Creating a graph with Quartz 2D: http://www.sitepoint.com/creating-a-graph-with-quartz-2d/
Sunday, June 11, 2023
Monday, October 10, 2022
Shell Script to detect events in ADB Logcat in a loop
The following shell script performs an action (tap) on the screen, then checks that a particular event does not happen on the device. It then performs another action (press back button) and then checks the target event happens only once. Then it closes a process and iterates through the same steps in a loop 50 times.
#!/bin/sh
# Clean up any reminiscent from previous run of the script
rm -rf script_logs
mkdir script_logs
for i in {1..50}
do
echo $i
echo "Clearing device logs"
adb logcat -c
echo "Starting log recording"
adb logcat >> script_logs/script_logs$i.txt &
logcat_pid=$!
echo "Clicking at a point on the screen"
adb shell input tap 200 300
echo "Waiting for 4 seconds for event to happen and logs generated"
sleep 4
events=`grep "<log_pattern>" script_logs/script_logs$i.txt | wc -l`
if [ $events == 0 ]
then
echo "No event found"
else
echo "$events were found, the test failed"
kill -9 $logcat_pid
exit 1
fi
adb shell input keyevent KEYCODE_BACK
echo "Waiting for 4 seconds for another event"
sleep 4
echo "Checking how many events were sent"
events=`grep "<log_pattern>" script_logs/script_logs$i.txt | wc -l`
if [ $events == 1 ]
then
echo "One and only one event was found"
else
echo "$events were found, the test failed"
kill -9 $logcat_pid
exit 1
fi
echo "Killing target process"
pid=`adb shell pidof <process_name>`
adb shell kill -9 $pid
echo "Stopping logcat"
kill -9 $logcat_pid
sleep 2
done
Pass by Pointer vs Pass by Reference in C++
Variables can be passed by pointer and by reference. Both produce the same result and have the same effect on the arguments passed in the calling function. The difference is that the pointer stores the address to a variable whereas a reference refers to an existing variable in a different name.
Reference: https://www.tutorialspoint.com/passing-by-pointer-vs-passing-by-reference-in-cplusplus
Pass by Pointer:
Code:
#include<iostream> using namespace std; void swapNum(int* a, int* b) { int t = *a; *a = *b; *b = t; } int main() { int i = 1; int j = 2; cout << "Before swapping " << i << " " << j << endl; swapNum(&i, &j); cout << "After swapping " << i << " " << j << endl; return 0; }
Output:
Before swapping 1 2
After swapping 2 1
Pass by Reference:
Code:
#include<iostream> using namespace std; void swapNum(int& a, int& b) { int t = a; a = b; b = t; } int main() { int i = 1; int j = 2; cout << "Before swapping " << i << " " << j << endl; swapNum(i, j); cout << "After swapping " << i << " " << j << endl; return 0; }
Output:
Before swapping 1 2
After swapping 2 1
Sunday, September 25, 2022
C++ Program for Tree Iterator
Problem
Given n-ary (n children per node) tree, write a C++ iterator to iterate over all the nodes.
Solution
Iterator Interface
One of the potential interface is as follows:
/**
* If there are more children to be traversed in the current layer
* @param index
* @return True if there are children yet to be traversed, false otherwise
*/
virtual bool hasMoreChildren(int index);
/**
* Move to child at index in a layer
* @param index
*/
virtual void moveToChildAt(int index);
/**
* Print the current node
* @param index
*/
virtual void printNode();
Implementation
For implementing the iterator, we will use a stack to keep track of the node being traversed in the tree.
private:
Node* mCurrentNode = nullptr;
std::stack<Node*> mNodeStack;
};
The mCurrentNode and mNodeStack are used in the implementation as follows:
C++ Code
bool TreeIterator::hasMoreChildren(int index) {
if (mNodeStack.empty()) return false;
mCurrentNode = mNodeStack.top();
// If no children, return false.
if (mCurrentNode->children().empty()) {
mNodeStack.pop();
if (!mNodeStack.empty()) {
mCurrentNode = mNodeStack.top();
}
return false;
}
auto it = mCurrentNode->children().begin();
it += index;
// If all children in this layer are traversed, return false.
if (it == mCurrentNode->children().end()) {
mNodeStack.pop();
if (!mNodeStack.empty()) {
mCurrentNode = mNodeStack.top();
}
return false;
}
// There are more children to be drawn, return true
return true;
}
void TreeIterator::moveToChildAt(int index) {
if (mCurrentNode->children().empty()) {
// No children, nothing to do in current layer
return;
}
auto it = mCurrentNode->children().begin();
it += index;
if (it == mCurrentNode->children().end()) {
// All children visited once, nothing to do in current layer
return;
}
mNodeStack.push(*it);
mCurrentNode = mNodeStack.top();
}
void TreeIterator::printNode() {
cout << mCurrentNode->data() << endl;
}
Using the iterator
/**
* Recursively traverse the tree hierarchy
*/
void traverse() {
int i = 0;
while (hasChildren(i)) {
moveToChildAt(i);
traverse();
i++;
}
}
int main() {
TreeIterator *it;
it->traverse();
}
Explanation
The above code is a recursively traverses the children of each node in the tree. The stack maintains the current node at the top and the index passed from the traverse() method determines how many children of a particular node have been visited.
