--- a/jdk/src/jdk.dev/share/classes/com/sun/tools/hat/resources/oqlhelp.html Mon May 25 09:13:41 2015 +0200
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-
-<html>
-<head>
-<style>
-.key { color: red; font-weight: bold }
-</style>
-<title>
-Object Query Language (OQL)
-</title>
-</head>
-<body>
-<h1>Object Query Language (OQL)</h1>
-
-<p>
-OQL is SQL-like query language to query Java heap. OQL allows to filter/select information
-wanted from Java heap. While pre-defined queries such as "show all instances of class X"
-are already supported by HAT, OQL adds more flexibility. OQL is based on JavaScript expression
-language.
-</p>
-
-<p>
-OQL query is of the form
-
-<pre>
-<code>
- <span class="key">select</span> <JavaScript expression to select>
- [ <span class="key">from</span> [<span class="key">instanceof</span>] <class name> <identifier>
- [ <span class="key">where</span> <JavaScript boolean expression to filter> ] ]
-</code>
-</pre>
-where class name is fully qualified Java class name (example: java.net.URL) or array class name.
-[C is char array name, [Ljava.io.File; is name of java.io.File[] and so on.
-Note that fully qualified class name does not always uniquely identify a
-Java class at runtime. There may be more than one Java class with the same
-name but loaded by different loaders. So, class name is permitted to be
-id string of the class object.
-
-If <span class="key">instanceof</span> keyword is used, subtype objects are selected. If this
-keyword is not specified, only the instances of exact class specified are selected. Both
-<span class="key">from</span> and <span class="key">where</span> clauses are optional.
-</p>
-
-
-<p>
-In <span class="key">select</span> and (optional) <span class="key">where</span> clauses, the expression
-used in JavaScript expression. Java heap objects are wrapped as convenient script objects so that
-fields may be accessed in natural syntax. For example, Java fields can be accessed with obj.field_name
-syntax and array elements can be accessed with array[index] syntax. Each Java object selected is
-bound to a JavaScript variable of the identifier name specified in <span class="key">from</span> clause.
-</p>
-
-<h2>OQL Examples</h2>
-
-<ul>
-<li>select all Strings of length 100 or more
-<pre>
-<code>
- select s from java.lang.String s where s.value.length >= 100
-</code>
-</pre>
-<li>select all int arrays of length 256 or more
-<pre>
-<code>
- select a from [I a where a.length >= 256
-</code>
-</pre>
-<li>show content of Strings that match a regular expression
-<pre>
-<code>
- select s.value.toString() from java.lang.String s
- where /java/.test(s.value.toString())
-</code>
-</pre>
-<li>show path value of all File objects
-<pre>
-<code</b>
- select file.path.value.toString() from java.io.File file
-</code>
-</pre>
-<li>show names of all ClassLoader classes
-<pre>
-<code>
- select <a href="#classof">classof</a>(cl).name
- from instanceof java.lang.ClassLoader cl
-</code>
-</pre>
-<li>show instances of the Class identified by given id string
-<pre>
-<code>
- select o from instanceof 0xd404b198 o
-</code>
-</pre>
-Note that 0xd404b198 is id of a Class (in a session). This is found by
-looking at the id shown in that class's page.
-</ul>
-
-<h2>OQL built-in objects, functions</h2>
-
-<h3>heap object</h3>
-
-The <b>heap</b> built-in object supports the following methods:
-
-<ul>
-<li><b>heap.forEachClass</b> -- calls a callback function for each Java Class
-<pre>
-<code>
- heap.forEachClass(callback);
-</code>
-</pre>
-<li><b>heap.forEachObject</b> -- calls a callback function for each Java object
-<pre>
-<code>
- heap.forEachObject(callback, clazz, includeSubtypes);
-</code>
-</pre>
-<code>clazz</code> is the class whose instances are selected. If not specified, defaults to java.lang.Object. <code>includeSubtypes</code> is a boolean flag
-that specifies whether to include subtype instances or not. Default value of
-this flag is true.
-<a name="findClass"></a>
-<li><b>heap.findClass</b> -- finds Java Class of given name
-<pre>
-<code>
- heap.findClass(className);
-</code>
-</pre>
-where <code>className</code> is name of the class to find. The resulting Class
-object has following properties:
-<ul>
-<li>name - name of the class.
