YAMI Core Library Reference

Introduction

The YAMI Core Library consists of two different parts:

the part that is supposed to be used directly by the end-user (by the programmer who wants to write programs using YAMI):
- Parameter Set API
- Agent API
- Synchronization Primitives
- Error Codes
the part that is not supposed to be used by the client code, but it can be useful for programmers writing their own low-level code:
- Domain Set
- Queue
- XDR Module
- Operating System Layer
Please refer to the comments in source code for further information about this second part.

To be exact, Synchronization Primitives are part of Operating System Layer that were made available to normal users to help them solve common problems in multithreaded YAMI applications.

Note: The YAMI library is not intended to be a library for multithreaded programming in general, but it can be freely mixed with other libraries providing their own primitives.

Every YAMI function returns YAMIOK integer code in case of success, unless otherwise specified.

Parameter Set

Parameter Set is the object used by the client code to encapsulate the functionality of the variable length sequence of variable type parameters. This object is not internally synchronized and is intended for use in one thread and per one message (however, the latter constraint is not strict).

Parameter Set is created when there is a need to send some data to the remote object and conceptually is similar to the set of parameters of the function or method.

In order to use Parameter Set functionality, the user code has to include yamiparams.h header.

typedef void* HPARAMSET;

Type of the handle to a Parameter Set.
The handle is opaque to the client.

enum paramType
{
     eNoType,
     eString,
     eWString,
     eInt,
     eDouble,
     eByte,
     eBinary
};

Enums defining types used in Parameter Set.
eNoType is used internally by the implementation.

int yamiCreateParamSet(HPARAMSET *pps, int parcount);

Creates a Parameter Set of the length designated by parcount, no parameter is initialized.

Typical error codes:: YAMIOUTOFRANGE (this may happen when parcount is invalid), YAMINOMEMORY.

int yamiDestroyParamSet(HPARAMSET paramset);

Destroys a Parameter Set.

Typical error codes:: YAMIBADHANDLE.

int yamiCopyParamSet(HPARAMSET *ppsdst, HPARAMSET pssrc);

Creates a copy of the Parameter Set.
The pssrc parameter is a handle to the existing (source) object and the ppdst parameter is a pointer to the place, where the handle of the copy (destination) will be stored.

Typical error codes:: YAMIBADHANDLE, YAMINOMEMORY.

int yamiCopyParameter(HPARAMSET psdst, int positiondst,
                      HPARAMSET pssrc, int positionsrc);

Copies a parameter from one Parameter Set to the other.

Typical error codes:: YAMIBADHANDLE, YAMINOMEMORY.

int yamiGetParamCount(HPARAMSET paramset, int *pparcount);

Gets the number of parameters in the Parameter Set.

Typical error codes:: YAMIBADHANDLE.

int yamiGetType(HPARAMSET paramset, int position,
                enum paramType *ptype);

Gets the type of the parameter at a given position.

Typical error codes:: YAMIBADHANDLE, YAMIOUTOFRANGE.

int yamiSetInt           (HPARAMSET paramset, int position,
                          int ivalue);
int yamiSetByte          (HPARAMSET paramset, int position,
                          char cvalue);
int yamiSetDouble        (HPARAMSET paramset, int position,
                          double dvalue);
int yamiSetBinary        (HPARAMSET paramset, int position,
                          const char *pbuf, int bufsize);
int yamiSetBinaryShallow (HPARAMSET paramset, int position,
                          const char *pbuf, int bufsize);
int yamiSetString        (HPARAMSET paramset, int position,
                          const char *pstr);
int yamiSetStringShallow (HPARAMSET paramset, int position,
                          const char *pstr);
int yamiSetWString       (HPARAMSET paramset, int position,
                          const wchar_t *pwstr);
int yamiSetWStringShallow(HPARAMSET paramset, int position,
                          const wchar_t *pwstr);

Set a value of appropriate type in a Parameter Set at a given position.
The yamiSetXXXShallow functions allow to set a parameter value without copying the data - only the pointers to the given buffer are set up in the Parameter Set. The user should not make any changes to the buffers used in this way through the lifetime of the Parameter Set object.

