diff options
author | 2017-08-02 16:42:56 +0200 | |
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committer | 2017-08-03 12:08:39 +0200 | |
commit | f6316bf122ff09753c3bfb7e48faae855731091f (patch) | |
tree | 483ba119a146eea8444fd7144335a334944c4f58 /src/main/java/com/google/devtools | |
parent | 98dbe037d7b6f2e815af1036373717e28d950698 (diff) |
Cleanup javadoc around Mutability / SkylarkMutable
Also throw IllegalArgumentException instead of AssertionError.
A follow-up CL will look to eliminate the SkylarkMutable#checkMutable(Location, Environment) override in favor of checkMutable(Location, Mutability). This will make it easier to manipulate Skylark values in specialized contexts aside from normal evaluation.
RELNOTES: None
PiperOrigin-RevId: 163978262
Diffstat (limited to 'src/main/java/com/google/devtools')
5 files changed, 150 insertions, 98 deletions
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/Environment.java b/src/main/java/com/google/devtools/build/lib/syntax/Environment.java index 4bec1c6012..0ae54ff2fd 100644 --- a/src/main/java/com/google/devtools/build/lib/syntax/Environment.java +++ b/src/main/java/com/google/devtools/build/lib/syntax/Environment.java @@ -238,7 +238,7 @@ public final class Environment implements Freezable { */ public void put(Environment env, String varname, Object value) throws MutabilityException { - Mutability.checkMutable(this, env); + Mutability.checkMutable(this, env.mutability()); bindings.put(varname, value); } @@ -247,7 +247,7 @@ public final class Environment implements Freezable { * be part of the public interface. */ void remove(Environment env, String varname) throws MutabilityException { - Mutability.checkMutable(this, env); + Mutability.checkMutable(this, env.mutability()); bindings.remove(varname); } diff --git a/src/main/java/com/google/devtools/build/lib/syntax/Mutability.java b/src/main/java/com/google/devtools/build/lib/syntax/Mutability.java index e1e77c1325..2ac152c024 100644 --- a/src/main/java/com/google/devtools/build/lib/syntax/Mutability.java +++ b/src/main/java/com/google/devtools/build/lib/syntax/Mutability.java @@ -22,24 +22,42 @@ import java.util.IdentityHashMap; import java.util.List; /** - * Manages the capability to mutate an {@link Environment} and its contained Skylark objects. + * An object that manages the capability to mutate Skylark objects and their {@link Environment}s. + * Collectively, the managed objects are called {@link Freezable}s. * - * <p>Once the {@code Environment} is done evaluating, its {@code Mutability} is irreversibly closed - * ("frozen"). At that point, it is no longer possible to mutate either the {@code Environment} or - * its objects. This protects each {@code Environment} from unintentional and unsafe modification. - * Before freezing, only a single thread may use the {@code Environment}, but after freezing, any - * number of threads may access it. + * <p>Each {@code Environment}, and each of the mutable Skylark values (i.e., {@link + * SkylarkMutable}s) that are created in that {@code Environment}, holds a pointer to the same + * {@code Mutability} instance. Once the {@code Environment} is done evaluating, its {@code + * Mutability} is irreversibly closed ("frozen"). At that point, it is no longer possible to change + * either the bindings in that {@code Environment} or the state of its objects. This protects each + * {@code Environment} from unintentional and unsafe modification. Before freezing, only a single + * thread may use the contents of the {@code Environment}, but after freezing, any number of threads + * may access it. * * <p>It is illegal for an evaluation in one {@code Environment} to affect another {@code - * Environment}, even if the second {@code Environment} has not yet been frozen. + * Environment}, even if the second {@code Environment} has not yet been frozen. In practice, the + * only unfrozen values that any {@code Environment} should be able to access are its own. * - * <p>A {@code Mutability} also tracks which {@link Freezable} objects in its {@code Environment} + * <p>A {@code Mutability} also tracks which {@code Freezable} objects in its {@code Environment} * are temporarily locked from mutation. This is used to prevent modification of iterables during * loops. A {@code Freezable} may be locked multiple times (e.g., nested loops over the same * iterable). Locking an object does not prohibit mutating its deeply contained values, such as in * the case of a list of lists. * - * <p>To ensure safety, {@code Mutability}s must be created using the try-with-resource style: + * We follow two disciplines to ensure safety. First, all mutation methods of a {@code Freezable} + * must take in a {@code Mutability} as a parameter, and confirm that + * <ol> + * <li>the {@code Freezable} is not yet frozen, + * <li>the given {@code Mutability} matches the one referred to by the {@code Freezable}, and + * <li>the {@code Freezable} is not locked. + * </ol> + * It is a high-level error ({@link MutabilityException}, which gets translated to {@link + * EvalException}) to attempt to modify a frozen or locked value. But it is a low-level error + * ({@link IllegalArgumentException}) to attempt to modify a value using the wrong {@link + * Mutability} instance, since the user shouldn't be able to trigger this situation under normal + * circumstances. + * + * <p>Second, {@code Mutability}s are created using the try-with-resource style: * <pre>{@code * try (Mutability mutability = Mutability.create(fmt, ...)) { ... } * }</pre> @@ -49,25 +67,27 @@ import java.util.List; * the result is used. The only code that should create a {@code Mutability} without using * try-with-resource is test code that is not part of the Bazel jar. */ -// TODO(bazel-team): When we start using Java 8, this safe usage pattern can be enforced -// through the use of a higher-order function. +// TODO(bazel-team): This safe usage pattern can be enforced through the use of a higher-order +// function. public final class Mutability implements AutoCloseable, Serializable { + /** + * If true, mutation of any {@link Freezable} associated with this {@code Mutability} is + * disallowed. + */ private boolean isFrozen; - // For each locked Freezable, store all Locations where it is locked. - // This field is set null once the Mutability is closed. This saves some - // space, and avoids a concurrency bug from multiple Skylark modules - // accessing the same Mutability at once. + /** + * For each locked {@link Freezable}, stores all {@link Location}s where it is locked. + * + * This field is set null once the {@code Mutability} is closed. This saves some space, and avoids + * a concurrency bug from multiple Skylark modules accessing the same {@code Mutability} at once. + */ private IdentityHashMap<Freezable, List<Location>> lockedItems; - private final String annotation; // For error reporting. + /** For error reporting; a name for the context in which this {@code Mutability} is used. */ + private final String annotation; - /** - * Creates a Mutability. - * @param annotation an Object used for error reporting, - * describing to the user the context in which this Mutability was active. - */ private Mutability(String annotation) { this.isFrozen = false; // Seems unlikely that we'll often lock more than 10 things at once. @@ -77,8 +97,9 @@ public final class Mutability implements AutoCloseable, Serializable { /** * Creates a Mutability. - * @param pattern is a {@link Printer#format} pattern used to lazily produce a string - * for error reporting + * + * @param pattern is a {@link Printer#format} pattern used to lazily produce a string name + * for error reporting * @param arguments are the optional {@link Printer#format} arguments to produce that string */ public static Mutability create(String pattern, Object... arguments) { @@ -103,11 +124,13 @@ public final class Mutability implements AutoCloseable, Serializable { /** * Return whether a {@link Freezable} belonging to this {@code Mutability} is currently locked. * Frozen objects are not considered locked, though they are of course immutable nonetheless. + * + * @throws IllegalArgumentException if the {@code Freezable} does not belong to this {@code + * Mutability} */ public boolean isLocked(Freezable object) { - if (!object.mutability().equals(this)) { - throw new AssertionError("trying to check the lock of an object from a different context"); - } + Preconditions.checkArgument(object.mutability().equals(this), + "trying to check the lock of an object from a different context"); if (isFrozen) { return false; } @@ -115,25 +138,29 @@ public final class Mutability implements