-<li>superclass - Class object for super class (or null if java.lang.Object).
-<li>statics - name, value pairs for static fields of the Class.
-<li>fields - array of field objects. field object has name, signature
-properties.
-<li>loader - ClassLoader object that loaded this class.
-<li>signers - signers that signed this class.
-<li>protectionDomain - protection domain to which this class belongs.
-</ul>
-Class objects have the following methods:
-<ul>
-<li>isSubclassOf - tests whether given class is direct or indirect
-subclass of this class or not.
-<li>isSuperclassOf - tests whether given Class is direct or indirect
-superclass of this class or not.
-<li>subclasses - returns array of direct and indirect subclasses.
-<li>superclasses - returns array of direct and indirect superclasses.
-</ul>
-<a name="findObject"></a>
-<li><b>heap.findObject</b> -- finds object from given object id
-<pre>
-<code>
- heap.findObject(stringIdOfObject);
-</code>
-</pre>
-<a name="classes"></a>
-<li><b>heap.classes</b> -- returns an enumeration of all Java classes
-<a name="objects"></a>
-<li><b>heap.objects</b> -- returns an enumeration of Java objects
-<pre>
-<code>
- heap.objects(clazz, [includeSubtypes], [filter])
-</code>
-</pre>
-<code>clazz</code> is the class whose instances are selected. If not specified, defaults to java.lang.Object. <code>includeSubtypes</code> is a boolean flag
-that specifies whether to include subtype instances or not. Default value of
-this flag is true. This method accepts an optional filter expression to filter
-the result set of objects.
-<a name="finalizables"></a>
-<li><b>heap.finalizables</b> -- returns an enumeration of Java objects that are
-pending to be finalized.
-<li><b>heap.livepaths</b> -- return an array of paths by which a given object
-is alive. This method accepts optional second parameter that is a boolean
-flag. This flag tells whether to include paths with weak reference(s) or not.
-By default, paths with weak reference(s) are not included.
-<pre>
-<code>
- select heap.livepaths(s) from java.lang.String s
-</code>
-</pre>
-Each element of this array itself is another array. The later array is
-contains an objects that are in the 'reference chain' of the path.
-<li><b>heap.roots</b> -- returns an Enumeration of Roots of the heap.
-<a name="rootobj"></a>
-Each Root object has the following properties:
-<ul>
-<li>id - String id of the object that is referred by this root
-<li>type - descriptive type of Root (JNI Global, JNI Local, Java Static etc)
-<li>description - String description of the Root
-<li>referrer - Thread Object or Class object that is responsible for this root or null
-</ul>
-</ul>
-
-Examples:
-<ul>
-<li>access static field 'props' of class java.lang.System
-<pre>
-<code>
- select heap.findClass("java.lang.System").statics.props
-</code>
-</pre>
-<li>get number of fields of java.lang.String class
-<pre>
-<code>
- select heap.findClass("java.lang.String").fields.length
-</code>
-</pre>
-<li> find the object whose object id is given
-<pre>
-<code>
- select heap.findObject("0xf3800b58")
-</code>
-</pre>
-<li>select all classes that have name pattern java.net.*
-<pre>
-<code>
- select <a href="#filter">filter</a>(heap.classes(), "/java.net./.test(it.name)")
-</code>
-</pre>
-</ul>
-
-<h3>functions on individual objects</h3>
-
-<ul>
-<li><a href="#allocTrace">allocTrace(jobject)</a>
-<li><a href="#classof">classof(jobject)</a>
-<li><a href="#forEachReferrer">forEachReferrer(callback, jobject)</a>
-<li><a href="#identical">identical(o1, o2)</a>
-<li><a href="#objectid">objectid(jobject)</a>
-<li><a href="#reachables">reachables(jobject, excludedFields)</a>
-<li><a href="#referrers">referrers(jobject)</a>
-<li><a href="#referees">referees(jobject)</a>
-<li><a href="#refers">refers(jobject)</a>
-<li><a href="#root">root(jobject)</a>
-<li><a href="#sizeof">sizeof(jobject)</a>
-<li><a href="#toHtml">toHtml(obj)</a>
-</ul>
-
-<a name="allocTrace"></a>
-<h4>allocTrace function</h4>
-
-This returns allocation site trace of a given Java object if available.