Typical error codes:: YAMIBADHANDLE, YAMINOMEMORY, YAMIOUTOFRANGE.

int yamiGetInt   (HPARAMSET paramset, int position,
                  int *pivalue);
int yamiGetByte  (HPARAMSET paramset, int position,
                  char *pcvalue);
int yamiGetDouble(HPARAMSET paramset, int position,
                  double *pdvalue);

Retrieve the value from the Parameter Set, from the specified position.

Typical error codes:: YAMIBADHANDLE, YAMIOUTOFRANGE, YAMIBADTYPE.

int yamiGetBinarySize  (HPARAMSET paramset, int position,
                        int *psize);
int yamiGetBinaryValue (HPARAMSET paramset, int position,
                        char *pbuf);
int yamiGetBinaryBuffer(HPARAMSET paramset, int position,
                        const char **ppbuf);

Retrieve the size of the binary data in a parameter and the data itself. The buffer of the appropriate size should be allocated by the client calling the yamiGetBinaryValue function.

Typical error codes:: YAMIBADHANDLE, YAMIOUTOFRANGE, YAMIBADTYPE.

int yamiIsASCIIString(HPARAMSET paramset, int position,
                      int *isascii);

Checks if the parameter is a plain, narrow ASCII string. If yes, *isascii will have value 1 or 0 otherwise.

int yamiGetStringLength(HPARAMSET paramset, int position,
                        int *plength);
int yamiGetStringValue (HPARAMSET paramset, int position,
                        char *pbuf);
int yamiGetStringBuffer(HPARAMSET paramset, int position,
                        const char **ppbuf);

Retrieve the length (number of characters, without terminating zero) of the string in a parameter and the string itself. The buffer of the appropriate size (length + place for terminating zero) should be allocated by the client calling the yamiGetStringValue function.

Typical error codes:: YAMIBADHANDLE, YAMIOUTOFRANGE, YAMIBADTYPE.

int yamiGetWStringLength(HPARAMSET paramset, int position,
                         int *plength);
int yamiGetWStringValue (HPARAMSET paramset, int position,
                         wchar_t *pbuf);
int yamiGetWStringBuffer(HPARAMSET paramset, int position,
                         const wchar_t **ppbuf);

Retrieve the length (number of characters, without terminating zero) of the wide string in a Parameter Set and the string itself. The buffer of the appropriate size (length + place for terminating zero) should be allocated by the client calling the yamiGetWStringValue function.

Typical error codes:: YAMIBADHANDLE, YAMIOUTOFRANGE, YAMIBADTYPE.

Note:
It is perfectly possible to set a value as a String and retrieve it as a WString.
It is possible to set a value as a WString and retrieve it as a String only if the value set does not contain characters outside of the ASCII range.
In both cases, the Parameter Set object performs the conversion.

int yamiGetPackedSize     (HPARAMSET paramset, int *packedsize);
int yamiGetPacked         (HPARAMSET paramset, char *pbuf);
int yamiCreatePSFromPacked(HPARAMSET *pps, int levelno,
                           const char *pbuf, int swap);

Pack the Parameter Set into the sequence of bytes that is appropriate for further transmission (the so-called marshalling) and create the Parameter Set from the sequence of bytes.
The buffer of the appropriate size should be allocated by the client calling this function.
The levelno parameter declares the level of YAMI specification. If the byte sequence doesn't conform to this level, the YAMIPARSEERROR will be reported.
If the swap parameter is non-zero, the bytes representing multi-byte data (like integer values) will be swapped to the reverse order.
These functions are not supposed to be called by the client code, although users can achieve some persistence functionality with them.

Typical error codes:: YAMIBADHANDLE, YAMINOTINITIALIZED, YAMINOMEMORY, YAMIPARSEERROR.

int yamiCheckRawBuffer(int levelno, const char *pbuf, int swap);

Checks if the buffer contains a valid data for a Parameter Set.
The levelno parameter declares the level of YAMI specification.
This function is not supposed to be called by the client code.

Typical error codes:: YAMIPARSEERROR.

Agent

Agent is responsible for routing, sending and receiving messages over the network. Conceptually, it is similar to the ORB in CORBA systems.

The Agent object is created in (almost) every program that uses the YAMI library, no matter if the given component acts as a client or as a server in the distributed system.

The multi-threading abilities (and other things that can vary between different Agents) of the Agent object greatly depend on the parameters that are provided during its creation - these parameters are called Policies.

In order to use Agent functionality, the user code has to include yamic.h header.

