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| <div class="sub-title"><span class="module-label-in-package">Module</span> <a href="../../../../../../module-summary.html">openj9.traceformat</a></div> |
| <h1 title="Package" class="title">Package com.ibm.jvm.trace.format.api</h1> |
| </div> |
| <hr> |
| <div class="package-signature">package <span class="element-name">com.ibm.jvm.trace.format.api</span></div> |
| <section class="package-description" id="package.description"> |
| <div class="block">This API is used to process trace buffers generated by OpenJ9. These buffers are analogous to the |
| UtTraceRecord's used in the native VM and are referred to as 'records' in the source to differentiate them from |
| the UtTraceBuffer native type which wrap the UtTraceRecord type. However, in messages from the API they are |
| called buffers to keep the naming consistent across the information output of the formatter and the -Xtrace |
| options. |
| |
| A single buffer contains trace data for a single thread with one exception: |
| "0x0 Exception trace pseudo-thread" |
| This "thread" contains data from any threads that have written into the exception buffer interleaved in |
| chronological order. There is no mapping from a trace point to its source thread for trace points in the |
| exception buffer. |
| |
| An instance of a JVM corresponds to an instance of a TraceContext object within the API. It is |
| possible to have multiple TraceContext instances, each the accessor for trace data from a single JVM. |
| |
| The primary inputs for the API are metadata from a JVM and trace buffers. |
| |
| A TraceContext is constructed using metadata from the JVM that's generating the trace records needing |
| formatting. This metadata is either present as a file header at the start of a trace file or can |
| be acquired via a call to the JVMTI extension com.ibm.GetTraceMetadata. |
| Also required is a data file describing the format of trace points for that level of the JVM. At |
| least one data file is required to construct a trace context but additional files can be added later |
| and they will be searched for a trace point specification in the order they are added. |
| |
| Trace buffers must be passed to the context corresponding to the JVM that produced them; they are not |
| valid in another context and must be added in-order within a single thread. Detecting that a buffer |
| has been added to the wrong context is not always possible so don't depend on an error being produced |
| to deduce the correct context. Trace buffers from the same thread must be added in chronological order. |
| |
| Trace points are organised by thread, and iterators are provided that allow access: |
| a. chronologically across all threads (global) |
| b. chronologically within a single thread (thread) |
| |
| The global iterator uses the thread iterators meaning that once a trace point has |
| been returned via either type of iterator it will not be returned again via the other type. |
| The iterators may return null (without becoming invalid) when there are no more trace points available |
| but return data after a new trace buffer has been added. iterator.hasNext() indicates whether a call to |
| iterator.next() will return null and says nothing about whether more trace points can be expected for a given |
| context or thread. |
| |
| Trace points are kept sorted across threads when using the global iterator, however this optimisation invariant |
| is broken by use of a thread iterator. Consequently there is a performance hit when the global iterator is |
| next used, as the threads must be resorted. This can be significant with large numbers of threads. |
| |
| Example fragment parsing a single buffer via the API: |
| // metadata - byte[] either from the header in a trace file or via jvmti |
| // formatData - File containing the trace point specifications |
| |
| TraceContext context = TraceContext.getContext(metadata, formatData, System.out, System.err, System.err, null); |
| TraceThread thread = context.addData(buffer); |
| |
| Iterator global = context.getTracepoints(); |
| while (global.hasNext()) { |
| try { |
| TracePoint tracepoint = global.next(); |
| } catch (MissingDataException e) { |
| System.out.println("Discarded "+(e.getMissingBytes() / context.getRecordSize())+"bytes of trace data for thread "+thread.toString()); |
| continue; |
| } |
| |
| System.out.println(tracepoint.toString()); |
| }</div> |
| </section> |
| <section class="summary"> |
| <ul class="summary-list"> |
| <li> |
| <div class="caption"><span>Interface Summary</span></div> |
| <div class="summary-table two-column-summary"> |
