Interface ProcessHandle

All Superinterfaces:
Comparable<ProcessHandle>
public interface ProcessHandle
extends Comparable<ProcessHandle>

ProcessHandle identifies and provides control of native processes. Each individual process can be monitored for liveness, list its children, get information about the process or destroy it. By comparison, Process instances were started by the current process and additionally provide access to the process input, output, and error streams.

The native process ID is an identification number that the operating system assigns to the process. The range for process id values is dependent on the operating system. For example, an embedded system might use a 16-bit value. Status information about a process is retrieved from the native system and may change asynchronously; processes may be created or terminate spontaneously. The time between when a process terminates and the process id is reused for a new process is unpredictable. Race conditions can exist between checking the status of a process and acting upon it. When using ProcessHandles avoid assumptions about the liveness or identity of the underlying process.

Each ProcessHandle identifies and allows control of a process in the native system. ProcessHandles are returned from the factory methods current(), of(long), children(), descendants(), parent() and allProcesses().

The Process instances created by ProcessBuilder can be queried for a ProcessHandle that provides information about the Process. ProcessHandle references should not be freely distributed.

A CompletableFuture available from onExit() can be used to wait for process termination, and possibly trigger dependent actions.

The factory methods limit access to ProcessHandles using the SecurityManager checking the RuntimePermission("manageProcess"). The ability to control processes is also restricted by the native system, ProcessHandle provides no more access to, or control over, the native process than would be allowed by a native application.

Implementation Requirements:
In the case where ProcessHandles cannot be supported then the factory methods must consistently throw UnsupportedOperationException. The methods of this class throw UnsupportedOperationException if the operating system does not allow access to query or kill a process.

The ProcessHandle static factory methods return instances that are value-based, immutable and thread-safe. Use of identity-sensitive operations (including reference equality (==), identity hash code, or synchronization) on these instances of ProcessHandle may have unpredictable results and should be avoided. Use equals or compareTo methods to compare ProcessHandles.

Since:
9
See Also:
Process

Nested Classes

Modifier and Type Interface Description
static interface  ProcessHandle.Info

Information snapshot about the process.

Methods

Modifier and Type Method Description
static Stream<ProcessHandle> allProcesses()

Returns a snapshot of all processes visible to the current process.
Stream<ProcessHandle> children()

Returns a snapshot of the current direct children of the process.
int compareTo​(ProcessHandle other)

Compares this ProcessHandle with the specified ProcessHandle for order.
static ProcessHandle current()

Returns a ProcessHandle for the current process.
Stream<ProcessHandle> descendants()

Returns a snapshot of the descendants of the process.
boolean destroy()

Requests the process to be killed.
boolean destroyForcibly()

Requests the process to be killed forcibly.
boolean equals​(Object other)

Returns true if other object is non-null, is of the same implementation, and represents the same system process; otherwise it returns false.
int hashCode()

Returns a hash code value for this ProcessHandle.
ProcessHandle.Info info()

Returns a snapshot of information about the process.
boolean isAlive()

Tests whether the process represented by this ProcessHandle is alive.
static Optional<ProcessHandle> of​(long pid)

Returns an Optional<ProcessHandle> for an existing native process.
CompletableFuture<ProcessHandle> onExit()

Returns a CompletableFuture<ProcessHandle> for the termination of the process.
Optional<ProcessHandle> parent()

Returns an Optional<ProcessHandle> for the parent process.
long pid()

Returns the native process ID of the process.
boolean supportsNormalTermination()

Returns true if the implementation of destroy() normally terminates the process.

Methods

pid

long pid()

Returns the native process ID of the process. The native process ID is an identification number that the operating system assigns to the process. The operating system may reuse the process ID after a process terminates. Use equals or compareTo to compare ProcessHandles.

Returns:
the native process ID of the process
Throws:
UnsupportedOperationException - if the implementation does not support this operation

of

static Optional<ProcessHandle> of(long pid)

Returns an Optional<ProcessHandle> for an existing native process.

Parameters:
pid - a native process ID
Returns:
an Optional<ProcessHandle> of the PID for the process; the Optional is empty if the process does not exist
Throws:
SecurityException - if a security manager has been installed and it denies RuntimePermission("manageProcess")
UnsupportedOperationException - if the implementation does not support this operation

current

static ProcessHandle current()

Returns a ProcessHandle for the current process. The ProcessHandle cannot be used to destroy the current process, use System.exit instead.

Returns:
a ProcessHandle for the current process
Throws:
SecurityException - if a security manager has been installed and it denies RuntimePermission("manageProcess")
UnsupportedOperationException - if the implementation does not support this operation

parent

Optional<ProcessHandle> parent()

Returns an Optional<ProcessHandle> for the parent process. Note that Processes in a zombie state usually don't have a parent.

Returns:
an Optional<ProcessHandle> of the parent process; the Optional is empty if the child process does not have a parent or if the parent is not available, possibly due to operating system limitations
Throws:
SecurityException - if a security manager has been installed and it denies RuntimePermission("manageProcess")

children

Stream<ProcessHandle> children()

Returns a snapshot of the current direct children of the process. The parent() of a direct child process is the process. Typically, a process that is not alive has no children.

Note that processes are created and terminate asynchronously. There is no guarantee that a process is alive.

Returns:
a sequential Stream of ProcessHandles for processes that are direct children of the process
Throws:
SecurityException - if a security manager has been installed and it denies RuntimePermission("manageProcess")

descendants

Stream<ProcessHandle> descendants()

Returns a snapshot of the descendants of the process. The descendants of a process are the children of the process plus the descendants of those children, recursively. Typically, a process that is not alive has no children.