-allocTrace returns array of frame objects. Each frame object has the following
-properties:
-<ul>
-<li>className - name of the Java class whose method is running in the frame.
-<li>methodName - name of the Java method running in the frame.
-<li>methodSignature - signature of the Java method running in the frame.
-<li>sourceFileName - name of source file of the Java class running in the frame.
-<li>lineNumber - source line number within the method.
-</ul>
-
-<a name="classof"></a>
-<h4>classof function</h4>
-
-Returns Class object of a given Java Object. The result object supports the
-following properties:
-<ul>
-<li>name - name of the class.
-<li>superclass - Class object for super class (or null if java.lang.Object).
-<li>statics - name, value pairs for static fields of the Class.
-<li>fields - array of field objects. Field objects have name, signature
-properties.
-<li>loader - ClassLoader object that loaded this class.
-<li>signers - signers that signed this class.
-<li>protectionDomain - protection domain to which this class belongs.
-</ul>
-Class objects have the following methods:
-<ul>
-<li>isSubclassOf - tests whether given class is direct or indirect
-subclass of this class or not.
-<li>isSuperclassOf - tests whether given Class is direct or indirect
-superclass of this class or not.
-<li>subclasses - returns array of direct and indirect subclasses.
-<li>superclasses - returns array of direct and indirect superclasses.
-</ul>
-
-Examples:
-<ul>
-<li>show class name of each Reference type object
-<pre>
-<code>
- select classof(o).name from instanceof java.lang.ref.Reference o
-</code>
-<li>show all subclasses of java.io.InputStream
-<pre>
-<code>
- select heap.findClass("java.io.InputStream").subclasses()
-</code>
-<li>show all superclasses of java.io.BufferedInputStream
-<pre>
-<code>
- select heap.findClass("java.io.BufferedInputStream").superclasses()
-</code>
-</pre>
-</ul>
-
-<a name="forEachReferrer"></a>
-<h4>forEachReferrer function</h4>
-
-calls a callback function for each referrer of a given Java object.
-
-<a name="identical"></a>
-<h4>identical function</h4>
-<p>
-Returns whether two given Java objects are identical or not.
-</p>
-Example:
-<pre>
-<code>
- select identical(heap.findClass("Foo").statics.bar, heap.findClass("AnotherClass").statics.bar)
-</code>
-</pre>
-
-<a name="objectid"></a>
-<h4>objectid function</h4>
-
-<p>
-Returns String id of a given Java object. This id can be passed to
-<a href="#findObject">heap.findObject</a> and may also be used to compare
-objects for identity.
-</p>
-Example:
-<pre>
-<code>
- select objectid(o) from java.lang.Object o
-</code>
-</pre>
-
-<a name="reachables"></a>
-<h4>reachables function</h4>
-<p>
-Returns an array of Java objects that are transitively referred from the
-given Java object. Optionally accepts a second parameter that is comma
-separated field names to be excluded from reachability computation.
-Fields are written in class_name.field_name pattern.
-</p>
-Examples:
-<ul>
-<li>print all reachable objects from each Properties instance.
-<pre>
-<code>
- select reachables(p) from java.util.Properties p
-</code>
-</pre>
-<li>print all reachables from each java.net.URL but omit the objects reachable
-via the fields specified.
-<pre>
-<code>
- select reachables(u, 'java.net.URL.handler') from java.net.URL u
-</code>
-</pre>
-</ul>
-
-<a name="referrers"></a>
-<h4>referrers function</h4>
-<p>
-Returns an enumeration of Java objects that hold reference to a given Java
-object.
-</p>
-Examples:
-<ul>
-<li> print number of referrers for each java.lang.Object instance
-<pre>
-<code>
- select count(referrers(o)) from java.lang.Object o
-</code>
-</pre>
-<li>print referrers for each java.io.File object
-<pre>
-<code>
- select referrers(f) from java.io.File f
-</code>
-</pre>
-<li>print URL objects only if referred by 2 or more
-<pre>
-<code>
- select u from java.net.URL u where count(referrers(u)) > 2
-</code>
-</pre>
-</ul>
-
-<a name="referees"></a>
-<h4>referees function</h4>
-<p>
-Returns an array of Java objects to which the given Java
-object directly refers to.
