Creating and establishing new connections require a fair amount of overhead and added latency. OkHttp will make every effort to reuse existing connections to avoid this overhead and added latency.

Every OkHttpClient uses a connection pool. Its job is to maintain a reference to all open connections. When an HTTP request is started, OkHttp will attempt to reuse an existing connection from the pool. If there are no existing connections, a new one is created and put into the connection pool. For...

 *
 * <p>{@code contains(x)}, {@code add(x)} and {@code remove(x)}, are all (expected and amortized)
 * constant time operations. Expected in the hashtable sense (depends on the hash function doing a
 * good job of distributing the elements to the buckets to a distribution not far from uniform), and
 * amortized since some operations can trigger a hash table resize.
 *

They tend to require more complex configurations, a message/job queue manager, like RabbitMQ or Redis, but they allow you to run background tasks in multiple processes, and especially, in multiple servers.

    public static final String ERRORS_not_load_from_server = "{errors.not_load_from_server}";

    /** The key of the message: Failed to start a job: {0}. */
    public static final String ERRORS_failed_to_start_job = "{errors.failed_to_start_job}";

    /** The key of the message: Failed to stop a job: {0}. */
    public static final String ERRORS_failed_to_stop_job = "{errors.failed_to_stop_job}";

        try {
            processHelper.sendCommand("nonexistent", "test command");
            fail("Expected JobNotFoundException");
        } catch (JobNotFoundException e) {
            assertTrue(e.getMessage().contains("Job for nonexistent is not found"));
        }
    }

    public void test_startProcess_basicCommand() {
        String sessionId = "test_session";
        List<String> cmdList = Arrays.asList("echo", "hello");

			<version>${commons.fileupload.version}</version>
		</dependency>

		<!-- scheduler -->
		<dependency>
			<groupId>org.lastaflute.job</groupId>
			<artifactId>lasta-job</artifactId>
			<version>${lasta.job.version}</version>
		</dependency>

		<!-- mail -->
		<dependency>
			<groupId>org.dbflute.mail</groupId>
			<artifactId>mailflute</artifactId>

                logger.info("Start scheduler \"{}\"", schedulerId);
                return;
            }
            ThreadUtil.sleep(1000L);
        }
        fail("could not start job.");
    }

    protected static void waitJob(final String namePrefix) {
        Boolean isRunning = false;
        int count = 0;

        while (count < 300 && !isRunning) { // Wait until the crawler starts

    public static final String LABELS_list_could_not_find_crud_table = "{labels.list_could_not_find_crud_table}";

    /** The key of the message: Job Scheduler */
    public static final String LABELS_scheduledjob_configuration = "{labels.scheduledjob_configuration}";

    /** The key of the message: Job */
    public static final String LABELS_scheduledjob_title_details = "{labels.scheduledjob_title_details}";

    public void sendCommand(final String sessionId, final String command) {
        final JobProcess jobProcess = runningProcessMap.get(sessionId);
        if (jobProcess == null) {
            throw new JobNotFoundException("Job for " + sessionId + " is not found.");
        }
        try {
            final OutputStream out = jobProcess.getProcess().getOutputStream();
            IOUtils.write(command + "\n", out, Constants.CHARSET_UTF_8);

### PID Limits graduates to General Availability