Android: Allow multiple instances of MuPDF to run simultaneously.

Previously, we had assumed that we'd only ever have one MuPDFActivity
running at once; this meant that we only had a single MuPDFCore, and
that it was safe to hold the native libraries state in global
variables.

Unfortunately, it seems that if you launch MuPDF from the apps list,
and open a file, then return to the home screen using 'Home' rather than
'Back', MuPDF is kept running in the background. Launching a PDF file
from a file manager then starts a new MuPDFActivity and things get
very confused.

The solution implemented here is first to move all the MuPDF global
variables into a 'globals' structure, and update the code to use
this. Next, we allocate this structure on 'openFile', and free it on
'destroying'. Finally, we return the pointer to this structure as a
java long from openFile, and store it in a private data pointer,
globals.

Each MuPDFCore native method can then retrieve the value of 'globals'
and get the global state back. This means that every MuPDFCore native
method must now be non-static (except isJavascriptSupported).

2 files changed, 307 insertions, 228 deletions

diff --git a/android/jni/mupdf.c b/android/jni/mupdf.c
index a89b773c..c0a8d791 100644
--- a/android/jni/mupdf.c
+++ b/android/jni/mupdf.c
@@ -49,20 +49,52 @@ typedef struct
 	fz_display_list *annot_list;
 } page_cache;
 
+typedef struct globals_s globals;
 
-/* Globals */
-fz_colorspace *colorspace;
-fz_document *doc;
-int resolution = 160;
-fz_context *ctx;
-fz_bbox *hit_bbox = NULL;
-int current;
-char *current_path = NULL;
+struct globals_s
+{
+	fz_colorspace *colorspace;
+	fz_document *doc;
+	int resolution;
+	fz_context *ctx;
+	fz_bbox *hit_bbox;
+	int current;
+	char *current_path;
+
+	page_cache pages[NUM_CACHE];
+
+	int alerts_initialised;
+	// fin_lock and fin_lock2 are used during shutdown. The two waiting tasks
+	// show_alert and waitForAlertInternal respectively take these locks while
+	// waiting. During shutdown, the conditions are signaled and then the fin_locks
+	// are taken momentarily to ensure the blocked threads leave the controlled
+	// area of code before the mutexes and condition variables are destroyed.
+	pthread_mutex_t fin_lock;
+	pthread_mutex_t fin_lock2;
+	// alert_lock is the main lock guarding the variables directly below.
+	pthread_mutex_t alert_lock;
+	// Flag indicating if the alert system is active. When not active, both
+	// show_alert and waitForAlertInternal return immediately.
+	int alerts_active;
+	// Pointer to the alert struct passed in by show_alert, and valid while
+	// show_alert is blocked.
+	fz_alert_event *current_alert;
+	// Flag and condition varibles to signal a request is present and a reply
+	// is present, respectively. The condition variables alone are not sufficient
+	// because of the pthreads permit spurious signals.
+	int alert_request;
+	int alert_reply;
+	pthread_cond_t alert_request_cond;
+	pthread_cond_t alert_reply_cond;
+};
 
-page_cache pages[NUM_CACHE] = {{0}};
+static jfieldID global_fid;
 
-static void drop_page_cache(page_cache *pc)
+static void drop_page_cache(globals *glo, page_cache *pc)
 {
+	fz_context  *ctx = glo->ctx;
+	fz_document *doc = glo->doc;
+
 	LOGI("Drop page %d", pc->number);
 	fz_free_display_list(ctx, pc->page_list);
 	pc->page_list = NULL;
@@ -74,111 +106,91 @@ static void drop_page_cache(page_cache *pc)
 	pc->hq_page = NULL;
 }
 
-static void clear_hq_pages()
+static void clear_hq_pages(globals *glo)
 {
 	int i;
+	fz_document *doc = glo->doc;
 
 	for (i = 0; i < NUM_CACHE; i++) {
-		fz_free_page(doc, pages[i].hq_page);
-		pages[i].hq_page = NULL;
+		fz_free_page(doc, glo->pages[i].hq_page);
+		glo->pages[i].hq_page = NULL;
 	}
 }
 
-static void dump_annotation_display_lists()
+static void dump_annotation_display_lists(globals *glo)
 {
+	fz_context *ctx = glo->ctx;
 	int i;
 
 	for (i = 0; i < NUM_CACHE; i++) {
-		fz_free_display_list(ctx, pages[i].annot_list);
-		pages[i].annot_list = NULL;
+		fz_free_display_list(ctx, glo->pages[i].annot_list);
+		glo->pages[i].annot_list = NULL;
 	}
 }
 
-static alerts_initialised = 0;
-// fin_lock and fin_lock2 are used during shutdown. The two waiting tasks
-// show_alert and waitForAlertInternal respectively take these locks while
-// waiting. During shutdown, the conditions are signaled and then the fin_locks
-// are taken momentarily to ensure the blocked threads leave the controlled
-// area of code before the mutexes and condition variables are destroyed.
-static pthread_mutex_t fin_lock;
-static pthread_mutex_t fin_lock2;
-// alert_lock is the main lock guarding the variables directly below.
-static pthread_mutex_t alert_lock;
-// Flag indicating if the alert system is active. When not active, both
-// show_alert and waitForAlertInternal return immediately.
-static int alerts_active;
-// Pointer to the alert struct passed in by show_alert, and valid while
-// show_alert is blocked.
-static fz_alert_event *current_alert;
-// Flag and condition varibles to signal a request is present and a reply
-// is present, respectively. The condition variables alone are not sufficient
-// because of the pthreads permit spurious signals.
-static int alert_request;
-static int alert_reply;
-static pthread_cond_t alert_request_cond;
-static pthread_cond_t alert_reply_cond;
-
-static void show_alert(fz_alert_event *alert)
+static void show_alert(globals *glo, fz_alert_event *alert)
 {
-	pthread_mutex_lock(&fin_lock2);
-	pthread_mutex_lock(&alert_lock);
+	pthread_mutex_lock(&glo->fin_lock2);
+	pthread_mutex_lock(&glo->alert_lock);
 
