Manage synchronized semaphores

README.md

@@ -5,7 +5,7 @@ BLC channel
 - Author    : [Arnaud Blanchard](http://arnaudblanchard.thoughtsheet.com)  
 - Licence   : [CeCILL v2.1](http://www.cecill.info/licences/Licence_CeCILL_V2-en.html)  
 
-Functions to easily share data through shared memory (shm_... functions). The advantage is that it is the fastest and the more econom in memory ( no copy in each process ) way to share informtation between processes. At this moment it only works in asynchronous mode.
+Functions to easily share data through shared memory (shm_... functions). It is the fastest, and the more econom in memory ( no copy in each process ), way to share informtation between processes. At this moment it only works in asynchronous mode.
 
 The idea is that you have a structure blc_channel which is like a blc_array ( https://framagit.org/blaar/blc_core/blob/master/t_array/main.cpp ) but has a name starting with '/' to identificate it on your system.
 
@@ -50,6 +50,24 @@ You will see all the existing blc_channels, the process reading or writing and t
 
 On Linux we can see and manipulate a virtual file containing this memory in /run/shm/<name of your shared memory>, on OSX you cannot but anyway it is only used for debug.
 
+Synchronisation
+===============
+
+Two semaphores associated to the shared memory are created:
+
+- `blc_channle<id>_new_data0` which indicates that new data is available on the shared memory
+- `blc_channle<id>_ack_data0` which acknowledges that the data has been read
+
+Proccesses which do not consider synchronisation use starting char '/'
+
+`[writer]/->[reader]` means no synchronization
+
+`[writer].->[reader]` means the reader waits for new data from the writer
+
+`[writer]^->[reader]` means the writer waits for the reader to read and acknowledge the data
+
+`[writer]:->[reader]` means both direction synchronization. The writer waits for acknowledgement and the reader wait for new data from the writer.
+ 
 
 C/C++ documentation
 ===================

include/blc_channel.h

@@ -44,24 +44,11 @@ Shared memory are opened with POSIX shm_open. The file /tmp/blc_channels.txt mai
 ///Defines channel in writting mode ( if memory can be written, we cannot disable reading )
 #define BLC_CHANNEL_WRITE   O_RDWR
 
-///Not yet in use
-#define BLC_CHANNEL_SYNC    4   // O_ACCMODE + 1 First flag after access mode
-///Not yet in use
-#define BLC_CHANNEL_BLOCK   (BLC_CHANNEL_SYNC | 8) //BLOCK has to be SYNC
 ///Size of parameters for a channel description. Parameter is not used at this moment
 #define BLC_PARAMETER_MAX 31
 ///Like EXIT_ON_ERROR but also display all debug informatin about the blc_channel
 #define EXIT_ON_CHANNEL_ERROR(channel, ...) blc_channel_fatal_error(channel, __FILE__, __FUNCTION__, __LINE__, __VA_ARGS__)
 
-///Not yet in use. Structure that will be used for synchronisation.
-typedef struct shared_control{
-    /*  pthread_mutex_t mutex;
-     pthread_cond_t writer_cond, reader_cond;*/
-    int writing, event_id, waitings_nb;
-    uint64_t new_value_flags, readers_flags, reading_flags; //bitfield max 64 blocking_readers;
-    struct timeval write_time;
-}blc_share_control;
-
 ///Extends **blc_array** allowing it to be share among processes through shared memory
 typedef struct blc_channel
 #ifdef __cplusplus
@@ -125,21 +112,38 @@ typedef struct blc_channel
     void remove();
     ///Map the shared memory with the blc_channel
     void map_memory(int mode);
+    
+    void open_semaphores(int create=0);
+
+    
+    /**Post new data if the semaphore exist (otherwise return -1). Return 1, if the data has been used ( sem_new_data busy  which is normal), 0 otherwise ( which means nobody is istening ).*/
+    int post_new_data();
+    /**Post acknoledged data  the semaphore exist (otherwise return -1). Return 1, if the data has been used ( sem_new_data busy which is normal ), 0 otherwise ( which means nobody is checking that).*/
+    int post_ack_data();
+
 
