Friday, 14 April 2023

JVM Garbage Collection GC#003 (How)

GC is a marvel of Java.

How to get GC Log so that we know what iss is happening , what is the foot print of execution phase image:

Let us explore the switches available for GC collection statistics in JVM

GC Logging Flags in Java 8 and Earlier

-XX:+PrintGC

-XX:+PrintGCDetails

-XX:+PrintGCDateStamps and -XX:+PrintGCTimeStamps

-Xloggc

eg : java -cp $CLASSPATH -Xloggc mypackage.MainClass

java -cp $CLASSPATH -Xloggc:/tmp/gc.log mypackage.MainClass

GC Logging Flags in Java 9 and Later

eg:

java -cp $CLASSPATH -Xlog:gc*=debug:file=/tmp/gc.log mypackage.MainClass

java -cp $CLASSPATH -Xlog:gc*=debug:stdout -Xlog:gc*=debug:file=/tmp/gc.log mypackage.MainClass

Thursday, 13 April 2023

Networ{k|th} - Tutorials

Network Commands

1. ipconfig /all will return bio-data of your n/w

C:\Users\rmcme>ipconfig /all

Windows IP Configuration

Host Name . . . . . . . . . . . . : LaptopDELL
Primary Dns Suffix . . . . . . . :
Node Type . . . . . . . . . . . . : Hybrid
IP Routing Enabled. . . . . . . . : No
WINS Proxy Enabled. . . . . . . . : No
DNS Suffix Search List. . . . . . : cable.rcn.com
Unknown adapter Local Area Connection:
Media State . . . . . . . . . . . : Media disconnected
Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : TAP-Windows Adapter V9
Physical Address. . . . . . . . . : 00-FF-86-58-B1-15
DHCP Enabled. . . . . . . . . . . : Yes
Autoconfiguration Enabled . . . . : Yes
Wireless LAN adapter Local Area Connection* 1:
Media State . . . . . . . . . . . : Media disconnected
Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : Microsoft Wi-Fi Direct Virtual Adapter
Physical Address. . . . . . . . . : 7C-67-A2-80-DA-69
DHCP Enabled. . . . . . . . . . . : Yes
Autoconfiguration Enabled . . . . : Yes
Wireless LAN adapter Local Area Connection* 2:
Media State . . . . . . . . . . . : Media disconnected
Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : Microsoft Wi-Fi Direct Virtual Adapter #2
Physical Address. . . . . . . . . : 7E-67-A2-80-DA-68
DHCP Enabled. . . . . . . . . . . : Yes
Autoconfiguration Enabled . . . . : Yes
Wireless LAN adapter Wi-Fi:
Connection-specific DNS Suffix . : cable.rcn.com
Description . . . . . . . . . . . : Intel(R) Dual Band Wireless-AC 3165
Physical Address. . . . . . . . . : 7C-67-A2-80-DA-68
DHCP Enabled. . . . . . . . . . . : Yes
Autoconfiguration Enabled . . . . : Yes
Link-local IPv6 Address . . . . . : fe80::7a8a:c454:b45:988b%16(Preferred)
IPv4 Address. . . . . . . . . . . : 192.168.0.34(Preferred)
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Lease Obtained. . . . . . . . . . : Thursday, April 13, 2023 2:37:54 PM
Lease Expires . . . . . . . . . . : Friday, April 14, 2023 2:37:53 PM
Default Gateway . . . . . . . . . : 192.168.0.1
DHCP Server . . . . . . . . . . . : 192.168.0.1
DHCPv6 IAID . . . . . . . . . . . : 159147938
DHCPv6 Client DUID. . . . . . . . : 00-01-00-01-28-A7-A0-21-7C-67-A2-80-DA-68
DNS Servers . . . . . . . . . . . : 208.59.247.45
208.59.247.46
NetBIOS over Tcpip. . . . . . . . : Enabled
Ethernet adapter Bluetooth Network Connection:
Media State . . . . . . . . . . . : Media disconnected
Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : Bluetooth Device (Personal Area Network)
Physical Address. . . . . . . . . : 7C-67-A2-80-DA-6C
DHCP Enabled. . . . . . . . . . . : Yes
Autoconfiguration Enabled . . . . : Yes
C:\Users\rmcme>

2.nslookup ipaddress

C:\Users\rmcme>nslookup ycrash.io

Server: ns2.dns.rcn.net
Address: 208.59.247.45
Non-authoritative answer:
Name: ycrash.io
Addresses: 52.8.222.182
52.8.184.141

C:\Users\rmcme>nslookup 142.251.163.100

Server: ns2.dns.rcn.net
Address: 208.59.247.45
Name: wv-in-f100.1e100.net
Address: 142.251.163.100

3. ping amazon.com

Pinging amazon.com [205.251.242.103] with 32 bytes of data:

Reply from 205.251.242.103: bytes=32 time=125ms TTL=236
Reply from 205.251.242.103: bytes=32 time=35ms TTL=236
Reply from 205.251.242.103: bytes=32 time=37ms TTL=236
Reply from 205.251.242.103: bytes=32 time=34ms TTL=236
Ping statistics for 205.251.242.103:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 34ms, Maximum = 125ms, Average = 57ms

4. tracert google.com

Tracing route to amazon.com [205.251.242.103]

over a maximum of 30 hops:

1 8 ms 16 ms 21 ms 192.168.0.1

2 171 ms 62 ms 46 ms 172.30.0.1

3 38 ms 96 ms 48 ms 216.80.78.77

4 12 ms 33 ms 215 ms 207.172.17.3

5 133 ms 16 ms 33 ms hge0-0-0-6.border1.eqnx.il.rcn.net [207.172.19.243]

6 36 ms 37 ms 35 ms 99.83.94.240

7 * * * Request timed out.

