PROG Mobile Java Application Development PROG Mobile Java Application Development Memory and Memory Issues Data Storage

10/17/2015Wendi Jollymore, ACES2 Types of BB Memory Internal Flash Memory aka application storage, onboard memory internal to the device contains the operating system and BB JVM (about 10MB to 15MB) only place where apps can be run available on all bb devices stores messages, organizer data, personal information, etc where persistent objects/data is stored older devices around 32MB or more storm is 128MB, storm 2 is 256MB, torch is 512MB

10/17/2015Wendi Jollymore, ACES3 Types of BB Memory SRAM ml Static RAM Working memory E.g. when a persistent object is accessed/edited it is copied to SRAM and worked on there Controls transient data objects data objects that have been created during an app session and not saved anywhere Controls runtime processes BlackBerry stopped posting amount of SRAM on devices :P

10/17/2015Wendi Jollymore, ACES4 Types of BB Memory External SD (Secure Digital) cards microSD card that can be inserted to extend storage on device optional, removable, contains a FAT file system supported on o/s 4.2 or later, except 8700 series amount of SD card storage varies the device can support up to a certain amount (see specs for each device) users might only have a certain sized card E.g. Storm, Storm2, Torch all support up to 32GB card, but some carriers include 8GB card with device

10/17/2015Wendi Jollymore, ACES5 Types of BB Memory Built-in media storage (device memory) embedded multimedia card (eMMC) not removable also known as internal memory or onboard device memory not on all devices, and size varies on those that have it E.g. Storm has 1GB, Storm 2 has 2GB, Torch has 4GB

10/17/2015Wendi Jollymore, ACES6 Persistence & Object Handles Persistent storage – storage that persists when app is not running and device shut off Data that isn’t deleted when app stops or device resets/shuts down The opposite is non-persistent storage Data that is still there as long as the device is running But is lost when the device shuts off/resets

10/17/2015Wendi Jollymore, ACES7 Persistence & Object Handles Two kinds of object handles: Object Handles (Transitive Object Handles) Every object you use requires a “handle” in memory Think of it sort of like a reference to that object Persistent Object Handles For objects that are persisted across device resets i.e. stored persistently on the device

10/17/2015Wendi Jollymore, ACES8 Persistence & Object Handles Example: A vector of 10 strings will consume 11 persistent object handles 1 handle for the vector 10 handles for each string in the vector There is a fixed number of persistent object handles available in the system Determined by the amount of flash memory. A 32MB device is limited to about 65,000 persistent object handles and 132,000 object handles. You could run out of persistent object handles well before you run out of memory

10/17/2015Wendi Jollymore, ACES9 Low Memory Manager If SRAM runs low, JVM swaps with flash memory If flash memory is full, problems! Garbage collector tries to free up memory no longer in use When SRAM and flash memory get full Garbage Collector runs more often and it will take longer

10/17/2015Wendi Jollymore, ACES10 Low Memory Manager Handles memory resources on the BB when available When resources fall below a certain thresh-hold Frees used memory to provide more available memory All apps work with the low memory manager to free as much memory as possible when device is low on memory When low memory manager will work: Amount of flash memory falls below a certain threshhold (usually 400KB to 800KB) # of persistent object handles available falls below 1000 # of object handles available falls below 1000

10/17/2015Wendi Jollymore, ACES11 Low Memory Manager Will remove low priority stuff like cached data Then will go to medium priority stuff old s and out of date calendar entries If critical, will remove more recent s, phone logs, etc

10/17/2015Wendi Jollymore, ACES12 Conserve Memory Resources Flash memory Refers to the raw persistent storage space that is available on each handheld. Remember that this is fixed Amount depends on device This is where persistent data and object handles are stored

10/17/2015Wendi Jollymore, ACES13 Conserve Memory Resources Reduce the number of objects! Fewer objects means fewer persistent object handles and object handles Recall Vector example with 10 String objects 11 handles If you had 3000 records, that’s 33,000 handles On some older devices with only 16MB memory, this is too much A device with 16MB flash memory can only hold 27,000 persistent object handles

10/17/2015Wendi Jollymore, ACES14 Conserve Memory Resources Data Structure Selection Make sure data structure contains minimum possible number of objects especially with vector or hashtable - great objects but resource heavy - avoid using if possible Use primitive types instead of objects - primitives require no object handle Note that an array is an object so an array of primitives requires one object handle Strings are equivalent to byte arrays so a string will take one object handle