 	LOGT("Enter show_alert: %s", alert->title);
 	alert->button_pressed = 0;
 
-	if (alerts_active)
+	if (glo->alerts_active)
 	{
-		current_alert = alert;
-		alert_request = 1;
-		pthread_cond_signal(&alert_request_cond);
-
-		while (alerts_active && !alert_reply)
-			pthread_cond_wait(&alert_reply_cond, &alert_lock);
-		alert_reply = 0;
-		current_alert = NULL;
+		glo->current_alert = alert;
+		glo->alert_request = 1;
+		pthread_cond_signal(&glo->alert_request_cond);
+
+		while (glo->alerts_active && !glo->alert_reply)
+			pthread_cond_wait(&glo->alert_reply_cond, &glo->alert_lock);
+		glo->alert_reply = 0;
+		glo->current_alert = NULL;
 	}
 
 	LOGT("Exit show_alert");
 
-	pthread_mutex_unlock(&alert_lock);
-	pthread_mutex_unlock(&fin_lock2);
+	pthread_mutex_unlock(&glo->alert_lock);
+	pthread_mutex_unlock(&glo->fin_lock2);
 }
 
 static void event_cb(fz_doc_event *event, void *data)
 {
+	globals *glo = (globals *)data;
+
 	switch (event->type)
 	{
 	case FZ_DOCUMENT_EVENT_ALERT:
-		show_alert(fz_access_alert_event(event));
+		show_alert(glo, fz_access_alert_event(event));
 		break;
 	}
 }
 
-static void alerts_init()
+static void alerts_init(globals *glo)
 {
-	fz_interactive *idoc = fz_interact(doc);
+	fz_interactive *idoc = fz_interact(glo->doc);
 
-	if (!idoc || alerts_initialised)
+	if (!idoc || glo->alerts_initialised)
 		return;
 
-	alerts_active = 0;
-	alert_request = 0;
-	alert_reply = 0;
-	pthread_mutex_init(&fin_lock, NULL);
-	pthread_mutex_init(&fin_lock2, NULL);
-	pthread_mutex_init(&alert_lock, NULL);
-	pthread_cond_init(&alert_request_cond, NULL);
-	pthread_cond_init(&alert_reply_cond, NULL);
+	glo->alerts_active = 0;
+	glo->alert_request = 0;
+	glo->alert_reply = 0;
+	pthread_mutex_init(&glo->fin_lock, NULL);
+	pthread_mutex_init(&glo->fin_lock2, NULL);
+	pthread_mutex_init(&glo->alert_lock, NULL);
+	pthread_cond_init(&glo->alert_request_cond, NULL);
+	pthread_cond_init(&glo->alert_reply_cond, NULL);
 
-	fz_set_doc_event_callback(idoc, event_cb, NULL);
+	fz_set_doc_event_callback(idoc, event_cb, glo);
 	LOGT("alert_init");
-	alerts_initialised = 1;
+	glo->alerts_initialised = 1;
 }
 
-static void alerts_fin()
+static void alerts_fin(globals *glo)
 {
-	fz_interactive *idoc = fz_interact(doc);
-	if (!alerts_initialised)
+	fz_interactive *idoc = fz_interact(glo->doc);
+	if (!glo->alerts_initialised)
 		return;
 
 	LOGT("Enter alerts_fin");
@@ -186,90 +198,111 @@ static void alerts_fin()
 		fz_set_doc_event_callback(idoc, NULL, NULL);
 
 	// Set alerts_active false and wake up show_alert and waitForAlertInternal,
-	pthread_mutex_lock(&alert_lock);
-	current_alert = NULL;
-	alerts_active = 0;
-	pthread_cond_signal(&alert_request_cond);
-	pthread_cond_signal(&alert_reply_cond);
-	pthread_mutex_unlock(&alert_lock);
+	pthread_mutex_lock(&glo->alert_lock);
+	glo->current_alert = NULL;
+	glo->alerts_active = 0;
+	pthread_cond_signal(&glo->alert_request_cond);
+	pthread_cond_signal(&glo->alert_reply_cond);
+	pthread_mutex_unlock(&glo->alert_lock);
 
 	// Wait for the fin_locks.
-	pthread_mutex_lock(&fin_lock);
-	pthread_mutex_unlock(&fin_lock);
-	pthread_mutex_lock(&fin_lock2);
-	pthread_mutex_unlock(&fin_lock2);
-
-	pthread_cond_destroy(&alert_reply_cond);
-	pthread_cond_destroy(&alert_request_cond);
-	pthread_mutex_destroy(&alert_lock);
-	pthread_mutex_destroy(&fin_lock2);
-	pthread_mutex_destroy(&fin_lock);
+	pthread_mutex_lock(&glo->fin_lock);
+	pthread_mutex_unlock(&glo->fin_lock);
+	pthread_mutex_lock(&glo->fin_lock2);
+	pthread_mutex_unlock(&glo->fin_lock2);
+
+	pthread_cond_destroy(&glo->alert_reply_cond);
+	pthread_cond_destroy(&glo->alert_request_cond);
+	pthread_mutex_destroy(&glo->alert_lock);
+	pthread_mutex_destroy(&glo->fin_lock2);
+	pthread_mutex_destroy(&glo->fin_lock);
 	LOGT("Exit alerts_fin");
-	alerts_initialised = 0;
+	glo->alerts_initialised = 0;
 }
 
-JNIEXPORT int JNICALL
+static globals *get_globals(JNIEnv *env, jobject thiz)
+{
+	return (globals *)(void *)((*env)->GetLongField(env, thiz, global_fid));
+}
+
+JNIEXPORT jlong JNICALL
 Java_com_artifex_mupdf_MuPDFCore_openFile(JNIEnv * env, jobject thiz, jstring jfilename)
 {
 	const char *filename;
-	int result = 0;
+	globals    *glo;
+	fz_context *ctx;
+	jclass      clazz;
 