-</p>
-Example: to print all static reference fields of java.io.File class
-<pre>
-<code>
- select referees(<a href="#findClass">heap.findClass</a>("java.io.File"))
-</code>
-</pre>
-
-<a name="refers"></a>
-<h4>refers function</h4>
-<p>
-Returns whether first Java object refers to second Java object or not.
-</p>
-
-<a name="root"></a>
-<h4>root function</h4>
-<p>
-If given object is a member of root set of objects, this function returns
-a descriptive <a href="#rootobj">Root object</a> describing why it is so.
-If given object is not a root, then this function returns null.
-</p>
-
-<a name="sizeof"></a>
-<h4>sizeof function</h4>
-
-Returns size of the given Java object in bytes
-Example:
-<pre>
-<code>
- select sizeof(o) from [I o
-</code>
-</pre>
-
-<a name="toHtml"></a>
-<h4>toHtml function</h4>
-
-Returns HTML string for the given Java object. Note that this is called
-automatically for objects selected by select expression. But, it may be useful
-to print more complex output.
-
-Example: print hyperlink in bold font weight
-<pre>
-<code>
- select "<b>" + toHtml(o) + "</b>" from java.lang.Object o
-</code>
-</pre>
-
-<h3>Selecting multiple values</h3>
-<p>
-Multiple values can be selected using JavaScript object literals or arrays.
-</p>
-
-Example: show name and thread for each thread object
-<pre>
-<code>
- select { name: t.name? t.name.toString() : "null", thread: t }
- from instanceof java.lang.Thread t
-</code>
-</pre>
-
-<h3>array/iterator/enumeration manipulation functions</h3>
-
-<p>
-These functions accept an array/iterator/enumeration and an
-expression string [or a callback function] as input. These functions iterate
-the array/iterator/enumeration and apply the expression (or function) on
-each element. Note that JavaScript objects are associative arrays. So,
-these functions may also be used with arbitrary JavaScript objects.
-</p>
-
-<ul>
-<li><a href="#concat">concat(array1/enumeration1, array2/enumeration2)</a>
-<li><a href="#contains">contains(array/enumeration, expression)</a>
-<li><a href="#count">count(array/enumeration, expression)</a>
-<li><a href="#filter">filter(array/enumeration, expression)</a>
-<li><a href="#length">length(array/enumeration)</a>
-<li><a href="#map">map(array/enumeration, expression)</a>
-<li><a href="#max">max(array/enumeration, [expression])</a>
-<li><a href="#min">min(array/enumeration, [expression])</a>
-<li><a href="#sort">sort(array/enumeration, [expression])</a>
-<li><a href="#sum">sum(array/enumeration, [expression])</a>
-<li><a href="#toArray">toArray(array/enumeration)</a>
-<li><a href="#unique">unique(array/enumeration, [expression])</a>
-</ul>
-
-<a name="concat"></a>
-<h4>concat function</h4>
-<p>
-Concatenates two arrays or enumerations (i.e., returns composite
-enumeration).
-</p>
-
-<a name="contains"></a>
-<h4>contains function</h4>
-<p>
-Returns whether the given array/enumeration contains an element
-the given boolean expression specified in code. The code evaluated
-can refer to the following built-in variables.
-</p>
-<ul>
-<li>it -> currently visited element
-<li>index -> index of the current element
-<li>array -> array/enumeration that is being iterated
-</ul>
-Example: select all Properties objects that are referred by
-some static field some class.
-<pre>
-<code>
- select p from java.util.Properties p
- where contains(<a href="#referrers">referrers</a>(p), "<a href="#classof">classof</a>(it).name == 'java.lang.Class'")
-</code>
-</pre>
-
-<a name="count"></a>
-<h4>count function</h4>
-<p>
-count function returns the count of elements of the input array/enumeration
-that satisfy the given boolean expression. The boolean expression code can
-refer to the following built-in variables.
-</p>
-<ul>
-<li>it -> currently visited element
-<li>index -> index of the current element
-<li>array -> array/enumeration that is being iterated
-</ul>
-Example: print number of classes that have specific name pattern
-<pre>
-<code>
- select count(<a href="#classes">heap.classes()</a>, "/java.io./.test(it.name)")
-</code>
-</pre>
-
-<a name="filter"></a>
-<h4>filter function</h4>
-<p>
-filter function returns an array/enumeration that contains elements
-of the input array/enumeration that satisfy the given boolean
-expression. The boolean expression code can refer to the following built-in
-variables.
