Breakpoint

In software development, a breakpoint is an intentional stopping or pausing place in a program, put in place for debugging purposes. It is also sometimes simply referred to as a pause. In software development, a breakpoint is an intentional stopping or pausing place in a program, put in place for debugging purposes. It is also sometimes simply referred to as a pause. More generally, a breakpoint is a means of acquiring knowledge about a program during its execution. During the interruption, the programmer inspects the test environment (general purpose registers, memory, logs, files, etc.) to find out whether the program is functioning as expected. In practice, a breakpoint consists of one or more conditions that determine when a program's execution should be interrupted. Breakpoints were invented for ENIAC, one of the earliest digital computers, by programmer Betty Holberton. In the initial design of ENIAC, program flow was set by plugging cables from one unit to another. To make the program stop at a certain point, a cable was removed, called a breakpoint. Early mainframe computers, such as the IBM/360, had console switches/dials that allowed breakpoints at specific instruction storage addresses and provided 'single cycle' operation, permitting the contents of registers and memory to be observed directly on console lights. The advent of multitasking limited the use of this option since the entire machine was halted. Programmers have used machine code patches to implement single destructive breakpoints to cause a core dump since the early days of computers. The core dump provided the state of the registers and memory at the exact moment of the deliberate 'crash'. The advent of teletypewriter consoles in the 1960s allowed more interactive command line debugging capabilities but it was not until the early 1970s and the arrival of ubiquitous video monitors connected to mainframes that fully interactive, full screen debugging in multitasking environments became a reality. This also permitted step-by-step program execution in a true program animation manner with optional register and memory alterations simultaneously displayed. Initially this type of animation was at the level of disassembled or Decompiled machine code, but later advanced to HLL source level animation. Breakpoints are most commonly used to interrupt a running program immediately before the execution of a programmer-specified instruction. This is often referred to as an instruction breakpoint. Other kinds of conditions can also be used, such as the reading, writing, or modification of a specific location in an area of memory. This is often referred to as a conditional breakpoint, a data breakpoint, or a watchpoint. On the other hand, non-breaking breakpoints, sometimes called logpoints, can show the full state of a piece of code at the breakpoint without stopping its execution.