Use semaphore to serialize test execution

Author: ameyapat

IdentityCore/tests/MSIDWorkPlaceJoinUtilTests.m

@@ -21,6 +21,8 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 // THE SOFTWARE.
 
+#include <semaphore.h>
+
 #import <XCTest/XCTest.h>
 #import "MSIDKeychainUtil.h"
 #import "MSIDWorkPlaceJoinUtil.h"
@@ -70,6 +72,8 @@ - (void)setUp
 #if TARGET_OS_OSX
     self.useIosStyleKeychain = NO;
 #endif
+    [self.class initialize];
+    [self.class acquireGlobalWPJTestLockWithTimeout:2.0];
 }
 
 - (void)tearDown
@@ -79,6 +83,7 @@ - (void)tearDown
         [self cleanWPJ:[self keychainGroup:YES]];
         [self cleanWPJ:[self keychainGroup:NO]];
     }
+    [self.class releaseGlobalWPJTestLock];
     [MSIDTestSwizzle reset];
 }
 
@@ -893,5 +898,64 @@ - (void)insertEccStkKeyForTenantIdentifier:(NSString *)tenantIdentifier
                   privateKeyTag:stkTag
                     accessGroup:keychainGroup];
 }
+# pragma mark -- Serial execution of tests
+
+// Global interprocess semaphore (named; no file fallback)
+static sem_t *s_wpjNamedSem = SEM_FAILED;
+
++ (void)initialize
+{
+    if (self != [MSIDWorkPlaceJoinUtilTests class]) return;
+
+    static dispatch_once_t onceToken;
+    dispatch_once(&onceToken, ^{
+        // Named POSIX semaphore (not file-based). Name must start with '/'.
+        s_wpjNamedSem = sem_open("/com.microsoft.msid.wpj.tests.sem", O_CREAT, 0666, 1);
+    });
+}
+
++ (BOOL)acquireGlobalWPJTestLockWithTimeout:(NSTimeInterval)timeoutSec
+{
+    if (s_wpjNamedSem == SEM_FAILED) return NO;
+
+    // Blocking acquire if timeout is negative
+    if (timeoutSec < 0) {
+        int rc;
+        do { rc = sem_wait(s_wpjNamedSem); } while (rc == -1 && errno == EINTR);
+        return rc == 0;
+    }
+
+    // Immediate try if timeout is zero
+    if (timeoutSec == 0) {
+        int rc;
+        do { rc = sem_trywait(s_wpjNamedSem); } while (rc == -1 && errno == EINTR);
+        return rc == 0;
+    }
+
+    CFAbsoluteTime deadline = CFAbsoluteTimeGetCurrent() + timeoutSec;
+    struct timespec sleepTs = { .tv_sec = 0, .tv_nsec = 10 * 1000 * 1000 }; // 10ms
+
+    for (;;) {
+        int rc = sem_trywait(s_wpjNamedSem);
+        if (rc == 0) return YES;
+
+        if (errno != EAGAIN && errno != EINTR) {
+            return NO; // unexpected error
+        }
+
+        if (CFAbsoluteTimeGetCurrent() >= deadline) {
+            return NO; // timed out
+        }
+
+        nanosleep(&sleepTs, NULL);
+    }
+}
+
++ (void)releaseGlobalWPJTestLock
+{
+    if (s_wpjNamedSem != SEM_FAILED) {
+        sem_post(s_wpjNamedSem);
+    }
+}
 
 @end