golang panic原理

数据结构与底层实现

Goroutine结构体

stack（栈内存范围）
结构体类型，包含 lo（低地址）和 hi（高地址）两个 uintptr 字段，描述 Goroutine 的栈内存区间 [lo, hi)。初始栈大小为 2KB，可动态扩容至 1GB。

m（Machine 绑定）
指向当前运行此 Goroutine 的内核线程（M）。调度器通过 M 将 Goroutine 映射到操作系统线程。

_panic 和 _defer（异常与延迟调用链）

• _panic：指向当前最内层的 panic 结构体链表，处理异常传播。
• _defer：指向延迟调用（defer）链表，按后进先出（LIFO）顺序执行清理操作。

type g struct {// Stack parameters.// stack describes the actual stack memory: [stack.lo, stack.hi).// stackguard0 is the stack pointer compared in the Go stack growth prologue.// It is stack.lo+StackGuard normally, but can be StackPreempt to trigger a preemption.// stackguard1 is the stack pointer compared in the //go:systemstack stack growth prologue.// It is stack.lo+StackGuard on g0 and gsignal stacks.// It is ~0 on other goroutine stacks, to trigger a call to morestackc (and crash).stack       stack   // offset known to runtime/cgostackguard0 uintptr // offset known to liblinkstackguard1 uintptr // offset known to liblink_panic    *_panic // innermost panic - offset known to liblink_defer    *_defer // innermost deferm         *m      // current m; offset known to arm liblinksched     gobuf......
}

panic结构体

从上述Goroutine结构体的定义，我们可以发现每一个Goroutine维护一个panic的链表，panic存储在栈上。

// _panic 保存了一个活跃的 panic 信息。// _panic 的值必须仅存在于栈上。// argp 和 link 字段是栈指针，但在栈增长时无需特殊处理：
// 由于它们是指针类型且 _panic 值仅存在于栈上，
// 常规的栈指针调整机制会自动处理这些字段。
type _panic struct {argp unsafe.Pointer // pointer to arguments of deferred call run during panic; cannot move - known to liblinkarg  any            // argument to paniclink *_panic        // link to earlier panic// startPC and startSP track where _panic.start was called.startPC uintptrstartSP unsafe.Pointer// The current stack frame that we're running deferred calls for.sp unsafe.Pointerlr uintptrfp unsafe.Pointer// retpc stores the PC where the panic should jump back to, if the// function last returned by _panic.next() recovers the panic.retpc uintptr// Extra state for handling open-coded defers.deferBitsPtr *uint8slotsPtr     unsafe.Pointerrecovered   bool // whether this panic has been recoveredgoexit      booldeferreturn bool
}

注意事项

golang中每个goroutine维护自己的panic信息，并不是全局的，所以，如果需要捕获panic信息需要在每个goroutine中处理。

所以，在下面的这个案例中recover不能捕获到panic信息。如果需要捕获到，需要在每个协程中都执行recover的逻辑。

func main() {defer func() {if r := recover(); r != nil {log.Printf("Recovered from panic: %v", r)os.Exit(1)}}()// 业务代码...go func() {testPanic()}()time.Sleep(1 * time.Second)
}