 #ifdef NDK_PROFILER
 	monstartup("libmupdf.so");
 #endif
 
+	clazz = (*env)->GetObjectClass(env, thiz);
+	global_fid = (*env)->GetFieldID(env, clazz, "globals", "J");
+
+	glo = calloc(1, sizeof(*glo));
+	if (glo == NULL)
+		return 0;
+	glo->resolution = 160;
+	glo->alerts_initialised = 0;
+
 	filename = (*env)->GetStringUTFChars(env, jfilename, NULL);
 	if (filename == NULL)
 	{
 		LOGE("Failed to get filename");
+		free(glo);
 		return 0;
 	}
 
 	/* 128 MB store for low memory devices. Tweak as necessary. */
-	ctx = fz_new_context(NULL, NULL, 128 << 20);
+	glo->ctx = ctx = fz_new_context(NULL, NULL, 128 << 20);
 	if (!ctx)
 	{
 		LOGE("Failed to initialise context");
+		free(glo);
 		return 0;
 	}
 
-	doc = NULL;
+	glo->doc = NULL;
 	fz_try(ctx)
 	{
-		colorspace = fz_device_rgb;
+		glo->colorspace = fz_device_rgb;
 
 		LOGE("Opening document...");
 		fz_try(ctx)
 		{
-			current_path = fz_strdup(ctx, (char *)filename);
-			doc = fz_open_document(ctx, (char *)filename);
-			alerts_init();
+			glo->current_path = fz_strdup(ctx, (char *)filename);
+			glo->doc = fz_open_document(ctx, (char *)filename);
+			alerts_init(glo);
 		}
 		fz_catch(ctx)
 		{
 			fz_throw(ctx, "Cannot open document: '%s'\n", filename);
 		}
 		LOGE("Done!");
-		result = 1;
 	}
 	fz_catch(ctx)
 	{
 		LOGE("Failed: %s", ctx->error->message);
-		fz_close_document(doc);
-		doc = NULL;
+		fz_close_document(glo->doc);
+		glo->doc = NULL;
 		fz_free_context(ctx);
-		ctx = NULL;
+		glo->ctx = NULL;
+		free(glo);
+		glo = NULL;
 	}
 
 	(*env)->ReleaseStringUTFChars(env, jfilename, filename);
 
-	return result;
+	return (jlong)(void *)glo;
 }
 
 JNIEXPORT int JNICALL
 Java_com_artifex_mupdf_MuPDFCore_countPagesInternal(JNIEnv *env, jobject thiz)
 {
-	return fz_count_pages(doc);
+	globals *glo = get_globals(env, thiz);
+
+	return fz_count_pages(glo->doc);
 }
 
 JNIEXPORT void JNICALL
@@ -282,17 +315,19 @@ Java_com_artifex_mupdf_MuPDFCore_gotoPageInternal(JNIEnv *env, jobject thiz, int
 	fz_matrix ctm;
 	fz_bbox bbox;
 	page_cache *pc;
+	globals *glo = get_globals(env, thiz);
+	fz_context *ctx = glo->ctx;
 
 	for (i = 0; i < NUM_CACHE; i++)
 	{
-		if (pages[i].page != NULL && pages[i].number == page)
+		if (glo->pages[i].page != NULL && glo->pages[i].number == page)
 		{
 			/* The page is already cached */
-			current = i;
+			glo->current = i;
 			return;
 		}
 
-		if (pages[i].page == NULL)
+		if (glo->pages[i].page == NULL)
 		{
 			/* cache record unused, and so a good one to use */
 			furthest = i;
@@ -300,7 +335,7 @@ Java_com_artifex_mupdf_MuPDFCore_gotoPageInternal(JNIEnv *env, jobject thiz, int
 		}
 		else
 		{
-			int dist = abs(pages[i].number - page);
+			int dist = abs(glo->pages[i].number - page);
 
 			/* Further away - less likely to be needed again */
 			if (dist > furthest_dist)
@@ -311,10 +346,10 @@ Java_com_artifex_mupdf_MuPDFCore_gotoPageInternal(JNIEnv *env, jobject thiz, int
 		}
 	}
 
-	current = furthest;
-	pc = &pages[current];
+	glo->current = furthest;
+	pc = &glo->pages[glo->current];
 
-	drop_page_cache(pc);
+	drop_page_cache(glo, pc);
 
 	/* In the event of an error, ensure we give a non-empty page */
 	pc->width = 100;
@@ -325,9 +360,9 @@ Java_com_artifex_mupdf_MuPDFCore_gotoPageInternal(JNIEnv *env, jobject thiz, int
 	fz_try(ctx)
 	{
 		LOGI("Load page %d", pc->number);
-		pc->page = fz_load_page(doc, pc->number);
-		zoom = resolution / 72;
-		pc->media_box = fz_bound_page(doc, pc->page);
+		pc->page = fz_load_page(glo->doc, pc->number);
+		zoom = glo->resolution / 72;
+		pc->media_box = fz_bound_page(glo->doc, pc->page);
 		ctm = fz_scale(zoom, zoom);
 		bbox = fz_round_rect(fz_transform_rect(ctm, pc->media_box));
 		pc->width = bbox.x1-bbox.x0;
@@ -342,15 +377,17 @@ Java_com_artifex_mupdf_MuPDFCore_gotoPageInternal(JNIEnv *env, jobject thiz, int
 JNIEXPORT float JNICALL
 Java_com_artifex_mupdf_MuPDFCore_getPageWidth(JNIEnv *env, jobject thiz)
 {
-	LOGE("PageWidth=%g", pages[current].width);
-	return pages[current].width;
+	globals *glo = get_globals(env, thiz);
+	LOGE("PageWidth=%d", glo->pages[glo->current].width);
+	return glo->pages[glo->current].width;
 }
 
 JNIEXPORT float JNICALL
 Java_com_artifex_mupdf_MuPDFCore_getPageHeight(JNIEnv *env, jobject thiz)
 {
-	LOGE("PageHeight=%g", pages[current].height);
-	return pages[current].height;
+	globals *glo = get_globals(env, thiz);
+	LOGE("PageHeight=%d", glo->pages[glo->current].height);
+	return glo->pages[glo->current].height;
 }
 