8 * * * Request timed out.

9 * * * Request timed out.

10 37 ms 33 ms 30 ms 150.222.212.43

11 * * * Request timed out.

12 * * * Request timed out.

13 * * * Request timed out.

14 * * * Request timed out.

15 *......

5. netstat -a

Active Connections

Proto Local Address Foreign Address State

TCP 0.0.0.0:135 LaptopDELL:0 LISTENING

TCP 0.0.0.0:445 LaptopDELL:0 LISTENING

TCP 0.0.0.0:3648 LaptopDELL:0 LISTENING

TCP 0.0.0.0:5040 LaptopDELL:0 LISTENING

TCP 0.0.0.0:6646 LaptopDELL:0 LISTENING

TCP 0.0.0.0:7070 LaptopDELL:0 LISTENING

TCP 0.0.0.0:7680 LaptopDELL:0 LISTENING

TCP 0.0.0.0:7779 LaptopDELL:0 LISTENING

TCP 0.0.0.0:49664 LaptopDELL:0 LISTENING

TCP 0.0.0.0:49665 LaptopDELL:0 LISTENING

TCP 0.0.0.0:49666 LaptopDELL:0 LISTENING

TCP 0.0.0.0:49667 LaptopDELL:0 LISTENING

TCP 0.0.0.0:49668 LaptopDELL:0 LISTENING

TCP 0.0.0.0:49670 LaptopDELL:0 LISTENING

TCP 127.0.0.1:27015 LaptopDELL:0 LISTENING

TCP 127.0.0.1:50051 LaptopDELL:0 LISTENING

TCP 127.0.0.1:55500 LaptopDELL:0 LISTENING

TCP 192.168.0.34:139 LaptopDELL:0 LISTENING

TCP 192.168.0.34:55453 relay-e24ffb83:https ESTABLISHED

TCP 192.168.0.34:55467 52.159.126.152:https ESTABLISHED

TCP 192.168.0.34:55518 20.25.241.18:https ESTABLISHED

TCP 192.168.0.34:55616 ec2-54-175-191-204:https ESTABLISHED

TCP 192.168.0.34:55635 52.96.170.82:https ESTABLISHED

TCP 192.168.0.34:55647 104.26.3.186:https ESTABLISHED

TCP 192.168.0.34:55846 52.96.79.226:https ESTABLISHED

TCP 192.168.0.34:55855 gb-in-f188:5228 ESTABLISHED

TCP 192.168.0.34:55856 bg-in-f188:5228 ESTABLISHED

TCP 192.168.0.34:56650 a23-7-28-47:https ESTABLISHED

TCP 192.168.0.34:56950 132.145.172.253:https ESTABLISHED

TCP 192.168.0.34:56985 a23-193-200-115:https CLOSE_WAIT

TCP 192.168.0.34:56986 a23-193-200-115:https CLOSE_WAIT

TCP 192.168.0.34:56987 a23-193-200-115:https CLOSE_WAIT

TCP 192.168.0.34:56988 a23-193-200-115:https CLOSE_WAIT

TCP 192.168.0.34:56989 a23-193-200-115:https CLOSE_WAIT

TCP 192.168.0.34:56990 a23-193-200-115:https CLOSE_WAIT

TCP 192.168.0.34:57038 bi-in-f191:https ESTABLISHED

TCP 192.168.0.34:57081 wv-in-f91:https ESTABLISHED

TCP 192.168.0.34:57134 lga34s30-in-f3:https ESTABLISHED

TCP 192.168.0.34:57205 bl-in-f156:https TIME_WAIT

TCP 192.168.0.34:57221 bl-in-f95:https TIME_WAIT

TCP 192.168.0.34:57243 ord37s43-in-f6:https CLOSE_WAIT

TCP 192.168.0.34:57251 bg-in-f138:https ESTABLISHED

TCP 192.168.0.34:57284 ord38s28-in-f6:https TIME_WAIT

TCP 192.168.0.34:57285 bj-in-f156:https TIME_WAIT

TCP 192.168.0.34:57286 ord38s30-in-f2:https TIME_WAIT

TCP 192.168.0.34:57291 ww-in-f99:https TIME_WAIT

TCP 192.168.0.34:57296 ec2-54-175-191-203:https TIME_WAIT

TCP 192.168.0.34:57302 e2a:https TIME_WAIT

TCP 192.168.0.34:57310 bh-in-f94:https ESTABLISHED

TCP 192.168.0.34:57311 ww-in-f102:https ESTABLISHED

TCP 192.168.0.34:57312 bl-in-f139:https ESTABLISHED

TCP 192.168.0.34:57315 kix06s05-in-f3:https ESTABLISHED

TCP 192.168.0.34:57321 wv-in-f113:https ESTABLISHED

TCP 192.168.0.34:57322 wv-in-f113:https TIME_WAIT

TCP 192.168.0.34:57332 wv-in-f119:https ESTABLISHED

TCP 192.168.0.34:57333 47:https ESTABLISHED

TCP 192.168.0.34:57337 ord38s33-in-f10:https ESTABLISHED

TCP 192.168.0.34:57338 bg-in-f95:https ESTABLISHED

