Memory Buffer Logging

Data Structures
struct	LogMembufData

Typedefs
typedef struct LogMembufData	LogMembufData

Functions
LogMembufData *	logmembufCreate (uint32 size)
LogDest *	logmembufRegister (int maxlevel, LogCategory *catfilter, LogMembufData *membuf)
LogDest *	logmembufRegisterWithDefer (int maxlevel, LogCategory *catfilter, LogMembufData *membuf, LogDest *deferdest)
void	logmembufMsgFunc (int level, LogCategory *cat, int64 timestamp, strref msg, uint32 batchid, void *userdata)
void	logmembufCloseFunc (void *userdata)

Detailed Description

Memory buffer logging destination that writes log messages to a fixed-size circular buffer in memory. Useful for debugging, testing, and capturing logs in memory-constrained environments. When the buffer fills, new messages wrap around and overwrite the oldest entries.

Basic Usage:

// Create 4KB buffer
LogMembufData *lmd = logmembufCreate(4096);
LogDest *dest = logmembufRegister(LOG_Debug, NULL, lmd);
 
// Log some messages
logStr(Info, _S"Test message");
logFlush();
 
// Access the buffer contents directly
printf("Buffered logs:\n%.*s\n", (int)lmd->cur, lmd->buf);
 
// Cleanup
logUnregisterDest(dest);

Typedef Documentation

LogMembufData

typedef struct LogMembufData LogMembufData

Memory buffer log destination state

Contains the circular buffer and current write position. When cur reaches size, new messages wrap to the beginning. The buffer is null-terminated when possible.

Function Documentation

logmembufCloseFunc()

void logmembufCloseFunc

(

void *

userdata

)

Cleanup callback for memory buffer destinations

Frees the buffer and releases resources.

Parameters

userdata

LogMembufData pointer from logmembufCreate()

logmembufCreate()

LogMembufData * logmembufCreate

(

uint32

size

)

Create a memory buffer log destination

Allocates a fixed-size circular buffer for log messages. The buffer uses a compact format with timestamps and single-character log levels. Messages longer than the buffer size are truncated.

Parameters

size	Buffer size in bytes

Returns

Memory buffer handle, or NULL on allocation failure

LogMembufData *lmd = logmembufCreate(8192);  // 8KB buffer

logmembufMsgFunc()

void logmembufMsgFunc	(	int	level,
		LogCategory *	cat,
		int64	timestamp,
		strref	msg,
		uint32	batchid,
		void *	userdata
	)

Log message callback for memory buffer destinations

Formats and writes a log message to the circular buffer. Uses a compact format: "YYYYMMDD HHMMSS L [Category]: Message\n"

Parameters

level	Log severity level
cat	Category, or NULL for default
timestamp	Wall clock timestamp
msg	Log message text
batchid	Batch identifier (unused)
userdata	LogMembufData pointer from logmembufCreate()

logmembufRegister()

LogDest * logmembufRegister	(	int	maxlevel,
		LogCategory *	catfilter,
		LogMembufData *	membuf
	)

Register a memory buffer destination with the logging system

Registers the memory buffer as a log destination. Messages will be formatted in a compact style and written to the circular buffer. The buffer destination will be automatically cleaned up when unregistered.

Parameters

maxlevel	Maximum log level to write to buffer
catfilter	Category filter, or NULL for all non-private categories
membuf	Memory buffer handle from logmembufCreate()

Returns

Destination handle for later unregistration, or NULL on failure

logmembufRegisterWithDefer()

LogDest * logmembufRegisterWithDefer	(	int	maxlevel,
		LogCategory *	catfilter,
		LogMembufData *	membuf,
		LogDest *	deferdest
	)

Register a memory buffer destination and flush deferred logs

Atomically registers a memory buffer destination while flushing previously deferred logs to it. Useful for capturing early startup logs in memory before other destinations are available.

Parameters

maxlevel	Maximum log level to write to buffer
catfilter	Category filter, or NULL for all non-private categories
membuf	Memory buffer handle from logmembufCreate()
deferdest	Deferred destination to flush (destroyed during this call)

Returns

Destination handle for later unregistration, or NULL on failure

// Early startup - defer logs
LogDeferData *deferdata = logDeferCreate();
LogDest *deferdest = logDeferRegister(LOG_Info, NULL, deferdata);
 
// Later - create memory buffer and transfer logs
LogMembufData *lmd = logmembufCreate(4096);
LogDest *dest = logmembufRegisterWithDefer(LOG_Info, NULL, lmd, deferdest);