 JNIEXPORT jboolean JNICALL
@@ -373,7 +410,10 @@ Java_com_artifex_mupdf_MuPDFCore_drawPage(JNIEnv *env, jobject thiz, jobject bit
 	fz_pixmap *pix = NULL;
 	float xscale, yscale;
 	fz_bbox rect;
-	page_cache *pc = &pages[current];
+	globals *glo = get_globals(env, thiz);
+	fz_context *ctx = glo->ctx;
+	fz_document *doc = glo->doc;
+	page_cache *pc = &glo->pages[glo->current];
 	int hq = (patchW < pageW || patchH < pageH);
 
 	if (pc->page == NULL)
@@ -421,7 +461,7 @@ Java_com_artifex_mupdf_MuPDFCore_drawPage(JNIEnv *env, jobject thiz, jobject bit
 			} else {
 				// There is only ever one hq patch, so we need
 				// cache only one page object for the sake of hq
-				clear_hq_pages();
+				clear_hq_pages(glo);
 				pc->hq_page = fz_load_page(doc, pc->number);
 			}
 		}
@@ -450,7 +490,7 @@ Java_com_artifex_mupdf_MuPDFCore_drawPage(JNIEnv *env, jobject thiz, jobject bit
 		rect.y0 = patchY;
 		rect.x1 = patchX + patchW;
 		rect.y1 = patchY + patchH;
-		pix = fz_new_pixmap_with_bbox_and_data(ctx, colorspace, rect, pixels);
+		pix = fz_new_pixmap_with_bbox_and_data(ctx, glo->colorspace, rect, pixels);
 		if (pc->page_list == NULL && pc->annot_list == NULL)
 		{
 			fz_clear_pixmap_with_value(ctx, pix, 0xd0);
@@ -458,7 +498,7 @@ Java_com_artifex_mupdf_MuPDFCore_drawPage(JNIEnv *env, jobject thiz, jobject bit
 		}
 		fz_clear_pixmap_with_value(ctx, pix, 0xff);
 
-		zoom = resolution / 72;
+		zoom = glo->resolution / 72;
 		ctm = fz_scale(zoom, zoom);
 		bbox = fz_round_rect(fz_transform_rect(ctm, pc->media_box));
 		/* Now, adjust ctm so that it would give the correct page width
@@ -533,12 +573,15 @@ Java_com_artifex_mupdf_MuPDFCore_updatePageInternal(JNIEnv *env, jobject thiz, j
 	page_cache *pc = NULL;
 	int hq = (patchW < pageW || patchH < pageH);
 	int i;
+	globals *glo = get_globals(env, thiz);
+	fz_context *ctx = glo->ctx;
+	fz_document *doc = glo->doc;
 
 	for (i = 0; i < NUM_CACHE; i++)
 	{
-		if (pages[i].page != NULL && pages[i].number == page)
+		if (glo->pages[i].page != NULL && glo->pages[i].number == page)
 		{
-			pc = &pages[i];
+			pc = &glo->pages[i];
 			break;
 		}
 	}
@@ -608,9 +651,9 @@ Java_com_artifex_mupdf_MuPDFCore_updatePageInternal(JNIEnv *env, jobject thiz, j
 		rect.y0 = patchY;
 		rect.x1 = patchX + patchW;
 		rect.y1 = patchY + patchH;
-		pix = fz_new_pixmap_with_bbox_and_data(ctx, colorspace, rect, pixels);
+		pix = fz_new_pixmap_with_bbox_and_data(ctx, glo->colorspace, rect, pixels);
 
-		zoom = resolution / 72;
+		zoom = glo->resolution / 72;
 		ctm = fz_scale(zoom, zoom);
 		bbox = fz_round_rect(fz_transform_rect(ctm, pc->media_box));
 		/* Now, adjust ctm so that it would give the correct page width
@@ -787,7 +830,9 @@ fillInOutlineItems(JNIEnv * env, jclass olClass, jmethodID ctor, jobjectArray ar
 JNIEXPORT jboolean JNICALL
 Java_com_artifex_mupdf_MuPDFCore_needsPasswordInternal(JNIEnv * env, jobject thiz)
 {
-	return fz_needs_password(doc) ? JNI_TRUE : JNI_FALSE;
+	globals *glo = get_globals(env, thiz);
+
+	return fz_needs_password(glo->doc) ? JNI_TRUE : JNI_FALSE;
 }
 
 JNIEXPORT jboolean JNICALL
@@ -795,11 +840,13 @@ Java_com_artifex_mupdf_MuPDFCore_authenticatePasswordInternal(JNIEnv *env, jobje
 {
 	const char *pw;
 	int         result;
+	globals    *glo = get_globals(env, thiz);
+
 	pw = (*env)->GetStringUTFChars(env, password, NULL);
 	if (pw == NULL)
 		return JNI_FALSE;
 
-	result = fz_authenticate_password(doc, (char *)pw);
+	result = fz_authenticate_password(glo->doc, (char *)pw);
 	(*env)->ReleaseStringUTFChars(env, password, pw);
 	return result;
 }
@@ -807,7 +854,9 @@ Java_com_artifex_mupdf_MuPDFCore_authenticatePasswordInternal(JNIEnv *env, jobje
 JNIEXPORT jboolean JNICALL
 Java_com_artifex_mupdf_MuPDFCore_hasOutlineInternal(JNIEnv * env, jobject thiz)
 {
-	fz_outline *outline = fz_load_outline(doc);
+	globals    *glo = get_globals(env, thiz);
+	fz_outline *outline = fz_load_outline(glo->doc);
+
 	return (outline == NULL) ? JNI_FALSE : JNI_TRUE;
 }
 
@@ -820,13 +869,14 @@ Java_com_artifex_mupdf_MuPDFCore_getOutlineInternal(JNIEnv * env, jobject thiz)
 	jobject       ol;
 	fz_outline   *outline;
 	int           nItems;
+	globals      *glo = get_globals(env, thiz);
 
 	olClass = (*env)->FindClass(env, "com/artifex/mupdf/OutlineItem");
 	if (olClass == NULL) return NULL;
 	ctor = (*env)->GetMethodID(env, olClass, "<init>", "(ILjava/lang/String;I)V");
 	if (ctor == NULL) return NULL;
 
