Analyze the Current Polling Loop
- Review the existing loop, looking specifically for overly high iteration counts or overly frequent execution without necessary conditions. Identify sections that may execute without bounds.
- Identify the purpose of the loop. Is it monitoring hardware statuses, waiting for events, or performing periodic tasks? Understanding its purpose can suggest conditions or time limits for termination.
Introduce Conditional Delays or Sleeps
- If the loop runs overwhelmingly fast, consider adding a delay. Use sleep functions to reduce CPU usage and avoid unnecessary iterations. For example, if using POSIX, you can integrate `nanosleep()` to create sleep intervals:
#include <time.h>
void delay(int milliseconds) {
struct timespec ts;
ts.tv_sec = milliseconds / 1000;
ts.tv_nsec = (milliseconds % 1000) * 1000000;
nanosleep(&ts, NULL);
}
// Inside your loop
while (condition) {
// Loop content
delay(100); // Pause for 100 milliseconds
}
Implement Timeout Mechanisms
- Introduce a timeout to avoid infinite loops, which can be particularly useful during unexpected conditions where immediate action isn't necessary. Consider tracking elapsed time and breaking the loop if it surpasses a set threshold:
#include <stdio.h>
#include <time.h>
#define TIMEOUT_MS 2000
int main() {
clock_t start = clock();
while (condition) {
// Loop content
// Check timeout
if ((clock() - start) * 1000 / CLOCKS_PER_SEC > TIMEOUT_MS) {
printf("Timeout occurred\n");
break;
}
}
return 0;
}
Check for External Events
- Ensure the polling loop monitors relevant events that can control the loop's execution, like hardware state changes or external signals.
- Interrupt-driven programming can be more efficient for firmware. Consider using interrupt service routines (ISRs) to break or manage loops when specific conditions are met.
Optimize Loop Logic
- Inspect and potentially refactor the logic. Combine conditions to minimize redundancy and reduce the cycle count. Instead of checking conditions linearly, use compound conditions to streamline logic.
- Algorithmically optimize operations inside the loop; moving invariant computations outside can significantly reduce operations within the loop.
Refactor Using State Machines
- Convert your polling loop to a state machine, offering better control over various states and transitions. State machines can reduce complexity and make systems more predictable and maintainable.
- Implement a basic state machine using enums to define states and switch cases to manage state transitions effectively:
typedef enum {
IDLE,
PROCESSING,
COMPLETED
} State;
void process() {
State currentState = IDLE;
while (currentState != COMPLETED) {
switch (currentState) {
case IDLE:
// Initialization
currentState = PROCESSING;
break;
case PROCESSING:
// Main operations
if (/* condition */) {
currentState = COMPLETED;
}
break;
case COMPLETED:
// Finalization
break;
}
}
}
Use Profiling Tools
- Apply profiling tools to analyze CPU usage and execution efficiency. This data-driven approach identifies bottlenecks and directs focus on critical sections needing improvement.
- Many development environments offer built-in profiling tools or plugins that help in measuring loop performance.
