Make 0 call sequence numbers be invalid.
This was part of a previous change I abandoned but this part still seems like
a good idea, since if you store sequence numbers for some reason, it's
impossible to store one indicating you haven't made a request.
I also worked to define the wraparound behavior since from a recent
Chromium-dev thread, I learned that signed overflow is not defined in C++. My
previous patch did this by using unsigned sequence numbers, but this is
discouraged by the style guide and is kind of difficult to change at this point
anyway.
BUG=
Review URL: https://codereview.chromium.org/11375003
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@166776 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/ppapi/proxy/plugin_resource.cc b/ppapi/proxy/plugin_resource.cc
index 22eba26..3a02309 100644
--- a/ppapi/proxy/plugin_resource.cc
+++ b/ppapi/proxy/plugin_resource.cc
@@ -4,6 +4,8 @@
#include "ppapi/proxy/plugin_resource.h"
+#include <limits>
+
#include "ppapi/proxy/ppapi_messages.h"
namespace ppapi {
@@ -12,7 +14,7 @@
PluginResource::PluginResource(Connection connection, PP_Instance instance)
: Resource(OBJECT_IS_PROXY, instance),
connection_(connection),
- next_sequence_number_(0),
+ next_sequence_number_(1),
sent_create_to_browser_(false),
sent_create_to_renderer_(false) {
}
@@ -74,13 +76,13 @@
DCHECK(!sent_create_to_browser_);
sent_create_to_browser_ = true;
}
- ResourceMessageCallParams params(pp_resource(), next_sequence_number_++);
+ ResourceMessageCallParams params(pp_resource(), GetNextSequence());
GetSender(dest)->Send(
new PpapiHostMsg_ResourceCreated(params, pp_instance(), msg));
}
void PluginResource::Post(Destination dest, const IPC::Message& msg) {
- ResourceMessageCallParams params(pp_resource(), next_sequence_number_++);
+ ResourceMessageCallParams params(pp_resource(), GetNextSequence());
SendResourceCall(dest, params, msg);
}
@@ -95,7 +97,7 @@
int32_t PluginResource::GenericSyncCall(Destination dest,
const IPC::Message& msg,
IPC::Message* reply) {
- ResourceMessageCallParams params(pp_resource(), next_sequence_number_++);
+ ResourceMessageCallParams params(pp_resource(), GetNextSequence());
params.set_has_callback();
ResourceMessageReplyParams reply_params;
bool success = GetSender(dest)->Send(new PpapiHostMsg_ResourceSyncCall(
@@ -105,5 +107,17 @@
return PP_ERROR_FAILED;
}
+int32_t PluginResource::GetNextSequence() {
+ // Return the value with wraparound, making sure we don't make a sequence
+ // number with a 0 ID. Note that signed wraparound is undefined in C++ so we
+ // manually check.
+ int32_t ret = next_sequence_number_;
+ if (next_sequence_number_ == std::numeric_limits<int32_t>::max())
+ next_sequence_number_ = 1; // Skip 0 which is invalid.
+ else
+ next_sequence_number_++;
+ return ret;
+}
+
} // namespace proxy
} // namespace ppapi
diff --git a/ppapi/proxy/plugin_resource.h b/ppapi/proxy/plugin_resource.h
index 3b564b4..33d1996a 100644
--- a/ppapi/proxy/plugin_resource.h
+++ b/ppapi/proxy/plugin_resource.h
@@ -81,13 +81,13 @@
// still be invoked but with the default values of the message parameters.
//
// Returns the new request's sequence number which can be used to identify
- // the callback.
+ // the callback. This value will never be 0, which you can use to identify
+ // an invalid callback.
//
- // Note: 1) all integers (including 0 and -1) are valid request IDs.
- // 2) when all plugin references to this resource are gone or the
+ // Note: 1) When all plugin references to this resource are gone or the
// corresponding plugin instance is deleted, all pending callbacks
// are abandoned.
- // 3) it is *not* recommended to let |callback| hold any reference to
+ // 2) It is *not* recommended to let |callback| hold any reference to
// |this|, in which it will be stored. Otherwise, this object will
// live forever if we fail to clean up the callback. It is safe to
// use base::Unretained(this) or a weak pointer, because this object
@@ -135,8 +135,11 @@
const IPC::Message& msg,
IPC::Message* reply_msg);
+ int32_t GetNextSequence();
+
Connection connection_;
+ // Use GetNextSequence to retrieve the next value.
int32_t next_sequence_number_;
bool sent_create_to_browser_;
