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examples: core_loading_thread: fix race condition

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A plain variable is insuffecient for inter-thread communication. Both the
compiler and the processor may reorder accesses. The compiler could even
cache dataLoaded with the result that STATE_FINISHED becomes unreachable.

Fix this by using C11 atomic_bool, which guarantees sequential consistency.

This fixes #827.
This commit is contained in:
Ahmad Fatoum 2019-05-04 19:02:50 +02:00
parent 53d9beb534
commit 6681fd7df2
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GPG key ID: C3EAC3DE9321D59B
1 changed files with 5 additions and 4 deletions
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9
examples/core/core_loading_thread.c
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@ -15,10 +15,11 @@
#include "raylib.h" #include "raylib.h"
#include "pthread.h" // POSIX style threads management #include "pthread.h" // POSIX style threads management
#include <stdatomic.h>
#include <time.h> // Required for clock() function #include <time.h> // Required for clock() function
static bool dataLoaded = false; // Loading data semaphore static atomic_bool dataLoaded = ATOMIC_VAR_INIT(false); // Data Loaded completion indicator
static void *LoadDataThread(void *arg); // Loading data thread function declaration static void *LoadDataThread(void *arg); // Loading data thread function declaration
static int dataProgress = 0; // Data progress accumulator static int dataProgress = 0; // Data progress accumulator
@ -59,7 +60,7 @@ int main()
break; break;
case STATE_LOADING: case STATE_LOADING:
framesCounter++; framesCounter++;
if (dataLoaded) if (atomic_load(&dataLoaded))
{ {
framesCounter = 0; framesCounter = 0;
state = STATE_FINISHED; state = STATE_FINISHED;
@ -69,7 +70,7 @@ int main()
if (IsKeyPressed(KEY_ENTER)) if (IsKeyPressed(KEY_ENTER))
{ {
// Reset everything to launch again // Reset everything to launch again
dataLoaded = false; atomic_store(&dataLoaded, false);
dataProgress = 0; dataProgress = 0;
state = STATE_WAITING; state = STATE_WAITING;
} }
@ -130,7 +131,7 @@ static void *LoadDataThread(void *arg)
} }
// When data has finished loading, we set global variable // When data has finished loading, we set global variable
dataLoaded = true; atomic_store(&dataLoaded, true);
return NULL; return NULL;
} }