TCP 192.168.0.34:57339 ec2-3-17-93-252:https ESTABLISHED

TCP 192.168.0.34:57341 bl-in-f102:https ESTABLISHED

TCP 192.168.0.34:57343 lga25s71-in-f3:https ESTABLISHED

TCP 192.168.0.34:57345 ec2-54-175-191-203:https ESTABLISHED

TCP 192.168.0.34:57347 13.68.233.9:https ESTABLISHED

TCP [::]:135 LaptopDELL:0 LISTENING

TCP [::]:445 LaptopDELL:0 LISTENING

TCP [::]:3648 LaptopDELL:0 LISTENING

TCP [::]:7680 LaptopDELL:0 LISTENING

TCP [::]:7779 LaptopDELL:0 LISTENING

TCP [::]:49664 LaptopDELL:0 LISTENING

TCP [::]:49665 LaptopDELL:0 LISTENING

TCP [::]:49666 LaptopDELL:0 LISTENING

TCP [::]:49667 LaptopDELL:0 LISTENING

TCP [::]:49668 LaptopDELL:0 LISTENING

TCP [::]:49670 LaptopDELL:0 LISTENING

TCP [::1]:49669 LaptopDELL:0 LISTENING

UDP 0.0.0.0:123 *:*

UDP 0.0.0.0:500 *:*

UDP 0.0.0.0:4500 *:*

UDP 0.0.0.0:5050 *:*

UDP 0.0.0.0:5353 *:*

UDP 0.0.0.0:5355 *:*

UDP 0.0.0.0:6646 *:*

UDP 0.0.0.0:50001 *:*

UDP 127.0.0.1:1900 *:*

UDP 127.0.0.1:49664 *:*

UDP 127.0.0.1:60146 *:*

UDP 127.0.0.1:64458 *:*

UDP 127.0.0.1:64459 *:*

UDP 192.168.0.34:137 *:*

UDP 192.168.0.34:138 *:*

UDP 192.168.0.34:1900 *:*

UDP 192.168.0.34:60145 *:*

UDP [::]:123 *:*

UDP [::]:500 *:*

UDP [::]:4500 *:*

UDP [::]:5353 *:*

UDP [::]:5355 *:*

UDP [::1]:1900 *:*

UDP [::1]:60144 *:*

UDP [fe80::7a8a:c454:b45:988b%16]:1900 *:*

UDP [fe80::7a8a:c454:b45:988b%16]:60143 *:*

6. arp -a

Interface: 192.168.0.34 --- 0x10

Internet Address Physical Address Type

192.168.0.1 0c-cb-85-f9-ad-ad dynamic

192.168.0.11 ec-b5-fa-0e-03-39 dynamic

192.168.0.22 dc-9a-7d-21-b3-4b dynamic

192.168.0.255 ff-ff-ff-ff-ff-ff static

224.0.0.22 01-00-5e-00-00-16 static

224.0.0.251 01-00-5e-00-00-fb static

224.0.0.252 01-00-5e-00-00-fc static

239.255.102.18 01-00-5e-7f-66-12 static

239.255.255.250 01-00-5e-7f-ff-fa static

255.255.255.255 ff-ff-ff-ff-ff-ff static

7. C:\Users\rmcme>route print

===========================================================================

Interface List

11...00 ff 86 58 b1 15 ......TAP-Windows Adapter V9

12...7c 67 a2 80 da 69 ......Microsoft Wi-Fi Direct Virtual Adapter

7...7e 67 a2 80 da 68 ......Microsoft Wi-Fi Direct Virtual Adapter #2

16...7c 67 a2 80 da 68 ......Intel(R) Dual Band Wireless-AC 3165

14...7c 67 a2 80 da 6c ......Bluetooth Device (Personal Area Network)

1...........................Software Loopback Interface 1

===========================================================================

IPv4 Route Table

===========================================================================

Active Routes:

Network Destination Netmask Gateway Interface Metric

0.0.0.0 0.0.0.0 192.168.0.1 192.168.0.34 55

127.0.0.0 255.0.0.0 On-link 127.0.0.1 331

127.0.0.1 255.255.255.255 On-link 127.0.0.1 331

127.255.255.255 255.255.255.255 On-link 127.0.0.1 331

192.168.0.0 255.255.255.0 On-link 192.168.0.34 311

192.168.0.34 255.255.255.255 On-link 192.168.0.34 311

192.168.0.255 255.255.255.255 On-link 192.168.0.34 311

224.0.0.0 240.0.0.0 On-link 127.0.0.1 331

224.0.0.0 240.0.0.0 On-link 192.168.0.34 311

255.255.255.255 255.255.255.255 On-link 127.0.0.1 331

255.255.255.255 255.255.255.255 On-link 192.168.0.34 311

===========================================================================

Persistent Routes:

None

IPv6 Route Table

===========================================================================

Active Routes:

If Metric Network Destination Gateway

1 331 ::1/128 On-link

16 311 fe80::/64 On-link

16 311 fe80::7a8a:c454:b45:988b/128

On-link

1 331 ff00::/8 On-link

16 311 ff00::/8 On-link

===========================================================================

Persistent Routes:

None

C:\Users\rmcme>

8. C:\Users\rmcme>systeminfo

Host Name: LAPTOPDELL

OS Name: Microsoft Windows 10 Home

OS Version: 10.0.19044 N/A Build 19044

OS Manufacturer: Microsoft Corporation

OS Configuration: Standalone Workstation

OS Build Type: Multiprocessor Free

Registered Owner: rmcmeera@gmail.com

Registered Organization: N/A

Product ID: 00325-96142-21539-AAOEM

Original Install Date: 9/23/2021, 12:24:43 PM

System Boot Time: 4/2/2023, 1:29:43 PM

System Manufacturer: Dell Inc.

System Model: Inspiron 13-7378

System Type: x64-based PC

Processor(s): 1 Processor(s) Installed.

[01]: Intel64 Family 6 Model 142 Stepping 9 GenuineIntel ~2901 Mhz

BIOS Version: Dell Inc. 1.27.0, 1/18/2019

Windows Directory: C:\WINDOWS

System Directory: C:\WINDOWS\system32

Boot Device: \Device\HarddiskVolume1

System Locale: en-us;English (United States)

Input Locale: en-us;English (United States)

Time Zone: (UTC-06:00) Central Time (US & Canada)

Total Physical Memory: 12,158 MB

Available Physical Memory: 4,834 MB

Virtual Memory: Max Size: 20,862 MB

Virtual Memory: Available: 11,273 MB

Virtual Memory: In Use: 9,589 MB

Page File Location(s): C:\pagefile.sys

Domain: WORKGROUP

Logon Server: \\LAPTOPDELL

Hotfix(s): 18 Hotfix(s) Installed.

[01]: KB5022502

[02]: KB4562830

[03]: KB5003791

[04]: KB5012170

[05]: KB5025221

[06]: KB5006753

[07]: KB5007273

[08]: KB5011352

[09]: KB5011651

[10]: KB5014032

[11]: KB5014671

[12]: KB5015895

[13]: KB5016705

[14]: KB5018506

[15]: KB5020372

[16]: KB5022924

[17]: KB5023794

[18]: KB5005699

Network Card(s): 3 NIC(s) Installed.

[01]: Intel(R) Dual Band Wireless-AC 3165

Connection Name: Wi-Fi

DHCP Enabled: Yes

DHCP Server: 192.168.0.1

IP address(es)

[01]: 192.168.0.34

[02]: fe80::7a8a:c454:b45:988b

[02]: Bluetooth Device (Personal Area Network)

Connection Name: Bluetooth Network Connection

Status: Media disconnected

[03]: TAP-Windows Adapter V9

Connection Name: Local Area Connection

Status: Media disconnected

Hyper-V Requirements: VM Monitor Mode Extensions: Yes

Virtualization Enabled In Firmware: Yes

Second Level Address Translation: Yes

Data Execution Prevention Available: Yes

9. pathping 127.0.0.1

Tracing route to LaptopDELL [127.0.0.1]

over a maximum of 30 hops:

0 LaptopDELL [127.0.0.1]

1 LaptopDELL [127.0.0.1]

Computing statistics for 25 seconds...

Source to Here This Node/Link

Hop RTT Lost/Sent = Pct Lost/Sent = Pct Address

0 LaptopDELL [127.0.0.1]

0/ 100 = 0% |

1 0ms 0/ 100 = 0% 0/ 100 = 0% LaptopDELL [127.0.0.1]

Trace complete.

pathping ycrash.io

Tracing route to ycrash.io [52.8.222.182]

over a maximum of 30 hops:

0 LaptopDELL.cable.rcn.com [192.168.0.34]

1 192.168.0.1

2 172.30.0.1

3 216.80.78.77

4 207.172.17.1

5 207.172.17.79

6 lag-107.ear4.Chicago2.Level3.net [4.26.123.5]

7 * * ae2.3608.ear7.Chicago2.level3.net [4.69.142.178]

8 52.95.217.36

9 15.230.18.69

10 52.95.62.31

11 * * *

Computing statistics for 250 seconds...............