 #else
     {
         blc_array array;// Not beautiful but makes it easy to convert C++ heritage of "class"  in C struct inclusion.
 #endif
-        int id, access_mode, potential_new_data, potential_ack_data;
+        int id, access_mode;
         char name[NAME_MAX+1];
         char parameter[BLC_PARAMETER_MAX+1];
-        int fd, ctrl_fd ; ///< shared memory file descriptor
-        blc_share_control *control; //<Part that we be share in purpose of control
-        sem_t *sem_new_data, *sem_ack_data, *sem_events[2], *sem_var;
-        uint64_t reader_flag;
+        int fd ; ///< shared memory file descriptor
+        sem_t *sem_new_data, *sem_ack_data;
     }blc_channel;
     
     START_EXTERN_C
+    
+    /** Wait until new data is available
+     We use void * to make it ablle to be use in callback*/
+    void blc_channel_wait_new_data(void *channel);
+    
+    /** Wait until sommeone has read and acknoledged the data.
+     We use void * to make it ablle to be use in callback*/
+    void blc_channel_wait_ack_data(void *channel);
+
+    
     /**Used by EXIT_ON_CHANNEL_ERROR*/
      void blc_channel_fatal_error(blc_channel *channel, const char *name_of_file, const char* name_of_function, int numero_of_line, const char *message, ...);
     /**Create a blc_channel with the name, the mode is BLC_CHANNEL_READ or BLC_CHANNEL_WRITE, the type of data UIN8, INT8, UI16, IN16, FL32, FL64. ( default 0:UIN8),
@@ -161,6 +165,11 @@ typedef struct blc_channel
     int blc_channel_get_info_with_name(blc_channel *info, char const *name);
     ///Remove the blc_channel **name**. The other processes using it will still work but no new ones can use it.
     void blc_remove_channel_with_name(char const *name);
+    
+    void blc_channel_post_event();
+
+    void blc_channel_check_for_event(void (*callback)(void*user_data), void *user_data);
+
     END_EXTERN_C
     ///@}
     

src/blc_channel.cpp

@@ -39,13 +39,13 @@
 
 static int blc_channel_id_max = 0;
 
-blc_channel::blc_channel(): access_mode(0), potential_new_data(0), potential_ack_data(0), fd(-1),control(NULL), sem_new_data(NULL), sem_ack_data(NULL){}
+blc_channel::blc_channel(): access_mode(0), fd(-1), sem_new_data(NULL), sem_ack_data(NULL){}
 
 blc_channel::blc_channel(char const *new_name, int mode){
     open(new_name, mode);
 }
 
-blc_channel::blc_channel(char const *new_name, int mode, uint32_t type, uint32_t format, int dims_nb, int length, ...):access_mode(0), potential_new_data(0), potential_ack_data(0), fd(-1),control(NULL), sem_new_data(NULL), sem_ack_data(NULL)
+blc_channel::blc_channel(char const *new_name, int mode, uint32_t type, uint32_t format, int dims_nb, int length, ...):access_mode(0), fd(-1), sem_new_data(NULL), sem_ack_data(NULL)
 {
     va_list arguments;
     
@@ -89,8 +89,7 @@ void blc_channel::fprint_info(FILE *file, int print_id){
     width=fprint_dims(file);
     fprintf(file, "%*c", 32-width, ' ');
     if (strlen(name)==0) EXIT_ON_ERROR("name is empty");
-    if (potential_new_data) fprintf(file, " .%s\n", name+1); //Replace first '/' by @
-    else fprintf(file, " %s\n", name);
+    fprintf(file, " %s\n", name);
 }
 
 //Should use code in common with fscan_info
@@ -125,7 +124,6 @@ int blc_channel::fscan_info(FILE *file, int scan_id){
     data=NULL;
     size=0;
     
-    
     if (scan_id){
         SYSTEM_ERROR_CHECK(ret = fscanf(file, "%d ", &id),-1, "Reading channel id");
         if (ret!=1) EXIT_ON_ERROR("impossible to read id");
@@ -141,12 +139,6 @@ int blc_channel::fscan_info(FILE *file, int scan_id){
     
     if (fscanf(file, " %"STRINGIFY_CONTENT(NAME_MAX)"[^\n]\n", name) != 1) EXIT_ON_ERROR("Impossible to read channel's name of channel id '%d'.", id);
     
-    if (name[0]=='.') {
-        potential_new_data=1;
-        name[0]='/';
-    }
-    else potential_new_data=0;
-    
     if (id > blc_channel_id_max) blc_channel_id_max=id;
     return id;
 }
@@ -164,47 +156,94 @@ void blc_channel::map_memory(int access_mode){
     