-	outline = fz_load_outline(doc);
+	outline = fz_load_outline(glo->doc);
 	nItems = countOutlineItems(outline);
 
 	arr = (*env)->NewObjectArray(env,
@@ -857,7 +907,10 @@ Java_com_artifex_mupdf_MuPDFCore_searchPage(JNIEnv * env, jobject thiz, jstring
 	int            i, n;
 	int            hit_count = 0;
 	const char    *str;
-	page_cache    *pc = &pages[current];
+	globals       *glo = get_globals(env, thiz);
+	fz_context    *ctx = glo->ctx;
+	fz_document   *doc = glo->doc;
+	page_cache    *pc = &glo->pages[glo->current];
 
 	rectClass = (*env)->FindClass(env, "android/graphics/RectF");
 	if (rectClass == NULL) return NULL;
@@ -874,10 +927,10 @@ Java_com_artifex_mupdf_MuPDFCore_searchPage(JNIEnv * env, jobject thiz, jstring
 	{
 		fz_rect rect;
 
-		if (hit_bbox == NULL)
-			hit_bbox = fz_malloc_array(ctx, MAX_SEARCH_HITS, sizeof(*hit_bbox));
+		if (glo->hit_bbox == NULL)
+			glo->hit_bbox = fz_malloc_array(ctx, MAX_SEARCH_HITS, sizeof(*glo->hit_bbox));
 
-		zoom = resolution / 72;
+		zoom = glo->resolution / 72;
 		ctm = fz_scale(zoom, zoom);
 		rect = fz_transform_rect(ctm, pc->media_box);
 		sheet = fz_new_text_sheet(ctx);
@@ -896,7 +949,7 @@ Java_com_artifex_mupdf_MuPDFCore_searchPage(JNIEnv * env, jobject thiz, jstring
 				rr = fz_union_bbox(rr, bboxcharat(text, pos + i));
 
 			if (!fz_is_empty_bbox(rr) && hit_count < MAX_SEARCH_HITS)
-				hit_bbox[hit_count++] = rr;
+				glo->hit_bbox[hit_count++] = rr;
 		}
 	}
 	fz_always(ctx)
@@ -927,10 +980,10 @@ Java_com_artifex_mupdf_MuPDFCore_searchPage(JNIEnv * env, jobject thiz, jstring
 
 	for (i = 0; i < hit_count; i++) {
 		rect = (*env)->NewObject(env, rectClass, ctor,
-				(float) (hit_bbox[i].x0),
-				(float) (hit_bbox[i].y0),
-				(float) (hit_bbox[i].x1),
-				(float) (hit_bbox[i].y1));
+				(float) (glo->hit_bbox[i].x0),
+				(float) (glo->hit_bbox[i].y0),
+				(float) (glo->hit_bbox[i].x1),
+				(float) (glo->hit_bbox[i].y1));
 		if (rect == NULL)
 			return NULL;
 		(*env)->SetObjectArrayElement(env, arr, i, rect);
@@ -940,29 +993,32 @@ Java_com_artifex_mupdf_MuPDFCore_searchPage(JNIEnv * env, jobject thiz, jstring
 	return arr;
 }
 
-static void close_doc()
+static void close_doc(globals *glo)
 {
 	int i;
 
-	fz_free(ctx, hit_bbox);
-	hit_bbox = NULL;
+	fz_free(glo->ctx, glo->hit_bbox);
+	glo->hit_bbox = NULL;
 
 	for (i = 0; i < NUM_CACHE; i++)
-		drop_page_cache(&pages[i]);
+		drop_page_cache(glo, &glo->pages[i]);
 
-	alerts_fin();
+	alerts_fin(glo);
 
-	fz_close_document(doc);
-	doc = NULL;
+	fz_close_document(glo->doc);
+	glo->doc = NULL;
 }
 
 JNIEXPORT void JNICALL
 Java_com_artifex_mupdf_MuPDFCore_destroying(JNIEnv * env, jobject thiz)
 {
+	globals *glo = get_globals(env, thiz);
+
 	LOGI("Destroying");
-	close_doc();
-	fz_free(ctx, current_path);
-	current_path = NULL;
+	close_doc(glo);
+	fz_free(glo->ctx, glo->current_path);
+	glo->current_path = NULL;
+	free(glo);
 
 #ifdef NDK_PROFILER
 	// Apparently we should really be writing to whatever path we get
@@ -987,6 +1043,7 @@ Java_com_artifex_mupdf_MuPDFCore_getPageLinksInternal(JNIEnv * env, jobject thiz
 	fz_link     *link;
 	int          count;
 	page_cache  *pc;
+	globals     *glo = get_globals(env, thiz);
 
 	linkInfoClass = (*env)->FindClass(env, "com/artifex/mupdf/LinkInfo");
 	if (linkInfoClass == NULL) return NULL;
@@ -994,14 +1051,14 @@ Java_com_artifex_mupdf_MuPDFCore_getPageLinksInternal(JNIEnv * env, jobject thiz
 	if (ctor == NULL) return NULL;
 
 	Java_com_artifex_mupdf_MuPDFCore_gotoPageInternal(env, thiz, pageNumber);
-	pc = &pages[current];
+	pc = &glo->pages[glo->current];
 	if (pc->page == NULL || pc->number != pageNumber)
 		return NULL;
 
-	zoom = resolution / 72;
+	zoom = glo->resolution / 72;
 	ctm = fz_scale(zoom, zoom);
 
-	list = fz_load_links(doc, pc->page);
+	list = fz_load_links(glo->doc, pc->page);
 	count = 0;
 	for (link = list; link; link = link->next)
 	{
@@ -1046,6 +1103,7 @@ Java_com_artifex_mupdf_MuPDFCore_getWidgetAreasInternal(JNIEnv * env, jobject th
 	float        zoom;
 	int          count;
 	page_cache  *pc;
+	globals     *glo = get_globals(env, thiz);
 
 	rectFClass = (*env)->FindClass(env, "android/graphics/RectF");
 	if (rectFClass == NULL) return NULL;
@@ -1053,15 +1111,15 @@ Java_com_artifex_mupdf_MuPDFCore_getWidgetAreasInternal(JNIEnv * env, jobject th
 	if (ctor == NULL) return NULL;
 