Helper definitions

enum eAgentLevel
{
     eLevel1 = 1,
     eLevel2 = 2
};

Enums defining levels of typing, for better verbosity where the level parameter is required.

Policies

struct yamipolicies
{
     int agentlevel;    /*       2 */
     int objqmaxlength; /*      10 */
     int objqmaxsize;   /* 1048576 */
     int dispatchers;   /*       1 */
     int hassender;     /*       1 */
     int sqmaxlength;   /*     256 */
     int sqmaxsize;     /* 1048576 */
     int connpoolsize;  /*      10 */
     int sendtries;     /*       5 */
     int hassocket;     /*       1 */
     int reuseaddr;     /*       0 */
     int hasreceiver;   /*       1 */
     int haswaker;      /*       1 */
     int mtuser;        /*       1 */
};

Set of Policies that can be passed during the Agent's creation. Meaning of the Policies (the default values are shown in comments above):

agentlevel: The level of the YAMI specification that this Agent will conform to. The Agent will not send nor receive messages from incompatible levels.
objqmaxlength: The maximum length of the queue that is kept for each registered object. If the queue is full with respect to this parameter and there is new incoming message for the given object, it will be rejected with eOverflow notification sent to the remote site (to the Agent that sent the message).
objmaxsize: The maximum size of the same queue (in bytes).
dispatchers: The number of threads that the Agent will use for message dispatching. If set to 1, all the calls to servants will be serialized, even if there are registered many different passive objects. If this parameter is more than 1, the user code has to assure that the servants are safe with respect to multiple threads. If set to 0, the calls to passive objects are made directly by the receiver module.
hassender: The flag stating if the separate sender thread is needed. If set to non-zero value, the sender thread takes care of all the packets that need to be sent to the remote Agents. If set to 0, the sender thread is not created and the sending is performed directly in the context of requesting thread.
sqmaxlength: The maximum length of queue for sender thread.
sqmaxsize: The maximum size of the same queue.
connpoolsize: The size of the connection pool (applies both to sending and receiving connections).
sendtries: The number of times the sender module should try to send the packet before giving up (and reporting an error), if there is a network problem.
hassocket: The flag stating if the Agent should create the listening socket. If set to zero, no receiving will be possible (this option can be useful for lightweight Agents that are created for one-way messaging).
reuseaddr: The flag stating if the Agent's listening socket should be created with the SO_REUSEADDR option (when the flag has non-zero value). This policy can be useful for Agents that are frequently created an destroyed on the same port.
hasreceiver: The flag stating if the separate receiver thread is needed. If set to non-zero value, the hassocket flag should be non-zero, too.
haswaker: The flag stating if the waker module is needed. The waker module requires a separate thread for its own and in some lightweight configurations is not necessary.
mtuser: The flag stating if the user code is multi-threaded. If the value is non-zero, the internal synchronization is provided so that all the Agent's functions are thread-safe. In single-threaded code, setting this value to 0 causes the Agent to bypass the internal synchronization whenever possible.

void yamiGetDefaultPolicies(struct yamipolicies *ppolicies);

Fills the Policies structure with the default values.

General API

typedef void* HYAMIAGENT;

Type of the handle to an Agent object.
The handle is opaque to the client.

int yamiCreateAgent(HYAMIAGENT *pagent, int port,
                    struct yamipolicies *ppolicies);

Creates a new Agent (and thus - new domain), working on the given IP port and with the given set of Policies.
If the ppolicies is NULL, the default values are used.

Typical error codes:: YAMIOUTOFRANGE, YAMINETERROR.

int yamiDestroyAgent(HYAMIAGENT agent);

Destroys the Agent and all its internal structures.

Typical error codes:: YAMIBADHANDLE.

Domains management

int yamiAgentDomainRegister(HYAMIAGENT agent,
                            const char *name, const char *addr,
                            int port, int level);
int yamiAgentDomainUnregister(HYAMIAGENT agent,
                              const char *name);

Registers and unregisters a domain in the Agent's private domain set.
name will identify the new entry in the address book.
addr is the network address; it can have a ``xxx.xxx.xxx.xxx'' form (for example "10.1.12.13") or a human-readable form (for example "comp.company.com").
port is a port number of the destination Agent.
level is a level understandable by the destination Agent.

Typical error codes:: YAMIBADHANDLE,
YAMICANNOTRESOLVEADDRESS, YAMINOTFOUND.