Alternate Solutions
Alternate solutions may use the following approach.
Visitor Pattern
Yet to write a working code, but this approach would mark a node as visited once it has been traversed to keep track of which child of a particular node should be visited next.
Parent Tracking
This requires modifying the tree node to contain a pointer to the parent node so that the mCurrentNode can be moved to the parent when all the children of a particular node are visited.
Python code to find the time difference between all occurrences of a pair of events in a log file
from datetime import datetime
import re
def parse_file(filename, expression1, expression2):
lines = tuple(open(filename, 'r'))
expression1Found = False
expression2Found = False
pattern = '(0[1-9]|1[0-2])-(0[1-9]|[1-2][0-9]|3[0-1]) (2[0-3]|[01][0-9]):[0-5][0-9]:[0-5][0-9].[0-9][0-9][0-9]'
for line in lines:
if expression1 in line:
timeString1 = re.search(pattern, line).group()
expression1Found = True
if expression2 in line:
timeString2 = re.search(pattern, line).group()
expression2Found = True
if expression1Found and expression2Found:
timePattern = '%m-%d %H:%M:%S.%f'
epoch = datetime(1970, 1, 1)
time1 = (datetime.strptime(timeString1, timePattern) - epoch)
time2 = (datetime.strptime(timeString2, timePattern) - epoch)
if int((time2 - time1).total_seconds() * 1000) > 1:
print(int((time2 - time1).total_seconds() * 1000))
# Reset and start searching for the next pair of occurrences of expression1 and expression2
expression1Found = False
expression2Found = False
if __name__ == "__main__":
parse_file('filepath', 'even1', 'event2')
Sunday, June 27, 2021
Automatic Train Controller System Code
TrainController class starts two infinite loops in separate threads:
- User Override Control Loop
- Automatic Control Loop
In this post, the Train class contains a few characteristics such as distance travelled from Origin and its speed, which can be abstracted into a separate class and can be handled in a more centralized manner inside TrainController class.
Also a few more features such as directionality of train movement and maximum distance from origin will be introduced.
Code
package com.example.lib;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
public class TrainController {
private final List mTrains = new ArrayList<>();
private final List mManuallyStoppedTrains = new ArrayList<>();
private final InstructionParser mInstructionParser = new InstructionParser();
public static void main(String[] args) {
final TrainController trainController = new TrainController();
trainController.createAndStartTrains(5);
// This is the main controller loop.
// 1. It monitors the distance between the pairs of trains and sends stop and start signals appropriately.
// 2. This is run in a separate thread so that the user input can be captured in the main thread.
Runnable controllerRunnable = new Runnable() {
@Override
public void run() {
while (true) {
trainController.checkAndControlTrains();
}
}
};
Thread controllerThread = new Thread(controllerRunnable);
controllerThread.start();
trainController.printAllCommands();
// Accept user input in a loop.
while (true) {
Scanner scanner = new Scanner(System.in);
int option = scanner.nextInt();
trainController.executeOption(option);
System.out.println("Waiting for the next input");
}
}
public void printAllCommands() {
System.out.println("Choose from the below options");
System.out.println("1. Start 5 trains");
System.out.println("2. Get status of all trains");
System.out.println("3. Stop all trains");
System.out.println("4. Start all trains");
System.out.println("5. Exit");
System.out.println("6. Control individual train");
System.out.println("7. Print all commands");
}
public void executeOption(final int option) {
switch (option) {
case 1:
createAndStartTrains(5);
break;
case 2:
printCurrentStateOfAllTrains();
break;
case 3:
stopAllTrains();
break;
case 4:
startAllTrains();
break;
case 5:
stopAllTrains();
System.exit(0);
case 6:
String instruction = System.console().readLine();
System.out.println("Instruction received: " + instruction);
if (instruction.toLowerCase().split(" ").length == 2) {
try {
int index = mInstructionParser.getIndex(instruction);
switch (instruction.toLowerCase().split(" ")[0]) {
case "start":
startTrain(index);
break;
case "stop":
stopTrain(index);
break;
}
} catch (IllegalArgumentException e) {
// Do nothing.
}
}
break;
case 7:
printAllCommands();
break;
}
}
/**
* Initialize trains with different speeds and start them on different threads.
