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package com.oracle.truffle.sl.runtime;
import com.oracle.truffle.api.*;
import com.oracle.truffle.api.interop.*;
import com.oracle.truffle.api.utilities.*;
/**
* Represents a SL function. On the Truffle level, a callable element is represented by a
* {@link RootCallTarget call target}. This class encapsulates a call target, and adds version
* support: functions in SL can be redefined, i.e. changed at run time. When a function is
* redefined, the call target managed by this function object is changed (and {@link #callTarget} is
* therefore not a final field).
*
* Function redefinition is expected to be rare, therefore optimized call nodes want to speculate
* that the call target is stable. This is possible with the help of a Truffle {@link Assumption}: a
* call node can keep the call target returned by {@link #getCallTarget()} cached until the
* assumption returned by {@link #getCallTargetStable()} is valid.
*
* The {@link #callTarget} can be {@code null}. To ensure that only one {@link SLFunction} instance
* per name exists, the {@link SLFunctionRegistry} creates an instance also when performing name
* lookup. A function that has been looked up, i.e., used, but not defined, has no call target.
*/
public final class SLFunction implements TruffleObject {
/** The name of the function. */
private final String name;
/** The current implementation of this function. */
private RootCallTarget callTarget;
/**
* Manages the assumption that the {@link #callTarget} is stable. We use the utility class
* {@link CyclicAssumption}, which automatically creates a new {@link Assumption} when the old
* one gets invalidated.
*/
private final CyclicAssumption callTargetStable;
protected SLFunction(String name) {
this.name = name;
this.callTargetStable = new CyclicAssumption(name);
}
public String getName() {
return name;
}
protected void setCallTarget(RootCallTarget callTarget) {
this.callTarget = callTarget;
/*
* We have a new call target. Invalidate all code that speculated that the old call target
* was stable.
*/
callTargetStable.invalidate();
}
public RootCallTarget getCallTarget() {
return callTarget;
}
public Assumption getCallTargetStable() {
return callTargetStable.getAssumption();
}
/**
* This method is, e.g., called when using a function literal in a string concatenation. So
* changing it has an effect on SL programs.
*/
@Override
public String toString() {
return name;
}
/**
* In case you want some of your objects to co-operate with other languages, you need to make
* them implement {@link TruffleObject} and provide additional {@link SLFunctionForeignAccess
* foreign access implementation}.
*/
@Override
public ForeignAccess getForeignAccess() {
return SLFunctionForeignAccess.INSTANCE;
}
}