Source to Here This Node/Link

Hop RTT Lost/Sent = Pct Lost/Sent = Pct Address

0 LaptopDELL.cable.rcn.com [192.168.0.34]

3/ 100 = 3% |

1 92ms 4/ 100 = 4% 1/ 100 = 1% 192.168.0.1

0/ 100 = 0% |

2 11ms 99/ 100 = 99% 96/ 100 = 96% 172.30.0.1

0/ 100 = 0% |

3 56ms 7/ 100 = 7% 4/ 100 = 4% 216.80.78.77

0/ 100 = 0% |

4 --- 100/ 100 =100% 97/ 100 = 97% 207.172.17.1

0/ 100 = 0% |

5 95ms 5/ 100 = 5% 2/ 100 = 2% 207.172.17.79

0/ 100 = 0% |

6 129ms 3/ 100 = 3% 0/ 100 = 0% lag-107.ear4.Chicago2.Level3.net [4.26.123.5]

1/ 100 = 1% |

7 126ms 4/ 100 = 4% 0/ 100 = 0% ae2.3608.ear7.Chicago2.level3.net [4.69.142.178]

96/ 100 = 96% |

8 --- 100/ 100 =100% 0/ 100 = 0% 52.95.217.36

0/ 100 = 0% |

9 --- 100/ 100 =100% 0/ 100 = 0% 15.230.18.69

0/ 100 = 0% |

10 --- 100/ 100 =100% 0/ 100 = 0% 52.95.62.31

Trace complete.

10. C:\Users\rmcme>hostname

LaptopDELL

11. C:\Users\rmcme>getmac

Physical Address Transport Name

=================== ==========================================================

7C-67-A2-80-DA-68 \Device\Tcpip_{AA418031-63C2-4732-8243-7417259E49D6}

7C-67-A2-80-DA-6C Media disconnected

00-FF-86-58-B1-15 Media disconnected

C:\Users\rmcme>

Wednesday, 12 April 2023

JVM - Garbage Collection GC #002

Garbage Collection : GC#2

GC traverses the object graph to find the dead objects.
Many types of GC collectors in Java. How to choose the right one.

Serial : Simplest, designed for small apps and on single thread.GC events are conducted serially in 1 thread. Stop the world approach. So it is not used in real time.

Parellel : Multiple threads are used for minor gC in young generation. A single thread is used for Major GC. Most suitable for Multiple thread environment where a lot of work to be done, long pauses are accepted..(ie : running a batch job)
It is the default since JDK 7

Concurrent Mark Sweep :

Concurrent low pause collector, multiple threads are used for minor garbage collection.

Major GC is multi threaded and runs concurrently alongside application. Use more CPUS.

If you can allocate ore CPU, the CMS GC is a preferre3d chice for better performance.

Garbage Firs (G1):

Replacement for CMS

Designed for multi-threaded apps that have large heap size available (>4 GB)

Does not have separate regions for young and old generations.

Partition the heap in to a set of equal size regions and use multiple[le threads to scan them.

After mark phase is over, G1 knows which regions contains the most garbage objects and performs GC on those regions first.

Experimental Garbage Collectors.

Epsilon : a -do- nothing (no-op) GC release as part of JDK 11. Does not implement any memory reclamation mechanism. Not preferable. Once Heap is exhausted, the JVM shuts down

Shenandoah: Release as part of JDK 12. GC cycle works currently with application threads. Can relocate objects concurrently. More CPU intensive.

ZGC : Release as part of JDK 11. Low latency, scalability and ease of use. Allows to application to continue running while it performs all garbage collection operations.

How to choose :

Factors : Most of the default setting will work.

Serial is fine for small data setup (>=100 MB) and or it will be run on a sigle processor with no-pause time requirements.

Parallel is preferable for peak performance for apps and with no-pause time requirements or pauses for 1 sec or longer are acceptable.

CMS/G1 is preferable is response time is important than overall throughput and garbage collection pauses must be kept shorter than approximately 1 sec.

Advantages of GC :

Makes code simple, java memory efficient. Don't worry about mem management (C++ should be manual not automatic mem management) .
Frees the heap mem to accommodate new objects.
Options for tuning the GC to improve its efficiency.

Best Practice:

It is possible to manually run the GC with System.gc() or Rintime.gc() methods.

If u don't have enough memory to run your application, you will experience slowdowns, hangs, long collection times, :stop the world" events, and eventually out of memory errors. You can take the help of monitoring tool like jstat or Java Flight recorder to see if the heap usage grows indefinitely, which might indicate a bug in your code.

If small, default settings will work.

Best approach to tuning JAVA garbage collection is settings flags on the JVM.

JVM - Garbage Collection - GC#001

Garbage Collection - GC#1

Process of reclaiminh the runtime unused memory by destroying the un used objects

Methods like free() in C and deletete() in c++ are used to perform clean garbage.

In Java, GC is automatic during the life time of a program

At any point of RT, heap memory consistes of 2 types of objects:

Live : Being used and referenced

Dead : not used and not referenced currently.

How to derefernce objects:

By making a reference null { object o1 = null;}

By assigning a reference to another { object o1 = o2;}

By using an anonymous object { new Object;}

How GC Works:

Many Versions of JVM. has its own implementation of GC .

Any version of JVM can be used but should meet the std spec like :

: mark the unreachable objects

: Destroy them

: Compacting the memory.