10/17/2015Wendi Jollymore, ACES15 Conserve Memory Resources Object consolidation Recall Vector example with 10 String objects and 3000 records net.rim.device.api.system.ObjectGroup allows you to group objects so that they take only one handle string example that takes 11 - can group this into 1) Problem: grouped objects are read only so if you edit, you must ungroup, change, re-group again – can affect performance also ungrouping it obviously requires all the object handles again

10/17/2015Wendi Jollymore, ACES16 Minimize Memory Usage Use primitive data types instead of objects E.g. use int instead of Integer Do not depend entirely on the garbage collector. Avoid creating many objects quickly. Set object references to null when you are finished using them. Reuse objects as much as possible. Move heavy processing to the server. Example: filter or sort data before sending it to the BlackBerry smartphone.

10/17/2015Wendi Jollymore, ACES17 Storage Choices MIDP RMS (record mgmt system) simple non-relational database format stores data in arrays of bytes not much support for sharing data between apps app data is attached to app, so when app is removed from device, so is data use this if you're developing for older devices or developing a MIDlet javax.microedition.rms package

10/17/2015Wendi Jollymore, ACES18 Storage Choices BlackBerry Persistent Store similar to RMS easier to store wider range of objects can store instances of custom classes offers optional compression and security most popular can be written only to the devices internal flash memory persists across device resets

10/17/2015Wendi Jollymore, ACES19 Storage Choices runtime store similar to persistent store doesn't persist across device resets used for apps to share info

10/17/2015Wendi Jollymore, ACES20 Storage Choices FileConnection API Allows access to BlackBerry file system files and folders Can access application storage, SD card, device memory File system is where media, pics, downloaded files, attachments from s, etc are stored Accessible by all apps on the device Good for large files, pics, documents Good for files that need to be accessible (e.g. thru desktop manager)

10/17/2015Wendi Jollymore, ACES21 Storage Choices SQLite (5.0 and later) Full database for structured data Can store and access data on device's internal memory and external sd cards

10/17/2015Wendi Jollymore, ACES22 BB Persistent Store Stores data to flash memory Can't access SD card not good for documents or anything large Flash memory contains the O/S, , other data still should be a lot free – check device specs

10/17/2015Wendi Jollymore, ACES23 BB Persistent Store net.rim.device.api.system.PersistentStore Manages a list of keys (long) and objects (PersistentObjects) List is global across all apps You don't know which keys are in use by other apps However, key space is large enough that conflicts never occur Think of key like the ID or file name

10/17/2015Wendi Jollymore, ACES24 BB Persistent Store net.rim.device.aip.system.PersistentObject PersistentStore.getPersistentObject() returns an instance of PersistentObject even if key hasn't been used before therefore, you will always get back a PO, but it might have a null value so either nothing has been saved with that key or it was deleted

10/17/2015Wendi Jollymore, ACES25 BB Persistent Store PersistentObject persistentObject = PersistentStore.getPersistentObject(0x2a5c 4229e L); Contents of the Persistent Object are accessed via the getContents() method, which might return null: Object contents = persistentObject.getContents(); To set or replace the contents of a PO, use setContents() method: Hashtable hashtable = new Hashtable(); persistentObject.setContents(hashtable);

10/17/2015Wendi Jollymore, ACES26 BB Persistent Store Setting contents doesn't necessarily mean object has persisted must call commit() method: persistObj.commit(); Persistent Object maintains a reference to its contents to change the data in the persistent object, you must modify the instance and call commit() you don't need to call setContents() again unless you want entirely different object to be associated with that key

10/17/2015Wendi Jollymore, ACES27 BB Persistent Store // This will persist MyKey and New Value // no need to call // persistentObject.setContents() again hashtable.put("MyKey", "New Value"); persistentObject.commit();

10/17/2015Wendi Jollymore, ACES28 What Can You Persist? Only objects, not primitives (use wrapper classes) Any object you persist must implement net.rim.device.api.util.Persistable interface Some other classes are allowed even though they don't implement Persistable: wrapper classses, Object, String, Vector, Hashtable Arrays of primitives and other persistable types

10/17/2015Wendi Jollymore, ACES29 What Can You Persist? Persistence saves entire object including all objects it references Objects your object references must also be persistable e.g You want to persist a Hashtable of Employee objects Employee class must be persistable (implement Persistable interface)

10/17/2015Wendi Jollymore, ACES30 Exercises Do the example in Beginning Blackberry (Persistent Store section) Do the tutorials and lab from the RIM materials There is also a lab using Runtime store from the RIM materals All of this is in the notes