Objects management

enum objectType
{
     polling,
     passive_singlethreaded,
     passive_multithreaded
};

Types of objects registered in the Agent.

polling: The object is responsible for asking the Agent for incoming messages.
passive_singlethreaded: The object will be up-called for each incoming message, but no more than one thread at a time will perform up-calls in case of many messages waiting in a queue.
passive_multithreaded: Like the previous, but possibly more than one of the Agent's threads can perform up-calls when many messages arrive.

typedef void (*DISPFUNCTION)(HINCMSG inc);

Type of the dispatch function, which will be called for a given object (if registered as passive) when the incoming message arrives.
The message will be considered rejected, unless the dispatch function has processed the message in some way. It means, that if the dispatch function did not process the message, it will be automatically rejected and the client (calling object) will receive appropriate notification.
The incoming message structure (handled by inc) is owned by the Agent, so the dispatch function should not release it by itself.
See later for description of HINCMSG handle.

#define YAMI_ANY_OBJECT NULL

The generic name which allows to register objects that will accept messages, when no other object name can match the object name in the message sent.
This facility is provided for implementing default objects.

int yamiAgentObjectRegister(HYAMIAGENT agent, const char *name,
                            enum objectType otype,
                            DISPFUNCTION df, void *hint);

Registers new object.
name is the object's name or YAMI_ANY_OBJECT. Only messages that have the destination object name matching with this parameter will be queued.
If the type is polling, then the df parameter is ignored. For passive\_{}... objects, it's the address of the function to call for each incoming message.
hint is a parameter that can be retrieved with each incoming message using yamiAgentIncomingMsgGetHint function.

Typical error codes:: YAMIBADHANDLE.

int yamiAgentObjectUnregister(HYAMIAGENT agent,
                              const char *name);

Unregisters the object. This means, that all waiting messages for this object (and all new that will be received) will be discarded with the unknown object reply message.

Typical error codes:: YAMIBADHANDLE, YAMINOTFOUND.

Sending new messages

typedef void* HMESSAGE;

Type of the handle to a message object.
The handle is opaque to the client.

enum msgStatus
{
     ePosted,
     ePending,
     eReplied,
     eRejected,
     eUnknownObj,
     eOverflow,
     eNetError,
     eTimedOut,
     eRejectByAgent
};

The states that the message sent can be in.

ePosted: The message was posted to the queue owned by the sender thread.
ePending: The message was successfully sent over the network.
eReplied: There is a reply available for the given message.
eRejected: The message was rejected by the remote object (but was received).
eUnknownObj: The message was rejected by the remote Agent, because no object was registered with a matching name.
eOverflow: The message was rejected by the remote Agent, because of the overflow in the remote object's queue.
eNetError: The message was not successfully sent over the network.
eTimedOut: The message was timed out by the waker module.
eRejectByAgent: The message was rejected by the destination Agent. This may happen if the message with the parameter set of Level2 was sent to the Agent running on Level1.

#define YAMI_THIS_DOMAIN NULL

This is the name that always corresponds to the same Agent through which the message is being sent.
This facility is provided for setting up the communication between objects living in the same domain.
Registering the domain with the same address and IP port as the Agent and sending the message using the name of that domain also works. In both cases, the shortcut routing will be performed.

int yamiAgentMsgSend(HYAMIAGENT agent, const char *domainname,
                     const char *objectname,
                     const char *messagename,
                     HPARAMSET paramset, HMESSAGE *phm);

Sends new message.
domainname is a name of the registered domain, where the message will be sent. It can be YAMI_THIS_DOMAIN.
objectname is a name of the remote object.
messagename is a name of the message being sent.
paramset is a handle to the Parameter Set that will be sent together with the message.
phm will receive the handle to the message structure. The client code can use this handle for retrieving the message status, the replies, and so on. If this parameter is NULL, no message structure is created and the message is of type one-way.

Typical error codes:: YAMIBADHANDLE.

int yamiAgentMsgSendAddr(HYAMIAGENT agent,
                     const char *addr, int port, int level,
                     const char *objectname,
                     const char *messagename,
                     HPARAMSET paramset, HMESSAGE *phm);

Sends new message to explicitly given address.
addr is the network address; it can have a ``xxx.xxx.xxx.xxx'' form (for example "10.1.12.13") or a human-readable form (for example "comp.company.com").
port is a port number of the destination Agent.
level is a level understandable by the destination Agent. objectname is a name of the remote object.
messagename is a name of the message being sent.
paramset is a handle to the Parameter Set that will be sent together with the message.
phm will receive the handle to the message structure. The client code can use this handle for retrieving the message status, the replies, and so on. If this parameter is NULL, no message structure is created and the message is of type one-way.