Note that processes are created and terminate asynchronously. There is no guarantee that a process is alive.

Returns:
a sequential Stream of ProcessHandles for processes that are descendants of the process
Throws:
SecurityException - if a security manager has been installed and it denies RuntimePermission("manageProcess")

allProcesses

static Stream<ProcessHandle> allProcesses()

Returns a snapshot of all processes visible to the current process.

Note that processes are created and terminate asynchronously. There is no guarantee that a process in the stream is alive or that no other processes may have been created since the inception of the snapshot.

Returns:
a Stream of ProcessHandles for all processes
Throws:
SecurityException - if a security manager has been installed and it denies RuntimePermission("manageProcess")
UnsupportedOperationException - if the implementation does not support this operation

info

ProcessHandle.Info info()

Returns a snapshot of information about the process.

A ProcessHandle.Info instance has accessor methods that return information about the process if it is available.

Returns:
a snapshot of information about the process, always non-null

onExit

CompletableFuture<ProcessHandle> onExit()

Returns a CompletableFuture<ProcessHandle> for the termination of the process. The CompletableFuture provides the ability to trigger dependent functions or actions that may be run synchronously or asynchronously upon process termination. When the process has terminated the CompletableFuture is completed regardless of the exit status of the process. The onExit method can be called multiple times to invoke independent actions when the process exits.

Calling onExit().get() waits for the process to terminate and returns the ProcessHandle. The future can be used to check if the process is done or to wait for it to terminate. Cancelling the CompleteableFuture does not affect the Process.

API Note:
The process may be observed to have terminated with isAlive() before the ComputableFuture is completed and dependent actions are invoked.
Returns:
a new CompletableFuture<ProcessHandle> for the ProcessHandle
Throws:
IllegalStateException - if the process is the current process

supportsNormalTermination

boolean supportsNormalTermination()

Returns true if the implementation of destroy() normally terminates the process. Returns false if the implementation of destroy forcibly and immediately terminates the process.

Returns:
true if the implementation of destroy() normally terminates the process; otherwise, destroy() forcibly terminates the process

destroy

boolean destroy()

Requests the process to be killed. Whether the process represented by this ProcessHandle object is normally terminated or not is implementation dependent. Forcible process destruction is defined as the immediate termination of the process, whereas normal termination allows the process to shut down cleanly. If the process is not alive, no action is taken. The operating system access controls may prevent the process from being killed.

The CompletableFuture from onExit() is completed when the process has terminated.

Note: The process may not terminate immediately. For example, isAlive() may return true for a brief period after destroy() is called.

Returns:
true if termination was successfully requested, otherwise false
Throws:
IllegalStateException - if the process is the current process

destroyForcibly

boolean destroyForcibly()

Requests the process to be killed forcibly. The process represented by this ProcessHandle object is forcibly terminated. Forcible process destruction is defined as the immediate termination of the process, whereas normal termination allows the process to shut down cleanly. If the process is not alive, no action is taken. The operating system access controls may prevent the process from being killed.

The CompletableFuture from onExit() is completed when the process has terminated.

Note: The process may not terminate immediately. For example, isAlive() may return true for a brief period after destroyForcibly() is called.

Returns:
true if termination was successfully requested, otherwise false
Throws:
IllegalStateException - if the process is the current process

isAlive

boolean isAlive()

Tests whether the process represented by this ProcessHandle is alive. Process termination is implementation and operating system specific. The process is considered alive as long as the PID is valid.

Returns:
true if the process represented by this ProcessHandle object has not yet terminated

hashCode

int hashCode()

Returns a hash code value for this ProcessHandle. The hashcode value follows the general contract for Object.hashCode(). The value is a function of the pid() value and may be a function of additional information to uniquely identify the process. If two ProcessHandles are equal according to the equals method, then calling the hashCode method on each of the two objects must produce the same integer result.

Overrides:
hashCode in class Object
Returns:
a hash code value for this object
See Also:
Object.equals(java.lang.Object), System.identityHashCode(java.lang.Object)

equals

boolean equals(Object other)

Returns true if other object is non-null, is of the same implementation, and represents the same system process; otherwise it returns false.

Overrides:
equals in class Object
Implementation Note:
It is implementation specific whether ProcessHandles with the same PID represent the same system process. ProcessHandle implementations should contain additional information to uniquely identify the process. For example, the start time of the process could be used to determine if the PID has been re-used. The implementation of equals should return true for two ProcessHandles with the same PID unless there is information to distinguish them.
Parameters:
other - another object
Returns:
true if the other object is non-null, is of the same implementation class and represents the same system process; otherwise returns false
See Also:
Object.hashCode(), HashMap

compareTo

int compareTo(ProcessHandle other)

Compares this ProcessHandle with the specified ProcessHandle for order. The order is not specified, but is consistent with Object.equals(java.lang.Object), which returns true if and only if two instances of ProcessHandle are of the same implementation and represent the same system process. Comparison is only supported among objects of same implementation. If attempt is made to mutually compare two different implementations of ProcessHandles, ClassCastException is thrown.

Specified by:
compareTo in interface Comparable<ProcessHandle>
Parameters:
other - the ProcessHandle to be compared
Returns:
a negative integer, zero, or a positive integer as this object is less than, equal to, or greater than the specified object.
Throws:
NullPointerException - if the specified object is null
ClassCastException - if the specified object is not of same class as this object

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