A resource manager.
A resource manager.
Resources can be registered with the manager by calling acquire
;
such resources will be released in reverse order of their acquisition
when the manager is closed, regardless of any exceptions thrown
during use.
See the main doc for Using
for full details of
suppression behavior.
It is recommended for API designers to require an implicit Manager
for the creation of custom resources, and to call acquire
during those
resources' construction. Doing so guarantees that the resource must be
automatically managed, and makes it impossible to forget to do so.
Example:
class SafeFileReader(file: File)(implicit manager: Using.Manager) extends BufferedReader(new FileReader(file)) { def this(fileName: String)(implicit manager: Using.Manager) = this(new File(fileName)) manager.acquire(this) }
A typeclass describing how to release a particular type of resource.
A typeclass describing how to release a particular type of resource.
A resource is anything which needs to be released, closed, or otherwise cleaned up in some way after it is finished being used, and for which waiting for the object's garbage collection to be cleaned up would be unacceptable. For example, an instance of java.io.OutputStream would be considered a resource, because it is important to close the stream after it is finished being used.
An instance of Releasable
is needed in order to automatically manage a resource
with Using
. An implicit instance is provided for all types extending
java.lang.AutoCloseable.
the type of the resource
Performs an operation using a resource, and then releases the resource, even if the operation throws an exception.
Performs an operation using a resource, and then releases the resource, even if the operation throws an exception.
See the main doc for Using
for full details of
suppression behavior.
a Try containing an exception if one or more were thrown, or the result of the operation if no exceptions were thrown
Performs an operation using a resource, and then releases the resource, even if the operation throws an exception.
Performs an operation using a resource, and then releases the resource, even if the operation throws an exception. This method behaves similarly to Java's try-with-resources.
See the main doc for Using
for full details of
suppression behavior.
the type of the resource
the return type of the operation
the resource
the operation to perform with the resource
the result of the operation, if neither the operation nor releasing the resource throws
Performs an operation using four resources, and then releases the resources in reverse order, even if the operation throws an exception.
Performs an operation using four resources, and then releases the resources in reverse order, even if the operation throws an exception. This method behaves similarly to Java's try-with-resources.
See the main doc for Using
for full details of
suppression behavior.
the type of the first resource
the type of the second resource
the type of the third resource
the type of the fourth resource
the return type of the operation
the first resource
the second resource
the third resource
the fourth resource
the operation to perform using the resources
the result of the operation, if neither the operation nor releasing the resources throws
Performs an operation using three resources, and then releases the resources in reverse order, even if the operation throws an exception.
Performs an operation using three resources, and then releases the resources in reverse order, even if the operation throws an exception. This method behaves similarly to Java's try-with-resources.
See the main doc for Using
for full details of
suppression behavior.
the type of the first resource
the type of the second resource
the type of the third resource
the return type of the operation
the first resource
the second resource
the third resource
the operation to perform using the resources
the result of the operation, if neither the operation nor releasing the resources throws
Performs an operation using two resources, and then releases the resources in reverse order, even if the operation throws an exception.
Performs an operation using two resources, and then releases the resources in reverse order, even if the operation throws an exception. This method behaves similarly to Java's try-with-resources.
See the main doc for Using
for full details of
suppression behavior.
the type of the first resource
the type of the second resource
the return type of the operation
the first resource
the second resource
the operation to perform using the resources
the result of the operation, if neither the operation nor releasing the resources throws
A utility for performing automatic resource management. It can be used to perform an operation using resources, after which it releases the resources in reverse order of their creation.
Usage
There are multiple ways to automatically manage resources with
Using
. If you only need to manage a single resource, theapply
method is easiest; it wraps the resource opening, operation, and resource releasing in aTry
.Example:
If you need to manage multiple resources,
Using.Manager
should be used. It allows the managing of arbitrarily many resources, whose creation, use, and release are all wrapped in aTry
.Example:
If you wish to avoid wrapping management and operations in a
Try
, you can useUsing.resource
, which throws any exceptions that occur.Example:
Suppression Behavior
If two exceptions are thrown (e.g., by an operation and closing a resource), one of them is re-thrown, and the other is added to it as a suppressed exception. If the two exceptions are of different 'severities' (see below), the one of a higher severity is re-thrown, and the one of a lower severity is added to it as a suppressed exception. If the two exceptions are of the same severity, the one thrown first is re-thrown, and the one thrown second is added to it as a suppressed exception. If an exception is a
ControlThrowable
, or if it does not support suppression (seeThrowable
's constructor with anenableSuppression
parameter), an exception that would have been suppressed is instead discarded.Exceptions are ranked from highest to lowest severity as follows:
java.lang.VirtualMachineError
java.lang.LinkageError
java.lang.InterruptedException
andjava.lang.ThreadDeath
scala.util.control.ControlThrowable
scala.util.control.ControlThrowable
When more than two exceptions are thrown, the first two are combined and re-thrown as described above, and each successive exception thrown is combined as it is thrown.