Initiates an orderly shutdown in which previously submitted
tasks are executed, but no new tasks will be accepted.
Invocation has no additional effect if already shut down.
<p>This method does not wait for previously submitted tasks to
complete execution. Use {@link #awaitTermination awaitTermination}
to do that.
@throws SecurityException if a security manager exists and
shutting down this ExecutorService may manipulate
threads that the caller is not permitted to modify
because it does not hold {@link
java.lang.RuntimePermission}{@code ("modifyThread")},
or the security manager's {@code checkAccess} method
denies access.
Initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted. Invocation has no additional effect if already shut down.
<p>This method does not wait for previously submitted tasks to complete execution. Use {@link #awaitTermination awaitTermination} to do that.
@throws SecurityException if a security manager exists and shutting down this ExecutorService may manipulate threads that the caller is not permitted to modify because it does not hold {@link java.lang.RuntimePermission}{@code ("modifyThread")}, or the security manager's {@code checkAccess} method denies access.