macOS: Fix a regression that could cause a crash on exit if any books were deleted while calibre was running. Fixes #1839044 [calibre crash when deleting ebook](https://bugs.launchpad.net/calibre/+bug/1839044)

src/calibre/db/delete_service.py

@@ -8,6 +8,7 @@ __copyright__ = '2013, Kovid Goyal <kovid at kovidgoyal.net>'
 import os, tempfile, shutil, errno, time, atexit
 from threading import Thread
 
+from calibre.constants import isosx, plugins
 from calibre.ptempfile import remove_dir
 from calibre.utils.filenames import remove_dir_if_empty
 from calibre.utils.recycle_bin import delete_tree, delete_file
@@ -33,6 +34,8 @@ class DeleteService(Thread):
     def __init__(self):
         Thread.__init__(self)
         self.requests = Queue()
+        if isosx:
+            plugins['cocoa'][0].enable_cocoa_multithreading()
 
     def shutdown(self, timeout=20):
         self.requests.put(None)

src/calibre/utils/cocoa.m

@@ -9,18 +9,21 @@
 #include <Cocoa/Cocoa.h>
 #include <string.h>
 
+void
+activate_cocoa_multithreading(void) {
+	if (![NSThread isMultiThreaded]) [[NSThread new] start];
+}
+
 const char*
 cocoa_send2trash(const char *utf8_path) {
-	NSString *path = [[NSString alloc] initWithUTF8String:utf8_path];
-	NSURL *url = [NSURL fileURLWithPath:path];
+	@autoreleasepool {
 	const char *ret = NULL;
 	NSError* ns_error = nil;
-	if (![[NSFileManager defaultManager] trashItemAtURL:url resultingItemURL:nil error:&ns_error]) {
+	if (![[NSFileManager defaultManager] trashItemAtURL:[NSURL fileURLWithPath:@(utf8_path)] resultingItemURL:nil error:&ns_error]) {
 		ret = strdup([[ns_error localizedDescription] UTF8String]);
 	}
-	[url release];
-	[path release];
 	return ret;
+	}
 }
 
 
@@ -32,35 +35,31 @@ extern void macos_notification_callback(const char*);
 
 void
 cocoa_send_notification(const char *identifier, const char *title, const char *subtitle, const char *informativeText, const char* path_to_image) {
+	@autoreleasepool {
     NSUserNotificationCenter *center = [NSUserNotificationCenter defaultUserNotificationCenter];
     if (!center) {return;}
     if (!center.delegate) center.delegate = [[NotificationDelegate alloc] init];
     NSUserNotification *n = [NSUserNotification new];
     NSImage *img = nil;
     if (path_to_image) {
-        NSString *p = [NSString stringWithUTF8String:path_to_image];
-        NSURL *url = [NSURL fileURLWithPath:p];
-        img = [[NSImage alloc] initWithContentsOfURL:url];
-        [url release]; [p release];
+		img = [[NSImage alloc] initWithContentsOfURL:[NSURL fileURLWithPath:@(path_to_image)]];
         if (img) {
             [n setValue:img forKey:@"_identityImage"];
             [n setValue:@(false) forKey:@"_identityImageHasBorder"];
         }
-        [img release];
+		[img release];
     }
 #define SET(x) { \
     if (x) { \
-        NSString *t = [NSString stringWithUTF8String:x]; \
-        n.x = t; \
-        [t release]; \
+        n.x = @(x); \
     }}
     SET(title); SET(subtitle); SET(informativeText);
 #undef SET
     if (identifier) {
-        n.userInfo = @{@"user_id": [NSString stringWithUTF8String:identifier]};
+        n.userInfo = @{@"user_id": @(identifier)};
     }
     [center deliverNotification:n];
-
+	}
 }
 
 @implementation NotificationDelegate

src/calibre/utils/cocoa_wrapper.c

@@ -10,6 +10,7 @@
 extern double cocoa_cursor_blink_time(void);
 extern void cocoa_send_notification(const char *identitifer, const char *title, const char *subtitle, const char *informativeText, const char* path_to_image);
 extern const char* cocoa_send2trash(const char *utf8_path);
+extern void activate_cocoa_multithreading(void);
 
 static PyObject *notification_activated_callback = NULL;
 
@@ -63,8 +64,15 @@ send2trash(PyObject *self, PyObject *args) {
 	Py_RETURN_NONE;
 }
 
+static PyObject*
+enable_cocoa_multithreading(PyObject *self, PyObject *args) {
+	activate_cocoa_multithreading();
+	Py_RETURN_NONE;
+}
+
 static PyMethodDef module_methods[] = {
     {"cursor_blink_time", (PyCFunction)cursor_blink_time, METH_NOARGS, ""},
+    {"enable_cocoa_multithreading", (PyCFunction)enable_cocoa_multithreading, METH_NOARGS, ""},
     {"set_notification_activated_callback", (PyCFunction)set_notification_activated_callback, METH_O, ""},
     {"send_notification", (PyCFunction)send_notification, METH_VARARGS, ""},
     {"send2trash", (PyCFunction)send2trash, METH_VARARGS, ""},