapp_showpage(app, 0, 0, 1, 0, 0);
 		break;
 
 	case 'j':
 		app->pany -= fz_pixmap_height(app->ctx, app->image) / 10;
-		pdfapp_showpage(app, 0, 0, 1, 0);
+		pdfapp_showpage(app, 0, 0, 1, 0, 0);
 		break;
 
 	case 'k':
 		app->pany += fz_pixmap_height(app->ctx, app->image) / 10;
-		pdfapp_showpage(app, 0, 0, 1, 0);
+		pdfapp_showpage(app, 0, 0, 1, 0, 0);
 		break;
 
 	case 'l':
 		app->panx -= fz_pixmap_width(app->ctx, app->image) / 10;
-		pdfapp_showpage(app, 0, 0, 1, 0);
+		pdfapp_showpage(app, 0, 0, 1, 0, 0);
 		break;
 
 	/*
@@ -1308,7 +1310,7 @@ void pdfapp_onkey(pdfapp_t *app, int c)
 		case DONT_PAN:
 			break;
 		}
-		pdfapp_showpage(app, loadpage, 1, 1, 1);
+		pdfapp_showpage(app, loadpage, 1, 1, 1, 0);
 	}
 }
 
@@ -1508,7 +1510,7 @@ void pdfapp_onmouse(pdfapp_t *app, int x, int y, int btn, int modifiers, int sta
 					app->resolution = MAXRES;
 				if (app->resolution < MINRES)
 					app->resolution = MINRES;
-				pdfapp_showpage(app, 0, 1, 1, 0);
+				pdfapp_showpage(app, 0, 1, 1, 0, 0);
 			}
 			else
 			{
@@ -1574,7 +1576,7 @@ void pdfapp_onmouse(pdfapp_t *app, int x, int y, int btn, int modifiers, int sta
 					if( app->pageno > 1 )
 					{
 						app->pageno--;
-						pdfapp_showpage(app, 1, 1, 1, 0);
+						pdfapp_showpage(app, 1, 1, 1, 0, 0);
 						newy = -fz_pixmap_height(app->ctx, app->image);
 					}
 					app->beyondy = 0;
@@ -1584,7 +1586,7 @@ void pdfapp_onmouse(pdfapp_t *app, int x, int y, int btn, int modifiers, int sta
 					if( app->pageno < app->pagecount )
 					{
 						app->pageno++;
-						pdfapp_showpage(app, 1, 1, 1, 0);
+						pdfapp_showpage(app, 1, 1, 1, 0, 0);
 						newy = 0;
 					}
 					app->beyondy = 0;