Avoid unnecessary ThreadInfoRequests (#416)

To query GDB's current thread ID, don't use "-thread-info", which does
an expensive roundtrip to the target (several kilobytes of XML
transmitted over the remote protocol connection). The current thread is
known by GDB itself, and while there does not seem to be a command to
query it directly, it can be read by evaluating convenience variable
$_gthread.

Signed-off-by: Christian Walther <walther@indel.ch>

Author: cwalther

src/gdb/GDBBackend.ts

@@ -18,6 +18,7 @@ import {
     MIBreakpointInsertOptions,
     MIBreakpointLocation,
     MIShowResponse,
+    sendDataEvaluateExpression,
     sendExecInterrupt,
 } from '../mi';
 import { VarManager } from '../varManager';
@@ -297,6 +298,17 @@ export class GDBBackend extends events.EventEmitter implements IGDBBackend {
         return isProcessActive(this.proc);
     }
 
+    public async queryCurrentThreadId(): Promise<number> {
+        const threadIdResult = await sendDataEvaluateExpression(
+            this,
+            this.gdbVersionAtLeast('7.11') ? '$_gthread' : '$_thread'
+        );
+        return threadIdResult.value !== undefined &&
+            threadIdResult.value !== 'void'
+            ? parseInt(threadIdResult.value, 10)
+            : -1;
+    }
+
     protected nextToken() {
         return this.token++;
     }

src/gdb/GDBDebugSessionBase.ts

@@ -436,12 +436,7 @@ export abstract class GDBDebugSessionBase extends LoggingDebugSession {
                 this.waitPaused = resolve;
             });
             if (this.gdb.isNonStopMode()) {
-                const threadInfo = await mi.sendThreadInfoRequest(this.gdb, {});
-
-                this.waitPausedThreadId = parseInt(
-                    threadInfo['current-thread-id'],
-                    10
-                );
+                this.waitPausedThreadId = await this.gdb.queryCurrentThreadId();
                 this.gdb.pause(this.waitPausedThreadId);
             } else {
                 this.gdb.pause();
@@ -1934,7 +1929,8 @@ export abstract class GDBDebugSessionBase extends LoggingDebugSession {
                     if (
                         this.waitPaused &&
                         resultData.reason === 'signal-received' &&
-                        this.waitPausedThreadId === id
+                        (this.waitPausedThreadId === id ||
+                            this.waitPausedThreadId === -1)
                     ) {
                         suppressHandleGDBStopped = true;
                     }

src/types/gdb.ts

@@ -128,6 +128,14 @@ export interface IGDBBackend extends EventEmitter {
     sendCommands(commands?: string[]): Promise<void>;
     gdbVersionAtLeast(targetVersion: string): boolean;
 
+    /** Ask GDB for its current thread ID.
+     *
+     * Can return 0 when GDB has no threads, or -1 in case of unexpected errors
+     * (which will in some cases make things work anyway because "--thread -1"
+     * is equivalent to omitting "--thread" - that is probably an implementation
+     * detail though). */
+    queryCurrentThreadId(): Promise<number>;
+
     on(
         event: 'consoleStreamOutput',
         listener: (output: string, category: string) => void