 	Java_com_artifex_mupdf_MuPDFCore_gotoPageInternal(env, thiz, pageNumber);
-	pc = &pages[current];
+	pc = &glo->pages[glo->current];
 	if (pc->number != pageNumber || pc->page == NULL)
 		return NULL;
 
-	idoc = fz_interact(doc);
+	idoc = fz_interact(glo->doc);
 	if (idoc == NULL)
 		return NULL;
 
-	zoom = resolution / 72;
+	zoom = glo->resolution / 72;
 	ctm = fz_scale(zoom, zoom);
 
 	count = 0;
@@ -1096,9 +1154,10 @@ Java_com_artifex_mupdf_MuPDFCore_getPageLink(JNIEnv * env, jobject thiz, int pag
 	fz_link *link;
 	fz_point p;
 	page_cache *pc;
+	globals *glo = get_globals(env, thiz);
 
 	Java_com_artifex_mupdf_MuPDFCore_gotoPageInternal(env, thiz, pageNumber);
-	pc = &pages[current];
+	pc = &glo->pages[glo->current];
 	if (pc->number != pageNumber || pc->page == NULL)
 		return -1;
 
@@ -1108,13 +1167,13 @@ Java_com_artifex_mupdf_MuPDFCore_getPageLink(JNIEnv * env, jobject thiz, int pag
 	/* Ultimately we should probably return a pointer to a java structure
 	 * with the link details in, but for now, page number will suffice.
 	 */
-	zoom = resolution / 72;
+	zoom = glo->resolution / 72;
 	ctm = fz_scale(zoom, zoom);
 	ctm = fz_invert_matrix(ctm);
 
 	p = fz_transform_point(ctm, p);
 
-	for (link = fz_load_links(doc, pc->page); link; link = link->next)
+	for (link = fz_load_links(glo->doc, pc->page); link; link = link->next)
 	{
 		if (p.x >= link->rect.x0 && p.x <= link->rect.x1)
 			if (p.y >= link->rect.y0 && p.y <= link->rect.y1)
@@ -1137,8 +1196,10 @@ Java_com_artifex_mupdf_MuPDFCore_getPageLink(JNIEnv * env, jobject thiz, int pag
 JNIEXPORT int JNICALL
 Java_com_artifex_mupdf_MuPDFCore_passClickEventInternal(JNIEnv * env, jobject thiz, int pageNumber, float x, float y)
 {
+	globals *glo = get_globals(env, thiz);
+	fz_context *ctx = glo->ctx;
 	fz_matrix ctm;
-	fz_interactive *idoc = fz_interact(doc);
+	fz_interactive *idoc = fz_interact(glo->doc);
 	float zoom;
 	fz_point p;
 	fz_ui_event event;
@@ -1149,7 +1210,7 @@ Java_com_artifex_mupdf_MuPDFCore_passClickEventInternal(JNIEnv * env, jobject th
 		return 0;
 
 	Java_com_artifex_mupdf_MuPDFCore_gotoPageInternal(env, thiz, pageNumber);
-	pc = &pages[current];
+	pc = &glo->pages[glo->current];
 	if (pc->number != pageNumber || pc->page == NULL)
 		return 0;
 
@@ -1159,7 +1220,7 @@ Java_com_artifex_mupdf_MuPDFCore_passClickEventInternal(JNIEnv * env, jobject th
 	/* Ultimately we should probably return a pointer to a java structure
 	 * with the link details in, but for now, page number will suffice.
 	 */
-	zoom = resolution / 72;
+	zoom = glo->resolution / 72;
 	ctm = fz_scale(zoom, zoom);
 	ctm = fz_invert_matrix(ctm);
 
@@ -1174,7 +1235,7 @@ Java_com_artifex_mupdf_MuPDFCore_passClickEventInternal(JNIEnv * env, jobject th
 		event.event.pointer.ptype = FZ_POINTER_UP;
 		changed |= fz_pass_event(idoc, pc->page, &event);
 		if (changed) {
-			dump_annotation_display_lists();
+			dump_annotation_display_lists(glo);
 		}
 	}
 	fz_catch(ctx)
@@ -1189,10 +1250,12 @@ JNIEXPORT jstring JNICALL
 Java_com_artifex_mupdf_MuPDFCore_getFocusedWidgetTextInternal(JNIEnv * env, jobject thiz)
 {
 	char *text = "";
+	globals *glo = get_globals(env, thiz);
+	fz_context *ctx = glo->ctx;
 
 	fz_try(ctx)
 	{
-		fz_interactive *idoc = fz_interact(doc);
+		fz_interactive *idoc = fz_interact(glo->doc);
 
 		if (idoc)
 		{
@@ -1215,6 +1278,8 @@ Java_com_artifex_mupdf_MuPDFCore_setFocusedWidgetTextInternal(JNIEnv * env, jobj
 {
 	const char *text;
 	int result = 0;
+	globals *glo = get_globals(env, thiz);
+	fz_context *ctx = glo->ctx;
 
 	text = (*env)->GetStringUTFChars(env, jtext, NULL);
 	if (text == NULL)
@@ -1225,7 +1290,7 @@ Java_com_artifex_mupdf_MuPDFCore_setFocusedWidgetTextInternal(JNIEnv * env, jobj
 
 	fz_try(ctx)
 	{
-		fz_interactive *idoc = fz_interact(doc);
+		fz_interactive *idoc = fz_interact(glo->doc);
 
