#ifndef AL_EVENT_H
#define AL_EVENT_H

#include "AL/al.h"
#include "AL/alc.h"

struct EffectState;


enum {
    /* End event thread processing. */
    EventType_KillThread = 0,

    /* User event types. */
    EventType_SourceStateChange = 1<<0,
    EventType_BufferCompleted   = 1<<1,
    EventType_Error             = 1<<2,
    EventType_Performance       = 1<<3,
    EventType_Deprecated        = 1<<4,
    EventType_Disconnected      = 1<<5,

    /* Internal events. */
    EventType_ReleaseEffectState = 65536,
};

struct AsyncEvent {
    unsigned int EnumType{0u};
    union {
        char dummy;
        struct {
            ALuint id;
            ALenum state;
        } srcstate;
        struct {
            ALuint id;
            ALsizei count;
        } bufcomp;
        struct {
            ALenum type;
            ALuint id;
            ALuint param;
            ALchar msg[232];
        } user;
        EffectState *mEffectState;
    } u{};

    AsyncEvent() noexcept = default;
    constexpr AsyncEvent(unsigned int type) noexcept : EnumType{type} { }
};


void StartEventThrd(ALCcontext *ctx);
void StopEventThrd(ALCcontext *ctx);

#endif

#ifndef AL_EVENT_H
#define AL_EVENT_H

#include "AL/al.h"
#include "AL/alc.h"

struct EffectState;


enum {
    /* End event thread processing. */
    EventType_KillThread = 0,

    /* User event types. */
    EventType_SourceStateChange = 1<<0,
    EventType_BufferCompleted   = 1<<1,
    EventType_Error             = 1<<2,
    EventType_Performance       = 1<<3,
    EventType_Deprecated        = 1<<4,
    EventType_Disconnected      = 1<<5,

    /* Internal events. */
    EventType_ReleaseEffectState = 65536,
};

struct AsyncEvent {
    unsigned int EnumType{0u};
    union {
        char dummy;
        struct {
            ALuint id;
            ALenum state;
        } srcstate;
        struct {
            ALuint id;
            ALsizei count;
        } bufcomp;
        struct {
            ALenum type;
            ALuint id;
            ALuint param;
            ALchar msg[1008];
        } user;
        EffectState *mEffectState;
    } u{};

    AsyncEvent() noexcept = default;
    constexpr AsyncEvent(unsigned int type) noexcept : EnumType{type} { }
};


void StartEventThrd(ALCcontext *ctx);
void StopEventThrd(ALCcontext *ctx);

#endif

--- 
+++ 
@@ -39,7 +39,7 @@
             ALenum type;
             ALuint id;
             ALuint param;
-            ALchar msg[1008];
+            ALchar msg[232];
         } user;
         EffectState *mEffectState;
     } u{};
Reduce the AsyncEvent struct size

The "user" message length is significantly reduced to fit the struct in 256
bytes, rather than 1KB.