Typical error codes:: YAMIBADHANDLE.

int yamiAgentSetUpTimeOut(HMESSAGE message, int timeout);

Sets the timeout for a given message.
timeout holds the number of seconds, after which the waker module will set the status of the message to eTimedOut (provided that the status of the message was still in the ePosted or ePending state).
This function allows to write recovery code for clients that without it would wait forever for replies.
This function does not have to be used (but can) when the client periodically polls for the message's status and can decide by itself that the timeout expired, but can be of great help for clients that decide to wait until the reply arrives.

Typical error codes:: YAMIBADHANDLE, YAMIOUTOFRANGE.

int yamiAgentMsgGetStatus(HMESSAGE hm, enum msgStatus *status);

Retrieves the message's status.

Typical error codes:: YAMIBADHANDLE.

int yamiAgentMsgWait(HMESSAGE hm);

This function blocks the calling thread until the status of the message changes to one of the codes: eReplied, eRejected, eUnknownObj, eOverflow, eNetError, eTimedOut or eRejectByAgent.
When this happens for any reason, the calling thread wakes up and should check for the message's status.
Clients calling this function should consider also yamiAgentSetUpTimeOut, because without it, the yamiAgentMsgWait can block forever (which can happen when the remote object crashes in the middle of processing).

Typical error codes:: YAMIBADHANDLE.

int yamiAgentMsgGetResponse(HMESSAGE hm, HPARAMSET *pps);

This function retrieves the Parameter Set that was sent back by the remote object.

Typical error codes:: YAMIBADHANDLE, YAMINOTAVAILABLE.

int yamiAgentMsgDestroy(HMESSAGE hm);

Destroys the message structure.

Typical error codes:: YAMIBADHANDLE.

Incoming messages

typedef void* HINCMSG;

Type of the handle to an incoming message object.
The handle is opaque to the client.

int yamiAgentIncomingMsgGetNext(HYAMIAGENT agent,
                                const char *objname,
                                HINCMSG *pinc, int wait);

This function gets the new incoming message for an object designated by the objname.
pinc will receive the handle to the incoming message structure, which can be used for retrieving the name of the message, its Parameter Set or to reply to it.
If the wait parameter is 0, this function will return immediately with the code YAMINOTAVAILABLE, when there is no incoming message for the given object and will wait if the wait is non-zero.

Typical error codes:: YAMIBADHANDLE, YAMINOTAVAILABLE.

int yamiAgentIncomingMsgGetMsgName(HINCMSG inc,
                                   const char **pname);

Gets the name of the message.

Typical error codes:: YAMIBADHANDLE.

int yamiAgentIncomingMsgGetObjectName(HINCMSG inc,
                                      const char **pname);

Gets the name of the object, to which the message was sent.
It can be useful for dispatch function registered for different objects or for objects registered as YAMI_ANY_OBJECT.

Typical error codes:: YAMIBADHANDLE.

int yamiAgentIncomingMsgGetParameters(HINCMSG inc,
                                      HPARAMSET *pps);

Retrieves the Parameter Set that was sent together with the message.
This function can return YAMINOTAVAILABLE if the message was sent without parameters.

Typical error codes:: YAMIBADHANDLE, YAMINOTAVAILABLE.

int yamiAgentIncomingMsgGetLevel(HINCMSG inc, int *levelno);

Retrieves the level of YAMI specification, to which the sending object complies.
It can help to choose the best reply, according to the abilities of the remote (sending) object.

Typical error codes:: YAMIBADHANDLE.

int yamiAgentIncomingMsgGetHint(HINCMSG inc, void **phint);

Retrieves the hint parameter that was set during the object's registration.

Typical error codes:: YAMIBADHANDLE.

int yamiAgentIncomingMsgEat(HINCMSG inc);

Marks the incoming message as already processed. The intent of this is to sink the message in the Agent so that no response (neither reply nor reject) is possible. This function is mainly needed for passive objects for implementing the one-way message semantics (so that the message is sent and received but no return information is sent to the originating object).