 		if (idoc)
 		{
@@ -1234,7 +1299,7 @@ Java_com_artifex_mupdf_MuPDFCore_setFocusedWidgetTextInternal(JNIEnv * env, jobj
 			if (focus)
 			{
 				result = fz_text_widget_set_text(idoc, focus, (char *)text);
-				dump_annotation_display_lists();
+				dump_annotation_display_lists(glo);
 			}
 		}
 	}
@@ -1251,7 +1316,8 @@ Java_com_artifex_mupdf_MuPDFCore_setFocusedWidgetTextInternal(JNIEnv * env, jobj
 JNIEXPORT int JNICALL
 Java_com_artifex_mupdf_MuPDFCore_getFocusedWidgetTypeInternal(JNIEnv * env, jobject thiz)
 {
-	fz_interactive *idoc = fz_interact(doc);
+	globals *glo = get_globals(env, thiz);
+	fz_interactive *idoc = fz_interact(glo->doc);
 	fz_widget *focus;
 
 	if (idoc == NULL)
@@ -1275,6 +1341,7 @@ Java_com_artifex_mupdf_MuPDFCore_getFocusedWidgetTypeInternal(JNIEnv * env, jobj
 JNIEXPORT jobject JNICALL
 Java_com_artifex_mupdf_MuPDFCore_waitForAlertInternal(JNIEnv * env, jobject thiz)
 {
+	globals *glo = get_globals(env, thiz);
 	jclass alertClass;
 	jmethodID ctor;
 	jstring title;
@@ -1283,20 +1350,20 @@ Java_com_artifex_mupdf_MuPDFCore_waitForAlertInternal(JNIEnv * env, jobject thiz
 	fz_alert_event alert;
 
 	LOGT("Enter waitForAlert");
-	pthread_mutex_lock(&fin_lock);
-	pthread_mutex_lock(&alert_lock);
+	pthread_mutex_lock(&glo->fin_lock);
+	pthread_mutex_lock(&glo->alert_lock);
 
-	while (alerts_active && !alert_request)
-		pthread_cond_wait(&alert_request_cond, &alert_lock);
-	alert_request = 0;
+	while (glo->alerts_active && !glo->alert_request)
+		pthread_cond_wait(&glo->alert_request_cond, &glo->alert_lock);
+	glo->alert_request = 0;
 
-	alert_present = (alerts_active && current_alert);
+	alert_present = (glo->alerts_active && glo->current_alert);
 
 	if (alert_present)
-		alert = *current_alert;
+		alert = *glo->current_alert;
 
-	pthread_mutex_unlock(&alert_lock);
-	pthread_mutex_unlock(&fin_lock);
+	pthread_mutex_unlock(&glo->alert_lock);
+	pthread_mutex_unlock(&glo->fin_lock);
 	LOGT("Exit waitForAlert %d", alert_present);
 
 	if (!alert_present)
@@ -1324,6 +1391,7 @@ Java_com_artifex_mupdf_MuPDFCore_waitForAlertInternal(JNIEnv * env, jobject thiz
 JNIEXPORT void JNICALL
 Java_com_artifex_mupdf_MuPDFCore_replyToAlertInternal(JNIEnv * env, jobject thiz, jobject alert)
 {
+	globals *glo = get_globals(env, thiz);
 	jclass alertClass;
 	jfieldID field;
 	int button_pressed;
@@ -1339,62 +1407,67 @@ Java_com_artifex_mupdf_MuPDFCore_replyToAlertInternal(JNIEnv * env, jobject thiz
 	button_pressed = (*env)->GetIntField(env, alert, field);
 
 	LOGT("Enter replyToAlert");
-	pthread_mutex_lock(&alert_lock);
+	pthread_mutex_lock(&glo->alert_lock);
 
-	if (alerts_active && current_alert)
+	if (glo->alerts_active && glo->current_alert)
 	{
 		// Fill in button_pressed and signal reply received.
-		current_alert->button_pressed = button_pressed;
-		alert_reply = 1;
-		pthread_cond_signal(&alert_reply_cond);
+		glo->current_alert->button_pressed = button_pressed;
+		glo->alert_reply = 1;
+		pthread_cond_signal(&glo->alert_reply_cond);
 	}
 
-	pthread_mutex_unlock(&alert_lock);
+	pthread_mutex_unlock(&glo->alert_lock);
 	LOGT("Exit replyToAlert");
 }
 
 JNIEXPORT void JNICALL
 Java_com_artifex_mupdf_MuPDFCore_startAlertsInternal(JNIEnv * env, jobject thiz)
 {
-	if (!alerts_initialised)
+	globals *glo = get_globals(env, thiz);
+
+	if (!glo->alerts_initialised)
 		return;
 
 	LOGT("Enter startAlerts");
-	pthread_mutex_lock(&alert_lock);
+	pthread_mutex_lock(&glo->alert_lock);
 
-	alert_reply = 0;
-	alert_request = 0;
-	alerts_active = 1;
-	current_alert = NULL;
+	glo->alert_reply = 0;
+	glo->alert_request = 0;
+	glo->alerts_active = 1;
+	glo->current_alert = NULL;
 
-	pthread_mutex_unlock(&alert_lock);
+	pthread_mutex_unlock(&glo->alert_lock);
 	LOGT("Exit startAlerts");
 }
 
 JNIEXPORT void JNICALL
 Java_com_artifex_mupdf_MuPDFCore_stopAlertsInternal(JNIEnv * env, jobject thiz)
 {
-	if (!alerts_initialised)
+	globals *glo = get_globals(env, thiz);
+
+	if (!glo->alerts_initialised)
 		return;
 
 	LOGT("Enter stopAlerts");
-	pthread_mutex_lock(&alert_lock);
+	pthread_mutex_lock(&glo->alert_lock);
 
-	alert_reply = 0;
-	alert_request = 0;
-	alerts_active = 0;
-	current_alert = NULL;
-	pthread_cond_signal(&alert_reply_cond);
-	pthread_cond_signal(&alert_request_cond);
+	glo->alert_reply = 0;
+	glo->alert_request = 0;
+	glo->alerts_active = 0;
+	glo->current_alert = NULL;
+	pthread_cond_signal(&glo->alert_reply_cond);
+	pthread_cond_signal(&glo->alert_request_cond);
 