-</p>
-<ul>
-<li>it -> currently visited element
-<li>index -> index of the current element
-<li>array -> array/enumeration that is being iterated
-<li>result -> result array/enumeration
-</ul>
-Examples:
-<ul>
-<li>show all classes that have java.io.* name pattern
-<pre>
-<code>
- select filter(<a href="#classes">heap.classes</a>(), "/java.io./.test(it.name)")
-</code>
-</pre>
-<li> show all referrers of URL object where the referrer is not from
-java.net package
-<pre>
-<code>
- select filter(<a href="#referrers">referrers</a>(u), "! /java.net./.test(<a href="#classof">classof</a>(it).name)")
- from java.net.URL u
-</code>
-</pre>
-</ul>
-
-<a name="length"></a>
-<h4>length function</h4>
-<p>
-length function returns number of elements of an array/enumeration.
-</p>
-
-<a name="map"></a>
-<h4>map function</h4>
-<p>
-Transforms the given array/enumeration by evaluating given code
-on each element. The code evaluated can refer to the following built-in
-variables.
-</p>
-<ul>
-<li>it -> currently visited element
-<li>index -> index of the current element
-<li>array -> array/enumeration that is being iterated
-<li>result -> result array/enumeration
-</ul>
-<p>
-map function returns an array/enumeration of values created by repeatedly
-calling code on each element of input array/enumeration.
-</p>
-Example: show all static fields of java.io.File with name and value
-<pre>
-<code>
- select map(<a href="#findClass">heap.findClass</a>("java.io.File").statics, "index + '=' + <a href="#toHtml">toHtml</a>(it)")
-</code>
-</pre>
-
-<a name="max"></a>
-<h4>max function</h4>
-<p>
-returns the maximum element of the given array/enumeration.
-Optionally accepts code expression to compare elements of the array.
-By default numerical comparison is used. The comparison expression can
-use the following built-in variables:
-</p>
-<ul>
-<li>lhs -> left side element for comparison
-<li>rhs -> right side element for comparison
-</ul>
-Examples:
-<ul>
-<li>find the maximum length of any String instance
-<pre>
-<code>
- select max(map(heap.objects('java.lang.String', false), 'it.value.length'))
-</code>
-</pre>
-<li>find string instance that has the maximum length
-<pre>
-<code>
- select max(heap.objects('java.lang.String'), 'lhs.value.length > rhs.value.length')
-</code>
-</pre>
-</ul>
-
-<a name="min"></a>
-<h4>min function</h4>
-<p>
-returns the minimum element of the given array/enumeration. Optionally
-accepts code expression to compare elements of the array. By default numerical
-comparison is used. The comparison expression can use the following built-in
-variables:
-</p>
-<ul>
-<li>lhs -> left side element for comparison
-<li>rhs -> right side element for comparison
-</ul>
-Examples:
-<ul>
-<li>find the minimum size of any Vector instance
-<pre>
-<code>
- select min(map(heap.objects('java.util.Vector', false), 'it.elementData.length'))
-</code>
-</pre>
-<li>find Vector instance that has the maximum length
-<pre>
-<code>
- select min(heap.objects('java.util.Vector'), 'lhs.elementData.length < rhs.elementData.length')
-</code>
-</ul>
-
-<a name="sort"></a>
-<h4>sort function</h4>
-<p>
-sorts given array/enumeration. Optionally accepts code expression to
-compare elements of the array. By default numerical comparison is used.
-The comparison expression can use the following built-in variables:
-</p>
-<ul>
-<li>lhs -> left side element for comparison
-<li>rhs -> right side element for comparison
-</ul>
-Examples:
-<ul>
-<li> print all char[] objects in the order of size.
-<pre>
-<code>
- select sort(<a href="#objects">heap.objects</a>('[C'), '<a href="#sizeof">sizeof</a>(lhs) - sizeof(rhs)')
-</code>
-</pre>
-<li> print all char[] objects in the order of size but print
-size as well.