     SYSTEM_ERROR_CHECK(data = mmap(0, size, prot, MAP_SHARED, fd, 0), MAP_FAILED,  "Mapping memory of %s (size %ld bytes), fd(%d), prot(%d).", name, size, fd, prot);
     if (data==NULL) EXIT_ON_CHANNEL_ERROR(this, "Fail mapping blc_channel");
+    blc_channel_post_event();
 }
 
+void blc_channel::open_semaphores(int create){
+    char tmp_name[NAME_MAX];
+    
+    sprintf(tmp_name, "blc_channel%d_sem_new_data0", id);
+    
+    if (create) SYSTEM_ERROR_CHECK(sem_new_data = sem_open(tmp_name, O_CREAT | O_EXCL, S_IRWXU, 0), SEM_FAILED, "Creating named semaphore '%s' for blc_channel '%s'", tmp_name, name);
+    else SYSTEM_ERROR_CHECK(sem_new_data = sem_open(tmp_name, NO_FLAG), SEM_FAILED, "Opening named semaphore '%s' for blc_channel '%s'", tmp_name, name);
+    
+    sprintf(tmp_name, "blc_channel%d_sem_ack_data0", id);
+    if (create) SYSTEM_ERROR_CHECK(sem_ack_data = sem_open(tmp_name, O_CREAT | O_EXCL, S_IRWXU, 0), SEM_FAILED, "Creating named semaphore '%s' for blc_channel '%s'", tmp_name, name);
+    else SYSTEM_ERROR_CHECK(sem_ack_data = sem_open(tmp_name, NO_FLAG), SEM_FAILED, "Opening named semaphore '%s' for blc_channel '%s'", tmp_name, name);
+}
 
 ///Create a channel once the blc_array is already defined
 void blc_channel::create(char const *new_name, int access_mode){
     blc_channel info;
     FILE *file;
-    char name_tmp[NAME_MAX];
+    int sync_new_data=0, sync_ack_data=0;
     
     strcpy(parameter, "NDEF");
     STRCPY(name, new_name);
     
-    if (name[0]=='.'){
-        potential_new_data=1;
-        name[0]='/'; //We remove @ which was just to indicate synchronisation.
+    switch (name[0]){
+        case '/':
+            break;
+        case '.':
+            sync_new_data=1;
+            break;
+        case '^':
+            sync_ack_data=1;
+            break;
+        case ':':
+            sync_new_data=1;
+            sync_ack_data=1;
+            break;
+        default:EXIT_ON_ERROR("Blc channel names must start with '/' for asynchrone mode or with '.',';',':' for synchrone mode. But it is '%s'", name);
+            break;
     }
-    else if (new_name[0]!='/') EXIT_ON_ERROR("Blc channel names must start with '/' for asynchrone mode or with '.' for synchrone mode");
+    name[0]='/'; //In any case the name start with '/'
     
     id = blc_channel_get_info_with_name(&info, name);
-    if (id !=-1 ) EXIT_ON_ERROR("The channel '%s' is already referenced in '" BLC_CHANNELS_LIST_PATH"'.\nYou may unlink it before:\n    ./run.sh i_channels --unlink %s", info.name);
+    if (id !=-1 ) EXIT_ON_ERROR("The channel '%s' is already referenced in '" BLC_CHANNELS_LIST_PATH"'.\nYou may unlink it before:\n    blc_channels --unlink %s", info.name);
     if (blc_channel_id_max == BLC_CHANNELS_MAX) EXIT_ON_CHANNEL_ERROR(this, "creation impossible, channel id (%d) too big", blc_channel_id_max);
     else blc_channel_id_max++;
     id = blc_channel_id_max;
     
-    
     SYSTEM_ERROR_CHECK(file=fopen(BLC_CHANNELS_LIST_PATH, "a+"), NULL, "Openning the file '" BLC_CHANNELS_LIST_PATH"' in order to reference the channel '%s'.", name);
     
     fd = shm_open(name, O_CREAT | O_EXCL | access_mode, S_IRWXU); // (O_EXCL first) is important in order to avoid a race condition.  We create it at the same time we check it does not exist. Otherwise someone else could create it in between.
     