GC Roots: to identify the live and dead objects

Local vars and input paramas

Active Threads

Static Fields of the Loaded classes

JNI In(ref)ferences

It traverse the full object graph in mem and marks live objects(visited). ALl not reacheble(not visited) by grtaph are identified as dead objects.

Sweep Phase and compact phase ( Fragmented mem blocks are made as contiguos blocks)

Generational GC strategy:

Marking will take a longer GC Time. All objects are mostly short lived.

Heap : (eden, S1, S2)

Young Generation : Newly

-Eden Space : all new objects start here, and initial mem is allocated to them

-Survivor Spaces : (S to S) - Objects are moved here from Eden after surviving one garbage collection cycle.

When eden space if filled , aminor GC is performed and all the survivir objects are moved to one of the survivor spaces.

Minor GC checks also the survivor space. All the dead objects are reoved when Minir GC is performed.

Second time Minor GC, is used Eden and Survivor space. At any point of time Survivor space is empty.

Old Generation : Long lived objects are eventually moved from the Young generation to the Old Generation.

This is also known as Tenured generation and conatins objects that have maintained in the survivor spaces for a long time.

When objects are garbage collected here, it is called as majot garbage collection event.

Permenant Generation :

Metat data such as classes and methods are stored in Perm Genearation

Classes thar are no longer in use may be GC from the permenant generation.

Now Metaspace memory soppace replaced the permenant generation. Heap is now automatically resized. Avoids the the pbm of apps going out of memory due to the limited size of

PermGen space of heap.

Classes that are no longer used is automatically cleaned when the metaspace searches its maximum size.

JVM - Basics #01

JVM

Java Virtual Machine implements Write once Run Anywhere approach

Supports many Scala, Kotlin in addition to Java

-> VM -> OS -> Application

Virtual M/C : H/W-> Hypervisor-> -> VM -> OS -> App..

-> VM -> OS -> App..

Java - Compiler - SC (Java) - > Byte code (class) ->

JVM :

Class Loader : Prepares the java classes and loads them into main memory.

Run Time Mem/ Data Area: Holds the the rT vars and Data

Execution Engine : Executes the code

Class Loader :

Loading : Boot strap Loader, Extension Class Loader, Application Class Loader

Bin representation :

Boot Strap Loader . Root Class Loader ..

Super class of Extension loads the std java packages like java.lang, java.net, java.util, java.io etc.

The above are available in rt.jar file

Extension Class Loader : Sub class of Bootstrap and the super class of thge Application class Loader.

Loads the files present in $JAVA_HOME/jre/lib/ext directory

Application Class Loader : subclass extensions loader, Loads the files present on the class path

By Default, the class path is set to the current directory of th application.

Linking :

Verification : Verify, Prepare and Resolve : check the structureal correctness of the .class file by checking it against a set of constraint rules . Check for Verify Exception..

Preperation : JVM allocates memory for stat fields of a class or interface. Initializes them with default values.

Resolution : Symbolic reference are substituted with direct references present in RT constant pool.

Initialization :

Clinit .

Assigning values, constructor call, stat block exec,
final stage of class loading. Also check for concurrency issues.
Handle thread safety issues for secured process.

Run Time Data Area:

Method Area :

Class level data as RT Constant Pool, field and code for methods. Memory is insufficent for the startup, JVM throws outofMemoryError

Memory for class instances and arrays is allocated.

Heap Area :

All the objects and their corresponding instance varaiables and arrays are stored here. Created on startup. Only one heap Area/JVM

Stack Area :

Local varsiables and temp results are stored here.
For every method call, one entry is made into stack frame:
Further divided in to local vars, operand stack, frame data

PC Register : Program Counter Register. JVM supports multiple threads. Each thread has its own PCR, to hold the address of currently executing JVM Instruction.

Once executed, PCR is updated

Native Method Stack : JVM supports native methods. ( written in c/C++)

Execution Engine :

Byte code is loaded then interpreter

Reads BC line by line.
JIT compiler : When EE finds the repeated code, it uses JIT-C, tot compile the en tire BC and change it to native code.
JITC Consists of 3 components : Intermediate code Generator, Code Optimizer, Target Code Generator.

Garbage Collector:

GC collects and removes un referenced objects.
Involves 2 phases : Mark and Sweep. Done automaticall by GC.
3 types of JC in KJVM, Serial, Parellel(through put) and G1 (for large heap sizes > 4 GB)

Java Native Interface

Supports execution of native code via JNI (c, C++ or ASM files).

Tuesday, 11 April 2023

Better Teacher

3 Steps

Focus on Learning of students rather than teaching

One rule is that people learn faster and better with varied repetition. Children who practice the piano twice a day are almost always better piano players than children who practice once a week. The same is true of speaking a foreign language, solving quadratic equations, and writing persuasive essays.

A second rule is that people learn faster and better when they receive frequent feedback on their performance. (A corollary to this rule is that prompt feedback is more effective than delayed feedback.)

A third rule is that incentives can play a crucial role in the classroom

Teachers can quiz students weekly and reveal the correct answers immediately. In this way, students receive prompt and frequent feedback. They also have an incentive to complete assigned readings and pay attention in class.

