From 6640324f7f2730dc5a120af90a849b8d8fee52fa Mon Sep 17 00:00:00 2001
From: Martin Ling <martin-git@earth.li>
Date: Sun, 22 Dec 2013 17:27:13 +0000
Subject: [PATCH] usb: Enforce that there can only be one USB event source for
 now.

---
 hardware/common/usb.c | 10 ++++++++++
 libsigrok-internal.h  |  1 +
 2 files changed, 11 insertions(+)

diff --git a/hardware/common/usb.c b/hardware/common/usb.c
index 64f887de..c4d78f90 100644
--- a/hardware/common/usb.c
+++ b/hardware/common/usb.c
@@ -277,6 +277,11 @@ SR_PRIV int usb_callback(int fd, int revents, void *cb_data)
 SR_PRIV int usb_source_add(struct sr_context *ctx, int timeout,
 		sr_receive_data_callback_t cb, void *cb_data)
 {
+	if (ctx->usb_source_present) {
+		sr_err("A USB event source is already present.");
+		return SR_ERR;
+	}
+
 #ifdef _WIN32
 	ctx->usb_event = CreateEvent(NULL, TRUE, FALSE, NULL);
 	g_mutex_init(&ctx->usb_mutex);
@@ -296,12 +301,16 @@ SR_PRIV int usb_source_add(struct sr_context *ctx, int timeout,
 		sr_source_add(lupfd[i]->fd, lupfd[i]->events, timeout, cb, cb_data);
 	free(lupfd);
 #endif
+	ctx->usb_source_present = TRUE;
 
 	return SR_OK;
 }
 
 SR_PRIV int usb_source_remove(struct sr_context *ctx)
 {
+	if (!ctx->usb_source_present)
+		return SR_OK;
+
 #ifdef _WIN32
 	ctx->usb_thread_running = FALSE;
 	g_mutex_unlock(&ctx->usb_mutex);
@@ -319,6 +328,7 @@ SR_PRIV int usb_source_remove(struct sr_context *ctx)
 		sr_source_remove(lupfd[i]->fd);
 	free(lupfd);
 #endif
+	ctx->usb_source_present = FALSE;
 
 	return SR_OK;
 }
diff --git a/libsigrok-internal.h b/libsigrok-internal.h
index a3fe2afe..c76f5983 100644
--- a/libsigrok-internal.h
+++ b/libsigrok-internal.h
@@ -60,6 +60,7 @@
 struct sr_context {
 #ifdef HAVE_LIBUSB_1_0
 	libusb_context *libusb_ctx;
+	gboolean usb_source_present;
 #ifdef _WIN32
 	GThread *usb_thread;
 	gboolean usb_thread_running;