-    if (fd==-1){
+    if (fd==-1){//Creation impossible
         fclose(file);
-        if (errno == EEXIST) EXIT_ON_ERROR("The shared memory '%s' already exists, you should destroy it before. e.g.:\n    ./run.sh i_channels -u%s", name, name);
+        if (errno == EEXIST) EXIT_ON_ERROR("The shared memory '%s' already exists, you should destroy it before. e.g.:\n    blc_channels --unlink%s", name, name);
         else EXIT_ON_SYSTEM_ERROR("Creating shared memory '%s'.", name);
     }
     else{
         fprint_info(file, 1);
         fclose(file);
         
-        if (potential_new_data){
-            sprintf(name_tmp, "blc_channel%d_sem_new_data0", id);
-            SYSTEM_ERROR_CHECK(sem_new_data = sem_open(name_tmp, O_CREAT | O_EXCL, S_IRWXU, 0), NULL, "Creating named semaphore '%s' for blc_channel '%s'", name_tmp, name);
+        open_semaphores(1);
+        
+        if (sync_new_data) {
+            if (access_mode==BLC_CHANNEL_READ){
+                while (sem_trywait(sem_new_data)==-1){ //If the semaphore is busy we post it until it is unlocked
+                    if (errno==EAGAIN) SYSTEM_ERROR_CHECK(sem_post(sem_new_data), -1,  "blc_channel '%s'", this->name);
+                    else EXIT_ON_SYSTEM_ERROR("blc_channel '%s'", this->name);
+                }
+                SYSTEM_ERROR_CHECK(sem_post(sem_ack_data), -1,  "blc_channel '%s'", this->name);
+            }
+        }else {
+            sem_close(sem_new_data);
+            sem_new_data=NULL;
+        }
+        
+        if (sync_ack_data) {
+            if (access_mode==BLC_CHANNEL_READ){
+                while (sem_trywait(sem_new_data)==-1){ //If the semaphore is busy we post it until it is unlocked
+                    if (errno==EAGAIN) SYSTEM_ERROR_CHECK(sem_post(sem_new_data), -1,  "blc_channel '%s'", this->name);
+                    else EXIT_ON_SYSTEM_ERROR("blc_channel '%s'", this->name);
+                }
+                SYSTEM_ERROR_CHECK(sem_post(sem_ack_data), -1,  "blc_channel '%s'", this->name);
+            }
+        }else {
+            sem_close(sem_ack_data);
+            sem_ack_data=NULL;
         }
         
         SYSTEM_ERROR_CHECK(ftruncate(fd, size), -1, "fd:%d, size '%ld'.", fd, size);
@@ -262,19 +301,54 @@ int blc_channel::conflict(const char *new_name){
 ///Open an existing channel
 void blc_channel::open(const char *name, int access_mode){
     char name_tmp[NAME_MAX];
+    int sync_new_data=0, sync_ack_data=0;
+    
     STRCPY(this->name, name);
     
+    switch (name[0]){
+        case '/':
+            break;
+        case '.':
+            sync_new_data=1;
+            break;
+        case '^':
+            sync_ack_data=1;
+            break;
+        case ':':
+            sync_new_data=1;
+            sync_ack_data=1;
+            break;
+        default:EXIT_ON_ERROR("Blc channel names must start with '/' for asynchrone mode or with '.','^',':' for synchrone mode. But it is '%s'", this->name);
+            break;
+    }
+    this->name[0]='/'; //In any case the nale start with '/'
     id = blc_channel_get_info_with_name(this, name);
     if (id==-1) EXIT_ON_ERROR("The blc_channel '%s' does not exist. Run  blc_channels", name);
     