Finally, teachers can take a page from video-gaming companies. Video gaming is a learned skill, and many gamers perform at a very high level. The makers of popular video games like Angry Birds and Super Mario exploit basic principles of learning. Players receive instantaneous feedback on their performance. They also gain expertise through repetition with variation. And leveling up is rewarding!

Key:

Teachers should think less about how to teach and more about how students learn.
Studies have identified potent enablers of learning such as varied repetition, prompt feedback, and mental elaboration.
Teachers can put these principles to work when they build courses, assignments, and tests

From Source

Tuesday, 21 March 2023

KIVY Crash course : Handson Exercises

Ex 1 kivyApp1.py

from kivy.app import App
from kivy.uix.label import Label


class MainApp(App):
    def build(self):
        label = Label(text='Hello from Kivy',
                      size_hint=(.5, .5),
                      pos_hint={'center_x': .5, 'center_y': .5})

       
        return label
       

if __name__ == '__main__':
    app = MainApp()
    app.run()

Output

Ex 2: kivyApp2.py

from kivymd.app import MDApp
from kivymd.uix.label import MDLabel
from kivymd.uix.screen import Screen


class Demo(MDApp):

    def build(self):
        # defining screenpip
        screen = Screen()

        # defining 1st label
        l = MDLabel(text="Hello!!", pos_hint={'center_x': 0.6,
                                              'center_y': 0.8},
                    theme_text_color="Custom",
                    text_color=(0.5, 0, 0.5, 1),
                    font_style='H1')

        # defining 2nd label
        l1 = MDLabel(text="Hello Kivy Welcome!", pos_hint={'center_x': 0.6,
                                                           'center_y': 0.6},
                     theme_text_color="Custom",
                     text_color=(0.5, 0, 0.5, 1),
                     font_style='H2')

        # defining 3rd label
        l2 = MDLabel(text="Hello Kivy Welcome!", pos_hint={'center_x': 0.6,
                                                           'center_y': 0.4},
                     theme_text_color="Custom",
                     text_color=(0.5, 0, 0.5, 1),
                     font_style='H3')

        screen.add_widget(l)

        screen.add_widget(l1)
        screen.add_widget(l2)
        return screen


if __name__ == "__main__":
    Demo().run()

Output

EX 3 : kivyApp3.py

# Program to Show how to use textinput (UX widget) in kivy

# import kivy module
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.textinput import TextInput
from kivy.uix.scatter import Scatter
from kivy.uix.floatlayout import FloatLayout
from kivy.uix.label import Label
import kivy

from kivy.app import App

kivy.require('1.9.0')

# Create the App class


class TutorialApp(App):
    def build(self):
        b = BoxLayout(orientation='vertical')

        # Adding the text input
        t = TextInput(font_size=50,
                      size_hint_y=None,
                      height=100)

        f = FloatLayout()

        s = Scatter()

        l = Label(text="      Hello !",
                  font_size=50)

        f.add_widget(s)
        s.add_widget(l)

        b.add_widget(t)
        b.add_widget(f)

        # Binding it with the label
        t.bind(text=l.setter('text'))

        return b


# Run the App
if __name__ == "__main__":
    TutorialApp().run()

Output :

Ex 4 : kivyApp4.py using .kv file

import kivy

from kivy.app import App

kivy.require('1.9.1')

class kvfileApp(App):
    pass

kv = kvfileApp()  # kvfile.kv

kv.run()

kvfile.kv

Label:
    text: "Hello"

Output

ex 5 : kivyApp5.py

from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
###############################################
# creating the root widget used in .kv file


class KVBL(BoxLayout):
    '''
            no need to do anything here as
            we are building things in .kv file
    '''
    pass

#################################################
# class in which name .kv file must be named KVBoxLayout.kv.


class KVBoxLayoutApp(App):

    def build(self):
        # returning the instance of KVBL class
        return KVBL()

##################################################


# creating the object root for BoxLayoutApp() class
root = KVBoxLayoutApp()

# run function runs the whole program
root.run()

KVBoxLayout.kv

<KVBL>:
    orientation: 'vertical'
#########################################################

    # defining the buttons in the box layout format
    # and adding colour, size etc to it.
    # you can use accordingly
    Button:
        text: "B1"
        background_color: 0, 1, 1, 1
        font_size: 20
        
    Button:
        text: "B2"
        background_color: 0, 1, 0, 1
        font_size: 20
        
    Button:
        text: "B3"
        background_color: 0, 0, 1, 1
        font_size: 20
        
    Button:
        text: "B4"
        background_color: 1, 0, 1, 1
        font_size: 20
        
    Button:
        text: "B5"
        background_color: 1, 0, 0, 1
        font_size: 20

Output:

Ex 6 : kivyApp6.py

import logging
from kivy.logger import Logger
from kivy.uix.widget import Widget
from kivy.uix.button import Button
from kivy.app import App
import kivy

kivy.require("1.9.1")

Logger.setLevel(logging.TRACE)

# Creating a widget class
# through this we add button
# the commands of the class is in .kv file


class Button_Widget(Widget):

    def __init__(self, **kwargs):