AutoCloseable, Serializable { } /** - * For a locked {@link Freezable} that belongs to this Mutability, return a List of the + * For a locked {@link Freezable} that belongs to this {@code Mutability}, return a List of the * {@link Location}s corresponding to its current locks. + * + * @throws IllegalArgumentException if the {@code Freezable} does not belong to this {@code + * Mutability} */ public List<Location> getLockLocations(Freezable object) { - if (!isLocked(object)) { - throw new AssertionError("trying to get lock locations for an object that is not locked"); - } + Preconditions.checkArgument(isLocked(object), + "trying to get lock locations for an object that is not locked"); return lockedItems.get(object); } /** - * Add a lock on a {@link Freezable} belonging to this Mutability. The object cannot be + * Add a lock on a {@link Freezable} belonging to this {@code Mutability}. The object cannot be * mutated until all locks on it are gone. For error reporting purposes each lock is * associated with its originating {@link Location}. + * + * @throws IllegalArgumentException if the {@code Freezable} does not belong to this {@code + * Mutability} */ public void lock(Freezable object, Location loc) { - if (!object.mutability().equals(this)) { - throw new AssertionError("trying to lock an object from a different context"); - } + Preconditions.checkArgument(object.mutability().equals(this), + "trying to lock an object from a different context"); if (isFrozen) { return; } @@ -149,53 +176,51 @@ public final class Mutability implements AutoCloseable, Serializable { /** * Remove the lock for a given {@link Freezable} that is associated with the given {@link - * Location}. It is an error if {@code object} does not belong to this mutability, or has no lock - * corresponding to {@code loc}. + * Location}. + * + * @throws IllegalArgumentException if the object does not belong to this {@code Mutability}, or + * if the object has no lock corresponding to {@code loc} */ public void unlock(Freezable object, Location loc) { - if (!object.mutability().equals(this)) { - throw new AssertionError("trying to unlock an object from a different context"); - } + Preconditions.checkArgument(object.mutability().equals(this), + "trying to unlock an object from a different context"); if (isFrozen) { // It's okay if we somehow got frozen while there were still locked objects. return; } - if (!lockedItems.containsKey(object)) { - throw new AssertionError("trying to unlock an object that is not locked"); - } + Preconditions.checkArgument(lockedItems.containsKey(object), + "trying to unlock an object that is not locked"); List<Location> locList = lockedItems.get(object); boolean changed = locList.remove(loc); - if (!changed) { - throw new AssertionError(Printer.format("trying to unlock an object for a location at which " - + "it was not locked (%r)", loc)); - } + Preconditions.checkArgument(changed, Printer.format( + "trying to unlock an object for a location at which it was not locked (%r)", loc)); if (locList.isEmpty()) { lockedItems.remove(object); } } /** - * Freezes this Mutability, marking as immutable all {@link Freezable} objects that use it. + * Freezes this {@code Mutability}, rendering all {@link Freezable} objects that refer to it + * immutable. + * + * Note that freezing does not directly touch all the {@code Freezables}, so this operation is + * constant-time. + * + * @return this object, in the fluent style */ - @Override - public void close() { + public Mutability freeze() { // No need to track per-Freezable info since everything is immutable now. lockedItems = null; isFrozen = true; + return this; } - /** - * Freezes this Mutability - * @return it in fluent style. - */ - public Mutability freeze() { - close(); - return this; + @Override + public void close() { + freeze(); } - /** - * A MutabilityException will be thrown when the user attempts to mutate an object he shouldn't. - */ + /** Indicates an illegal attempt to mutate a frozen or locked {@link Freezable}. */ static class MutabilityException extends Exception { MutabilityException(String message) { super(message); @@ -203,49 +228,48 @@ public final class Mutability implements AutoCloseable, Serializable { } /** - * Each {@code Freezable} object possesses a {@link Mutability} that determines whether the object - * is