-    if (this->name[0]=='.') this->name[0]='/'; //We remove ! which was just to indicate synchronisation.
-    else if (this->name[0]!='/') EXIT_ON_ERROR("Blc channel names must start with '/' for asynchrone mode or with '.' for synchrone mode");
-    
     SYSTEM_ERROR_CHECK(fd = shm_open(this->name, access_mode, S_IRWXU), -1, "Impossible to open shared memory '%s'with mode %d.", name, access_mode);
-   
-    if (name[0]=='.'){
+    
+    if (sync_new_data) {
         sprintf(name_tmp, "blc_channel%d_sem_new_data0", id);
-        SYSTEM_ERROR_CHECK(sem_new_data = sem_open(name_tmp, O_CREAT, S_IRWXU, 0), NULL, "Creating  or opening named semaphore '%s' for blc_channel '%s'", name_tmp, name);
+        SYSTEM_ERROR_CHECK(sem_new_data = sem_open(name_tmp, NO_FLAG), SEM_FAILED, "Opening named semaphore '%s' for blc_channel '%s'", name_tmp, name);
+       /* if (access_mode==BLC_CHANNEL_READ){ //As we have just started. Any data is new
+            while (sem_trywait(sem_new_data)==-1){ //If the semaphore is busy we post it until it is unlocked
+                if (errno==EAGAIN) SYSTEM_ERROR_CHECK(sem_post(sem_new_data), -1,  "blc_channel '%s'", this->name);
+                else EXIT_ON_SYSTEM_ERROR("blc_channel '%s'", this->name);
+            }
+            SYSTEM_ERROR_CHECK(sem_post(sem_new_data), -1,  "blc_channel '%s'", this->name);
+        }*/
+    }
+    
+    if (sync_ack_data){
+        sprintf(name_tmp, "blc_channel%d_sem_ack_data0", id);
+        SYSTEM_ERROR_CHECK(sem_ack_data = sem_open(name_tmp, NO_FLAG), SEM_FAILED, "Opening named semaphore '%s' for blc_channel '%s'", name_tmp, name);
+        if (access_mode==BLC_CHANNEL_READ){ //As we have just started. Any data is new
+            while (sem_trywait(sem_ack_data)==-1){ //If the semaphore is busy we post it until it is unlocked
+                if (errno==EAGAIN) SYSTEM_ERROR_CHECK(sem_post(sem_ack_data), -1,  "blc_channel '%s'", this->name);
+                else EXIT_ON_SYSTEM_ERROR("blc_channel '%s'", this->name);
+            }
+            SYSTEM_ERROR_CHECK(sem_post(sem_ack_data), -1,  "blc_channel '%s'", this->name);
+        }
     }
     map_memory(access_mode);
 }
@@ -291,12 +365,12 @@ int blc_channel::create_or_open(char const *new_name, int access_mode, uint32_t
         created=1;
     }
     else{
-        if (info.dims_nb!=dims_nb) EXIT_ON_CHANNEL_ERROR(&info, "Reopening a blc_channel with different dims_nb '%d'. You may want to unlink it:\n    ./run.sh i_channels --unlink %s", dims_nb, name);
-        if (info.type!=type) EXIT_ON_CHANNEL_ERROR(&info, "Reopening blc_channel with another type '%.4s'. You may want to unlink it:\n    ./run.sh i_channels --unlink %s", UINT32_TO_STRING(new_type_str, type), name);
-        if (info.format!=format) EXIT_ON_CHANNEL_ERROR(&info, "Reopening blc_channel with another format '%.4s'. You may want to unlink it:\n    ./run.sh i_channels --unlink %s", UINT32_TO_STRING(new_format_str, format), name);
+        if (info.dims_nb!=dims_nb) EXIT_ON_CHANNEL_ERROR(&info, "Reopening a blc_channel with different dims_nb '%d'. You may want to unlink it:\n    blc_channels  --unlink %s", dims_nb, info.name);
+        if (info.type!=type) EXIT_ON_CHANNEL_ERROR(&info, "Reopening blc_channel with another type '%.4s'. You may want to unlink it:\n    blc_channels --unlink %s", UINT32_TO_STRING(new_type_str, type), info.name);
+        if (info.format!=format) EXIT_ON_CHANNEL_ERROR(&info, "Reopening blc_channel with another format '%.4s'. You may want to unlink it:\n    blc_channels --unlink %s", UINT32_TO_STRING(new_format_str, format), info.name);
         if (info.dims_nb!=0){
             for(dim=0; dim != info.dims_nb; dim++) {
-                if (dims[dim].length!=info.dims[dim].length)  EXIT_ON_ERROR("The reopening dimension '%d' length '%d' of '%s' differ from the existing one '%d'. You may want to unlink it:\n    ./run.sh i_channels --unlink %s", dim, info.dims[dim].length, info.name, dims[dim].length, info.name);
+                if (dims[dim].length!=info.dims[dim].length)  EXIT_ON_ERROR("The reopening dimension '%d' length '%d' of '%s' differ from the existing one '%d'. You may want to unlink the blc_channel before:\n    blc_channels --unlink %s", dim, dims[dim].length,  info.name, info.dims[dim].length, info.name);
             }
         }
         open(new_name, access_mode);
@@ -367,6 +441,7 @@ blc_channel::~blc_channel(){
     