Typical error codes:: YAMIBADHANDLE.

int yamiAgentIncomingMsgReject(HINCMSG inc);

Marks the incoming message as rejected. No further processing (for example sending reply) will be possible.

Typical error codes:: YAMIBADHANDLE.

int yamiAgentIncomingMsgReply(HINCMSG incoming,
                              HPARAMSET paramset);

Sends the reply, together with the Parameter Set to the remote object.

Typical error codes:: YAMIBADHANDLE.

int yamiAgentIncomingMsgForward(HINCMSG inc,
                                const char *domainname,
                                const char *objectname,
                                const char *messagename,
                                HPARAMSET paramset);

Forwards the incoming message to the object designated by objectname to the domain registered as domainname.
It is possible to change the name of the message and its Parameter Set. This can be useful for load-balancing, routers or adapters.

Typical error codes:: YAMIBADHANDLE.

int yamiAgentIncomingMsgForwardAddr(HINCMSG inc,
                                const char *domainaddr,
                                int domainport,
                                int domainlevel,
                                const char *objectname,
                                const char *messagename,
                                HPARAMSET paramset);

Forwards the incoming message to the object designated by objectname to the domain with explicitly given address.
domainaddr is the network address of the destination domain; it can have a ``xxx.xxx.xxx.xxx'' form (for example "10.1.12.13") or a human-readable form (for example "comp.company.com").
domainport is a port number of the destination Agent.
domainlevel is a level understandable by the destination Agent. objectname is a name of the remote object.
messagename is a name of the message being sent.
paramset is a handle to the Parameter Set that will be sent together with the message.
It is possible to change the name of the message and its Parameter Set. This can be useful for load-balancing, routers or adapters.

Typical error codes:: YAMIBADHANDLE.

int yamiAgentDestroyIncomingMsg(HINCMSG inc);

Destroys the incoming message structure.

Typical error codes:: YAMIBADHANDLE.

Additional functions

int yamiEasySend(const char *address, int port, int level,
                 const char *objectname, const char *messagename,
                 HPARAMSET paramset);

Creates an ad-hoc lightweight Agent and sends a one-way message to the given domain and object.
The Agent created for sending the message is immediately destroyed, so this function is provided for convenience where messages are sent rarely or where the performance of communication infrastructure is of no concern. For purposes where many messages are sent to remote objects, it is preferred to create full Agent object once and use it for sending many messages.

Typical error codes:: YAMIBADHANDLE, YAMINETERROR.

int yamiAgentGetLocalAddress(HYAMIAGENT agent, char *pbuf);

Writes in the provided buffer the local network address in the standard form xxx.xxx.xxx.xxx.
It can be useful for objects that need to pass their location to remote objects.

Typical error codes:: YAMIBADHANDLE.

int yamiAgentProcessEvent(HYAMIAGENT agent, int timeout);

Processes the single event on the listening socket or on the receiving connection pool. The function returns after the timeout milliseconds with the YAMINOTAVAILABLE code if there is no incoming connection. The negative value of the timeout causes the function to block until there is some incoming packet to process. The incoming packet is processed in the same way as by the receiver thread - in fact, this function implements one iteration of the receiving module. It is provided for those who want to have complete control everywhere.
This function requires that the Agent has a listening socket, but no receiver thread (see policies).

Note: In explicit event loop, the responsiveness of the Agent (as seen by other communicating components) depends on the frequency of event processing. This function is supposed to be used in tight loops.

Typical error codes:: YAMIBADHANDLE, YAMINOSUCHSERVICE.

int yamiNetInitialize(void);
int yamiNetCleanup(void);

Perform the network initialization and cleanup on platforms which require this (for example Windows).
They are empty functions otherwise, but programmers should use them anyway as a mean of writing portable code.
These functions can be omitted if the client code does perform required initialization by itself (because it uses the network for other purposes).

Typical error codes:: YAMINETERROR.

Synchronization Primitives

The synchronization primitives are provided for convenience and to help resolve problems that naturally arise in multi-threading environments. In YAMI, multi-threading can be a consequence of using passive objects, especially in combination with multiple dispatching threads. Users of the YAMI library can use any set of synchronization primitives from any other library (including the native primitives available on the specific platform). In this context, the synchronization primitives in the YAMI core library are provided only for completeness.

