|
|
|
Modern Operating Systems by Herbert Bos and Andrew S. Tanenb...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf
Showing 859-860 out of 1137
Modern Operating Systems by Herbert Bos and Andrew...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Modern Operating Systems by Herbert...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Page 859
828
CASE STUDY 1: UNIX, LINUX, AND ANDROID
CHAP. 10
with the appropriate
ActivityRecord
.
This activity is in a state called
resumed
since
it is now in the foreground of the user interface.
Activity manager in system_server process
Email app process
MailMainActivity
Task: Email
ActivityRecord
(MailMainActivity)
RESUMED
Figure 10-52.
Starting an email application’s main activity.
If the user were now to switch away from the email application (not exiting it)
and launch a camera application to take a picture, we would be in the state shown
in Fig. 10-53. Note that we now have a new camera process running the camera’s
main activity, an associated
ActivityRecord
for it in the activity manager, and it is
now the resumed activity.
Something interesting also happens to the previous
email activity: instead of being resumed, it is now
stopped
and the
ActivityRecord
holds this activity’s
saved state
.
Activity manager in system_server process
Camera app process
Email app process
MailMainActivity
CameraMainActivity
Task: Camera
ActivityRecord
(CameraMainActivity)
ActivityRecord
(MailMainActivity)
Saved state
STOPPED
RESUMED
Task: Email
Figure 10-53.
Starting the camera application after email.
When an activity is no longer in the foreground, the system asks it to ‘‘save its
state.’’ This involves the application creating a minimal amount of state infor-
mation representing what the user currently sees, which it returns to the activity
Page 860
SEC. 10.8
ANDROID
829
manager and stores in the
system
server
process, in the
ActivityRecord
associated
with that activity.
The saved state for an activity is generally small, containing for
example where you are scrolled in an email message, but not the message itself,
which will be stored elsewhere by the application in its persistent storage.
Recall that although Android does demand paging (it can page in and out clean
RAM that has been mapped from files on disk, such as code), it does not rely on
swap space.
This means all dirty RAM pages in an application’s process
must
stay
in RAM.
Having the email’s main activity state safely stored away in the activity
manager gives the system back some of the flexibility in dealing with memory that
swap provides.
For example, if the camera application starts to require a lot of RAM, the sys-
tem can simply get rid of the email process, as shown in Fig. 10-54. The
Activi-
tyRecord
, with its precious saved state, remains safely tucked away by the activity
manager in the
system
server
process. Since the
system
server
process hosts all of
Android’s core system services, it must always remain running, so the state saved
here will remain around for as long as we might need it.
Activity manager in system_server process
Camera app process
CameraMainActivity
Task: Camera
ActivityRecord
(CameraMainActivity)
ActivityRecord
(MailMainActivity)
Task: Email
Saved state
STOPPED
RESUMED
Figure 10-54.
Removing the email process to reclaim RAM for the camera.
Our example email application not only has an activity for its main UI, but in-
cludes another
ComposeActivity
.
Applications can declare any number of activities
they want. This can help organize the implementation of an application, but more
importantly it can be used to implement cross-application interactions.
For ex-
ample, this is the basis of Android’s cross-application sharing system, which the
ComposeActivity
here is participating in.
If the user, while in the camera applica-
tion, decides she wants to share a picture she took, our email application’s
Com-
poseActivity
is one of the sharing options she has.
If it is selected, that activity will
Ace your assessments! Get Better Grades
Browse thousands of Study Materials & Solutions from your Favorite Schools
Concordia University
Concordia_University
School:
Operating_Systems
Course:
Great resource for chem class. Had all the past labs and assignments
Leland P.
Santa Clara University
Introducing Study Plan
Using AI Tools to Help you understand and remember your course concepts better and faster than any other resource.
Find the best videos to learn every concept in that course from Youtube and Tiktok without searching.
Save All Relavent Videos & Materials and access anytime and anywhere
Prepare Smart and Guarantee better grades
Know more
Students also viewed documents
lab 18.docx
lab_18.docx
Course
Course
3
Module5QuizSTA2023.d...
Module5QuizSTA2023.docx.docx
Course
Course
10
Week 7 Test Math302....
Week_7_Test_Math302.docx.docx
Course
Course
30
Chapter 1 Assigment ...
Chapter_1_Assigment_Questions.docx.docx
Course
Course
5
Week 4 tests.docx.do...
Week_4_tests.docx.docx
Course
Course
23
Week 6 tests.docx.do...
Week_6_tests.docx.docx
Course
Course
106
