cannot call function while another function call is already

Error message

cannot call function while another function call is already in progress

What it means

errFuncCallInProgress is returned by EvalExpressionWithCalls when a function-call injection is already running on the target; Delve allows only one injected call at a time per process. Issuing a second call before the first completes or is unwound would corrupt the injected-call state machine.

Source

Thrown at pkg/proc/fncall.go:61

//  - evalop.CallInjectionStart
//  - evalop.CallInjectionSetTarget
//  - evalCallInjectionCopyArg
//  - evalCallInjectionComplete
//
// When the target has runtime.debugPinner then evalCallInjectionPinPointer
// must be also called in a loop until it returns false.

const (
	debugCallFunctionNamePrefix1 = "debugCall"
	debugCallFunctionNamePrefix2 = "runtime.debugCall"
	maxDebugCallVersion          = 2
	maxArgFrameSize              = 65535
)

var (
	errFuncCallUnsupported        = errors.New("function calls not supported by this version of Go")
	errFuncCallUnsupportedBackend = errors.New("backend does not support function calls")
	errFuncCallInProgress         = errors.New("cannot call function while another function call is already in progress")
	errNoGoroutine                = errors.New("no goroutine selected")
	errGoroutineNotRunning        = errors.New("selected goroutine not running")
	errNotEnoughStack             = errors.New("not enough stack space")
	errTooManyArguments           = errors.New("too many arguments")
	errNotEnoughArguments         = errors.New("not enough arguments")
	errNotAGoFunction             = errors.New("not a Go function")
	errFuncCallNotAllowedStrAlloc = errors.New("literal string can not be allocated because function calls are not allowed without using 'call'")
)

type functionCallState struct {
	// savedRegs contains the saved registers
	savedRegs Registers
	// err contains a saved error
	err error
	// expr is the expression being evaluated
	expr *ast.CallExpr
	// fn is the function that is being called
	fn *Function

View on GitHub (pinned to a23773e6c3)

Solutions

Resume the target (continue) until the in-progress call finishes, then retry
Use the unwind/cancel mechanism for the current call before issuing a new one
Serialize function calls across clients: only one caller issues 'call' at a time

Example fix

// before: second call while first is paused
dlv> call a()
(dlv) call b()   // errFuncCallInProgress
// after
dlv> call a()
(dlv) continue   // let a() finish
(dlv) call b()

Defensive patterns

Strategy: retry

Validate before calling

// track injected-call state in your client; allow only one outstanding call
var callInFlight bool

Try / catch

if errors.Is(err, proc.ErrFuncCallInProgress) {
    time.Sleep(100 * time.Millisecond) // or continue until previous call completes, then retry once
}

Prevention

Complete or unwind the current function call before issuing another
Serialize 'call' usage across multiple RPC clients
After a call hits a breakpoint inside, continue to completion before new evaluations

When it happens

Trigger: Calling EvalExpressionWithCalls while an outstanding injected call is paused (e.g. the called function hit a breakpoint); issuing a second 'call' from a client before finishing/resuming the previous one; concurrent RPC clients issuing calls simultaneously.

Common situations: Multi-client setups where one client's 'call' is suspended at a breakpoint and another issues commands; scripted evaluations firing while a manual 'call' is in flight; forgetting to complete (continue/unwind) the first call.

Related errors

AI-assisted analysis of go-delve/delve@a23773e6c3 (2026-08-31). Data as JSON: /api/errors/34d207fc5a439ca6. Report an issue: GitHub.