The Java Virtual Machine Tool Interface (JVMTI) is a programming interface used by development tools to obtain information about the running state of a Java Virtual Machine (JVM). It also provides the ability to manipulate the JVM's state, such as suspending and resuming threads, setting breakpoints, and getting and setting local variables.
JVMTI information can be divided into two categories: information about the JVM itself, and information about the threads and methods running inside the JVM.
Information about the JVM itself can be obtained through the JVMTI Environment structure. This structure contains a number of functions that can be used to query the JVM's capabilities, memory usage, garbage collector status, and more.
Information about threads and methods running inside the JVM can be obtained through the JVMTI Thread and JVMTI Method structures. These structures contain a number of functions that can be used to query the current state of a thread or method, such as the stack trace, local variables, and line number.
The JVMTI provides a number of functions for manipulating the JVM's state. These functions can be used to suspend and resume threads, set breakpoints, and get and set local variables.
The JVMTI provides functions for suspending and resuming threads. These functions can be used to temporarily stop a thread from running, or to prevent a thread from starting.
The following code example shows how to use the JVMTI to suspend a thread:
jvmtiEnv* jvmti;
jvmtiError error;
// Get the JVMTI environment
error = (*jvmti)->GetEnv(jvmti, &jvmti, JVMTI_VERSION_1);
if (error != JVMTI_ERROR_NONE) {
// Handle error
}
// Suspend the thread
error = (*jvmti)->SuspendThread(jvmti, thread);
if (error != JVMTI_ERROR_NONE) {
// Handle error
}
The JVMTI provides functions for setting breakpoints. These functions can be used to set a breakpoint at a specific line of code, or at a specific method.
The following code example shows how to use the JVMTI to set a breakpoint at a specific line of code:
jvmtiEnv* jvmti;
jvmtiError error;
// Get the JVMTI environment
error = (*jvmti)->GetEnv(jvmti, &jvmti, JVMTI_VERSION_1);
if (error != JVMTI_ERROR_NONE) {
// Handle error
}
// Set the breakpoint
error = (*jvmti)->SetBreakpoint(jvmti, method, line_number);
if (error != JVMTI_ERROR_NONE) {
// Handle error
}
The JVMTI provides functions for getting and setting local variables. These functions can be used to inspect the value of a local variable, or to change the value of a local variable.
The following code example shows how to use the JVMTI to get the value of a local variable:
jvmtiEnv* jvmti;
jvmtiError error;
// Get the JVMTI environment
error = (*jvmti)->GetEnv(jvmti, &jvmti, JVMTI_VERSION_1);
if (error != JVMTI_ERROR_NONE) {
// Handle error
}
// Get the value of the local variable
error = (*jvmti)->GetLocalVariable(jvmti, thread, method,
local_variable, &value);
if (error != JVMTI_ERROR_NONE) {
// Handle error
}
The following code example shows how to use the JVMTI to set the value of a local variable:
jvmtiEnv* jvmti;
jvmtiError error;
// Get the JVMTI environment
error = (*jvmti)->GetEnv(jvmti, &jvmti, JVMTI_VERSION_1);
if (error != JVMTI_ERROR_NONE) {
// Handle error
}
// Set the value of the local variable
error = (*jvmti)->SetLocalVariable(jvmti, thread, method,
local_variable, value);
if (error != JVMTI_ERROR_NONE) {
// Handle error
}
The Java Virtual Machine Tool Interface (JVMTI) is a powerful programming interface that can be used to obtain information about the running state of a Java Virtual Machine (JVM). It also provides the ability to manipulate the JVM's state, such as suspending and resuming threads, setting breakpoints, and getting and setting local variables.