still mutable. All {@code Freezable} objects created in the same {@link Environment} will - * share the same {@code Mutability}, inherited from this {@code Environment}. Only evaluation in - * the same {@code Environment} is allowed to mutate these objects, and only until the - * {@code Mutability} is irreversibly frozen. + * An object that refers to a {@link Mutability} to decide whether to allow mutation. All + * {@link Freezable} Skylark objects created within a given {@link Environment} will share the + * same {@code Mutability} as that {@code Environment}. */ public interface Freezable { /** - * Returns the {@link Mutability} associated with this Freezable object. - * This should not change over the lifetime of the object. + * Returns the {@link Mutability} associated with this {@code Freezable}. This should not change + * over the lifetime of the object. */ Mutability mutability(); } /** - * Checks that this Freezable object can be mutated from the given {@link Environment}. - * If the object is mutable, it must be from the environment. - * @param object a Freezable object that we check is still mutable. - * @param env the {@link Environment} attempting the mutation. - * @throws MutabilityException when the object was frozen already, or is locked. + * Checks that the given {@code Freezable} can be mutated using the given {@code Mutability}, and + * throws an exception if it cannot. + * + * @throws MutabilityException if the object is either frozen or locked + * @throws IllegalArgumentException if the given {@code Mutability} is not the same as the one + * the {@code Freezable} is associated with */ - public static void checkMutable(Freezable object, Environment env) + public static void checkMutable(Freezable object, Mutability mutability) throws MutabilityException { if (object.mutability().isFrozen()) { - // Throw MutabilityException, not AssertionError, even if the object was from + // Throw MutabilityException, not IllegalArgumentException, even if the object was from // another context. throw new MutabilityException("trying to mutate a frozen object"); } - // Consider an {@link Environment} e1, in which is created {@link UserDefinedFunction} f1, - // that closes over some variable v1 bound to list l1. If somehow, via the magic of callbacks, - // f1 or l1 is passed as an argument to some function f2 evaluated in {@link Environment} e2 - // while e1 is still mutable, then e2, being a different {@link Environment}, should not be - // allowed to mutate objects from e1. It's a bug, that shouldn't happen in our current code - // base, so we throw an AssertionError. If in the future such situations are allowed to happen, + // Consider an {@link Environment} e1, in which is created {@link UserDefinedFunction} f1, that + // closes over some variable v1 bound to list l1. If somehow, via the magic of callbacks, f1 or + // l1 is passed as an argument to some function f2 evaluated in {@link Environment} e2 while e1 + // is still mutable, then e2, being a different {@link Environment}, should not be allowed to + // mutate objects from e1. It's a bug, that shouldn't happen in our current code base, so we + // throw an IllegalArgumentException. If in the future such situations are allowed to happen, // then we should throw a MutabilityException instead. - if (!object.mutability().equals(env.mutability())) { - throw new AssertionError("trying to mutate an object from a different context"); + if (!object.mutability().equals(mutability)) { + throw new IllegalArgumentException("trying to mutate an object from a different context"); } - if (env.mutability().isLocked(object)) { + if (mutability.isLocked(object)) { Iterable<String> locs = - Iterables.transform(env.mutability().getLockLocations(object), Location::print); + Iterables.transform(mutability.getLockLocations(object), Location::print); throw new MutabilityException( "trying to mutate a locked object (is it currently being iterated over by a for loop " + "or comprehension?)