How to Measure CPU Time of a Specific Set of Threads

How can I measure CPU time of a specific set of threads?

To get CPU clock ID of every thread you can use: pthread_getcpuclockid
and using this CPU clock ID you can retrieve the current thread CPU time using: clock_gettime.

Following is the sample code to demonstrate the same:

struct timespec currTime;
clockid_t threadClockId;

//! Get thread clock Id
pthread_getcpuclockid(pthread_self(), &threadClockId);
//! Using thread clock Id get the clock time
clock_gettime(threadClockId, &currTime);

Obtaining CPU thread usage in Java

You can use ThreadMXBean to get cpu usage statistics from all running threads. In the example below the CPU usage per thread is calculated:

private int sampleTime = 10000;
private ThreadMXBean threadMxBean = ManagementFactory.getThreadMXBean();
private RuntimeMXBean runtimeMxBean = ManagementFactory.getRuntimeMXBean();
private OperatingSystemMXBean osMxBean = ManagementFactory.getOperatingSystemMXBean();
private Map<Long, Long> threadInitialCPU = new HashMap<Long, Long>();
private Map<Long, Float> threadCPUUsage = new HashMap<Long, Float>();
private long initialUptime = runtimeMxBean.getUptime();

ThreadInfo[] threadInfos = threadMxBean.dumpAllThreads(false, false);
for (ThreadInfo info : threadInfos) {
threadInitialCPU.put(info.getThreadId(), threadMxBean.getThreadCpuTime(info.getThreadId()));
}

try {Thread.sleep(sampleTime);} catch (InterruptedException e) {}

long upTime = runtimeMxBean.getUptime();

Map<Long, Long> threadCurrentCPU = new HashMap<Long, Long>();
ThreadInfo[] threadInfos = threadMxBean.dumpAllThreads(false, false);
for (ThreadInfo info : threadInfos) {
threadCurrentCPU.put(info.getThreadId(), threadMxBean.getThreadCpuTime(info.getThreadId()));
}

// CPU over all processes
//int nrCPUs = osMxBean.getAvailableProcessors();
// total CPU: CPU % can be more than 100% (devided over multiple cpus)
long nrCPUs = 1;
// elapsedTime is in ms.
long elapsedTime = (upTime - initialUptime);
for (ThreadInfo info : threadInfos) {
// elapsedCpu is in ns
Long initialCPU = threadInitialCPU.get(info.getThreadId());
if (initialCPU != null) {
long elapsedCpu = threadCurrentCPU.get(info.getThreadId()) - initialCPU;
float cpuUsage = elapsedCpu / (elapsedTime * 1000000F * nrCPUs);
threadCPUUsage.put(info.getThreadId(), cpuUsage);
}
}

// threadCPUUsage contains cpu % per thread
System.out.println(threadCPUUsage);
// You can use osMxBean.getThreadInfo(theadId) to get information on every thread reported in threadCPUUsage and analyze the most CPU intentive threads


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