     if (fd!=-1){
         close(fd);
+        blc_channel_post_event();
     }
 }
 
@@ -376,8 +451,16 @@ void blc_channel::remove(){
 }
 
 void blc_channel::publish(){
-    if (sem_new_data) fprintf(stdout, ".%s\n", name+1); //Replace first '/' by '.'
-    else fprintf(stdout, "%s\n", name);
+    char sync_char;
+    
+    if (sem_new_data && sem_ack_data) sync_char=':'; // <=>
+    else if (sem_new_data)  sync_char='.'; // ->
+    else if (sem_ack_data)  sync_char='\''; // <-
+    else sync_char='/';   //No synchronisation
+    
+    fprintf(stdout, "%c%s\n", sync_char, name+1); //Replace first '/' by '.'
+    
+    //This is needed with pipe. "\n" dos not flush whane the program is piped
     fflush(stdout);
 }
 
@@ -390,3 +473,50 @@ void blc_channel::fprint_debug(FILE *file){
     if (data==NULL) fprintf(file, "data is null\n");
 }
 
+
+
+int blc_channel::post_new_data(){
+    
+    int listenner = -1;
+    if (this->sem_new_data) {
+        if (sem_trywait(this->sem_new_data)==0) listenner=0;
+        else if (errno==EAGAIN) listenner=1;
+        else EXIT_ON_SYSTEM_ERROR("blc_channel '%s'", this->name); // EAGAIN just means semaphore is busy
+        
+        SYSTEM_ERROR_CHECK(sem_post(this->sem_new_data), -1, "Sem new_data of blc_channel '%s'", this->name); //We signal new_data
+    }
+    return listenner;
+}
+
+int blc_channel::post_ack_data(){
+    
+    int listenner = -1;
+    if (this->sem_new_data) {
+        if (sem_trywait(this->sem_ack_data)==0) listenner=0;
+        else if (errno==EAGAIN) listenner=1;
+        else EXIT_ON_SYSTEM_ERROR("blc_channel '%s'", this->name); // EAGAIN just means semaphore is busy
+        
+        SYSTEM_ERROR_CHECK(sem_post(this->sem_ack_data), -1, "Sem new_data of blc_channel '%s'", this->name); //We signal new_data
+    };
+    
+    return listenner;
+}
+
+START_EXTERN_C
+
+void blc_channel_wait_new_data(void *channel_pt){
+    blc_channel *channel=(blc_channel*)channel_pt;
+    
+    SYSTEM_ERROR_CHECK(sem_wait(channel->sem_new_data), -1, "Waiting new data for channel '%s'", channel->name);
+}
+
+void blc_channel_wait_ack_data(void *channel_pt){
+    blc_channel *channel=(blc_channel*)channel_pt;
+    
+    SYSTEM_ERROR_CHECK(sem_wait(channel->sem_new_data), -1, "Waiting ack data for channel '%s'", channel->name);
+}
+
+
+
+END_EXTERN_C
+

src/channel_file.cpp

@@ -38,7 +38,15 @@
 #define BLC_CHANNELS_LIST_PATH "/tmp/blc_channels.txt"
 
 static int blc_channel_id_max = 0;
+static sem_t *blc_channel_event[2]={NULL, NULL};
+static int blc_channel_event_id=0;
 
+//NULL, *blc_channel_event=NULL;
+;
+static void (*blc_channel_event_callback)(void*)=NULL;
+static void *blc_channel_event_user_data=NULL;
+
+pthread_t thread;
 
 START_EXTERN_C
 
@@ -82,20 +90,10 @@ void blc_remove_channel_with_name(char const *name){
     if (info.id==blc_channel_id_max) blc_channel_id_max--;
     