\n" @@ -254,5 +278,6 @@ public final class Mutability implements AutoCloseable, Serializable { } } + /** A singular instance for permanently immutable things. */ public static final Mutability IMMUTABLE = create("IMMUTABLE").freeze(); } diff --git a/src/main/java/com/google/devtools/build/lib/syntax/SkylarkDict.java b/src/main/java/com/google/devtools/build/lib/syntax/SkylarkDict.java index 40c9c9ddb3..bb9dbbab55 100644 --- a/src/main/java/com/google/devtools/build/lib/syntax/SkylarkDict.java +++ b/src/main/java/com/google/devtools/build/lib/syntax/SkylarkDict.java @@ -233,6 +233,11 @@ public final class SkylarkDict<K, V> extends MutableMap<K, V> return this.containsKey(key); } + @Override + public String toString() { + return Printer.repr(this); + } + public static <K, V> SkylarkDict<K, V> plus( SkylarkDict<? extends K, ? extends V> left, SkylarkDict<? extends K, ? extends V> right, diff --git a/src/main/java/com/google/devtools/build/lib/syntax/SkylarkList.java b/src/main/java/com/google/devtools/build/lib/syntax/SkylarkList.java index eb642d2200..abb5031599 100644 --- a/src/main/java/com/google/devtools/build/lib/syntax/SkylarkList.java +++ b/src/main/java/com/google/devtools/build/lib/syntax/SkylarkList.java @@ -203,6 +203,11 @@ public abstract class SkylarkList<E> extends MutableCollection<E> return getClass().hashCode() + 31 * getContentsUnsafe().hashCode(); } + @Override + public String toString() { + return Printer.repr(this); + } + /** * Cast a {@code List<?>} to a {@code List<T>} after checking its current contents. * @param list the List to cast diff --git a/src/main/java/com/google/devtools/build/lib/syntax/SkylarkMutable.java b/src/main/java/com/google/devtools/build/lib/syntax/SkylarkMutable.java index a1da805bf0..d95456e855 100644 --- a/src/main/java/com/google/devtools/build/lib/syntax/SkylarkMutable.java +++ b/src/main/java/com/google/devtools/build/lib/syntax/SkylarkMutable.java @@ -27,19 +27,33 @@ import java.util.Set; import javax.annotation.Nullable; /** - * Base class for data structures that are only mutable with a proper Mutability. + * Base class for data structures that are only mutable using a proper, unfrozen {@link Mutability}. */ public abstract class SkylarkMutable implements Freezable, SkylarkValue { - protected SkylarkMutable() {} - /** - * Check whether this object is mutable in the current evaluation Environment. - * @throws EvalException if the object was not mutable. + * Checks whether this object is currently mutable in the given {@link Environment}, and throws + * an exception if it is not. + * + * @deprecated prefer {@link #checkMutable(Location, Mutability)} instead */ + @Deprecated protected void checkMutable(Location loc, Environment env) throws EvalException { + checkMutable(loc, env.mutability()); + } + + /** + * Checks whether this object is currently mutable using the given {@link Mutability}, and throws + * an exception if it is not. + * + * @throws EvalException if the object is not mutable. This may be because the object (i.e., its + * {@code Mutability} was frozen, or because it is temporarily locked from mutation (due to + * being iterated over by a loop), or because it is associated with a different {@code + * Mutability} than the one given. + */ + protected void checkMutable(Location loc, Mutability mutability) throws EvalException { try { - Mutability.checkMutable(this, env); + Mutability.checkMutable(this, mutability); } catch (MutabilityException ex) { throw new EvalException(loc, ex); } @@ -50,11 +64,6 @@ public abstract class SkylarkMutable implements Freezable, SkylarkValue { return mutability().isFrozen(); } - @Override - public String toString() { - return Printer.repr(this); - } - /** * Add a new lock at {@code loc}. No effect if frozen. */ @@ -69,6 +78,11 @@ public abstract class SkylarkMutable implements Freezable, SkylarkValue { mutability().unlock(this, loc); } + /** + * Base class for a {@link SkylarkMutable} that is also a {@link Collection}. + * + * <p>The mutating methods from {@code Collection} are not supported. + */ abstract static class MutableCollection<E> extends SkylarkMutable implements Collection<E> { protected MutableCollection() {} @@ -167,10 +181,13 @@ public abstract class SkylarkMutable implements Freezable, SkylarkValue { } } + /** + * Base class for a {@link SkylarkMutable} that is also a {@link Map}. + * + * <p>The mutating methods from {@code Map} are not supported. + */ abstract static class MutableMap<K, V> extends SkylarkMutable implements Map<K, V> { - MutableMap() {} - /** * The underlying contents is a (usually) mutable data structure. * Read access is forwarded to these contents. |