Allow arbitrary switching between threads

README.md

@@ -89,6 +89,8 @@ Once inside a debugging session, the following commands may be used:
 
 * `threads` - Print status of all traced threads.
 
+* `thread $tid` - Switch to another thread.
+
 * `goroutines` - Print status of all goroutines.
 
 * `breakpoints` - Print information on all active breakpoints.

command/command.go

@@ -9,6 +9,7 @@ import (
 	"os"
 	"regexp"
 	"sort"
+	"strconv"
 	"strings"
 
 	"github.com/derekparker/delve/proctl"
@@ -48,6 +49,7 @@ func DebugCommands() *Commands {
 		command{aliases: []string{"step", "si"}, cmdFn: step, helpMsg: "Single step through program."},
 		command{aliases: []string{"next", "n"}, cmdFn: next, helpMsg: "Step over to next source line."},
 		command{aliases: []string{"threads"}, cmdFn: threads, helpMsg: "Print out info for every traced thread."},
+		command{aliases: []string{"thread", "t"}, cmdFn: thread, helpMsg: "Switch to the specified thread."},
 		command{aliases: []string{"clear"}, cmdFn: clear, helpMsg: "Deletes breakpoint."},
 		command{aliases: []string{"goroutines"}, cmdFn: goroutines, helpMsg: "Print out info for every goroutine."},
 		command{aliases: []string{"breakpoints", "bp"}, cmdFn: breakpoints, helpMsg: "Print out info for active breakpoints."},
@@ -136,6 +138,22 @@ func threads(p *proctl.DebuggedProcess, ars ...string) error {
 	return nil
 }
 
+func thread(p *proctl.DebuggedProcess, ars ...string) error {
+	oldTid := p.CurrentThread.Id
+	tid, err := strconv.Atoi(ars[0])
+	if err != nil {
+		return err
+	}
+
+	err = p.SwitchThread(tid)
+	if err != nil {
+		return err
+	}
+
+	fmt.Printf("Switched from %d to %d\n", oldTid, tid)
+	return nil
+}
+
 func goroutines(p *proctl.DebuggedProcess, ars ...string) error {
 	return p.PrintGoroutinesInfo()
 }

proctl/proctl.go

@@ -311,12 +311,22 @@ func (dbp *DebuggedProcess) Step() (err error) {
 	return dbp.run(fn)
 }
 
+// Change from current thread to the thread specified by `tid`.
+func (dbp *DebuggedProcess) SwitchThread(tid int) error {
+	if th, ok := dbp.Threads[tid]; ok {
+		dbp.CurrentThread = th
+		return nil
+	}
+	return fmt.Errorf("thread %d does not exist", tid)
+}
+
 // Obtains register values from what Delve considers to be the current
 // thread of the traced process.
 func (dbp *DebuggedProcess) Registers() (Registers, error) {
 	return dbp.CurrentThread.Registers()
 }
 
+// Returns the PC of the current thread.
 func (dbp *DebuggedProcess) CurrentPC() (uint64, error) {
 	return dbp.CurrentThread.CurrentPC()
 }