-<pre>
-<code>
- select <a href="#map">map</a>(sort(<a href="#objects">heap.objects</a>('[C'), '<a href="#sizeof">sizeof</a>(lhs) - sizeof(rhs)'), '{ size: sizeof(it), obj: it }')
-</code>
-</pre>
-</ul>
-
-<a name="sum"></a>
-<h4>sum function</h4>
-<p>
-This function returns the sum of all the elements of the given input array or
-enumeration. Optionally, accepts an expression as second param. This is used
-to map the input elements before summing those.
-</p>
-Example: return sum of sizes of the reachable objects from each Properties object
-<pre>
-<code>
- select sum(<a href="#map">map</a>(<a href="#reachables">reachables</a>(p), '<a href="#sizeof">sizeof</a>(it)'))
- from java.util.Properties p
-
- // or omit the map as in ...
- select sum(<a href="#reachables">reachables</a>(p), '<a href="#sizeof">sizeof</a>(it)')
- from java.util.Properties p
-</code>
-</code>
-</pre>
-
-<a name="toArray"></a>
-<h4>toArray function</h4>
-<p>
-This function returns an array that contains elements of the input
-array/enumeration.
-</p>
-
-<a name="unique"></a>
-<h4>unique function</h4>
-<p>
-This function returns an array/enumeration containing unique elements of the
-given input array/enumeration
-</p>
-Example: select unique char[] instances referenced from Strings. Note that
-more than one String instance can share the same char[] for the content.
-<pre>
-<code>
- // number of unique char[] instances referenced from any String
- select count(unique(map(heap.objects('java.lang.String'), 'it.value')))
-
- // total number of Strings
- select count(heap.objects('java.lang.String'))
-</code>
-</pre>
-
-<h3>More complex examples</h3>
-
-<h4>Print histogram of each class loader and number of classes loaded by it</h4>
-
-<pre>
-<code>
- select <a href="#map">map</a>(<a href="#sort">sort</a>(map(heap.objects('java.lang.ClassLoader'),
- '{ loader: it, count: it.classes.elementCount }'), 'lhs.count < rhs.count'),
- 'toHtml(it) + "<br>"')
-</code>
-</pre>
-<p>
-The above query uses the fact that, <b>java.lang.ClassLoader</b> has a private
-field called <b>classes</b> of type <b>java.util.Vector</b> and Vector has a
-private field named <b>elementCount</b> that is number of elements in the
-vector. We select multiple values (loader, count) using JavaScript object
-literal and map function. We sort the result by count (i.e., number of classes
-loaded) using sort function with comparison expression.
-</p>
-
-<h4>Show parent-child chain for each class loader instance</h4>
-
-<pre>
-<code>
- select <a href="#map">map</a>(heap.objects('java.lang.ClassLoader'),
- function (it) {
- var res = '';
- while (it != null) {
- res += toHtml(it) + "->";
- it = it.parent;
- }
- res += "null";
- return res + "<br>";
- })
-</code>
-</pre>
-<p>
-Note that we use <b>parent</b> field of <b>java.lang.ClassLoader</b> class
-and walk until parent is null using the callback function to map call.
-</p>
-
-<h4>Printing value of all System properties</h4>
-
-<pre>
-<code>
- select <a href="#map">map</a>(<a href="#filter">filter(<a href="#findClass">heap.findClass</a>('java.lang.System').statics.props.table, 'it != null'),
- function (it) {
- var res = "";
- while (it != null) {
- res += it.key.value.toString() + '=' +
- it.value.value.toString() + '<br>';
- it = it.next;
- }
- return res;
- });
-</code>
-</pre>
-<p>
-The above query uses the following facts:
-<ul>
-<li>java.lang.System has static field by name 'props' of type java.util.Properties.
-<li>java.util.Properties has field by 'table' of type java.util.Hashtable$Entry
-(this field is inherited from java.util.Hashtable). This is the hashtable
-buckets array.
-<li>java.util.Hashtable$Entry has 'key', 'value' and 'next' fields. Each
-entry points the next entry (or null) in the same hashtable bucket.
-<li>java.lang.String class has 'value' field of type char[].
-</ul>
-<p>
-<b>Note that this query (and many other queries) may not be stable - because
-private fields of Java platform classes may be modified/removed without any
-notification! (implementation detail)</b>. But, using such queries on user
-classes may be safe - given that user has the control over the classes.
-</p>
-
-</body>
-</html>