1 ============================ 2 'hotspot' PROBES DESCRIPTION 3 ============================ 4 5 This directory contains D scripts which demonstrate usage of 'hotspot' provider probes. 6 7 The 'hotspot' provider makes available probes that can be used to track the 8 lifespan of the VM, thread start and stop events, GC and memory pool 9 statistics, method compilations, and monitor activity. With a startup flag, 10 additional probes are enabled which can be used to monitor the running Java 11 program, such as method enter and return probes, and object allocations. All 12 of the hotspot probes originate in the VM library (libjvm.so), so they are 13 also provided from programs which embed the VM. 14 15 Many of the probes in the provider have arguments that can be examined to 16 provide further details on the state of the VM. Many of these probes' 17 arguments are opaque IDs which can be used to link probe firings to each 18 other, however strings and other data are also provided. When string values 19 are provided, they are always present as a pair: a pointer to unterminated 20 modified UTF-8 data (see JVM spec: 4.4.7) , and a length value which 21 indicates the extent of that data. Because the string data (even when none 22 of the characters are outside the ASCII range) is not guaranteed to be 23 terminated by a NULL character, it is necessary to use the length-terminated 24 copyinstr() intrinsic to read the string data from the process. 25 26 You can find more information about HotSpot probes here: 27 http://java.sun.com/javase/6/docs/technotes/guides/vm/dtrace.html 28 29 30 =========== 31 THE SCRIPTS 32 =========== 33 34 The following scripts/samples which demonstrate 'hotspot' probes usage are 35 available: 36 37 - class_loading_stat.d 38 The script collects statistics about loaded and unloaded Java classes and 39 dump current state to stdout every N seconds. 40 41 - gc_time_stat.d 42 The script measures the duration of a time spent in GC. 43 The duration is measured for every memory pool every N seconds. 44 45 - hotspot_calls_tree.d 46 The script prints calls tree of fired 'hotspot' probes. 47 48 - method_compile_stat.d 49 The script prints statistics about N methods with largest/smallest 50 compilation time every M seconds. 51 52 - method_invocation_stat.d 53 The script collects statistics about Java method invocations. 54 55 - method_invocation_stat_filter.d 56 The script collects statistics about Java method invocations. 57 You can specify package, class or method name to trace. 58 59 - method_invocation_tree.d 60 The script prints tree of Java and JNI method invocations. 61 62 - monitors.d 63 The script traces monitor related probes. 64 65 - object_allocation_stat.d 66 The script collects statistics about N object allocations every M seconds. 67 68 69 ========== 70 HOW TO RUN 71 ========== 72 73 To run any D script from hotspot directory you can do either: 74 75 # dscript.d -c "java ..." 76 77 or if you don't have Solaris 10 patch which allows to specify probes that 78 don't yet exist ( Hotspot DTrace probes are defined in libjvm.so and as 79 result they could be not been yet loaded when you try to attach D script to 80 the Java process) do: 81 82 # ../helpers/dtrace_helper.d -c "java ..." dscript.d 83 84 or if your application is already running you can just simply attach 85 the D script like: 86 87 # dscript.d -p JAVA_PID 88