        # Python super() function allows us to
        # refer to the parent class explicitly.

        super(Button_Widget, self).__init__(**kwargs)

        # creating Button
        btn1 = Button(text='Hello World 1', font_size="15sp",
                      background_color=(1, 1, 1, 1),
                      color=(1, 1, 1, 1),
                      # size =(32, 32),
                      # size_hint =(.2, .2),
                      pos=(300, 250))

        # Arranging a callback to a button using
        # bind() function in kivy.
        btn1.bind(on_press=self.callback)
        self.add_widget(btn1)

    # callback function tells when button pressed
    # It tells the state and instance of button.
    def callback(self, instance):
        print("Button is pressed ")
        print('The button % s state is <%s>' % (instance, instance.state))

# create App class


class ButtonApp(App):

    def build(self):
        # return the widget
        return Button_Widget()


# run the App
if __name__ == "__main__":
    ButtonApp().run()

output

Once you click hello world1 button, it changes to blue.

Ex 7 kivyApp7.kv

from kivy.uix.pagelayout import PageLayout
import kivy

# base Class of your App inherits from the App class.
# app:always refers to the instance of your application
from kivy.app import App
kivy.require('1.9.0')

# The PageLayout class is used to create
# a simple multi-page layout,
# in a way that allows easy flipping from
# one page to another using borders.

# creating the root widget used in .kv file


class PageLayout(PageLayout):
    pass

# creating the App class in which name
# .kv file is to be named PageLayout.kv


class PageLayoutApp(App):
    # defining build()
    def build(self):
        # returning the instance of root class
        return PageLayout()


# creating object of PageLayoutApp() class
plApp = PageLayoutApp()

# run the class
plApp.run()

pagelayout.kv

# creating simple Pagelayout using.kv

# creating simple Pagelayout using.kv

# creating page Layout
<PageLayout>:

    # Creating Page 1
    
    # Using BoxLayout inside PageLayout
    BoxLayout:

        # creating Canvas
        canvas:
            Color:
                rgb: 0, .5, .95, 1
            Rectangle:
                pos: self.pos
                size: self.size

        # Providing orientation to the BoxLayout
        orientation: "vertical"

        # creating Button
        Button:
            text: "Page 1"
            size_hint_y: .4

        # Adding Label to Page 1
            
        Label:
            markup: True
            text: "RMC"
            color: 0, 0, 0, 1
            outline_color: 0, 0.5, 0.5, 1
            font_size: 30


    # Creating Page 2
    BoxLayout:
        orientation: "vertical"
        
        canvas:
            Color:
                rgba: 109 / 255., 8 / 255., 57 / 255., 1
            Rectangle:
                pos: self.pos
                size: self.size
        Label:
            markup: True
            text: " Kivy[b]PageLayout[/b]!!!!! "
            color: 0, 0, 0, 1
            outline_color: 0, 0.5, 0.5, 1
            font_size: 30

            
        Button:
            text: "Page 2"
            size_hint_y: .2


    # Creating Page 3
    BoxLayout:
        
        orientation: 'vertical'

        canvas:
            Color:
                rgba: 100 / 555., 9 / 155., 37 / 455., 1
            Rectangle:
                pos: self.pos
                size: self.size

        Label:
            text: 'page 3'

        # This Image is directly from the websource
        # By using AsyncImage you can use that
        AsyncImage:
            source: 'http://kivy.org/logos/kivy-logo-black-64.png'
        


    # Creating Page 4
    Button:
        # Adding image
        # image must be .png
        # and present at the same folder where
        # .kv and main file is saved
        Image:
            source: "download.png"
            center_x: self.parent.center_x
            center_y: self.parent.center_y

output:

You can go to any page by pulling the pages.

Pl refer kivy Tutorials :

1. Tutorials — Kivy 2.1.0 documentation

2. Kivy Tutorial - GeeksforGeeks

AMET-SOLID

Friday, 14 April 2023

JVM Garbage Collection GC#003 (How)

GC Logging Flags in Java 8 and Earlier

-XX:+PrintGC

-XX:+PrintGCDetails

-XX:+PrintGCDateStamps and -XX:+PrintGCTimeStamps

-Xloggc

Thursday, 13 April 2023

Networ{k|th} - Tutorials

1. ipconfig /all will return bio-data of your n/w

2.nslookup ipaddress

C:\Users\rmcme>nslookup ycrash.io

C:\Users\rmcme>nslookup 142.251.163.100

3. ping amazon.com

4. tracert google.com

5. netstat -a

6. arp -a

7. C:\Users\rmcme>route print

8. C:\Users\rmcme>systeminfo

9. pathping 127.0.0.1

pathping ycrash.io

Computing statistics for 250 seconds...............

10. C:\Users\rmcme>hostname

11. C:\Users\rmcme>getmac

Wednesday, 12 April 2023

JVM - Garbage Collection GC #002

JVM - Garbage Collection - GC#001

JVM - Basics #01

Tuesday, 11 April 2023

Better Teacher

Tuesday, 21 March 2023

KIVY Crash course : Handson Exercises

index.html

Happy open and Distance Learning!

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