/**
* Copyright 2014 Netflix, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package rx.exceptions;
import java.util.HashSet;
import java.util.Set;
/**
* @warn javadoc class description missing
*/
public class Exceptions {
private Exceptions() {
}
/**
* @warn javadoc missing
* @return
*/
public static RuntimeException propagate(Throwable t) {
/*
* The return type of RuntimeException is a trick for code to be like this:
*
* throw Exceptions.propagate(e);
*
* Even though nothing will return and throw via that 'throw', it allows the code to look like it
* so it's easy to read and understand that it will always result in a throw.
*/
if (t instanceof RuntimeException) {
throw (RuntimeException) t;
} else if (t instanceof Error) {
throw (Error) t;
} else {
throw new RuntimeException(t);
}
}
/**
* Throws a particular {@code Throwable} only if it belongs to a set of "fatal" error varieties. These
* varieties are as follows:
* <ul>
* <li>{@link OnErrorNotImplementedException}</li>
* <li>{@link OnErrorFailedException}</li>
* <li>{@code StackOverflowError}</li>
* <li>{@code VirtualMachineError}</li>
* <li>{@code ThreadDeath}</li>
* <li>{@code LinkageError}</li>
* </ul>
* This can be useful if you are writing an operator that calls user-supplied code, and you want to
* notify subscribers of errors encountered in that code by calling their {@code onError} methods, but only
* if the errors are not so catastrophic that such a call would be futile, in which case you simply want to
* rethrow the error.
*
* @param t
* the {@code Throwable} to test and perhaps throw
* @see <a href="https://github.com/Netflix/RxJava/issues/748#issuecomment-32471495">RxJava: StackOverflowError is swallowed (Issue #748)</a>
*/
public static void throwIfFatal(Throwable t) {
if (t instanceof OnErrorNotImplementedException) {
throw (OnErrorNotImplementedException) t;
} else if (t instanceof OnErrorFailedException) {
Throwable cause = ((OnErrorFailedException) t).getCause();
if (cause instanceof RuntimeException) {
throw (RuntimeException) cause;
} else {
throw (OnErrorFailedException) t;
}
}
// values here derived from https://github.com/Netflix/RxJava/issues/748#issuecomment-32471495
else if (t instanceof StackOverflowError) {
throw (StackOverflowError) t;
} else if (t instanceof VirtualMachineError) {
throw (VirtualMachineError) t;
} else if (t instanceof ThreadDeath) {
throw (ThreadDeath) t;
} else if (t instanceof LinkageError) {
throw (LinkageError) t;
}
}
private static final int MAX_DEPTH = 25;
/**
* Adds a {@code Throwable} to a causality-chain of Throwables, as an additional cause (if it does not
* already appear in the chain among the causes).
*
* @param e
* the {@code Throwable} at the head of the causality chain
* @param cause
* the {@code Throwable} you want to add as a cause of the chain
*/
public static void addCause(Throwable e, Throwable cause) {
Set<Throwable> seenCauses = new HashSet<Throwable>();
int i = 0;
while (e.getCause() != null) {
if (i++ >= MAX_DEPTH) {
// stack too deep to associate cause
return;
}
e = e.getCause();
if (seenCauses.contains(e.getCause())) {
break;
} else {
seenCauses.add(e.getCause());
}
}
// we now have 'e' as the last in the chain
try {
e.initCause(cause);
} catch (Throwable t) {
// ignore
// the javadocs say that some Throwables (depending on how they're made) will never
// let me call initCause without blowing up even if it returns null
}
}
/**
* Get the {@code Throwable} at the end of the causality-chain for a particular {@code Throwable}
*
* @param e
* the {@code Throwable} whose final cause you are curious about
* @return the last {@code Throwable} in the causality-chain of {@code e} (or a "Stack too deep to get
* final cause" {@code RuntimeException} if the chain is too long to traverse)
*/
public static Throwable getFinalCause(Throwable e) {
int i = 0;
while (e.getCause() != null) {
if (i++ >= MAX_DEPTH) {
// stack too deep to get final cause
return new RuntimeException("Stack too deep to get final cause");
}
e = e.getCause();
}
return e;
}
}