| <div class="table-header col-first">Interface</div> |
| <div class="table-header col-last">Description</div> |
| <div class="col-first even-row-color"><a href="TracePoint.html" title="interface in com.ibm.jvm.trace.format.api">TracePoint</a></div> |
| <div class="col-last even-row-color"> |
| <div class="block">Class to represent a tracepoint produced by IBM JVM's trace engine.</div> |
| </div> |
| </div> |
| </li> |
| <li> |
| <div class="caption"><span>Class Summary</span></div> |
| <div class="summary-table two-column-summary"> |
| <div class="table-header col-first">Class</div> |
| <div class="table-header col-last">Description</div> |
| <div class="col-first even-row-color"><a href="ActiveSection.html" title="class in com.ibm.jvm.trace.format.api">ActiveSection</a></div> |
| <div class="col-last even-row-color"> |
| <div class="block">Active section of a file header.</div> |
| </div> |
| <div class="col-first odd-row-color"><a href="ByteStream.html" title="class in com.ibm.jvm.trace.format.api">ByteStream</a></div> |
| <div class="col-last odd-row-color"> </div> |
| <div class="col-first even-row-color"><a href="Component.html" title="class in com.ibm.jvm.trace.format.api">Component</a></div> |
| <div class="col-last even-row-color"> </div> |
| <div class="col-first odd-row-color"><a href="DataHeader.html" title="class in com.ibm.jvm.trace.format.api">DataHeader</a></div> |
| <div class="col-last odd-row-color"> </div> |
| <div class="col-first even-row-color"><a href="Message.html" title="class in com.ibm.jvm.trace.format.api">Message</a></div> |
| <div class="col-last even-row-color"> </div> |
| <div class="col-first odd-row-color"><a href="MessageFile.html" title="class in com.ibm.jvm.trace.format.api">MessageFile</a></div> |
| <div class="col-last odd-row-color"> |
| <div class="block">Acts as a template for mapping trace ids to messages.</div> |
| </div> |
| <div class="col-first even-row-color"><a href="ProcessorSection.html" title="class in com.ibm.jvm.trace.format.api">ProcessorSection</a></div> |
| <div class="col-last even-row-color"> |
| <div class="block">Processor section of a file header</div> |
| </div> |
| <div class="col-first odd-row-color"><a href="ServiceSection.html" title="class in com.ibm.jvm.trace.format.api">ServiceSection</a></div> |
| <div class="col-last odd-row-color"> |
| <div class="block">Service section of a file header.</div> |
| </div> |
| <div class="col-first even-row-color"><a href="StartupSection.html" title="class in com.ibm.jvm.trace.format.api">StartupSection</a></div> |
| <div class="col-last even-row-color"> |
| <div class="block">Startup section of a file header.</div> |
| </div> |
| <div class="col-first odd-row-color"><a href="TraceContext.html" title="class in com.ibm.jvm.trace.format.api">TraceContext</a></div> |
| <div class="col-last odd-row-color"> </div> |
| <div class="col-first even-row-color"><a href="TraceFileHeader.html" title="class in com.ibm.jvm.trace.format.api">TraceFileHeader</a></div> |
| <div class="col-last even-row-color"> |
| <div class="block">Encapsulates the header for a trace file.</div> |
| </div> |
| <div class="col-first odd-row-color"><a href="TracePointDebugInfo.html" title="class in com.ibm.jvm.trace.format.api">TracePointDebugInfo</a></div> |
| <div class="col-last odd-row-color"> </div> |
| <div class="col-first even-row-color"><a href="TracePointImpl.html" title="class in com.ibm.jvm.trace.format.api">TracePointImpl</a></div> |
| <div class="col-last even-row-color"> </div> |
| <div class="col-first odd-row-color"><a href="TraceRecord.html" title="class in com.ibm.jvm.trace.format.api">TraceRecord</a></div> |
| <div class="col-last odd-row-color"> </div> |
| <div class="col-first even-row-color"><a href="TraceSection.html" title="class in com.ibm.jvm.trace.format.api">TraceSection</a></div> |
| <div class="col-last even-row-color"> |
| <div class="block">Trace section of a file header.</div> |
| </div> |
| <div class="col-first odd-row-color"><a href="TraceThread.html" title="class in com.ibm.jvm.trace.format.api">TraceThread</a></div> |
| <div class="col-last odd-row-color"> </div> |
| </div> |
| </li> |
| <li> |
| <div class="caption"><span>Exception Summary</span></div> |
| <div class="summary-table two-column-summary"> |
| <div class="table-header col-first">Exception</div> |
| <div class="table-header col-last">Description</div> |
| <div class="col-first even-row-color"><a href="MissingDataException.html" title="class in com.ibm.jvm.trace.format.api">MissingDataException</a></div> |
| <div class="col-last even-row-color"> </div> |
| </div> |
| </li> |
| </ul> |
| </section> |
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