In order to use synchronization functionality, the user code has to include yamisynchro.h header.

typedef void* HMUTEX;
typedef void* HSEMAPHORE;

Types of the handles to mutex and semaphore objects.
The handles are opaque to the client.

int yamiCreateMutex(HMUTEX *pm);
int yamiDestroyMutex(HMUTEX m);

Creates and destroys the mutex object.

Typical error codes:: YAMISYNCHROERROR.

int yamiMutexLock(HMUTEX m);
int yamiMutexUnlock(HMUTEX m);

Locks and unlocks the mutex object.

Typical error codes:: YAMIBADHANDLE, YAMISYNCHROERROR.

int yamiCreateSemaphore(HSEMAPHORE *ps, int initval);
int yamiDestroySemaphore(HSEMAPHORE s);

Creates and destroys the semaphore object.
initval is the initial value of the semaphore object.

Typical error codes:: YAMISYNCHROERROR.

int yamiSemaphoreAcquire(HSEMAPHORE s);
int yamiSemaphoreTryAcquire(HSEMAPHORE s);
int yamiSemaphoreRelease(HSEMAPHORE s);

Standard p and v operations on the semaphore object.
If the semaphore is not available, the yamiSemaphoreTryAcquire function returns YAMINOTAVAILABLE.

Typical error codes:: YAMIBADHANDLE, YAMISYNCHROERROR,
YAMINOTAVAILABLE.

int yamiSleep(int timeout);

Stops the calling thread for timeout milliseconds. The value 0 causes the calling thread to stop for infinite period of time.

Typical error codes:: YAMISYNCHROERROR.

Error Codes

With very small exceptions, all the YAMI core library functions return some error code.

All error codes are preprocessor macros with integer values and are divided into two groups:

logic errors - these are programming errors that result from wrong usage of the YAMI library
run-time errors - these are errors that result from factors that are outside of the YAMI library, for example network problems, memory shortages, etc.

In order to use the YAMI error codes, the user code needs to include yamierrors.h header.

const char * yamiErrorString(int cc);

Returns a human-readable description of a given error code.
If the code is not defined, returns NULL pointer.
This function can help in debugging.

YAMIOK

No error. The operation completed successfully.

Logic error codes

YAMIISLOGICERROR(e)

The macro that resolves to 1 if the provided error code is in the logic errors group and 0 otherwise.

YAMIBADHANDLE

This is returned when the handle passed is invalid (has a NULL value) or points to the object of unexpected type.

YAMIOUTOFRANGE

This is returned when the argument passed is out of the valid range, for example when referring to the parameter position in a Parameter Set.

YAMICANNOTINITIALIZETWICE

This error code is no longer used.

YAMIBADTYPE

This is returned when there is a request for a parameter in a Parameter Set that has incompatible type. For example, the parameter holds the integer value and the double was requested.

YAMINOTINITIALIZED

This is returned while trying to pack the Parameter Set where not all parameters were already initialized or when the user tries to retrieve the parameter value that was not yet set.

YAMIALREADYREGISTERED

This is returned while trying to register a domain or object with the name that was already registered.

YAMINOTFOUND

This is returned when looking up unknown entity (for example domain or object that was not registered).

YAMIQUEUEEMPTY

This is returned when trying to pop a packet while the queue is empty.
This error is used internally and should never appear in the user code.

YAMIPARSEERROR

This is returned when trying to parse an invalid packet.

YAMICANNOTPROCESSTWICE

This is returned while trying to reply a second time to the same incoming message or to reply when the message was already rejected, eaten, etc.

YAMIBADLENGTH

This is returned when the user code provides parameters (especially string or binary values), which lengths are outside of the YAMI specification.

YAMINOSUCHSERVICE

This is returned when the client code tries to use a feature that was not provided. For example, when the user creates an Agent object without the waker module and later tries to set up time-outs on some message.

Run-time error codes

YAMIISRUNTIMEERROR(e)

The macro that resolves to 1 if the provided error code is in the run-time errors group and 0 otherwise.

YAMINOTAVAILABLE

This can be returned when a resource (for example semaphore) cannot be acquired without blocking and the non-blocking operation was requested. This error can also appear when trying to fetch the new incoming message and there is no message or when trying to get the response for the message sent and there is no response, etc.