-	pthread_mutex_unlock(&alert_lock);
+	pthread_mutex_unlock(&glo->alert_lock);
 	LOGT("Exit stopAleerts");
 }
 
 JNIEXPORT jboolean JNICALL
 Java_com_artifex_mupdf_MuPDFCore_hasChangesInternal(JNIEnv * env, jobject thiz)
 {
-	fz_interactive *idoc = fz_interact(doc);
+	globals *glo = get_globals(env, thiz);
+	fz_interactive *idoc = fz_interact(glo->doc);
 
 	return (idoc && fz_has_unsaved_changes(idoc)) ? JNI_TRUE : JNI_FALSE;
 }
@@ -1426,7 +1499,10 @@ static char *tmp_path(char *path)
 JNIEXPORT void JNICALL
 Java_com_artifex_mupdf_MuPDFCore_saveInternal(JNIEnv * env, jobject thiz)
 {
-	if (doc && current_path)
+	globals *glo = get_globals(env, thiz);
+	fz_context *ctx = glo->ctx;
+
+	if (glo->doc && glo->current_path)
 	{
 		char *tmp;
 		fz_write_options opts;
@@ -1435,7 +1511,7 @@ Java_com_artifex_mupdf_MuPDFCore_saveInternal(JNIEnv * env, jobject thiz)
 		opts.do_garbage = 1;
 		opts.do_linear = 0;
 
-		tmp = tmp_path(current_path);
+		tmp = tmp_path(glo->current_path);
 		if (tmp)
 		{
 			int written;
@@ -1443,7 +1519,7 @@ Java_com_artifex_mupdf_MuPDFCore_saveInternal(JNIEnv * env, jobject thiz)
 			fz_var(written);
 			fz_try(ctx)
 			{
-				fz_write_document(doc, tmp, &opts);
+				fz_write_document(glo->doc, tmp, &opts);
 				written = 1;
 			}
 			fz_catch(ctx)
@@ -1453,8 +1529,8 @@ Java_com_artifex_mupdf_MuPDFCore_saveInternal(JNIEnv * env, jobject thiz)
 
 			if (written)
 			{
-				close_doc();
-				rename(tmp, current_path);
+				close_doc(glo);
+				rename(tmp, glo->current_path);
 			}
 
 			free(tmp);
diff --git a/android/src/com/artifex/mupdf/MuPDFCore.java b/android/src/com/artifex/mupdf/MuPDFCore.java
index 13718508..1f9da3a6 100644
--- a/android/src/com/artifex/mupdf/MuPDFCore.java
+++ b/android/src/com/artifex/mupdf/MuPDFCore.java
@@ -15,47 +15,49 @@ public class MuPDFCore
 	private int numPages = -1;
 	private float pageWidth;
 	private float pageHeight;
+	private long globals;
 
 	/* The native functions */
-	private static native int openFile(String filename);
-	private static native int countPagesInternal();
-	private static native void gotoPageInternal(int localActionPageNum);
-	private static native float getPageWidth();
-	private static native float getPageHeight();
-	private static native void drawPage(Bitmap bitmap,
+	private native long openFile(String filename);
+	private native int countPagesInternal();
+	private native void gotoPageInternal(int localActionPageNum);
+	private native float getPageWidth();
+	private native float getPageHeight();
+	private native void drawPage(Bitmap bitmap,
 			int pageW, int pageH,
 			int patchX, int patchY,
 			int patchW, int patchH);
-	private static native void updatePageInternal(Bitmap bitmap,
+	private native void updatePageInternal(Bitmap bitmap,
 			int page,
 			int pageW, int pageH,
 			int patchX, int patchY,
 			int patchW, int patchH);
-	private static native RectF[] searchPage(String text);
-	private static native int getPageLink(int page, float x, float y);
-	private static native int passClickEventInternal(int page, float x, float y);
-	private static native int setFocusedWidgetTextInternal(String text);
-	private static native String getFocusedWidgetTextInternal();
-	private static native int getFocusedWidgetTypeInternal();
-	private static native LinkInfo [] getPageLinksInternal(int page);
-	private static native RectF[] getWidgetAreasInternal(int page);
-	private static native OutlineItem [] getOutlineInternal();
-	private static native boolean hasOutlineInternal();
-	private static native boolean needsPasswordInternal();
-	private static native boolean authenticatePasswordInternal(String password);
-	private static native MuPDFAlertInternal waitForAlertInternal();
-	private static native void replyToAlertInternal(MuPDFAlertInternal alert);
-	private static native void startAlertsInternal();
-	private static native void stopAlertsInternal();
-	private static native void destroying();
-	private static native boolean hasChangesInternal();
-	private static native void saveInternal();
+	private native RectF[] searchPage(String text);
+	private native int getPageLink(int page, float x, float y);
+	private native int passClickEventInternal(int page, float x, float y);
+	private native int setFocusedWidgetTextInternal(String text);
+	private native String getFocusedWidgetTextInternal();
+	private native int getFocusedWidgetTypeInternal();
+	private native LinkInfo [] getPageLinksInternal(int page);
+	private native RectF[] getWidgetAreasInternal(int page);
+	private native OutlineItem [] getOutlineInternal();
+	private native boolean hasOutlineInternal();
+	private native boolean needsPasswordInternal();
+	private native boolean authenticatePasswordInternal(String password);
+	private native MuPDFAlertInternal waitForAlertInternal();
+	private native void replyToAlertInternal(MuPDFAlertInternal alert);
+	private native void startAlertsInternal();
+	private native void stopAlertsInternal();
+	private native void destroying();
+	private native boolean hasChangesInternal();
+	private native void saveInternal();
 
 	public static native boolean javascriptSupported();
 
 	public MuPDFCore(String filename) throws Exception
 	{
-		if (openFile(filename) <= 0)
+		globals = openFile(filename);
+		if (globals == 0)
 		{
 			throw new Exception("Failed to open "+filename);
 		}
@@ -109,6 +111,7 @@ public class MuPDFCore
 
 	public synchronized void onDestroy() {
 		destroying();
+		globals = 0;
 	}
 
 	public synchronized void drawPage(BitmapHolder h, int page,