Difference between revisions of "Serializing and deserializing root objects"
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===Serialize=== | ===Serialize=== | ||
| − | ROOT TMessage objects can hold serialized ROOT objects. | + | ROOT TMessage objects can hold serialized ROOT objects. |
<pre> | <pre> | ||
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tm->WriteObject(some_root_object); | tm->WriteObject(some_root_object); | ||
| − | // get pointer to TMessage internal buffer and length | + | // get pointer to TMessage internal buffer holding object and its length in bytes |
char *buffer = tm->Buffer(); | char *buffer = tm->Buffer(); | ||
| − | int bufferLength = tm->Length()); | + | int bufferLength = tm->Length()); |
</pre> | </pre> | ||
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| − | // create special object from byte buffer, length in bytes | + | // create special TMessage object from byte buffer, length in bytes |
MyTMessage *myTM = new MyTMessage(buffer,length); | MyTMessage *myTM = new MyTMessage(buffer,length); | ||
Revision as of 14:36, 30 June 2009
Introduction
ROOT objects can be serialized to a byte array or reconstructed from the byte array quite easily. One reason to do this might be to store or transport ROOT objects in a way not supported by ROOT itself. An example is transport of a ROOT histogram from a producer to a consumer program via the cMsg package, a publish/subscribe messaging system that will be used extensively in the Hall D online monitoring system (see Example Programs below).
Serialize
ROOT TMessage objects can hold serialized ROOT objects.
#include "TMessage.h" // create TMessage object capable of holding serialized ROOT object TMessage *tm = new TMessage(kMESS_OBJECT); // fill with serialized version of some ROOT object tm->WriteObject(some_root_object); // get pointer to TMessage internal buffer holding object and its length in bytes char *buffer = tm->Buffer(); int bufferLength = tm->Length());
Deserialize
Deserializing involves a trick due to limitations of the TMessage class. The required constructor is protected, so a covering class must be created to expose it:
#include "TMessage.h"
// special class needed to expose protected TMessage constructor
class MyTMessage : public TMessage {
public:
MyTMessage(void *buf, Int_t len) : TMessage(buf, len) { }
};
// create special TMessage object from byte buffer, length in bytes
MyTMessage *myTM = new MyTMessage(buffer,length);
// reconstruct original object, here assumed to be a histogram
TH1 *hist = (TH1*)myTM->ReadObject(myTM->GetClass());
Example Programs
cMsgRootProducer.cc,cMsgRootConsumer.cc,Makefile Examples demonstrate transport via cMsg package.