* @param count of trains to start
*/
public void createAndStartTrains(final int count) {
final String trainName = "Train ";
for (int i = 0; i < count; i++) {
Train train = new Train(trainName + i, i * 1000);
mTrains.add(train);
train.startTrain();
}
}
/**
* Checks that the distance between successive trains is more than 1000 units.
* Whenever the distance between successive trains is less than 1000 units, it calls {@link Train#stopTrain()} on the rear train.
* Whenever the distance between successive trains is more than 1000 units, it calls {@link Train#startTrain()} on the rear train.
*/
private void checkAndControlTrains() {
// Loop to stop a train if it is within 1000 units of the train ahead of it.
for (int i = 0; i < mTrains.size() - 1; i++) {
if (mTrains.get(i + 1).getDistance() - mTrains.get(i).getDistance() - 3 * mTrains.get(i).getSpeed() <= 1000) {
mTrains.get(i).stopTrain();
}
}
// Loop to start a train if it is more than 1000 units away from the train ahead of it and it was not stopped manually.
for (int i = 0; i < mTrains.size() - 1; i++) {
if (mTrains.get(i + 1).getDistance() - mTrains.get(i).getDistance() - mTrains.get(i).getSpeed() > 1000) {
Train train = mTrains.get(i);
if (!mManuallyStoppedTrains.contains(train) && !train.isRunning()) {
train.startTrain();
}
}
}
}
private void printCurrentStateOfAllTrains() {
if (mTrains.size() == 0) {
System.out.println("No train is in running state");
return;
}
System.out.println("Printing status of all trains");
for (Train train : mTrains) {
train.printCurrentState();
}
}
private void stopAllTrains() {
for (Train train : mTrains) {
train.stopTrain();
}
}
private void startAllTrains() {
for (Train train : mTrains) {
train.startTrain();
}
}
/**
* Stop the train with the provided index.
* @param trainIndex the index of the train to stop
*/
private void stopTrain(int trainIndex) {
// First add the train to the list of manually stopped trains. Otherwise the checkAndControl loop will start the train again.
mManuallyStoppedTrains.add(mTrains.get(trainIndex));
mTrains.get(trainIndex).stopTrain();
}
/**
* Start the train with the provided index safely.
* This checks if the train ahead is more than 1000 units ahead before starting the train.
* @param trainIndex the index of the train to start
*/
private void startTrain(int trainIndex) {
if (trainIndex < mTrains.size() - 1) {
if (mTrains.get(trainIndex + 1).getDistance() - mTrains.get(trainIndex).getDistance() <= 1000) {
System.out.println("Cannot start train " + trainIndex + " since the train ahead is within 1000");
return;
}
System.out.println("Starting train " + trainIndex + " since the train ahead is more than 1000");
}
// First remove the train from the list of manually stopped trains. Otherwise the checkAndControl loop will not start the train again.
mManuallyStoppedTrains.remove(mTrains.get(trainIndex));
mTrains.get(trainIndex).startTrain();
}
private static class InstructionParser {
public int getIndex(final String instruction) {
String lowerCaseInstruction = instruction.toLowerCase();
if (!lowerCaseInstruction.startsWith("start") &&
!lowerCaseInstruction.startsWith("stop")) {
System.out.println("Invalid instruction");
throw new IllegalArgumentException("Invalid instruction provided. Cannot proceed");
}
return Integer.parseInt(lowerCaseInstruction.split(" ")[1]);
}
}
private static class Train extends Thread {
private final int mSpeed;
private boolean mIsRunning;
private int mDistance = 0;
private int dummyLooper = 0;
private boolean mIsInitialized;
public Train(String name, int speed) {
super(name);
mSpeed = speed;
}
@Override
public void run() {
while (true) {
dummyLooper++; // dummyLooper is just to keep this thread from becoming No-op when mIsRunning is false.
while (mIsRunning) {
dummyLooper = 0;
try {
// The train runs at mSpeed units per second.
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
mDistance += mSpeed;
}
if (dummyLooper > 0) {
mIsRunning = false;
}
}
}
public int getDistance() {
return mDistance;
}
public int getSpeed() {
return mSpeed;
}
public boolean isRunning() {
return mIsRunning;
}
/**
* Sets the mIsRunning to true starts this thread.
*/
public void startTrain() {
mIsRunning = true;
// Calling start always causes {@link IllegalThreadStateException}. Hence mIsInitialized is used as a check.
if (!mIsInitialized) {
mIsInitialized = true;
start();
}
}
public void stopTrain() {
mIsRunning = false;
}
public void printCurrentState() {
if (mIsRunning) {
System.out.println(getName() + " is running and has reached " + mDistance);
} else {
System.out.println(getName() + " is stopped and has reached " + mDistance);
}
}
}
}
Friday, June 18, 2021
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