     SYSTEM_ERROR_CHECK(shm_unlink(name), -1, "unlinking blc_channel '%s'", name);
-    if (info.potential_new_data){
-        sprintf(tmp_name, "blc_channel%d_sem_new_data0", info.id);
-        SYSTEM_ERROR_CHECK(sem_unlink(tmp_name), -1, "Unlinking sem_new_data '%s' for blc_channel '%s'", tmp_name, name);
-    }
-    /*  SPRINTF(control_filename, "/blc_channel%d-var", info.id);
-     SYSTEM_ERROR_CHECK(sem_unlink(control_filename), -1, NULL);
-     SPRINTF(control_filename, "/blc_channel%d-event0", info.id);
-     SYSTEM_ERROR_CHECK(sem_unlink(control_filename), -1, NULL);
-     SPRINTF(control_filename, "/blc_channel%d-event1", info.id);
-     SYSTEM_ERROR_CHECK(sem_unlink(control_filename), -1, NULL);
-     
-     if (shm_unlink(control_filename)==-1) if (errno!=ENOENT) EXIT_ON_SYSTEM_ERROR("unlinking blc_channel '%s'", name); // It does not matter if the file does not exist
-     
-     */
+    sprintf(tmp_name, "blc_channel%d_sem_new_data0", info.id);
+    SYSTEM_ERROR_CHECK(sem_unlink(tmp_name), -1, "Unlinking sem_new_data '%s' for blc_channel '%s'", tmp_name, name);
+    sprintf(tmp_name, "blc_channel%d_sem_ack_data0", info.id);
+    SYSTEM_ERROR_CHECK(sem_unlink(tmp_name), -1, "Unlinking sem_ack_data '%s' for blc_channel '%s'", tmp_name, name);
 }
 
 // Envoie un message d'erreur avec name_of_file, name_of_function, number_of_line et affiche le message formate avec les parametres variables. Puis exit le programme avec le parametre EXIT_FAILURE. To be used with EXIT_ON_ERROR.
@@ -216,5 +214,57 @@ int blc_channel_remove(blc_channel * channel)
     else channel->remove();
     return 1;
 }
+
+static void init_blc_channel_sem_event(){
+   SYSTEM_ERROR_CHECK(blc_channel_event[0]=sem_open("blc_channel_event0", O_CREAT, S_IRWXU, 0), SEM_FAILED, NULL);
+   SYSTEM_ERROR_CHECK(blc_channel_event[1]=sem_open("blc_channel_event1", O_CREAT, S_IRWXU, 0), SEM_FAILED, NULL);
+}
+
+void blc_channel_post_event(){
+    if (blc_channel_event[0]==NULL || blc_channel_event[1]==NULL) init_blc_channel_sem_event();
+    
+    //If the event is already free it is not the good one. We free the other one to trigger the event
+    if (sem_trywait(blc_channel_event[blc_channel_event_id])==0){
+        SYSTEM_ERROR_CHECK(sem_post(blc_channel_event[blc_channel_event_id]), -1, NULL);
+        SYSTEM_ERROR_CHECK(sem_post(blc_channel_event[1-blc_channel_event_id]), -1, NULL);
+    }
+    else {     //If the event is not free, we free it to trigger the event
+        if (errno!=EAGAIN) EXIT_ON_SYSTEM_ERROR(NULL);
+        SYSTEM_ERROR_CHECK(sem_post(blc_channel_event[blc_channel_event_id]), -1, NULL);
+    }
+    blc_channel_event_id=1-blc_channel_event_id;
+}
+
+
+/**Block until event. It may produce false positive in connection */
+static void *blc_channel_thread_manager(void*){
+    int i=0;
+    
+    //If the event is already free it is not the good one. We will wait for the other one
+    if (sem_trywait(blc_channel_event[i])==0){
+        SYSTEM_ERROR_CHECK(sem_post(blc_channel_event[i]), -1, NULL);
+        i=1-i;
+    }
+    
+    while(1){
+        //We wait for event
+        SYSTEM_ERROR_CHECK(sem_wait(blc_channel_event[i]), -1, NULL);
+        //We free event for the others
+        SYSTEM_ERROR_CHECK(sem_post(blc_channel_event[i]), -1, NULL);
+        i=1-i;
+        while(sem_trywait(blc_channel_event[i])==0);
+        if (errno!=EAGAIN) EXIT_ON_SYSTEM_ERROR(NULL);
+        blc_channel_event_callback(blc_channel_event_user_data);
+    }
+}
+
+void blc_channel_check_for_event(void (*callback)(void*), void *user_data) {
+    if (blc_channel_event[0]==NULL || blc_channel_event[1]==NULL) init_blc_channel_sem_event();
+    
+    blc_channel_event_callback=callback;
+    blc_channel_event_user_data=user_data;
+    BLC_PTHREAD_CHECK(pthread_create(&thread, NULL, blc_channel_thread_manager, NULL), NULL);
+}
+
 END_EXTERN_C