YAMINOMEMORY

This is returned when memory allocation was not successful.

YAMICANNOTRESOLVEADDRESS

This is returned when the network address cannot be resolved to the 4-byte IP address, for example during domain registration.

YAMIBADADDRTYPE

This is returned when the network address resolution returned address of type other than AF_INET.

YAMICANNOTSTARTTHREAD

This is returned when there was a (platform-dependent) error while trying to start a new thread.

YAMITHREADERROR

This is returned when there was an unspecified threading error.

YAMISYNCHROERROR

This is returned when there was an unspecified (and platform-dependent) synchronization error.

YAMINETERROR

This is returned when there was an unspecified (and platform-dependent) network error.

YAMIOVERFLOW

This is returned for example while trying to push an element to the queue if it would break the queue's limits. The client code can see this error when trying to send a new message and there is no place in the sender thread's queue.

YAMIINTERNAL

This indicates a serious internal error, caused for example by synchronization or network problems in one of the Agent's threads. Agent returning this error cannot be used anymore and there is possible resource leak.

YAMINOHANDSHAKE

This indicates the lack of handshake in the network communication. The client code should never see this error.

YAMI Constants

The YAMI specification and the YAMI core library depend on some specific constant values, like the maximum length of the message name, the default size of connection pool, etc. Some of those values are defined by the YAMI specification and every implementation should comply to these values. The defaults are not so restricted - moreover, they are often arbitrarily chosen and other developers could have chosen them differently. The yamilimits.h header contains all the constants used by the YAMI core library.

The user is allowed to change the definitions in this header file and recompile the library, but it is important to note that Agents compiled with different limits may have communication problems.

Specification constants

#define MAXPARAMSETSIZE 1048576

Maximum size (in bytes) of the Parameter Set after packing to the sequence of bytes.

#define MAXPARAMSIZE      65536

Maximum size of a single parameter raw data. This value affects the variable-length types: strings, wide strings and binary objects.

#define MAXPARAMS         65536

Maximum number of parameters in a Parameter Set.

#define MAXNAMELEN          256

Maximum length of a name (message or object; it is also used to limit the length of domain name, although it is not defined in the specification).

Default values

#define YAMIDEFAULT_AGENTLEVEL          2
#define YAMIDEFAULT_OBJQMAXLENGTH      10
#define YAMIDEFAULT_OBJQMAXSIZE   1048576
#define YAMIDEFAULT_DISPATCHERS         1
#define YAMIDEFAULT_HASSENDER           1
#define YAMIDEFAULT_SQMAXLENGTH       256
#define YAMIDEFAULT_SQMAXSIZE     1048576
#define YAMIDEFAULT_CONNPOOLSIZE       10
#define YAMIDEFAULT_SENDTRIES           5
#define YAMIDEFAULT_HASSOCKET           1
#define YAMIDEFAULT_REUSEADDR           0
#define YAMIDEFAULT_HASRECEIVER         1
#define YAMIDEFAULT_HASWAKER            1
#define YAMIDEFAULT_MTUSER              1

These constants affect the default values that are assigned to the Agent's Policies.

Compilation options and possible problems

The following compilation options are provided:

Compilation for non-threaded platforms

It is possible to compile the library without the need to link with pthreads. To do this, define the YAMI_NO_THREADS identifier as a compilation flag when compiling the library. This, of course, influences the functionality of the library:

It is not possible to have additional threads in the Agent: the policies dispatchers, hassender, hasreceiver, haswaker and mtuser should be set to 0 when the Agent is constructed. As a result, the explicit event loop is the only possibility to get the incoming messages processed.
It is not possible to call any function that has blocking semantics implied. For example, it is not possible to wait until there is a message for given object (only non-blocking polling or direct dispatch is possible) or until there is a reply for a message. Any attempt to use the blocking functions will result in error YAMINOSUCHSERVICE or YAMISYNCHROERROR.
It is not possible to use synchronization primitives provided with the library (and there would be hardly any reason to use them anyway).

This option is provided for those who want to experiment with YAMI on platforms that do not implement threading in the form of pthreads library (for example, old Unix or some embedded systems) and for those who want minimal builds.

This flag should not be used when compiling Python or Tcl modules.

The YAMI_NO_THREADS flag can be used on MS Windows, but there is no reason to do so.

Maciej Sobczak 2003-10-08